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A new superhybrid composite material: Vinylon-reinforced aluminium laminate (VIRALL)
A new superhybrid composite material: Vinylon-reinforced aluminium laminate (VIRALL) SUI GUOXIN, ZHOU BENLIAN, ZHENG ZONGGUANG, ZHOU CHENGTI and SHI CHANGXU (Academia Sinica, People's Republic of China) Received July 1992; revised 8 October 1992 A n e w composite material, VlRALL, has been developed by alternately laminating V i n y l o n / e p o x y prepreg layers and aluminium alloy sheets. Compared w i t h the corresponding aluminium alloy, VIRALL exhibits about a 24% increase in tensile strength and a 36% decrease in tensile modulus. These results are discussed in terms of the rule of mixtures. The most fascinating feature is that VlRALL has a lower density and a lower price than the corresponding aluminium alloy. Therefore a future possible use of VIRALL could be as a partial substitute for civil aluminium .alloys.
Key words: Vinylon-reinforced aluminium laminate; VIRALL; strength; density; price Composite materials are currently widely used in the aerospace and aircraft, marine and automobile industries and for sports and leisure equipment by offering higher strength, better fatigue properties and lighter weight than conventional metal alloys. However, some conditions such as temperature, humidity and acidity/alkalinity can often limit the use of traditional advanced composites, e.g., carbon fibre-reinforced resin-matrix composites, which are laminated with only one type of prepreg material. To circumvent the problems associated with the traditional resin-matrix composites, hybrid composites consisting of two or more types of prepreg material have been introduced. One successful example of such hybrid composites is ARALLt 7, which was originally developed by Vogelesang and associates at Delft University and is currently marketed by the Aluminium Company of America (Alcoa). ARALL is a registered trade mark of a series laminates which consist of thin layers of aramid/ epoxy prepreg sandwiched between aluminium alloy sheets. ARALL has so many attractive properties--such as good damage tolerance properties, very high fatigue crack growth resistance, high static strength along the fibre direction, low density and resistance to the effects of temperature, humidity and acidity/alkalinity as well as to the ageing effect of ultraviolet rays, because of the outer aluminium alloy sheets--that it has already been applied in aircraft structures where fatigue is an important design criterion. Following the development of the A R A L L family, another
class of composites, C A R A L L s, comprising thin layers of carbon fibre/epoxy prepreg sandwiched between aluminium sheets, has been developed. It has been shown that this class of materials offers high modulus, high tensile strength, low density and superior fatigue crack propagation resistance in the longitudinal direction, so that it also can be used in the aerospace and aircraft industries. However, neither ARALL nor CARALL can be largely applied in civil product industries where low price is required, because of the expensive reinforcing components--Kevlar (aramid fibre) and carbon fibre. In order to develop a composite that can be used for civil products, high-strength, high-modulus polyvinyl acetate (PVA) fibre (Vinylon) has been used as the reinforcing agent in a new hybrid composite, VIRALL,developed by alternately laminating Vinylon/epoxy prepreg layers and aluminium alloy sheets.
EXPERIMENTAL PROCEDURE Materials VIRALL specimens were prepared according to the scheme shown in Fig. 1 from the following components: 1) long, continuous, high-strength, high-modulus PVA fibre (Vinylon) with a diameter of 10 lam and a tensile strain to failure of 7-9% for a single fibre; 2) 618 (E51) epoxy resin adhesive; and 3) LYI2 aluminium alloy (corresponding to 2024-A1) sheets at mild state with a thickness of 0.3 mm.
0010-4361/93/050433-03 O 1 993 Butterworth-Heinemann Ltd COMPOSITES . VOLUME 24 . NUMBER 5 . 1993
433
~
Fibre/epoxy] Pl~eyPerres g {'~ [A)ternate ,ay-upl , r si 1 - J L_!of AI sheets andl-~ C°mp es on,[~Jvt#Ai t I S u r f a c e ] [ [ prepreg layers [ i heat J LZS...... ]
~
I~h~ j l treatment j-Fig. 1 Processingfor VlRALL fabrication
According to the rules of mixtures, the tensile strength and tensile modulus of VIRALL laminate can be calculated as follows:
s°° I
O"c =
t~
Comparing these calculated values with those in Table 1, it can be seen that the experimental results are in good agreement with the rule-of-mixtures values.
