- Email: [email protected]
Nanoscale mechanical characterization of glass fibers
December 1996
ELSEVIER
Materials Letters 29 (1996) 215-220
Nanoscale mechanical characterization of glass fibers Xiaodong Li a,*, Bharat Bhushan a, Peter B. McGinnis b ’ Computer Microtribology and Contamination Laboratory, Depurtment of Mechanical Engineering, The Ohio State University Columbus, OH43210-1107, WA b Owens Corning Science nnd Technology Center, 2790 Columbus Rood, Route 16. Granrille, Ohio 43023-1200,
USA
Received 28 May 1996; revised 3 June 1996; accepted 8 June 1996
Abstract The hardness and elastic modulus of E-and S-glass fibers with small diameters (8 to 20 km) have been measured by nanoindentation. As expected, the hardness and elastic modulus of S-glass fibers was found to be greater than those of E-glass fibers. As compared with E-glass fibers, S-glass fibers exhibit higher resistance to plastic deformation. The change in diameter of E-glass fibers does not affect the hardness and elastic modulus. No change in hardness and elastic modulus across diameters was observed for both E-and S-glass fibers. The present work shows that nanoindentation is a very powerful method for studying mechanical properties of small diameter glass fibers or short glass fibers of which the mechanical properties cannot be measured in fiber form using conventional mechanical testing techniques. Keywords: Micromechanical
properties;
Hardness:
Young’s
modulus of elasticity;
1. Introduction Glass fiber insulation is used as a thermal and acoustical barrier and is produced using discontinuous glass fibers. Continuous glass fibers are used as reinforcements in a variety of materials including plastic, rubber, and cement. E-glass and S-glass are two examples of continuous glass fiber formulations. E-glass was originally patented by Owens Coming in 1943 [ l] for applications which required the glass fiber to have a high electrical resistivity. Because of the excellent mechanical properties and water durability, the range of applications for E-glass has grown considerably and is today the most widely used continuous glass fiber formulation. E-glass fibers are
* Corresponding
author.
Glass; Fibers
commonly used as reinforcements in a wide range of applications including, boats, skis, underground storage tanks, asphalt roofing shingles, as well as many aerospace and automotive applications. S-glass was originally developed by Owens Coming for applications requiring higher strengths and elastic moduli and is used in various aerospace and military applications such as armor plating. Continuous glass fibers are manufactured by first melting raw materials into a homogeneous liquid using a recuperative fired furnace. The molten glass is subsequently “pulled” through holes in an electrically heated platinum crucible (or bushing) thus forming glass fibers which are then wound onto a rotating cylinder (or collet). Various texts may be consulted for greater detail on the commercial manufacturing of continuous glass fibers [2,3].
00167-577X/96/$12.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved PII SO 167-577X3(96)001 54. I
Continuous filament glass fibers demonstrate excellent mechanical properties for use as reinforcements. Certain mechanical properties, such as tensile strength and elastic modulus, can easily be measured in fiber form. Other mechanical properties, such as microhardness, need to be measured on larger glass samples. For a small diameter glass fiber, it is impossible to measure its hardness using conventional microhardness techniques. Recent developments in small-scale hardness testing have now made it possible to make hardness indentations in materials and derive meaningful mechanical data from depths as small as a few nanometers. By proper analysis of the load-displacement data, it is also possible to determine a number of material properties which cannot normally be obtained using conventional microhardness testing, for example, the elastic modulus. Nanoindentation has been proven to be a useful analytical tool in the determination of the mechanical properties of thin films and small volumes of material. However, until now there have been no reports on the nanoindentation of glass fibers with diameters less than 20 km. In the present investigation, hardness and elastic modulus of small diameter glass fibers (8 to 20 rJ,m> were measured. Glass fibers made from E-and Sglasses were selected for the present study. We have conducted cyclic nanoindentation experiments to understand the elastic-plastic deformation behavior of the glass fibers. To assess structural and mechanical heterogeneity, hardness and elastic modulus across diameters of the glass fibers have been measured.
