Cryogenic properties of unidirectional composites

Cryogenic properties of unidirectional composites R.P. Reed and M. Golda* Cryogenic Materials, Inc., 2625 Iliff, Boulder, CO 80303, USA * Electrical Machinery Technology Branch, Machinery Research and Development Directorate, Carderock Division, Naval SurfaceWarfare Center, Annapolis, MD 21402-5067, USA

Received2 February 1994; revised 18April 1994 The tensile, compressive, fatigue, thermal expansion, thermal conductivity and specific heat of unidirectional laminates reinforced with boron, alumina, aramid, S-glass, E-glass, and high strength, high modulus and medium modulus carbon fibres are reviewed. The ratio of strength to thermal conductivity is used to assess the suitability of various fibre-reinforced laminates for supporting struts (experiencing compression) or straps (experiencing tension) at cryogenic temperatures. The relationships between laminate properties and reinforcement fibres are discussed.

Keywords: undirectional composites; fibre reinforcement; physical properties; review

All structures operating at cryogenic temperatures must be supported and connected to ambient temperature structures. The supports require sufficient mechanical strength to maintain the cryogenic system more or less rigidly in place and low thermal conductivity to minimize the heat flow from ambient to cryogenic temperatures. In many space applications, where the cryogenic systems must be maintained for long periods of time with a limited liquid helium supply, a support structure employing an array of composite straps has been used. Nuclear magnetic resonance equipment also uses straps for partial mechanical support of the superconducting magnet. Straps, of course, experience tension, and both the cold and warm structures must be designed to resist tensile loads. Support straps consist of unidirectional fibre reinforcement with an epoxy matrix. Typical reinforcement fibres that have been used are E-glass and S-glass (T-glass in Japan and R-glass in Europe) and carbon. A range of properties, from high modulus to high strength, is obtained from carbon fibres. Recently, the use of y-alumina fibres has been explored. Straps are efficient; the tensile strength of the fibres in the straps approaches that of the fibre stength; fibre volume fractions in the straps are typically 70%. The efficient design of strap-supported structures must consider that the weak mechanical link is located at the end fixtures, where the curvature of the pin

0011-2275/94/110909-20 © 1994

Butterworth-HeinemannLtd

loading provides shear as well as tensile forces on the unidirectonal fibre reinforcement. To minimize other forces and to provide a sufficient bearing surface for load transfer, the ratio o f pin diameter to strap thickness should be mote than about 15. Indeed, there is some evidence that ratios up to 30 provide even higher tensile strengths. In some applications, such as superconducting magnetic energy storage, composite struts (tubes) are being considered for use. The struts support the load between the ambient and cold structures in compression; thus, these structures must be designed to withstand compressive forces. Composite support struts generally have lower compressive strengths than the tensile strengths of their counterpart straps. Usually, the filament winding process is used to produce composite tubes. This process results in the 'unidirectional' fibres being approximately +8 ° . In addition to these near-0° fibres, struts must have offaxis filament windings (hoop reinforcement) to reduce the buckling tendency along the length of the tube. Buckling is also prevented by making the tube wall thicknesses and diameter sufficiently large relative to the tube length. End fixtures are also critical for strut-loading systems, and care must be taken to prevent brooming of the composite tubes. A third type of composite support structure is the passive orbital disconnect system (PODS), which is

Cryogenics 1994 Volume 34, Number 11 909

Cryogenic properties of unidirectiona/ composites: R.P. Reed and M. Golda basically two, nearly concentric, tubes. One tube is stronger and designed to withstand sudden high loads, such as those that occur during a launch into space. The other tube is designed to withstand operating loads; it is more thermally efficient. During operation, the larger tube is physically disconnected from the cryogenic system, but when the device experiences a sudden large load, the deflection between the cryogenic and ambient structures places the larger tube in contact with both the warm and cryogenic structures. PODSs have difficulty with transverse or off-axis loads, because they tend to bring the concentric tubes into contact. Kittel 1 has recently reviewed PODS concepts. Composite support struts generally have lower compressive strengths than the tensile strengths of their counterpart straps. Struts must have off-axis filament windings as well as unidirectional (near 0°) fibres. These off-axis fibres are required for hoop reinforcement to reduce buckling along the length of the tube. Although the fibre orientation in straps is very close to 0°, the filament winding process of struts results in the 'unidirectional' fibres being approximately +8 °. Pultrusion of support struts has not yet resulted in compressive strengths higher than those of filament-wound tubes. In most composite applications, material screening and initial design data are obtained by testing a unidirectional fibre-reinforced plate. A plate is much easier to fabricate than the actual structural system, which usually requires the preparation of moulds and specimen test apparatus. Thus, a body of unidirectional composite data is now being developed that can be used to select the type of reinforcement and to obtain preliminary design data. Support structures span the temperature interval from room to cryogenic. At low temperatures, the strengths of fibre-reinforced, epoxy-matrix composites usually increase; thus the weak link, from the standpoint of stength, is at room temperature. Conservative testing, then, must take place at room temperature, and so the room temperature data developed for other, non-cryogenic applications can be used. Some previous reviews of composite behaviour at cryogenic temperatures have included laminate properties. Kasen has comprehensively reviewed research in high pressure laminates (with glass weaves and directional-ply laminates) at low temperatures2'3. Hartwig has also reviewed the low temperature properties of fibre-reinforced composites4. The utilization of composites for low temperature structures has been hindered by the inconsistency of mechanical property data. The two primary reasons for the large variability of reported strengths and strains to failure for fibre-reinforced laminates are as follows. The manufacture of laminates has been inconsistent. Relatively large variability of porosity in the resin matrix is common. Strength and local failure modes depend strongly on the degree of fibre waviness and relative alignment, which has not been

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Cryogenics 1994 Volume 34, Number 11

adequately controlled in some studies. Local buckling of the fibres is also dependent on the elastic properties of the matrix resin; variations of elastic stiffness are found in different epoxy systems. Both Kasen 2'3 and Hartwig 4 have addressed this issue in their earlier reviews. Specimens and testing techniques are not standardized. For example, in both tension and compression, it is especially difficult to grip composite specimens, and in so doing, to not influence the failure mode and corresponding strength. Gradually, more reliable testing techniques have evolved; however, in a review such as this, inevitably a number of different testing techniques coupled with different specimen dimensions and configurations are compared. The reader is cautioned that, in some cases, variations in test procedures and specimens are sufficient to account for the differences in data. An effort was made to include all cryogenic data published after 1980 in this review. Low temperature data reported from earlier than 1980 have been included in the reviews of Kasen 2'3. Not all room temperature data on fibre-reinforced, unidirectional laminates are included. Only those data contained in the references of cryogenic reports, those that appear in general reviews, or those that have otherwise come to the attention of the authors are used as base-line room temperature data. The authors' intent is to review the mechanical and thermal properties, at room and low temperatures, of the candidate types of fibre reinforcements for straps and struts. This review focuses on the properties of unidirectional composites from moulded laminate plates. Reinforcement fibres include boron, alumina, aramid, S-glass, E-giass and carbon. The mechanical properties of unidirectional laminates of each type of fibre are discussed in the first section. In the second section, the mechanical properties of the fibres are compared, and the thermal conductivity and thermal contraction data are given for each fibre. In the last section, the relationships between laminate properties and reinforcement fibres are discussed.

Fibre-reinforced, unidirectional laminates Boron Boron fibres are stronger and stiffer than the other competitive fibres - alumina, aramid, glass and carbon. Boron fibre-reinforced composites are unique among fibre-reinforced composites because they have higher compressive strengths than tensile strengths. Their thermal conductivity at room temperature is higher than those of glass and alumina fibres, but lower than that of carbon fibre. On cooling, boron fibres contract more than carbon and aramid fibres, but less than glass and alumina fibres. Boron fibres are produced by slowly moving a hot

C r y o g e n i c p r o p e r t i e s o f u n i d i r e c t i o n a l c o m p o s i t e s : R.P. R e e d a n d M. Golda

Table 1 Tensile and compressive properties of boron unidirectional laminates

Author

Fibre grade

(year)

(supplier)

Swartz5 (1966) Nadler et al.6 (1969) Suarez et al.7 (1972) Weeton et aLe (1974) Bert9 (1975) Renton1° (1977) Schramm and Kasen11 (1977) Ledbetter 12 (1979) Tsai and Hahn~3

(1980) Rosen and Dow TM (1988) Best values

Resin

Fibre volume

Density

system

(K)

(%)

(gcm -~)

E

Epoxy

295

67

2.08

204

Epoxy

295 77 295 218 295 218 295

Epoxy Epoxy

5.6 mil

Tension (GPa)

Test temperature

Epoxy (505) Epoxy (505) Epoxy (2387) Epoxy (2387) Epoxy (505) Epoxy Epoxy

Compression (GPa) ~u

E

~ru

1.9 3.0 210 217 205-215 205-220 207

219 223 1.27-1.45 1.24-1.38

2.58-3.07 3.10-3.31

295

50

1.99

207

1.59

221

2.48

295 76 4 295

52 52 52 52

2.00 2.00 2.00 2.00

231 233 238 226 a

1.63 1.68 1.82

212 230 239

2.72

2.00

204

1.26

2.5

1.86

274

1.31

2.48

210 230 240

1.4 1.7 1.8

295 295

60

295 76

50 50 50

4

220

2.5 ~3.2 ~2.8

aDynamic measurement

tungsten wire, which serves as the substrate, through a mixture of BC12 and 1-12gas. Boron reduction occurs on the substrate and the tungsten core reacts to form tungsten borides. As the tungsten core reacts, it expands from an initial 12.5/zm diameter to about a 17.5~m diameter. The surface-deposited boron has a polycrystalline fl-rhombohedral structure with an average grain size of about 0.2#m. Typical fibre diameters are 100 and 140/zm. Variations of the ultimate tensile strength of individual fibres at room temperature range from about 2.5 to 5.5 GPa. Strengths as high as about 6.9 GPa have been measured after polishing the fibre surface or removing the core of the fibre. Average tensile strengths for both 100 and 140/zm diameter fibres are 3.6GPa; however, mean values range to 4.5 GPa. This marked distinction arises from the skew of the frequency of strength from multiple tests of similar fibres. The modulus of elasticity of boron fibres is 400 GPa at room temperature. The density of the 100/zm diameter fibres is 2.57gem -3 and of the 140gin diameter fibres, 2.49gcm-3; the variation relates to the relative contribution of the tungsten-boride core structure. Boron fibre is typically used in composites in the form of a prepreg tape. The tape consists of an array of fibres supported on one side by a light fibreglass fabric and preimpregnated with epoxy resin. Design compatible compressive strengths for boron/epoxy composites over the temperature range 218-460K were

developed in the late 1960s and early 1970s for use in aircraft wing structures 7. A summary of the data reported for boron unidirectional laminate is presented in Table 1. Although the data are less clear, the compressive strengths appear to increase slightly more than 10% at low temperatures when the room temperature data of Nadler et al. 6, which are considerably lower than other reported values, are discounted. Schramm and Kasen report one compressive strength measurement of 3.66GPa at 4 K n ; this value is perhaps the highest compressive strength ever reported for a composite laminate. Their other data, included in the average reported value of 2.72 GPa, are 1.92 and 2.59 GPa. As is typical of low temperature composite data spread, the variability is very large and the lower values reflect material or test inconsistencies. Schramm and Kasen also measured low temperature strain to failure of unidirectional boron laminate. They report average strains to failure in tension of 0.0073, 0.0077 and 0.0076 for 295, 76 and 4 K tests, respectively. Standard deviations for the tensile data were low (about 0.05). In compression, their reported strains to failure were less precise; however, linear-elastic stressstrain curves were reported. Recommended or 'best values' are also included in Table 1. For boron, they represent mean or average values for the 295 K data. Notice that the compressive strengths at all temperatures (4-295 K) are almost a factor of two higher than the tensile strengths. The measured elastic moduli (E) are slightly more than half