300
200
E
o z
100
I
I
l i 2
l
l 3
l
i
l
i
l
4
l
l
5
6
7
Normal s t r a i n (&) Fig. 2 Tensile stress/strain curves of V I R A L L laminate ( O ) , aluminium alloy ( © ) and V i n y l o n / e p o x y composite ( A )
Curing conditions were 300-500 kPa pressure, 100°C and 3 h holding time. Mechanical tests
The specimens used in the tests comprised 3/2 VIRALL laminate, i.e., two Vinylon/epoxy prepreg layers sandwiched between three aluminium alloy sheets. The thickness of the prepreg layer was 0.4-0.5 mm, and the fibre volume fraction in the prepreg was 60%. Mechanical properties were tested along the fibre direction at room temperature. RESULTS AND DISCUSSION
Typical tensile stress/strain curves of VIRALL and its components are shown in Fig. 2 with the corresponding mechanical properties being listed in Table 1. As shown in Table 1, the longitudinal tensile strength of VIRALL exhibits a small increase, 24%, compared with that of the corresponding aluminium alloy while the tensile modulus decreases by 36%. This result may be discussed in terms of the rule of mixtures. Before this discussion, the following symbols should be defined: VA~ Vr~ O'A~ ore o'c EA~ Ere Ec
volume fraction of aluminium in VIRALL; volume fraction of Vinylon/epoxy in VIRALL; tensile strength of aluminium; longitudinal tensile strength of Vinylon/epoxy; longitudinal tensile strength of VIRALL; tensile modulus of aluminium; longitudinal tensile modulus of Vinylon/epoxy; longitudinal tensile modulus of VIRALL.
The specimens used in the tests are 3/2 VIRALL, compris-
434
O'AIVAI-~- O'feVfe = 3 7 5 M P a
E c = EA1VAI Jr- EfeVfe = 4 3 . 2 G P a
400
13-
ing three layers of aluminium sheet of thickness 0.3 mm and two layers of Vinylon/epoxy prepreg of thickness 0.4 mm. Thus VA~ = 0.529 and Vfe = 0.471. From Table 1, tYAl = 300 MPa, O'fe= 460 MPa, EA~ = 67.6 GPa and Ere = 15.8 GPa.
C O M P O S I T E S . N U M B E R 5 . 1993
VIRALL has an ultimate tensile strain (Table 1) which is larger than that of most current fibre-reinforced composite materials containing carbon and aramid fibres. This result is due to the differences in tensile strain of the three types of fibre, the tensile strain of Vinylon approaching 7-9% while that of carbon and aramid fibres is less than 3%. The large tensile strain to failure of Vinylon fibre is an advantage in fabricating fibre-reinforced composite materials. It can also be seen from Table 1 that the flexural strength and flexural modulus are not high. However, the flexibility of VIRALL is good; as shown in Fig. 3, a bend specimen is not destroyed until the flexural strain approaches 50%. This indicates that further shaping deformation is possible for VIRALL laminates. Therefore processes for making VIRALL products may be simplified, and some traditional metal processing technologies could be used. Table 1 also indicates that VIRALL has a lower density and a lower price than the corresponding aluminium. This is very important for a civil material. If VIRALLwere to be used as a substitute for civil aluminium alloys or other metals in suitable applications, the weight and price of the structure may be lowered considerably. As mentioned above, VIRALL has improved mechanical properties compared with the corresponding aluminium. However, owing to its low density and low price, VIRALL may find applications in some areas where high mechanical properties are not necessary but light weight and low price are required, such as in containers and non-loadbearing parts in machines, planes and automobiles. It is anticipated that VIRALL may become a partial substitute for civil materials such as aluminium alloys.
CONCL USlONS
The present work presents a new family of hybrid composite materials, VIRALL, which possesses some interesting properties that can be summarized as follows.