2. Experimental 2.1. Test samples The types and diameters of the glass fibers used in this study are presented in Table 1. Fibers A through D were made from the identical E-glass formulation (E-glass #l> and varied only in fiber diameter. Fiber Q was made from a second E-glass formulation (E-glass #2) and fiber S was made from S-glass. E-glass is based on the eutectic composition in the system CaO-Al,O,-SiO, with the total alkali content restricted to less than 2% by weight. S-glass was developed to produce high tensile strengths from
Table I Types and diameters
of the glass fibers used in this study
Fiber
Glass
A B C
E-glass E-glass E-glass E-glass E-glass S-glass
a” S
Diameter (pm) #I #I # 1 #I #2
8 12 16 20 16 16
a composition (of SiO, , Al,O, and MgO) that could be easily melted. The compositions and mechanical properties of E-and S-glasses are shown in Table 2. Fibers were prepared by re-melting glass cullet in a single hole platinum bushing and pulling fibers at various speeds and temperatures to achieve the desired thickness. A “bundle” of fiber was then selected and mounted in epoxy. After the epoxy was allowed to cure, the sample was ground and polished using l/4 micron diamond abrasive. The polished fiber cross sections were subsequently measured using the nanoindenter. 2.2. Mechanical
characterization
Hardness and elastic modulus are calculated from the load displacement data obtained by nanoindentation on each sample at six different indentation loads ranging from 0.1 to 5 mN using a commercially available nanoindenter [4]. This instrument monitors and records the dynamic load and displacement of the three-sided pyramidal diamond (Berkovich) indenter during indentation with a force resolution of about 75 nN and displacement resolution of about 0.1 nm. In the present study, a typical indentation experiment consists of seven successive steps: (1) approaching the surface; (2) loading to peak load; (3) unloading 90% of peak load; (4) holding the indenter after 90% unloading; (5) reloading to peak load; (6) holding the indenter at peak load; and finally (7) unloading completely. Multiple loading and unloading steps are performed to examine the reversibility of the deformation and thereby making sure that the unloading data used for analysis purposes exhibited mostly elastic behavior. The first hold segment is included to incorporate the corrections due to thermal drift. The second hold segment is included to
X. Li et al. /Materials
0.1 and 5 mN peak indentation loads together with the SEM micrographs of 50 mN indentations on fibers C, Q and S are shown in Fig. 1. In load-displacement plots, greater indentation depths indicate a lower hardness. Lower slopes of the unloading curve indicate a lower stiffness (elastic modulus) of the sample. Fiber S exhibits the lowest indentation depths and highest slopes of the unloading curve, followed by fibers Q and C. Load-displacement plots of indentations made at 0.1 mN peak indentation loads on all fibers exhibit
avoid the influence of creep on the unloading characteristics. Indentations were observed using scanning electron microscopy @EM).
3. Results and discussion The hardness and elastic modulus of glass fibers made from two types of glasses with the same diameter were measured and compared. Representative load-displacement plots of indentations made at
(a)
0.1 mN peak load
217
Letters 29 (19961 215-220
5 mN peak load
0.12 ,
6 I
0.12
. Fiber
0
5
I
S
IO
15
20
25
0
Displacement,
50
100
150
200
250
nm
Fig. I. Representative load-displacement plots of indentations made at 0.1 and 5 mN peak indentation micrographs of 50 mN indentations, (b) on fibers C, Q and S.
loads: (a) together
with the SEM
218
X. LI et al. /Materids
300 200
“, s T3
100
% E
~ot------i
300 Fiber S
0
100
200
2 w
300
Depth, nm Fig. 2. Hardness and elastic modulus depth for fibers C, Q and S.