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

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Cryogenic properties o f unidirectional composites: R.P. Reed a n d M. Golda Table 2

Tensile and compressive properties of alumina unidirectional laminates

Fibre

Compression (GPa)

Tension

Test

Fibre

temperature (K)

volume (%)

(g cm --3)

E

O'u

Weeton et aLTM

295

44

1.75

(1987)

295

14

1.64

165 41 134

0.50 0.78

94 101 95

0.83 1.34 1.03

Author (year)

grade (supplier)

Mesuria TM (1988)

Kriz and McColskey ~7 (1990) GuTM (1992) Ohtani et al. TM (1992) Best values

~, (Sumitomo) FP (DuPont) 7 (Sumitomo)

Resin system

APC-2 PEEK PEEK

295 295 76

43 43

4

43

Epoxy (35D1-6) Epoxy

295 77 295

55 55

PEEK

295 77

45 45

4

45

the fibre modulus (400 GPa), which is expected for unidirectional plies with 50 to 52 fibre vol%. The low temperature tensile and compressive properties were measured to 4 K by Schramm and Kasen 1~ and to 77K by Nadler et al. 6. In tension, there is very little change in strength (~10%) on cooling from 295 to 4K.

Alumina

Alumina fibres have been considered for structural reinforcement of cryogenic systems for applications in which low heat leakage (low thermal conductivity) is important. Alumina (A1203) has relatively low thermal conductivity, only slightly higher than that of glass, but it has higher strength and elastic moduli. Thus, better fatigue resistance is also expected. The initial alumina fibre, manufactured under the label FP, is an a-phase, polycrystalline material with an average grain size of the order of 0.5/zm. The surface of the fibre is rather rough, and the fibre strength can be increased by coating the fibre surface with silica. Unfortunately, this fibre is difficult to use in fabrication because it is relatively brittle and, therefore, susceptible to cracking during bending. More recently, a y-phase fibre that is more flexible has become commercially available, and all recent studies reported here have used this fibre. It contains about 15 wt% silica and has a density of 3.2 g cm-3 with an average fibre diameter of 17/~m. At room temperature, the average tensile strength of this fibre is about 1.5 GPa, and its elastic modulus is 200 GPa. A summary of the meagre data for alumina unidirectional-ply laminates is presented in Table 2. Note especially that the PEEK resin system has been used to produce some specimens that are included in the table. Low temperature (77 K) data with an epoxy

912

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

Density

(GPa)

E

1.18

o"u

1.24 95.8 133 113

0.8 1.27 1.51 0.79 1.14

0.8

100

0.8

1.3 1.0

130

1.3 1.5

103

90 100 100

resin system were obtained by Gu is and with a PEEK resin system at 77 and 4 K by Kriz and McColskey17. Within the large disparities among most data sets, a distinction between the tensile or compressive properties of PEEK- and epoxy-based resin systems is not apparent. In Table 2, the best values are based on data obtained from a PEEK-containing composite, since this resin system was used in the very low temperature study. A better temperature dependence of the strength and moduli can be obtained from the fourpoint flexural data of Takeno et al. 2°, which were obtained by using 50 vol% y-alumina unidirectional fibres. The elastic modulus increased 5% on cooling to 77K and 15% on cooling to 4K from 295K. The breaking strength was 70% more at 77 K and 80% more at 4 K than at room temperature. Thus, the increases of the best value compressive strengths at 77 and 4 K and of the tensile strength at 77 K compare favourably with the data of Takeno et al., but the best value elastic moduli and tensile strength at 4K are not in close agreement. Aramid

Fibres produced from aromatic polyamides, containing many benzine rings, are referred to as aramids. Aramid fibres have been considered for cryogenic applications owing to their relatively high strength and very low density. They have strong anisotropic thermal contraction tendencies: parallel to the aramid molecules (fibre axis), they expand on cooling, but in the transverse direction, they contract. These thermal trends produce a very complex state of residual stress in the adjacent resin matrix, which tends to be reflected in the directional laminate properties at low temperatures. The strong molecular anisotropies of this fibre also lead to brittleness in the transverse fibre direction,

Cryogenic properties o f unidirectional composites: R.P, Reed a n d M. Golda Table 3 Tensile and compressive properties of aramid unidirectional laminates

Author (year)

Fibre grade (supplier)

elements and Moore22 (1977) Renton1° (1977) Ledbetter ~2 (1979) Tsai and Hahn13 (1980) Chamis et al.2a

Kevlar 49

Kasen24 (1982)

Kevlar 49

Hartwig and Knaak2s (1984) Weeton et al) s (1987) Rosen and DowTM (1988) Morris 2e

Kevlar 49

Kevlar 49 Kevlar 29 Kevlar 49 Kevlar 49 Kevlar 49

Resin system

Fibre volume (%)

Tension (GPa) Density (g cm -~)

E

Compression (GPa) ~ru

E

~u

83

1.85

81.8

0.24

75.8 34.5 66 a

1.38 1.38

75.8 34.5

0.28 0.28

Epoxy (DGEBA) Epoxy tape Epoxy tape Epoxy (934) Epoxy

295

295

76

1.40

Epoxy prepreg (PR288) Epoxy (934)

295

77.2

1.28

295 76 4 4

71.4 99.4 99.4 100

Kevlar 49

Epoxy (C8221/Hy979) Epoxyprepreg tape Epoxy

Kevlar 49

Epoxy

Kevlar 49

Test temperature (K)

(1989)

(SCIREZ 081 )

Best values

Epoxy

295 295 295

60 60

1.38 1.38

60

295

0.24

1.13 1.15 1.14 1.3-1.5

0.23 0.29 0.37 0.32

1.45

46

1.36

1.30

76

1.38

0.28 0.30

295

60

295

66

87

1.54

295 76 4

60 60 60

80 99 100

1.4 1.4 1.4

41

80

0.21

0.25 0.29 0.37

aDynamic measurement

especially at low temperatures. This brittleness increases the tendencies for microcracking and fibre failures during winding or other bending operations during the course of composite fabrication. An excellent review of aramid fibres has been provided by Morgan and Allred 21. The aramid fibre, which was developed to replace steel in radial tires, is commercially supplied mainly by DuPont under the trade name Kevlar. There are three grades of Kevlar: Kevlar (for elastomer reinforcement), Kevlar 29 (for ropes, cables and so on) and Kevlar 49 (same strength, higher modulus than Kevlar 29, for organic-matrix reinforcement). The tensile strength at room temperature of Kevlar 49 has been reported from 2.3 to 3.6 GPa, and the elastic modulus is about 130GPa. Its thermal conductivity at room temperature is comparable to that of alumina, higher than that of glass fibre and lower than that of carbon fibre. Kevlar 49 has a density of 1.45gem -3 with a typical fibre diameter of 12/zm. Diameter variations along the fibre length as high as 20% have been reported 21. Data on unidirectional laminate tensile and compressive properties of aramid at room and low temperatures are summarized in Table 3. Kasen 24 and Hartwig and Knaak 25 have reported low temperature properties. Since the data of Kasen have been reported for three temperatures, these data indicate that there is virtually no dependence of strength on temperature. Note, however, that the Kasen tensile data are about 15% lower than the other room temperature and 4K

data. The best value for the tensile strength represents the average value (1.4GPa) of all data at room temperature, and following the trend of the Kasen data, it is assumed that the strength is independent of temperature. The best value of tensile strength at 4 K falls within the data scatter reported by Hartwig and Knaak. The compressive strengths of aramid-fibre directionally reinforced laminates are much lower than their tensile strengths. Presumably, this reflects the effects of anisotropic thermal contraction on the transverse and shear laminate properties, which, in turn, affect the microinstabilities that influence compressive laminate failure modes. S-Glass

S-Glass is a 'high strength' glass fibre, having about one-third more tensile strength at room temperature than E-glass fibre. At room temperature, the typical fibre tensile strength is 4.6GPa, and the elastic modulus is 86 GPa. S-Glass contains about 65% silica, 25% alumina and 10% magnesia by weight; unlike E-glass, it does not contain boron oxide. S-Glass fibres are about 3.5 times more expensive per unit weight than E-glass fibres. The density of S-Glass is 2.49 g cm-3. Glass fibres are produced by flowing molten glass through holes in a high temperature alloy (platinumrhodium) bushing with the temperature, and thus the viscosity, carefully controlled. After drawing down the

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C r y o g e n i c p r o p e r t i e s o f u n i d i r e c t i o n a l c o m p o s i t e s : R.P. R e e d a n d M. Golda Table 4

Tensile and compressive properties of S-glass unidirectional laminates

Fibre grade (supplier)

Resin system

Toth et al. 27 (1966)

S

Epoxy (E-787)

Broutman 2s (1967) Berta (1975) Kasen2 (1975)

S

Epoxy (Scotchply) Epoxy Epoxy

Author (year)

Renton1° (1977) Schramm and Kasen11 (1977) Chamis et al. 23 (1981) Kasen3 (1981)

S E/S

S-2 tape $901

Lamothe and Nunes29 (1983) Weeton et al. is (1987)

S-2 S S-2 tape

Epoxy (DGEBA) Epoxy (SP-250) Epoxy Epoxy (prepreg)

Berg and Adams3° (1989) Morris 28 (1989)

S-2

Epoxy (3501-6)

S-2

Slivka 31 (1989)

S-2

Tsai and Kim32 (1990)

S

Epoxy (SCIREZ 081) Epoxy (828/MPDA) Epoxy

Best values

R

Epoxy (flexible) NASA resin 2

Test temperature (K) 295 197 77 20 295 295 295 200 76 4 295 295 76 4 295

72

60 66 66 66

63

295 295 295 295

60

295

66

295

60

295

76

2.12

1.82

Tension (GPa)

Compression (GPa)

E

or u

E

56.4 62.6 60.9 65.8 66.2

1.94 2.32 2.28 2.05 1.90

1.04 1.19 1.64 1.63 1.38

61.4 62 65 65 72 43.4 57 58 60 47.9

1.6 1.9 2.0 2.0 1 . 2 4 41.4 1.36 1.96 1.94 1.33

0.6 0.7 0.9 0.9 0.76 0.50 1.36 1.42

50 54

1.15 1.55

50

295 76 4

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

Density (g cm -~) 2.00

295 76, 4 295

individual filaments, sizing (chemical coating) is applied. The chemical composition of the sizing, which usually has a silane base, depends on the filament application and the type of resin to be used. Following winding on a toilet or spool fixture, the fibres are converted to strands and, hence, continuous rovings for use in filament winding, pultrusion or other such composite-fabrication procedures. The number of filaments in a strand varies from about 50 to 1225; average filament diameters range from 4.44 to 13.3/zm. Tensile and compressive properties of unidirectional laminates constructed with S-glass are summarized in T a b l e 4. Best values calculated based on the mean of the available data are included. Notice that the tensile and compressive elastic moduli are comparable and that the tensile strengths are 30-40% higher than the compressive strengths. Low temperature tests were conducted by Toth et al. 27 and by Schramm and Kasen 11. Earlier low temperature studies have been summarized by Kasen 2,3. The considerable scatter in the S-glass data is due to a number of factors: 1, many of the reported tests were conducted in the 1970s and even earlier- thus, the data

914

Fibre volume (%)

2.00 2.02

51.0 52 55.2 56.7

2.03

2.00 1.69 1.38

o" u

17.9

0.42

60

0.83

54.4-58.3

1.12-1.32

1.60....