1) The longitudinal tensile strength is higher, the tensile modulus in the fibre direction is lower and the density is 26% lower than that of the corresponding
T a b l e 1. M e c h a n i c a l
properties
Tensile strength (M Pa) Tensile modulus (GPa) Tensile strain (%) Flexural strength (MPa) Flexural modulus (GPa) Flexural strain (%) Density (103 kg m 3) Price (Yuan kg 1)*
of aluminium
alloy, Vinylon/epoxy
composite
and VIRALL
Aluminium
Vinylon/epoxy
VI RALL
300 67.6 11 -
460 15.8 7 -
372 43.5 6 276 28.5
-
49.5
1.35 <15
2.0 <18
-
2.7 20
laminate
* Sl = 5.4 Yuan
REFERENCES I
2 3
4
5
6 Fig. 3
2)
3)
4)
V I R A L L bend specimen
aluminium alloy. These results are in good agreement with the rule of mixtures. The tensile strain to failure is about 6%, larger than that of most traditional composites. This indicates that further shaping deformation of VIRALL is possible. The price is lower than that of the aluminium alloy. This is very attractive to civil-product manufacturers. V I R A L L laminates may find application in some civil product areas and become a partial substitute for the civil aluminium alloys.
7
8
Vogelesang, L.B. and Gunnik, J.W. 'Aramid atuminium laminate (ARALL): a material for the next generation of aircraft' A state of the art. N 84-21674 Vogelesang, L.B. and Gunnik, J.W. 'New developments in ARALL laminates' ICAS-88-5.10.3 Bucci, R.J. and Mueller, L.N. "ARALL laminates: properties and design update' 33rd Int S A M P E Syrup 7 10 March 1988 pp 1237 1248 Vogelesang, L.B. and Gnnnik, J.W. 'ARALL: a material challenge for the next generation of aircraft' Materials and Design 7 No 6 (1986) pp 287 300 Gunnik, J.W. 'Damage tolerance and supportability aspects of ARALL laminates aircraft structures' Composite Struct 10 (1988) pp 83-104 Maeheret, J., Teply, J.L. and Winter, E.F.M. 'Delamination shape effects in aramid~poxy aluminium (ARALL) laminates with fatigue cracks' Polym Composites 10 No 5 (1989) pp 322-327 Ritchie, R.O., Weikang Yu and Bueci, R.J. "Fatigue crack propagation in ARALL laminates: measurement of the effect of crack-tip shielding from crack bridging' Engng Fract Mech 32 No 3 (1989) pp 361 377 Lin, C.T., Kao, P.W. and Yang, F.S. 'Fatigue behaviour of carbon fibre-reinforced aluminium laminates' Composites 22 No 2 (1991) pp 135 141
AUTHORS The authors are with the Institute of Metal Research at Academia Sinica, 72 Wenhua Road, Shenyang 110015, People's Republic of China. Correspondence should be addressed to G.X. Svi.
COMPOSITES. NUMBER 5. 1993
435
Key words: Vinylon-reinforced aluminium laminate; VIRALL; strength; density; price Composite materials are currently widely used in the aerospace and aircraft, marine and automobile industries and for sports and leisure equipment by offering higher strength, better fatigue properties and lighter weight than conventional metal alloys. However, some conditions such as temperature, humidity and acidity/alkalinity can often limit the use of traditional advanced composites, e.g., carbon fibre-reinforced resin-matrix composites, which are laminated with only one type of prepreg material. To circumvent the problems associated with the traditional resin-matrix composites, hybrid composites consisting of two or more types of prepreg material have been introduced. One successful example of such hybrid composites is ARALLt 7, which was originally developed by Vogelesang and associates at Delft University and is currently marketed by the Aluminium Company of America (Alcoa). ARALL is a registered trade mark of a series laminates which consist of thin layers of aramid/ epoxy prepreg sandwiched between aluminium alloy sheets. ARALL has so many attractive properties--such as good damage tolerance properties, very high fatigue crack growth resistance, high static strength along the fibre direction, low density and resistance to the effects of temperature, humidity and acidity/alkalinity as well as to the ageing effect of ultraviolet rays, because of the outer aluminium alloy sheets--that it has already been applied in aircraft structures where fatigue is an important design criterion. Following the development of the A R A L L family, another
class of composites, C A R A L L s, comprising thin layers of carbon fibre/epoxy prepreg sandwiched between aluminium sheets, has been developed. It has been shown that this class of materials offers high modulus, high tensile strength, low density and superior fatigue crack propagation resistance in the longitudinal direction, so that it also can be used in the aerospace and aircraft industries. However, neither ARALL nor CARALL can be largely applied in civil product industries where low price is required, because of the expensive reinforcing components--Kevlar (aramid fibre) and carbon fibre. In order to develop a composite that can be used for civil products, high-strength, high-modulus polyvinyl acetate (PVA) fibre (Vinylon) has been used as the reinforcing agent in a new hybrid composite, VIRALL,developed by alternately laminating Vinylon/epoxy prepreg layers and aluminium alloy sheets.