0.97

55.2

57 59 62

1.6 2.1 2.0

74

1.90

57

1.0 1.5 1.5

were obtained by different test techniques; 2, some of the unidirectional panels were constructed from prepreg tapes, others used S-glass rovings, and 3, a number of resins were used in these studies, some are more flexible than others. E-Glass

The most common glass fibre is E-glass (E designates electrical), which is commonly used as a plasticreinforcing material and in textile products. It has a calcium alumino-borosilicate composition - about 54% silica, 14% alumina, 20.5% calcium oxide, 0.5% magnesia, 8% boron oxide, 1% soda, 1% calcium fluoride and 1% minor oxides. The density of E-glass is 2.5gcm -3. At room temperature, the typical tensile strength is 3.45 GPa and the elastic modulus is 73 GPa. Processing of glass fibres is discussed briefly in the S-glass section. E-glass costs about one-third less than S-glass per unit weight. At room temperature, the strength of S-glass is about one-third higher than that of E-glass. Therefore, even though more E-glass must be used for strength-controlled composite applications at room

Cryogenic properties of unidirectional composites: R.P. Reed and IV/. Golda Table 5 Tensile and compressive properties of E-glass unidirectional laminates

Resin system

Test temperature (K)

Fibre volume (%)

Density (gcm -3)

Tension (GPa)

Compression (GPa)

E

~ru

E

Author (year)

Fibre grade (supplier)

Broutman 28 (1967) Scala33 (1968) Hedgepeth and Haskel134 (1967) Renton1° (1977) DahlerupPeterson3s (1980) Tsai and Hahn~z (1980) Hartwig and Knaak 25 (1984) Leslie38 (1986)

Scotchply 1002 Epoxy Scotchply 1009 Epoxy Epoxy Epoxy

295 295 295 295

73 56

2.17 1.97

55.8 42.7 35.6 51.7

1.64 1.03

Scotchply 1002

Epoxy

295 295 77

60 51 51

1.80

39.3 41.1 45.1

1.10 1.05 1.34

Scotchply 1002

Epoxy

295

1.80

38.6

1.06

0.61

45.0

1.1-1.8

0.7-1,0

1.99

45

0.76

Weeton et al. TM (1987) 3M37 (1988)

Tape

1.90

41

1.14 1.24 0.95 1.04

45

1.22

47 52

1.54 1.41 1.1 1.0

4 Epoxy Epoxy Epoxy

295 295 295 295

60 65 50

295 219 76 11 295 295

60 60

Epoxy

295 295 76

Chamis38 (1988) Rosen and DowTM (1988) Slivka31 (1989) Gu and Abdelsalam39 (1990) Reed and McColskeya° (1992)

Epoxy (1002) Epoxy

Epoxy (DGEBA) Epoxy (DGEBA) Epoxy (DGEBA)

Best values

Epoxy Epoxy Epoxy Epoxy Epoxy

1.94

45

60 50 50

2.08

44.8

295 76 4

72 72 72

1.85 1.85 1.85

295 295 295 76 4

50 60 70 70 70

temperature (to achieve equivalent load sharing), the overall material costs of the E-glass structure will be less. The tensile and compressive data for unidirectional, E-glass fibre-reinforced laminates are summarized in Table 5. At room temperature, the compressive strength is lower than the tensile strength, but at low temperatures, they are the same. The difference at room temperature probably reflects the role of the matrix resin in affecting the tensile and compressive strengths of these laminates; a greater contribution to strength under compressive loading is contributed by the resin through its tendency to resist microbuckling. At room temperature, the resin is relatively soft and provides less resistance; at low temperature, the resin strengths and moduli are at least twice those at room temperature, providing greater resistance to localized fibre microbuckling. Low temperature tests on E-glass laminates have been conducted by Reed and McColsky4°, DahlerupPeterson 35, Hartwig and Knaak 25, and the Boeing Company, as reported by 3M 37. All data are relatively consistent and suggest strong increases in compressive

~u 0.60

31.7

41

0.62

0.83 0.88 1.10 0.62 0.55 0.82 1.23

39.8 44.0 45.2

1.01 1.32 1.15

50.7 54.3 55.1

0.77 1.40 1.44

41 43 43 45 47

1.0 1.1 1.1 1.4 1.3

32 51 54 55

0.67 0.82 1.40 1.44

strengths at low temperatures and moderate increases in tensile strengths at low temperatures. Why the elastic moduli in compression, as reported by Reed and McColsky4°, are larger than the tensile elastic moduli is not clear. The method of laminate production for their specimens was essentially filament winding, which should provide adequate tension on the unidirectional fibres. In both types of tests, strain gauges were used for strain sensing. Best values are also presented in Table 5. They represent the mean values of the available data for each fibre volume per cent and temperature.

Carbon One low density, allotropic form of the element carbon is graphite. In the hexagonal, layered planes of graphite, there is very strong covalent bonding that produces extremely high elastic stiffness and strength. Bonding between the layers, however, is weak, yielding low elastic properties in the shear and transverse directions. The stacking of the layers of graphite (a structure called graphene) strongly determines the

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

915

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda Table 8 Tensile and compressive properties of carbon unidirectional laminates

Author (year)

Fibre grade (supplier)

Berts (1975) Hancox41 (1975)

Thornel 50 Morganite II 'Type 2, treated'

Schramm and Kasen 11 (1977) Renton1° (1977)

AS

DahlerupPeterson 3s (1980) Tsai and Hahn TM (1980) Chamis eta/. 23 (1981) Clark and Lisagor42 (1981) Grimes '~ (1981) Hartwig = (1982) Kasen24 (1982)

Resin system

Tension Test Fibre (GPa) temperature volume Density (K) (%) (gcm ~) E

T300 AS AS HM-S T300

Epoxy (E798) 295 Epoxy (2387) 295 Epoxy(DGEBA) 295 295 295 Epoxy 295 77 4 Epoxy (3501) 295 Epoxy (934) 295 Epoxy (5208) 295 Epoxy (5208) 295 Epoxy (934) 295 Epoxy (5208) 295 Epoxy (5208) 295 Epoxy 295 77 4 Epoxy (5208) 295 Epoxy (3501) 295 Epoxy 295 Epoxy 295 Epoxy (5208) 295

AS

Epoxy (3501-6) 295

HS (T300) HM (M40A) HM (GY-70)

Epoxy Epoxy Epoxy

MM (HM-S)

Epoxy

HS (AS)

Epoxy

295 76

HMS

Epoxy (2002)

298 111

T300

T300

Epoxy 293 (CY221/HY979) 77 Epoxy 293 (CY221/HY979) 77 Epoxy (5208) 295

55

AS T300

Epoxy (PR288) 295 Epoxy (5208) 295

53 59

T300, T700

Epoxies (4901, 295 5208, BP907)

HS (T300) HM (M40A) AS (AS-4) 'Standard' tape 1.5% strain tape 1.5% strain tape IM tape HM tape UHM tape Pitch 100 tape

Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy prepreg Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy

HS (AS) MM (HMS) HTS HS (T300) GY-70 MOD-I MOD-II HM-S

77 77 295 76 4 295 76

50 60 70 64 64 64 60

1.56 1.56 1.56 1.54 1.63 1.55 1.69 1.67 1.54

1.6 1.6

Lamothe and Nunes~ (1983) Sinclair and Chamis47 (1983) Hahn and Williams '~ (1984) Hartwig and Knaak2s (1984) Weeton et al. TM (1987)

HT HM A GY-70 HS HS MS HM

916

Cryogenics 1994 Volume 34, Number 11

4 4 4 295 295 295 295 295 295 295 295 295 295 295 295 295 295 295 295 295

118 101 117 128 207 172 138 276 214 165 172 172 180 181 138 125 183

1.32 1.23 1.31 1.45 0.83 1.48 1.45 0.59 0.83 1.28 1.21 1.33 1.51 1.50 1.45 1.47 1.05

62.5

65

64

4

T300

~=

E

or,

110 172 165 138 262 200 200

1.1 1.25 1.4 0.55 0.79 0.69 1.17 0.62 1.07 1.45 0.52 0.69 0.69

146 135

4

Philpot and Randolph45 (1982) Weiss '~ (1982)

Compression (GPa)

60 60 60 1.58 1.60 1.61 1.60 1.80 1.83 1.83 1.83 1.60

140 240 323 328 326 186 192 189 115 100 110 181 176

2.2 1.3 0.73 0.72 0.72 1.19 1.13 1.04 1.35 1.21 1.30 0.90 0.57

132 141 135 137

1.7 2.0

1.50 1.45 133

1.55

110

1.40

368

164 179

0.43 0.64 0.69 0.81 0.88 0.80 0.50 0.75 0.75 0.66 0.78

142

1.57 1.17 1.45

129

125 131

1.47 1.50

107 131

140

1.6-2.2

110-140 0.5-1.6

140 240 130 131 134 138 165 239 314 421 125-143 129 138 165 136 290 145 138 147 215

2.0 1.5 1.52 1.89 2.58 2.76 0.78 0.76 1.04 1.13-1.89 1.31 1.29 0.72 1.16 0.62 1.24 1.62 1.46 1.24

0.8-1.3 131 131 134 145 228 316 310 100-145 124

1.31 1.58 1.38 1.38 0.34 0.35 0.26 0.87-1.93 1.10

113 131 177

0.99 1.40 0.76

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda

Table 6 Tensile and compressive properties of carbon unidirectional laminates (continued)

Author (year) Ahlborn 49 (1988)

Fibre grade (supplier)

Resin system

T300

Epoxy (rigid)

295

60

Epoxy

295

HS (AS-4)

Epoxy (3501-6, tape) Epoxy (SCIREZ 081) Epoxy (SCIREZ 081) Epoxy (3501-6) Epoxy

295

62

295

66

182

2.87

1.90

295

66

189

3.61

2.38

JM-6

AS-4 IM-6 AS-4 AS-4

AS-4 HTA7 HS (T300) M40A

630-500 T300 M40JR T300 AS-4 AS-4

Ohtanietal. TM (1992) Be= values

~ru

Epoxy

HTA7

Pannkoke and Wagner se (1991) Hartwig and Pannkokes7 (1992)

E

T-300 GY-700 AS-4

AS-4

T-1000

Ahlborn s4 (1991) Bansemir and Haiderss (1991)

~ru

60 60 60 60 60 60 60

HTA7

Swansonsl (1990) Tsai and Kim 32 (1990) Adams and Odom 52 (1991) Ahlborn s3 (1991)

Compression (GPa)

293 77 Epoxy 293 (semiflexible) 77 PC 293 (thermoplastic) 77 4 PEEK 295

T300

Mesuria TM (1988) Rosen and Dow TM (1988) Shuarts° (1988) Berg and Adams3° (1989) Morris 2s (1989)

Tension Test Fibre (GPa) temperature volume Density (K) (%) (gcm -3) E

Pan Pitch High strength (HS) (T-300, AS-4) Medium modulus (MM) (HM-S) High modulus (HM) (GY-70)

134 1.47 1.61

132

295 295 295 PEEK 295 77 4 Polycarbonate 295 77 4 PEEK 77 Polycarbonate 77 Epoxy 293 (M10 and 77 CY221/HY979) Epoxy 293 (CY221/HY979) Epoxy 77 (CY2091HT972) Epoxy 77

70 67 67 64 64 64 64 64 64 64

124-133 1.17-1.39

168

1.49 1.60 1.76 1.67

60 60

138 150

2.15 2.3 2.35 1.7 1.9 2.1 2.27 1.98 1.68 2.21

60

226

1.42

60

240

1.25

60

2.35

77

159

1.79

77

229

2.10

77 77 77

151 154 167

1.64 2.49 2.52

295 295

105 278

295 77-4 295 77-4 295 77-4

133 145 185 191 296 327

properties of carbon fibres. When the graphene has a three-dimensional order, the fibre is elastically stiffer, and it is called graphite. When the layers are translated or rotated relative to each other, with just the two-

0.83 0.62 0.96

128 60

Epoxy (3501-6)

1.04

1.24 0.69

295 295

Epoxy (semiflexible) Epoxy (semiflexible) PEEK PEEK Epoxy (semiflexible) Epoxy Epoxy

132 320 128

1.7 1.4 1.8 2.2 1.7 1.9 2.0 2.03

1.46 1.88 1.07 1.23 0.62 0.69

130 167 179 258

1.28 0.75 0.70 0.82 0.51 0.66

dimensional order of each layer preserved, the fibres are not as stiff, elastically, and they are called carbon fibres. Heat treatment at higher temperatures provides better ordering of the layers and, thus, graphite fibres.

Cryogenics 1994 Volume 34, Number 11 917

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda There is a difference in the microstructure (low moduli fibres typically have a higher percentage of carbon-like microstructures, and high moduli fibres typically have a higher percentage of graphite-like microstructures), but since all originate from the carbon element, for simplicity, all of these fibres are called carbon fibres in this review. Owing to the different microstructures achievable by heat treatment and the strong influence of the microstructure on mechanical properties, a large range of fibre elastic stiffness values is achievable. Low modulus fibres have tensile moduli of about 230 GPa at room temperature, whereas fibres with tensile moduli higher than 700 MPa are also produced. The density of carbon fibres also increases with increasing percentage of graphite structure; low modulus fibres have densities in the range 1.7-1.8gcm -3, and very high modulus fibres have densities in the range 1.9-2.0 g cm -3. Unfortunately, the production of high modulus (HM) fibres results in deterioration of fibre strength. In fibres produced from some chemicals, onion skin or smooth surfaces (or both) are formed, which provide poor matrix bonding. On cool-down from the high heat treatment temperatures, microcracking occurs more frequently owing to the strong differences in axial and radial thermal contraction. Another complication in the characterization of carbon fibres is that a least three different materials are currently used to produce them: polyacrylonitrile (PAN), rayon and pitches from petroleum asphalt, coal tar or polyvinyl chloride. Most fibres are now produced from PAN precursors. Fibres produced from PAN precursors are considered to have fewer surface defects, which leads to higher strength. Typical room temperature elastic moduli of the common carbon fibre grades are 230-255 GPa [high strength (HS), low modulus], 270-285 GPa [medium modulus (MM)] and 380-390GPa (HM). Very high modulus and ultrahigh modulus fibres are produced that have elastic moduli of about 520 and 690-830 GPa, respectively. The corresponding ranges of tensile strengths are 3.3-15.2 GPa (HS), 4.8-6.8 GPa (MM), 2.4-5.5 GPa (HM) and 1.7-2.4 GPa (higher modulus). The densities of all grades of carbon fibres range from 1.76 to 2.0gcm -3, and average filament diameters usually range from 4 to 8/zm. Higher modulus grades contain 96-100% carbon; lower modulus grades contain 92-97% carbon, with nitrogen as the principal additional element. A summary of the data on carbon-based fibres is provided in Table 6. Note the wide variability in both the elastic moduli and strengths. For this reason, plots of strength versus elastic moduli for both tensile and compressive forces are presented in Figures 1 and 2, respectively. Also indicated on these figures are the approximate ranges for the HS, MM and HM fibres. The tensile strengths are, on average, higher than the compressive strengths when the two figures are compared. The general trend of Figures 1 and 2 is a reduction in strength with increasing moduli. However,

918

Cryogenics 1994 Volume 34, Number 11

3.00 o

0

"~2.50 11. (.9

++

uE 2.00 -4--

L.4-

+ +

o+ oo

I [

HS 1.50

(/)

~8

+ +

0 O~

c~°oo

+

~

°°o° 0

++OF oF o o o 0

1.00 om (0

c: F-- 0 . 5 0

~b

+

o

o o

o

•

0.00 50

o4>1-

o%

I

I

I

100

150

200

-

HM

I 250

300

I

350

Tensile Modulus (GPa) Figure I Tensile strength v e r s u s tensile m o d u l u s for unidirectional (0 °) carbon fibre laminates. O, Data at 295K; +, data at 77 and 4 K

the relationship between strength and elastic stiffness is not linear for the three grades; in general, the strengths of the laminates produced from high strength fibres are disproportionately higher than those of the other two grades. The tensile results are separated according to test temperature to show the slight increase in strength (with very large data scatter) and elastic modulus on cooling to low temperatures. Within the scatter, this trend is not as apparent for the compressive data, and hence all data are plotted together. From Figures I and 2, it is noticeable that the tensile and compressive strengths and elastic moduli of the unidirectional laminates constructed from HS fibres fall into 'blocks'. From these blocks of random data points, the variability can be estimated for the tensile data: +0.5GPa strength and +30GPa modulus. This produces an average uncertainty of about +33% for the strength and +20% for the elastic modulus at room temperature. When the three, very high (>2.5 GPa) room temperature data points are included, the uncertainty of the strength increases to about +85%. For the compressive data, the uncertainties of the strength and 2.00

0 13(.9 j:

1.50

o> t-

0

Hs

o00 0

S

0

l_

O

Ul 1.00 q)

0

0

#

.>

Oo

0

0.50 Q.

O

E

o o

o

MM

0.00 5O

I 100

I 150

I 200

•

I 250

HM

I 300

350

Compressive Modulus (GPa) Flgure 2 Compressive strength v e r s u s compressive m o d u l u s for unidirectional (0 °) carbon fibre laminates

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda elastic modulus are about +25%. The best values for the three grades are also included in Table 6. Generally, the elastic moduli of the laminates increase about 10% on cooling to the range 77-4 K. Tensile strengths increase from 10 to 30% on cooling, whereas the temperature dependence of the compressive values are inconsistent from author to author.

2.50 o I:1.. (_9 2.00 t-D~ k.

"g 1-

._..._~--~

1.50

1.oo

Comparison of laminate properties -i

Mechanical properties

0.50 0

High modulus carbon fibres have considerably greater elastic stiffness than the other fibres considered in this review, as illustrated in Figure 3, a plot of the elastic moduli of all reinforcement fibres versus temperature. The lowest elastic moduli result from E-glass reinforcement; S-glass reinforced laminates have about 30% greater stiffness with the same temperature dependence. Alumina-fibre reinforcement adds considerably more to the elastic stiffness than glass fibre reinforcement and has a similar dependence on temperature. Of the non-carbon fibre reinforcements, boron has the highest elastic modulus and also a larger temperature dependence than alumina and glass fibres. High tensile strength at all temperatures is demonstrated by unidirectional laminates reinforced with boron, HS carbon and S-glass fibres. All tensile strength data are plotted in Figure 4. Laminates reinforced with HM carbon fibres have the lowest tensile strengths at all temperatures. Of the three highest strength laminates, S-glass reinforcement produces the highest tensile strengths, on average, at all temperatures. Boron reinforcements produce the lowest strengths of these higher strength laminates. The

I

I

I

I

50

100

150

200

250

500

Temperature (K) • boron O aluminl

O aramid n S~lass

• •

E-glass HS carbon

Z~ MM carbon • HM carbon

Figure 4

Tensile strength as a function of temperature for unidirectional (0°) fibre-reinforced laminates

lower tensile strengths at 4 K than at 77 K of boron reinforcement may reflect testing irregularities rather than material properties. The room temperature tensile strengths of unidirectional, 0° orientated fibre-reinforced laminates with epoxy matrices are directly related to the fibre tensile strength. This is demonstrated in Figure 5. Only the alumina fibre laminate data appear to fall slightly below the major trend of the other fibres. This dependence strongly suggests that the matrix resin plays a secondary role in affecting the tensile strengths of unidirectional (0° fibre orientation) laminates and that the tensile strength of the fibre plays the major role. This influence may well extend to low temperature laminate strengths, but at present this is impossible to demonstrate owing to the lack of fibre tensile data at cryogenic temperatures.

350 A--__

I

2.50

__

300 0_ (D 250

(~2.00 r"

-.1~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(n

~

2OO ~

150

U3

o-- . . . . .