EXPERIMENTAL PROCEDURE Materials VIRALL specimens were prepared according to the scheme shown in Fig. 1 from the following components: 1) long, continuous, high-strength, high-modulus PVA fibre (Vinylon) with a diameter of 10 lam and a tensile strain to failure of 7-9% for a single fibre; 2) 618 (E51) epoxy resin adhesive; and 3) LYI2 aluminium alloy (corresponding to 2024-A1) sheets at mild state with a thickness of 0.3 mm.
0010-4361/93/050433-03 O 1 993 Butterworth-Heinemann Ltd COMPOSITES . VOLUME 24 . NUMBER 5 . 1993
433
~
Fibre/epoxy] Pl~eyPerres g {'~ [A)ternate ,ay-upl , r si 1 - J L_!of AI sheets andl-~ C°mp es on,[~Jvt#Ai t I S u r f a c e ] [ [ prepreg layers [ i heat J LZS...... ]
~
I~h~ j l treatment j-Fig. 1 Processingfor VlRALL fabrication
According to the rules of mixtures, the tensile strength and tensile modulus of VIRALL laminate can be calculated as follows:
s°° I
O"c =
t~
Comparing these calculated values with those in Table 1, it can be seen that the experimental results are in good agreement with the rule-of-mixtures values.
300
200
E
o z
100
I
I
l i 2
l
l 3
l
i
l
i
l
4
l
l
5
6
7
Normal s t r a i n (&) Fig. 2 Tensile stress/strain curves of V I R A L L laminate ( O ) , aluminium alloy ( © ) and V i n y l o n / e p o x y composite ( A )
Curing conditions were 300-500 kPa pressure, 100°C and 3 h holding time. Mechanical tests
The specimens used in the tests comprised 3/2 VIRALL laminate, i.e., two Vinylon/epoxy prepreg layers sandwiched between three aluminium alloy sheets. The thickness of the prepreg layer was 0.4-0.5 mm, and the fibre volume fraction in the prepreg was 60%. Mechanical properties were tested along the fibre direction at room temperature. RESULTS AND DISCUSSION
Typical tensile stress/strain curves of VIRALL and its components are shown in Fig. 2 with the corresponding mechanical properties being listed in Table 1. As shown in Table 1, the longitudinal tensile strength of VIRALL exhibits a small increase, 24%, compared with that of the corresponding aluminium alloy while the tensile modulus decreases by 36%. This result may be discussed in terms of the rule of mixtures. Before this discussion, the following symbols should be defined: VA~ Vr~ O'A~ ore o'c EA~ Ere Ec
volume fraction of aluminium in VIRALL; volume fraction of Vinylon/epoxy in VIRALL; tensile strength of aluminium; longitudinal tensile strength of Vinylon/epoxy; longitudinal tensile strength of VIRALL; tensile modulus of aluminium; longitudinal tensile modulus of Vinylon/epoxy; longitudinal tensile modulus of VIRALL.
The specimens used in the tests are 3/2 VIRALL, compris-
434
O'AIVAI-~- O'feVfe = 3 7 5 M P a
E c = EA1VAI Jr- EfeVfe = 4 3 . 2 G P a
400
13-
ing three layers of aluminium sheet of thickness 0.3 mm and two layers of Vinylon/epoxy prepreg of thickness 0.4 mm. Thus VA~ = 0.529 and Vfe = 0.471. From Table 1, tYAl = 300 MPa, O'fe= 460 MPa, EA~ = 67.6 GPa and Ere = 15.8 GPa.