1.00

.+--

(1)

~-

1.50

100

D c"~ 0.50 0 __J

O ........

c43--

F-0 0

I

I

I

50

100

150

~-

200

I

0.00

I

250

300

•

boron

Flgure 3

O aramid

•

E-glass

Z~ MM carbon

13 S-glass

•

HScarbon

•

HM carbon

Tensile modulus as a function of temperature for unidirectional (0°) fibre-reinforced laminates

I

3.0

4.0

5.0

Fiber Strength (GPa)

Temperature (K) O alumina

I

2.0

1.0

•

boron

O aramid

•

E-glass

A

MM carbon

0

alumina

[]

•

HS carbon

•

HM carbon

S-glass

Figure 5 Tensile strength of unidirectional (0°) fibre-reinforced laminates as a function of fibre tensile strength at 295 K

Cryogenics 1994 Volume 34, Number 11 919

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda

~

2.00

i

" ~ 1.75 Q_ (.~

,r- 1.50 1.25 $-,4-,

b~ _~ 1.oo

I---

295 K

_4K ~~

~

0.75

I 150

0.50 100

I 200

I 250

I 300

350

Tensile Modulus (GPo) Rgure 6 Tensile strength versus tensile modulus of carbon fibre, unidirectional (0°) laminates for three grades (HS, M M and HM)

The tensile strength is also dependent on the fibre volume per cent under similar processing and resin conditions. However, careful examination of the tabular data (Tables 1-6) does not indicate this correlation. The data presented in Figure 5 represent 50-60 fibre vol%. In general, there is no relation between the elastic

Table 7

modulus of the laminate and the tensile (or compressive) strength of the laminates. For carbon fibres, however, as the tensile elastic modulus increases, the tensile strength decreases, as shown in Figure 6 for the three grades included in this review at room and low temperatures. This dependence is related to the effects of the surface and material properties or fracture mechanisms of the three grades with differing percentages of the graphene structure, which are discussed earlier in the carbon section. The compressive strengths of boron unidirectional laminates are far superior to those of all others. Indeed, boron's compressive strength is a factor of two better than those of its competitors. This probably arises from the composite nature of the boron fibre (see earlier discussion) that reduces the tendency for microbuckling. The compressive strengths of both S-glass and alumina show good improvement at low temperatures, but the properties of laminates reinforced with carbon or aramid fibres either degrade or show little increase at low temperatures. Thus at cryogenic temperatures, the S-glass and alumina laminates have compressive strengths about twice as high as those of the carbon and aramid laminates. In general, following boron, the second best fibre for compressive reinforcement appears to be S-glass.

Fatigue strengths of boron, alumina, aramid, S-glass and E-glass unidirectional laminates

Author (year) Weeton e t a / . (1987) Morris 2e (1989) Hartwig and Knaak2s (1984)

Resin system

Test mode

Fatigue strength (GPa) Test temperature 100 102 103 104 10s (K)

Boron

Epoxy

Tension

295

1.23 1.19 1.14 1.07 0.94

Alumina

Epoxy

Tension

295

0.91 0.75 0.62 0.52 0.48

Fibre TM

Fibre type

Fibre volume (%)

108

10~

0.84

1.3

Aramid

Kevlar 49

Epoxy

Tension

77

Weetoneta/. is Aramid

Kevlar 49

Tension

295

1.12 1.07 1.00 0.94

Morris 28 Aramid (1989) Weeton e t a l ? s Glass (1987) Morris 2e Glass (1989) Brivio e t a l . 5s Glass (1983) Glass Glass Kasen2 Glass (1975)

Kevlar 49

Epoxy (3MSP-306) Epoxy

Tension

295

1.14 1.07 1.00

S

Epoxy

Tension

295

S

Epoxy

Tension

295

0.79 0.48 0.35 0.28 0.28

Epoxy (5216) Epoxy (920) Epoxy (920) Epoxy Scotchply 1002 Epoxy

Tension Tension Tension Tension

295 295 295 76

1.05 0.83 0.67 0.53 0.44 1.15 0.97 0.86 0.68 0.51 0.38 0.95 0.80 0.63 0.50 0.42 0.43

Tension Tension

295 77 20 295

Tension

295

Compression 295

R R S-2 E

67 76 68

Kasenz (1975)

Glass

E (woven)

Hwang and Han s9 (1989) Morris 26 (1989) Gu and Abdelsalam 39 (1990)

Glass

E

Glass

E

Epoxy Scotchply 1002 Epoxy

Glass

E

Epoxy

aNot provided in report; 'best value' assumed for tensile strength

920

Cryogenics 1994 Volume 34, Number 11

1.60 a

0.83

0.48 0.43 0.32 0.25

0.12 0.28 0.28 0.77

0.68 0.62 0.51 0.42 0.35 0.24 0.14 0.09

0.82

0.70 0.65 0.60 0.55 0.50

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda Table 8 Fatigue strength of carbon unidirectional laminates

Author (year)

Fibre

Fibre type

Grimes 4a

Carbon

AS

Carbon

T-300 M40A

Carbon

AS

Carbon

AS

Carbon

Weeton e t a / . (1987) Ahlborn 49

TM

Test Fatigue strength (GPa) temperature (K) 100 102 103 104

Resin system

Test mode

Epoxy (3501-6) Epoxy Epoxy

Compression 295

1.34

Tension Tension

77 77

2.1 1.4

Tension

295

AS

Epoxy (3501) Epoxy (3501) Epoxy

Tension

295

Carbon

T-300

Rigid epoxy

Tension

77

Carbon

AS-4

Epoxy

Tension

295

(1981) Hartwig and Knaak2s (1984) Rosen and Hashin 60 (1987)

Fibre volume (%)

1.25

10s

108

107

1.20 1.10 1.00 0.89 1.78 1.19

1.3

Compression 295

1.0

0.98 0.97 0.97

1.2

1.1

0.97 0.86

1.46 a 1.0

0.95 0.90 0.89 0.88 0.88

1.25

1.23 1.20 1.17 1.15 1.12

1.24

(1988) Lee et al. 6~ (1989) Morris 26 (1989) Ahlborn s3 (1991) Bansemir and Haider 5s (1991) Pannkoke and Wagner s8 ( 1991 ) Hartwig and Pannkoke s7 (1992)

Carbon

1.50 ~ 1.40

1.33 1.26 1.18 1.11 1.31 1.19 1.10 0.97

Epoxy

295 77 77 293 76

1.9 2.3

1.84 2.23 1.65 2.20

1.71 2.07 1.62 2.16

Carbon Carbon Carbon

HTA7 AS4 T-300

PC Tension PEEK Tension Epoxy (M10) Bending

1.56 1.89 1.55 2.13

Carbon Carbon

PEEK Epoxy

Tension Tension

77 77

2.30 2.35

1.98 2.02

1.61 1.40 1.20 1.08 0.92 1.88 1.72 1.57 1.46 1.41

Carbon

As-4 G30500 AS-4

Tension

77

2.52

2.4

2.3

2.1

1.88 1.6

1.3

Carbon

M40

Tension

77

1.79

1.7

1.65 1.6

1.55 1.5

1.45

Carbon

T-300

Tension

77

2.10

2.1

2.0

1.4

Carbon

T-300

Semiflexible epoxy Semiflexible epoxy Semiflexible epoxy Brittle epoxy

Tension

77

1.66

1.5

1.45 1.4

1.5

1.29 1.56 1.42 2.02

1.03 1.24 1.29 1.89

0.84 0.99 1.20 1.80

1.25 1.15

1.35 1.3

1.25

aNot provided in report; 'best value' assumed for tensile strength

Fatigue

The limited fatigue tests performed on unidirectional fibre-reinforced laminates at low temperatures are summarized in Table 7 for all fibres except carbon and in Table 8 for carbon fibres. Most fatigue tests are tensile with small, positive R ratios (minimum stress or strain/maximum stress or strain); the effects of the R ratio on fatigue life cannot be determined from the few data available. Most of the non-carbon fibre tests included in this review were conducted at room temperature; most of the carbon fibre data, at low temperatures. The data of Kasen2 for a woven glass fabric reinforcement were included because they were tested at a lower temperature (20K) than the other fibres. Very generally, at room temperature, the laminate high cycle (106 cycle) fatigue strengths depend on the elastic moduli of the laminate, as shown in Figure 7. In the figure there appear to be two regions: one at tensile moduli less than about 130 GPa, and one at higher moduli. These two regions also appear for the available low temperature data, except that within the higher region, the fatigue strength seems to be constant and independent of the tensile moduli. However, the data are meagre, and the reader is cautioned that, perhaps, the reported data reflect scatter that leads to fortuitous

trend lines. Also, conflicting with these trends are the aramid fibre laminate data at room temperature; the

13~ 1.50 (.9 In 0) o

,/

77 K

"5 >, 1.00

290K

c0.50 O3 G)

0.00

0

I

I

{

I

50

100

150

200

Tensile

I 250

I 300

350

Modulus (OPa)

•

boron

<> aramid

•

E-glass

o

alumina

O S-glass

•

HS carbon

•

HM carbon

Figure 7 Average fatigue strength at 106 cycles (R = +) versus tensile modulus of unidirectional (0°) fibre-reinforced laminates. Circled symbols are data at 77 K; other symbols are data at 295 K

Cryogenics

1994 Volume

34, N u m b e r

11

921

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda fatigue strength reported by Weeton et al. 15 and Morris26 (perhaps representing the same data) is clearly much higher, considering the tensile modulus, than other data. The stronger dependence of the fatigue strength on tensile moduli of the low temperature data (clearly stronger than the room temperature dependences)

probably reflects the increase in the resin modulus at low temperatures. This supports the work of Hartwig and Pannkoke57, who used both brittle and semi° flexible epoxy resins in laminates that were tested only at 77 K. They found less sensitivity to fatigue (a lower per cent reduction of fatigue life) when brittle resins were used. Similarly, from Figure 7, at low tempera-

Table 9 Thermal expansion of unidirectional fibre composites

Author (year)

Material type

Fibre

Resin system

Schramm and Kasen" (1977) Kolek e t al. 62 (1978) Takeno e t al. z° (1986)

Boron

5.6 mil

2387

Boron

Fibre volume (%)

~/.JL (%) 295--,77 K

295--,4 K

-0.043

-0.05

50

-0.048

-0.06 *

50

-0.09

-0.10"

60

+0.082

+0.090

-0.06

-0.07

Alumina

~,

Hartwig and Knaak28 1984) Schramm and Kasen" 1977) Kasen3 1981) Rosenberg ~ 1982) Hartwig and Knaak28 1984) Takeno e t al. 2° 1986)

Aramid

Kevlar 49

Araldite (CY205/HY905/ DY040/DY061 ) X183/HY905

Glass

S

Resin 2 epoxy

Glass Glass Glass

R E

DGEBA DGEBA Epoxy

63 51 75

-0.08 -0.12 -0.085

-0.09 -0.14 -0.095

Glass

E

DGEBA

70

-0.177

-0.162

Glass

E

50

-0.14

Wang e t al. 94 (1990)

Glass Glass Glass

E E E

Reed et a/. 65

Glass

E

Araldite (CY205/HY905/ DY040/DY061 ) Epoxy Epoxy PPC DGEBA

54 54 56 72

-0.02 -0.60 -0.11 -0.11

-0.12

Carbon

Epoxy (3002) Epoxy (P13N) Epoxy (3002) Epoxy (Resin 2)

66 58 56

Carbon

HS graphite HS graphite HM graphite A8 graphite

+0.0080 +0.0068 +0.0094 -0.010

-0.01

Carbon

HMS graphite

DGEBA

55

+0.01

+0.02

Carbon Carbon Carbon Carbon Carbon

Graphite (M40A) Graphite (T-300) HT graphite A graphite Graphite (M40A)

60

+0.013 +0.003 +0.073

+0.0215 +0.0274 +0.017 +0.007 +0.15

Carbon

HS graphite (T-300)

50

-0.012

-0.03"

Carbon

HS graphite (T-300)

70

+0.037

+0.044

Carbon

HS graphite (T-300)

+0.039

+0.045

Carbon Carbon Carbon

HS graphite (T-300) HS graphite (T-300) Graphite (M40A)

+0.16

Carbon

(1992) Freeman and Campbell es (1972) Schramm and Kasen11 (1977) Kasen3 (1981) Hartwig44 (1982) Rosenberg 83 (1982) Weiss ~ (1982) Takeno e t a / , 2° (1986) Hartwig4 (1988) Kramer 87 (1990) Wang e t al. ~ (1990) Bansemir and Haider ss (1991) Schwartz e t al. 69 (1991) Best vaues

Boron Alumina Aramid Glass Glass Carbon Carbon

Epoxy Epoxy Epoxy (CY221/HY979) Epoxy [Araldite (CY205/HY905/ DY040/DY061)] Epoxy (X183/HY905) Epoxy

51 56 60

-0.01 -0.02 +0.1

HS graphite (AS-4) HS graphite (HTA7)

PPC Epoxy Epoxy (CY221/HY979) PEEK Polycarbonate

51 61

0 0

7 Kevlar 49 E S HS graphite HM graphite

Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy

50 50 60 70 60 60 60

• Extrapolated from 295-77 K data

922

6O 60

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

-0.048 -0.09 +0.082 -0.11 -0.08 -0.020 +0.016

-0.054 -0.10 +0.090 -0.12 -0.09 -0.025 +0.020

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda tures the more brittle resin (with respect to room temperature values) results in higher than expected high cycle fatigue strengths.

v

10 2 ¢

t

10 ~

•~

Thermal properties The per cent thermal expansion or contraction of unidirectional laminates produced from each fibre on cooling from 293 K to low temperatures is plotted in Figure 8. The source and characterization of the cryogenic data are summarized in Table 9. Two fibres, carbon and aramid, expand in their axial direction on cooling; the aramid fibres expand as much as 0.09% on cooling to 4 K. There is a small difference between the expansion characteristics of the various grades of carbon fibres; the higher the elastic modulus, the less the carbon fibre expands in the axial direction on cooling. Both aramid and carbon fibres and laminates contract in their normal (transverse) directions on cooling. Of the other fibres, glass contracts more (0.12%) and boron less (=0.05%) on cooling to 4 K. Apparently, Sglass laminates contract slightly less than E-glass (see Table 9), although precise measurements from the same laboratory would provide more conclusive evidence. Epoxy resins contract from 0.85 to 1.2% on cooling from 293 to 4 K, about an order of magnitude more than glass and alumina fibres, but much more than the other fibres contract. These strong contraction differences on cooling are suspected to enhance the existing residual stresses at the fibre/matrix interface. In instances of sudden cooling or at locations of stress concentrations, these residual stresses tend to result in local microcracking and reduced strength levels. In these cases, the fibres that contract more on cooling (E-glass, S-glass and alumina) may be better suited for use in such structures.

0.10

o~

0.05

C 0

(-

o.o0

__

-0.05

(0 O. X LU ¢0

- . . . . . . .

/ . ./.-.--;~---~-~........................................

10 ~

1 I~"fJB~

I-- 10-20 r"

50

1O0

150

200

250

}00

Temperature (K) •

boron

0

aramid

•

HS carbon

0

alumina

0

S-glass

•

HM carbon

Figure 9 Thermal conductivity at low temperatures of unidirectional (0°) fibre-reinforced laminates

As mentioned earlier, the aramid and carbon fibres have negative coefficients of thermal expansion in their axial direction. In contrast, these fibres contract on cooling in directions transverse to the axis of the fibres. For the aramid Kevlar49, the contraction on cooling to 4 K in the transverse direction is about 1.5%, larger than that of typical epoxies (0.84-1.3%). These directional contraction disparities are caused by the strong axial and weak transverse bonds of the aramid and carbon structures. Thermal conductivity of fibres for unidirectional composite cryogenic structures is usually very impor-. tant in cryogenic support structures. In Figure 9, the thermal conductivities from 295 to 4 K that have been measured for unidirectional laminates produced with each type of fibre are plotted. The sources and characterization of the studies are summarized in Table 10. Note the strong, higher dependence of the thermal conductivity of the carbon fibres on elastic modulus; the higher the elastic stiffness, the higher the thermal conductivity. This dependence apparently changes at very low (<5 K) temperatures. In Table 10, there is large disparity between the reported thermal conductivity data for the aramid fibre laminates. The results of Hartwig and Knaak 25 have been selected as most representative and are plotted in

Figure 9.

E (D .E

~)

L)~

-

-0.10 -0.15 0

I

I

I

I

I

50

100

150

200

250

300

Temperature (K) •

boron

O alumina

O aramid

•

E-glass

C2 S-glass

•

HS carbon

•

HM carbon

Figure $ Thermal expansion on cooling from 295K to low temperatures of unidirectional (0 °) fibre-reinforced laminates

The crossing over of the carbon and glass thermal conductivity curves at about 30 K has led to consideration at low temperatures (<77 K) of carbon-reinforced composites and at high temperatures (77-295 K) of glass-reinforced composites for structures in which heat leakage is a significant factor. At low temperatures, the thermal conductivity of boron laminates is clearly the highest, and the temperature of the initiation of the strong decrease of thermal conductivity with decreasing temperature is the lowest, not occurring until about 50 K. In laminates at higher (ambient) temperatures, the fibre conductivity domin-

Cryogenics 1994 Volume 34, Number 11

923

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda Table 10 Thermal conductivity of unidirectional fibre composites Fibre volume (%)

Author (year)

Material type

Chamis88 (1968)

Boron

Kasen3 (1981) Evans and Morgan7° Takeno e t al. 2° (1986)

Boron Boron Alumina

y

Kasen3 (1981) Evans and Morgan71 (1983) Hartwig and Knaak28 (1964) Bansemir and Haiderss (1991) Chamis69 (1968)

Aramid Aramid

Kevlar 49 Kevlar

Aramid

Kevlar

Aramid

Kevlar

Glass

Epoxy Epoxy Epoxy Epoxy Epoxy

50a 60 a 70"

Glass Glass Glass

E E E E S E

65

Glass

E

Epikote 828, NMA, BDMA

Kasen2 (1975) Kasen3 (1981) Evans and Morgan7° (1982) Radcliffe and Rosenberg72 (1982) Rosenberge3 (1982) Evans and Morgan71 (1983) Takeno e t a / . 2° (1986)

Fibre

Resin system Epoxy Epoxy Epoxy Epoxy Epoxy Araldite (CY205/HY905/ DY044/DN061) Epoxy Epoxy

~" (W m-1 K-l) Density (g cm -°)

50" 60 ° 70 a 52 50 50

4K

0.23

77 K

0.06 0.064 0.025

1.0 0.17

2.0

57 60

0.05

1.0

2.0

0.30

0.75

0.18 0.10 0.08

0.325 0.45 0.26

0.65 0.74 0.85 0.75 0.90 0.6

0.087 0.070 0.063 0.09

0.46

Glass

Epoxy

Glass

Epoxy

70

0.4

0.94

Araldite (CY205/HY905/ DY044/DN061)

50

0.10

0.32

Dmirevsky e t al. 73 (1987) Mclvor e t aZ 74 (1990) Rule and Reed78 (1992) Kasen3 (1981) Hartwig '~ (1982)

Glass

Radcliffe and Rosenberg72 (1982)

Carbon

Rosenberge3 (1982)

Carbon

Evans and Morgan71 (1983) Takeno e t al. 2° (1986)

Carbon

E

50

Glass

R

Fibrelux 914

Glass

E

DGEBA

Carbon Carbon

Graphite Graphite (T-300) Graphite (M40A) A graphite HT graphite HM graphite HM graphite HM graphite HT graphite A graphite Graphite

Epoxy Epoxy

Carbon

HS graphite (T-300)

Mclvor e t aZ 74 (1990) Bansemir and Haider55 (1991)

Carbon

Graphite (GY-80)

Carbon

Graphite (M40A) HT graphite HM graphite

Best values

Boron Alumina Aramid Glass Caron Carbon

y Kevlar HM graphite HS graphite

1.7 2.0 2.3 2.1

2.0 1.1 0.4

70 45 35 60

Glass

295 K

1.85

1.2

0.05

0.65

0.054 0.73 0.097

60 60 31 46 51 51 60 60 60 55

0.45 0.036 0.036 0.03 0.025 0.025 0.03 0.024 0.024 0.03 0.2

0.98 0.95 5.0 2.2 4.0 10.2 9.0 9 2 0.8 7.0

5.0 5.0 28

50 Araldite (CY205/HY905/ DY044/DN061) Code 69

0.05

0.65

3.2

EY221/HY979 Epoxy

0.025

9 1.6 7

34 8 32

0.23 0.06 0.05 0.09 0.030 0.036

2.0 0.4 1.0 0.37 9 1.7

2.1 1.2 2.0 0.70 32 5.3

Epikote 828, NMA, BDMA Epoxy Epoxy Epoxy Epoxy Epoxy

Epoxy Epoxy Epoxy Epoxy Epoxy Epoxy

60 60 60

0.372

0.675

72

2.3

eEstimate

ates in the 0° orientation (axial fibre axis). In general, the conductivity of the fibres (especially carbon/ graphite) is more temperature dependent than that of

924

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

the epoxy resin matrix. At very low temperatures, the thermal conductivity of the resin is higher than that of carbon/graphite fibres and about equivalent to that of

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda Table 11 Specific heat of epoxy, E-glass and E-glass-reinforced composites

C (J g-1 K-l) Author

Material type

Resin system

Kasen2 (1975) Evans and Morgan 77 (1986) Okada e t al. 76 (1990)

E-glass E-glass

Epoxy

E-glass

Epoxy Epoxy

Best values

E-glass

Epoxy

(year)

Density

(g cm -a)

4K

76 K

295 K

0.002

0.22 0.52 0.18 0.19

0.90 1.04 0.74 0.82

0.002

0.20

0.85

=0.01

glass fibres. Hartwig 44 and Hartwig and Knaak 25 have attributed the strong dependence of the thermal conductivity of carbon/graphite fibre laminates to the freezing-in of the very strong electronic contribution of the conductivity. The magnitude of the room temperature thermal conductivity is, therefore, related to the electrical conductivity of these fibres, and the electrical conductivity of the HM fibres is about 2.5 times higher than that of the HS fibres. This large difference is caused by the larger areas of graphite structure in the HM fibre. The degree of anisotropy of the thermal conductivity in carbon/graphite fibres also diminishes at low temperatures and tends to be isotropic when phonons are the dominant transport mechanism. As might be expected, then, the thermal conductivity of unidirectional, fibre-reinforced laminates is anisotropic. This anisotropy is strong at room temperature, but diminishes at low temperatures, where phonon transport dominates and the conductivities of fibre and resin are about the same. For a glass/epoxy laminate at room temperature, Evans and Morgan reported ~50% less thermal conductivity along the 0° fibre orientation than in the through-thickness (transverse) direction. At 77 K, this anisotropy was about 30% 7°. Kasen has reviewed the low temperature (300- 77 K) specific heat data for E-glass reinforced composites2. Later, Okada et al. reported the specific heat of an E-glass-reinforced composite over the temperature range 300-4 K 76. Evans reported the low temperature specific heat of epoxy resin and glass77. Their data are summarized in Table 11. To a first approximation, the specific heat of glass/ epoxy composites is linear with temperature over the range 77-300K. Below about 10-15K, the specific heat decreases more rapidly with decreasing temperature and approaches zero. The specific heat of a glass composite is comparable to that of metals, especially aluminium. Many other alloys, such as stainless steel, have much lower specific heats, especially near room temperature.