C O M P O S I T E S . N U M B E R 5 . 1993
VIRALL has an ultimate tensile strain (Table 1) which is larger than that of most current fibre-reinforced composite materials containing carbon and aramid fibres. This result is due to the differences in tensile strain of the three types of fibre, the tensile strain of Vinylon approaching 7-9% while that of carbon and aramid fibres is less than 3%. The large tensile strain to failure of Vinylon fibre is an advantage in fabricating fibre-reinforced composite materials. It can also be seen from Table 1 that the flexural strength and flexural modulus are not high. However, the flexibility of VIRALL is good; as shown in Fig. 3, a bend specimen is not destroyed until the flexural strain approaches 50%. This indicates that further shaping deformation is possible for VIRALL laminates. Therefore processes for making VIRALL products may be simplified, and some traditional metal processing technologies could be used. Table 1 also indicates that VIRALL has a lower density and a lower price than the corresponding aluminium. This is very important for a civil material. If VIRALLwere to be used as a substitute for civil aluminium alloys or other metals in suitable applications, the weight and price of the structure may be lowered considerably. As mentioned above, VIRALL has improved mechanical properties compared with the corresponding aluminium. However, owing to its low density and low price, VIRALL may find applications in some areas where high mechanical properties are not necessary but light weight and low price are required, such as in containers and non-loadbearing parts in machines, planes and automobiles. It is anticipated that VIRALL may become a partial substitute for civil materials such as aluminium alloys.
CONCL USlONS
The present work presents a new family of hybrid composite materials, VIRALL, which possesses some interesting properties that can be summarized as follows.
1) The longitudinal tensile strength is higher, the tensile modulus in the fibre direction is lower and the density is 26% lower than that of the corresponding
T a b l e 1. M e c h a n i c a l
properties
Tensile strength (M Pa) Tensile modulus (GPa) Tensile strain (%) Flexural strength (MPa) Flexural modulus (GPa) Flexural strain (%) Density (103 kg m 3) Price (Yuan kg 1)*
of aluminium
alloy, Vinylon/epoxy
composite
and VIRALL
Aluminium
Vinylon/epoxy
VI RALL
300 67.6 11 -
460 15.8 7 -
372 43.5 6 276 28.5
-
49.5
1.35 <15
2.0 <18
-
2.7 20
laminate
* Sl = 5.4 Yuan
REFERENCES I
2 3
4
5
6 Fig. 3
2)
3)
4)
V I R A L L bend specimen
aluminium alloy. These results are in good agreement with the rule of mixtures. The tensile strain to failure is about 6%, larger than that of most traditional composites. This indicates that further shaping deformation of VIRALL is possible. The price is lower than that of the aluminium alloy. This is very attractive to civil-product manufacturers. V I R A L L laminates may find application in some civil product areas and become a partial substitute for the civil aluminium alloys.
7
8
Vogelesang, L.B. and Gunnik, J.W. 'Aramid atuminium laminate (ARALL): a material for the next generation of aircraft' A state of the art. N 84-21674 Vogelesang, L.B. and Gunnik, J.W. 'New developments in ARALL laminates' ICAS-88-5.10.3 Bucci, R.J. and Mueller, L.N. "ARALL laminates: properties and design update' 33rd Int S A M P E Syrup 7 10 March 1988 pp 1237 1248 Vogelesang, L.B. and Gnnnik, J.W. 'ARALL: a material challenge for the next generation of aircraft' Materials and Design 7 No 6 (1986) pp 287 300 Gunnik, J.W. 'Damage tolerance and supportability aspects of ARALL laminates aircraft structures' Composite Struct 10 (1988) pp 83-104 Maeheret, J., Teply, J.L. and Winter, E.F.M. 'Delamination shape effects in aramid~poxy aluminium (ARALL) laminates with fatigue cracks' Polym Composites 10 No 5 (1989) pp 322-327 Ritchie, R.O., Weikang Yu and Bueci, R.J. "Fatigue crack propagation in ARALL laminates: measurement of the effect of crack-tip shielding from crack bridging' Engng Fract Mech 32 No 3 (1989) pp 361 377 Lin, C.T., Kao, P.W. and Yang, F.S. 'Fatigue behaviour of carbon fibre-reinforced aluminium laminates' Composites 22 No 2 (1991) pp 135 141
AUTHORS The authors are with the Institute of Metal Research at Academia Sinica, 72 Wenhua Road, Shenyang 110015, People's Republic of China. Correspondence should be addressed to G.X. Svi.
COMPOSITES. NUMBER 5. 1993
435