Thermomechanical properties Although many 'figures of merit' can be used for

composite support structures for cryogenic applications, one of the most common is the ratio of strength to thermal conductivity. In Figure 10 the ratio of tensile strength to thermal conductivity is plotted for each type of fibre reinforcement. Clearly, the S-glass is superior at all temperatures above 20K; below 20K, the HS carbon fibre laminate properties have a higher figure of merit. At very low temperatures, the lowest figure of merit is that of boron; at higher temperatures, the lowest figures of merit are those of HM carbon fibre laminates. The ratio of compressive strength to thermal conductivity, from the best values of Tables 1-6 and 10, are plotted versus temperature in Figure 11. Despite the extraordinarily high compressive strength of the boron laminates, the compressive figure of merit of this reinforcement is slightly less than that of S-glass at all temperatures. At very low temperatures (<--50K), alumina reinforcement offers the best combination of compressive strength and thermal conductivity, and HS carbon fibres are also slightly better than glass fibres at4K. When the tensile and compressive figures of merit (Figures 10 and 11, respectively) are compared, it is clear that the best laminates in tension are superior to .~_~

10 2

~" ~

101

"'~..

10-1~ 10-2 0

50

1 O0

150

200

250

300

Temperature (K) • boron

0 alumina

O ira.mid [3

S-glass

• HS carbon •

HMcarbon

Figure 10 Ratio of tensile strength/thermal conductivity for unidirectional (0°) fibre-reinforced laminates as a function of temperature

C r y o g e n i c s 1994 V o l u m e 34, N u m b e r 11

925

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda o_ > +~ "E~ ¢.-

10 2

101

O~

~ I o° ~(~

10 -1

(f)

In-2

~''~L

.

t 0

I

I

200

250

J

50

100

150

300

Temperature (K) •

boron

O alumina

0

aramid

•

E-glass

O S-glass

•

HS carbon

•

HM carbon

Figure 11 Ratio of compressive strength to thermal conductivity for unidirectional (0°) fibre-reinforced laminates as a function of temperature

the best laminates in compression. For example, in the temperature range 295-77K, the S-glass tensile-tothermal conductivity ratios between 1.9 and 5.3 GPa/ (Wm -1K -I) are at least 25% higher than the compressive values [1.4-4.0GPa/(Wm-tK-1)]. At lower temperatures, even greater advantage can be gained by using tensile loads, since the ratios in tension from 77 to 4K are 5.3-52GPa/(Wm-lK -1) and 4.1-25GPa/ (Wm -1K -1) in compression. Thus a factor of two is gained in these parameters under tensile loading. Cryogenic support structures usually are subjected to fatigue loading, in addition to static tensile or compression loading. In such cases, the fatigue strength can be design limiting. In Figure 12, the ratio of fatigue strength at 106 cycles to the thermal conductivity (from

~. > o_ 4-J O

102

"O C

101

lO°

\

"~'~'~ --~T . . . . . . . . . . .

o•O

r-~

I--c03

10_ 2 0

I

50

I

100

I

I

150

200

I

250

300

Temperature (K) •

boron

O aramid

O

alumina

[] S-glass

• •

E-glass

•

HM carbun

HS carbon

Figure 12 Ratio of tensile fatigue strength at 106 cycles to thermal conductivity of unidirectional, fibre-reinforced laminates v e r s u s temperature

926 Cryogenics 1994 Volume 34, Number 11

data given in Tables 7, 8 and 10) is plotted versus temperature. The data are scarce, and the reader is cautioned to view Figure 12 as very preliminary. Do not select material on the basis of these plots. In the temperature range 295-77 K, owing to the paucity of low temperature data for boron, alumina and S-glass, it is not dear which fibre reinforcement is better. However, all of these fibres plus aramid and E-glass are probably superior to carbon fibres under fatigue loading. At very low temperatures, carbon fibre reinforcement is again competitive and is indeed superior to other fibre reinforcements; on the basis of dynamic loading criteria, HM carbon fibre reinforcements are very competitive. The very approximate temperature range for carbon fibre superiority under fatigue loading is 4-25 K. It is strongly recommended that additional fatigue tests be conducted to establish maximum allowable cyclic stresses for any fibre reinforcement for cryogenic structural supports.

Summary The mechanical and thermal properties of fibrereinforced composites at low temperatures (4-295 K) have been critically reviewed. The review is restricted to unidirectional fibre layout in the 0° orientation (parallel to the fibre) of epoxy matrix laminate plates. Fibres that were included are boron, alumina, aramid, R-glass, S-glass, E-glass and carbon (graphite). The properties include tensile, compressive, fatigue, thermal conductivity, thermal expansion and specific heat. The data indicate that composite tensile strengths and moduli depend primarily on the fibre strength and moduli, but compressive and fatigue properties depend also on the matrix resin. Unidirectional laminate strengths are always stronger at low (~<77 K) temperatures than at room temperature. S-glass and high strength carbon fibre-reinforced laminates have the highest room and low temperature strengths in tension. Boron reinforcement leads to the highest compressive strengths at all temperatures. The fibres have a wide range of thermal properties at low temperatures. Two fibres, aramid and carbon (graphite), expand axially on cooling to low temperatures. The thermal conductivities of glass and alumina are relatively low at ambient temperatures, but at very low temperatures (<30 K), the thermal conductivities of carbon fibres are the lowest. Specific heats of fibrereinforced composites are comparable to, or higher than, those of metals and alloys used in cryogenic structures. On the basis of the mechanical and thermal properties, but independent of fibre cost, S-glass is suggested for cryogenic support structures at temperatures above 20 K; below 20 K, high strength carbon (graphite) fibres are recommended. In applications where fatigue loading to stresses of the order of 25% of the major loads

Cryogenic properties of unidirectional composites: R.P. Reed and M. Golda occurs, carbon (graphite) fibre reinforcement is likely to result in less heat leakage owing to its better fatigue resistance.

24 25

References 1 Kittcl, P. Comparison of Dewar supports for space applications Cryogenics (1993) 33 429-434 2 Kasen, M.B. Mechanical and thermal properties of filamentaryreinforced structural composites at cryogenic temperatures. 1: Glass-reinforced composites Cryogenics (1975) 15 327-349 3 Kasen, M.B. Cryogenic properties of filamentary-reinforced composites: an update Cryogenics (1981) 21 323-340 4 Hartwig, G. Overview of advanced fibre composites Cryogenics (1988) 28 216-219 5 Swartz, H.S. Part 1, AFML-TR-66-404, Air Force Materials Laboratory, Dayton, Ohio, USA (August 1966) 6 Nadler, M.A., Yoshino, S.Y. and Darms, F.J. Report SD 68-99501, North American Rockwell Space Division, Canoga Park, California, USA (1969) 7 Suarez, J.A., Whiteslde, J.B. and Hadcoek, R.N. The influence of local failure modes on the compressive strength of boronepoxy composites, in: Composite Materials: Testing and Design (Second Conference) ASTM STP 497, American Society for Testing and Materials, Philadelphia, USA (1972) 237-256 8 Weeton, J.W. and Scala, E. 0gds) Composites: State of the Art Proceedings of the Metallurgical Society of AIME, American Institute of Metallurgical Engineers, New York, USA (1974) 52 9 Bert, C.W. Experimental characterization of composites, in: Structural Design and Analysis: Part II (Ed Chamis, C.C.) Vol 8, Academic Press, New York, USA (1975) Ch 9, 73-133 10 Renton, W.J. (Ed) Hybrid and Select Metal-Matrix Composites American Institute of Aeronautics and Astronautics, New York, USA (1977) 15, 16 11 Sehramm, R.E. and Ka~n, M.B. Cryogenic mechanical properties of boron-, graphite- and glass-reinforced composites Mater Sci Eng (1977) 30 197-204 12 Ledbetter, H.M. Dynamic elastic modulus and internal friction in fibrous composites, in: Nonmetallic Materials and Composites at Low Temperatures (Eds Clark, A.F., Reed, R.P, and Hartwig, G.) Plenum, New York, USA (1979) 267-281 13 Tsai, S.W. and Hahn, H.T. Introduction to Composite Materials Technomic, Lancaster, UK (1980) 19,292-295 14 Rosen, B.W. and Dow, N.E. Overview of composite materials analysis and design, in: Engineered Materials Handbook. Vol 1: Composites ASM International, Metals Park, Ohio, USA (1988) 175-184 15 Weeton, J.W., Peters, D.M., and Thomas, K.L. (Eds) Polymer data: polymer matrix composites, in: Engineers' Guide to Composite Materials ASM International, Metals Park, Ohio, USA (1987) Section 6, 6-43-6-68 16 Mesnria, U. A new fibre reinforced thermoplast composite for potential radom application: PEEK-alumina, APC Development Laboratory, ICI Advanced Materials, Wilton, UK (paper presented at the University of Liverpool, UK, 23-25 March 1988) 17 Kriz, R.D. and McColskey, .I.D. Mechanical properties of Alumina-PEEK unidirectional composite: compression, shear, and tension Adv Cryog Eng Mater (1990) 36 921-927 18 Gu, Y.IL Compressive properties of continuous alumina fibreepoxy at 295 K and 77 K Cryogenics (1992) 32 399-402 19 Ohtani, Y., Nishijima, S., Okada, T. and Asano, K. Consideration of thermal insulating support system under radiation environment Adv Cryog Eng Mater (1992) 38 445-452 20 Takeno, M., Nishijima, S., Okada, T., Fujioka, K. et M. Thermal and mechanical properties of advanced composite materials at low temperatures Adv Cryo Eng Mater (1986) 32 217-224 21 Morgan, R.J. and Ailred, R.E. Aramid fiber reinforcements, in: Reference Book for Composite Technology (Ed Lee, S.M.) Technomic Publishing, Lancaster, Pennsylvania, USA (1989) 143-166 22 Clements, L.L. and Moore, R.L. SAMPE Q. (1977) 9 6 23 Chamis, C.C., Lark, R.F. and Sindalr, J.H. Mechanical property characterization of intraply hybrid composites, in:

26

27

28 29

30 31 32 33 34

35 36 37 38

39 40

41 42

43

44 45

Test Methods and Design Allowables for Fibrous Composites ASTM STP 734 (Ed Chamis, C.C.) American Society for Testing and Materials, Philadelphia, USA (1981) 261-280 Kasen, M.B. Mechanical performance of graphite- and aramidreinforced composites at cryogenic temperatures Adv Cryog Eng Mater (1982) 28 165-177 l-Iartwig, G. and Knaak, S. Fibre-epoxy composites at low temperatures Cryogenics (1984) 24 639-647 Morris, V.L. Advanced composite structures for cryogenic applications Proc 14th lnt SAMPE Symp Company Report: Structural Composites, Inc., Pomona, California, USA (May 1989) 1867-1876 Toth, L.W., Boner, T.J., Butcher, I.R., Kariotts, A.H. et M. Program for the evaluation of structural reinforced plastic materials at cryogenic temperatures, Final Report GER 12792 to George C. Marshall Space Flight Center, NASA by Goodyear Aerospace Corp. (August 1966) Broutman, L.J. Fiber-reinforced plastics, in: Modern Composite Materials (Eds Broutman, L.J. and Krock, R.) AddisonWesley, Reading, Massachusetts, USA (1967) 337-441 Lamothe, R.M. and Nunes, J. Evaluation of fixturing for compression testing of metal matrix and polymer-epoxy composites, in: Compression Testing of Homogeneous Materials and Composites ASTM STP 808 (Eds Chair, R. and Papirno, R.) American Society for Testing and Materials, Philadelphia, USA (1983) 241-253 Berg, J.S. and Adams, D.F. An evaluation of composite material compression test methods J Compos Technol Res (1989) 11 41-46 Sfivka, D.C. Unpublished report, Battelle Columbus Division, Columbus, Ohio, USA (1989) Tsai, S.W. and Kim, R.Y. Compression testing on composite rings Adv Cryog Eng Mater (1990) 36 843-851 Scala, E. Polymeric composites, in: Composite Materials for Combined Functions Hayden Book Company, Rochelle Park, New Jersey, USA (1968) Ch 13,200-227 Hedgepeth, J.M. and Haskeli, D.F. Structural mechanics of fiber-reinforced composites, in: Mechanics of Composite Materials (Eds Wendt, F.W., Liebowitz, H., and Perrone, N.) Pergamon, New York, USA (1967) 405-437 Dahlerup-Peterson, K. Tests of composite materials at cryogenic temperatures: facilities and results Adv Cryog Eng Mater (1980) 26 268-279 Leslie, J.C. Properties and performance requirements, in: Advanced Thermoset Composites (Ed Margulis, J.M.) Van Nostrand Reinhold, New York, USA (1986) 74-109 Scotchply 1002 Data Sheet, 3M Company, St Paul, Minnesota, USA (1988) Chamis, C.C. Simplified composite micromechanics equations for mechanical, thermal, and moisture-related properties, in: Engineers' Guide to Composite Materials (Eds Weeton, W., Peters D.M. and Thomas, K.L.) ASM International, Metals Park, Ohio, USA (1988) 3-8-3-24 Gu, Y.H. and Abdelsalam, M.K. Fatigue life of composites at room and cryogenic temperatures Adv Cryog Eng Mater (1990) 36 929-936 Reed, R.P. and McColskey, J.D. Properties of directionaily reinforced composites, in: Composite Struts for SMES Plants NISTIR-5011 (Eds Reed, R.P. and McColskey, J.D.), Report to Defense Nuclear Agency, Materials Reliability Division, National institute of Standards and Technology, Boulder, Colorado, USA (March 1994) Ch 5 Hancox, N.L. The compression strength of unidirectional carbon fibre reinforced plastic J Mater Sci (1975) 10 234-242 Clark, R.K. and Lisagor, W.B. Compression testing of graphiteepoxy composite materials, in: Test Methods and Design Allowables for Fibrous Composite ASTM STP 734 (Ed Chamis, C.C.) American Society for Testing and Materials, Philadelphia, USA (1981) 34-53 Grimes, G.C. Experimental study of compression-compression fatigue of graphite-epoxy composites, in: Test Methods and Design Allowables for Fibrous Composite ASTM STP 734 (Ed Chamis, C.C.) American Society for Testing and Materials, Philadelphia, USA (1981) 281-337 Hartwig, G. Reinforced polymers at low temperatures Adv Cryo Eng Mater (1982) 28 179-189 Philpot, K.A. and Randolph, R.E. The use of graphite-epoxy composites in aerospace structures subject to low temperatures, in: Non-metallic Materials and Composites at Low Temperatures

Cryogenics 1994 Volume 34, Number 11

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Cryogenic properties of unidirectional composites: R.P. Reed and/14. Golda

46

47

48 49 50

51

52 53 54

55 56 57 58

59

60 61

(Eds Hatwig, G. and Evans, D.) Vol 2, Plenum, New York, USA (1982) 311-325 Weiss, W. Low temperature properties of carbon fibre reinforced epoxide resins, in: Nonmetallic Materials and Composites at Low Temperatures (Eds I-Iartwig, G. and Evans, D.) Vol 2, Plenum, New York, USA (1982) 293-309 Sinclair, J.H. and C.C. Chamis. Compressive behavior of unidirectional fibrous composites, in: Compression Testing of Homogeneous Materials and Composites ASTM STP 808 (Eds Chait, R. and Papirno, R.) American Society for Testing and Materials, Philadelphia, USA (1983) 155-174 Hahn, H.T. and Williams, J.G. Compression failure mechanisms in unidirectional composites, NASA Technical Memorandum 85834 (August 1984) 1-41 Aldborn, K. Fatigue behaviour of carbon fibre reinforced plastic at cryogenic temperatures Cryogenics (1988) 28 267-272 Shuart, M.J. Failure of compression-loaded multi-directional composite laminates, AIAA paper no. 88-2293, presented at 29th Structural Dynamics and Materials Conf (April 1988) 631641 Swanson, S.R. A model for compression failure in fiber composite laminates, paper presented at Recent Developments in Composite Materials Structures, ASME Winter Meeting, American Society of Mechanical Engineers, New York, USA (1990) 81-85 Adams, D.F. and Odom, E.M. Influence of specimen tabs on the compressive strength of a unidirectional composite material J Compos Mater (1991) 25 774-786 Ahlborn, K. Cryogenic mechanical response of carbon fibre reinforced plastics with thermoplastic matrices to quasi-static loads Cryogenics (1991) 31 252-256 Aldborn, K. Durability of carbon fibre reinforced plastics with thermoplastic matrices under cyclic mechanical and cyclic thermal loads at cryogenic temperatures Cryogenics (1991) 31 257-264 Bansemir, H. and Halder, O. Basic material data and structural analysis of fibre composite components for space application Cryogenics (1991) 31 298-306 pannkoke, K. and Wagner, H.J. Fatigue properties of unidirectional carbon fibre composites at cryogenic temperatures Cryogenics (1991) 31 248-251 Hartwig, G. and Pannkoke, K. Fatigue behavior of UD-carbonfibre composites at cryogenic temperatures Adv Cryog Eng Mater (1992) 38 453-457 BHvio, A., Parenti, G., Wagner, V. etM. Consideration of the fatigue damage of specimens used for composite critical components qualification, in: The Role of the Polymeric Matrix in the Processing and Structural Properties of Composite Materials (Eds Seferis, J. C. and Nicolais, L.) Plenum Press, New York, USA (1983) 607-623 Hwang, W.-B. and Han, K.S. Fatigue of composite materials damage model and life production, in: Composite Materials: Fatigue and Fracture Vol 2 (Ed Lagace, P.A.) American Society for Testing and Materials, Philadelphia, Pennsylvania, USA (1989) 87-102 Risen, B.W. and Hashin, Z. Analysis of material properties, in: Engineered Materials Handbook. Vol 1: Composites ASM International, Metals Park, Ohio, USA (1987) 173-282 Lee, J.-W., Daniel, I.M. and Yaniv, G. Fatigue life prediction of cross-ply composite laminates, in: Composite Materials: Fatigue and Fracture Vol 2 (Ed Lagace, P.A.) American Society for Testing and Materials, Philadelphia, Pennsylvania, USA (1989)

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19-28 62 Kolek, R.L., Blaugher, R.D. and McCabria, J.L. Stainless steel fiber organic matrix composites for cryogenic application Adv Cryog Eng (1978) 24 256-261 63 Rosenberg, H.M. The thermal conductivity and thermal expansion of non-metallic composite materials at low temperatures, in: Nonmetallic Materials and Composites at Low Temperatures Vnl 2 (Eds Hartwig, G. and Evans, D.) Plenum, New York, USA (1982) 181-195 64 Wang, Y.A., NishUima, S., Okada, T. and Koudoh, K. Cryoganic properties of composites with thermo-plastic matrix Adv Cryog Eng Mater (1990) 36 957-964 65 Reed, R.P., Waish, R.P. and Austin, M.A. Properties of directinnally reinforced composites. Part 2: Thermal contraction, in: Composite Struts for SMES Plants NISTIR-5011 (Eds Reed, R.P. and McColskey, J.D.) Report to Defense Nuclear Agency, Materials Reliability Division, National Institute of Standards and Technology, Boulder, Colorado, USA (March 1994) Ch 5 66 Freeman, W.T. and Campbell, M.D. Thermal expansion characteristics of graphite reinforced composite materials, in: Composite Materials: Testing and Design (Second Conference) ASTM ST/' 497, American Society for Testing and Materials, Philadelphia, USA (1972) 121-142 67 Kramer, M.S. Composites for Cryogenics ACPT, Inc., Huntington Beach, California, USA (1990) 68 Schwarz, G., Kralm, F. and Hartwig, G. Thermal expansion of carbon fibre composites with thermoplastic matrices Cryogenics (1991) 31 244-247 69 Chamis, C.C. Thermoelastic properties of unidirectional iliamentary composites by a semiempirical micromechanics theory, paper I-4-5 Sci Adv Mater Proc Eng (1968) 14 32 70 Evans, D. and Morgan, J.T. Physical properties of epoxide resinglass fibre composites at low temperatures, in: Nonmetallic Materials and Composites at Low Temperatures Vol 2 (Eds Hartwig, G. and Evans, D.) Plenum, New York, USA (1982) 245-258

71 Evans, D. and Morgan, J.T. A review of the thermal properties of epoxide resins and composites at low temperatures, in: Proc Int Cryogenic Materials Conf (Eds Tachikawa, K. and Clark, A.) Butterworths, London, UK (1983) 446-450 72 Radcliffe, D.J. and Rosenberg, H.M. The thermal conductivity of glass-fiber and carbon-fiber epoxy composites from 2 to 80 K Cryogenics (1982) 22 245-249 73 Dmitrevsky, Yu P., Kozub, S.S. and Escber, U. Thermal conductivity of various glass-reinforced plastics at temperatures below 80 K Cryogenics (1987) 27 429-432 74 McIvor, S., Din-by, M.I., Wostanholm, G.H., Yates, B. et M. Thermal conductivity measurements of some glass fibre- and carbon fibre-reinforced plastics J Mater Sci (1990) 25 3127-3132 75 Rule, D.L. and Reed, R.P. Properties of directionally reinforced composites. Part 3: Thermal conductivity, in: Composite Struts for SMES Plants NISTIR-5011 (Eds Reed, R.P. and McColskey, J.D.) Report to Defense Nuclear Agency, Materials Reliability Division, National Institute of Standards and Technology, Boulder, Colorado, USA (March 1994) Ch 5 76 Okada, T., Rugalganisa, B. and Nishijima, S. Data base: properties of organic composite materials at low temperatures Adv Cryog Eng Mater (1990) 36 1027-1035 77 Evans, D. and Morgan, J.T. Cryogen containment in composite vessels Adv Cryog Eng Mater (1986) 32 127-136