as a function
of indentation
several displacement discontinuities or pop-in marks during the first and second loading steps of the indentation, as shown by arrows in Fig. 1. Pop-in marks in the loading curves result from sudden penetrations of the tip into the sample. Fiber S exhibits the smallest pop-in marks, followed by fibers Q and C. The smallest pop-in marks in fiber S suggest that it probably has the highest resistance to
Table 2 Compositions Material
E-glass S-glass
and mechanical Composition
properties
[ 11 of E- and S-glasses
215-220
plastic deformation as well as crack formation and crack propagation. All fibers do not exhibit an anomalous behavior, i.e. hysteresis in the displacement of the tip in cyclic indentations made at different loads. SEM micrographs (Fig. 1b) show that fiber S has a smaller indentation mark than fibers Q and C, indicating that fiber S is harder than fibers Q and C. No cracks were seen on any fibers at magnifications up to 15000 X , however, deformation bands on the surfaces of the indentations were present. Fiber S exhibits small deformation bands while fibers Q and C exhibit large deformation bands, which are probably consistent with the pop-in marks of the load-displacement plots as shown in Fig. la. We also note that the edges of the indentations of fiber S are not as sharp as those of fibers Q and C. This indicates that the initiation of plastic deformation for fiber S is more difficult than that for fibers Q and C. Hardness and elastic modulus as a function of indentation depth for fibers C, Q and S are shown in Fig. 2. Hardness and elastic modulus data of all samples measured at the lowest and highest indentation depths are summarized in Table 3. Indentation depths at the minimum and maximum indentation loads are also included in Table 3. Fiber S exhibits the highest hardness of about 9 GPa and elastic modulus of about 95 GPa, followed by fibers Q and C. The elastic modulus obtained from the present study is in excellent agreement with the elastic modulus in Table 2. The hardness values for all fibers are about 2 times more than their strengths. The hardness and elastic modulus of all fibers decrease with increasing indentation depths/peak indentation loads. This behavior may be due to hardening of the surface caused by the grinding and polishing steps used during sample preparation. The hardness and elastic modulus across the diameters of fibers C, Q and S are shown in Fig. 3.
o.s
15
o-o
Letters 29 il99hi
a Mechanical
(wt%)
SiO,
Al,O,
B,O,
MgO
CaO
Na,O
K,O
FezO,
F
TiO,
52-56 65
12-16 25
5-10
O-5 10
16-25
o-2
o-2
O-0.8
O-I
o-2
a For reference,
hardness
properties
tensile strength (GPa)
elastic modulus (GPa)
3.8 4.5
75 85
and elastic modulus of bulk glass are 3 to 4 GPa and about 74 GPa. respectively.
X. Li et al. / Materials Letters 29 CI9961 2 15-220
5
100
z o-
Oa” 300 0 200
4
2
10
:
H
0 Ir-_.i -10 -5
0 .rl 2 300 3 u 200
5
16
20
24
Fig. 4 shows the hardness and elastic modulus as a function of the glass fiber diameter for fibers made from E-glass # 1. No change in hardness and elastic modulus occurred with varying diameters. This suggests that, for this type of glass fibers, under the present manufacturing conditions, the change in diameter does not affect their hardness and elastic modulus.
0 0
12
Fig. 4. Hardness and elastic modulus as a function of diameter for E-glass # 1 fibers.
100
PE
0
8
Diameter, pm
3 100 8
5
219
10
Distance from center, pm Fig. 3. Hardness and elastic fibers C, Q and S.
modulus
across
the diameters
of
4. Conclusions
These fibers do not show a change in hardness and elastic modulus as a function of distance from the center of the fiber. This suggests that E-and S-glass fibers with diameters less than 20 pm have homogeneous mechanical properties across the diameter of the fiber.
Table 3 Hardness
and elastic modulus of all samples obtained by nanoindentation
Fiber
Indentation
C
24 235 23 230 21 215
Q s
depth (nm)
S-glass fibers have a higher hardness and elastic modulus than E-glass fibers. This is in good agreement with previous studies. As compared with Eglass fibers, S-glass fibers exhibit higher resistance to plastic deformation. No change in hardness and elastic modulus was observed across the diameters of the fibers examined in the present study. The change
at loads from 0.1 to 5 mN
Load (mN)
Hardness (GPa)
Elastic modulus (GPa)
0.1 5 0.1 5 0.1 5
7.3 I 8 7.5 9 8
80 70 85 15 95 85
220
X. Li et ul./Materinls
in diameter of E-glass #I fibers does not affect the hardness and elastic modulus.
Let&w 29 (19%) 215-220
References [II J.R. Gonterman and W.W. Wolf, in: Advances in the fusion of
Acknowledgements The authors would like to thank John C. Mitchell for experimental assistance with SEM. The authors would also like to thank Timothy Gilbert and Terry Gano for their help in preparing the samples. Financial support for this research was provided by Owens Coming Science and Technology Center, Granville, Ohio, USA.
glass, eds. by D. F. Bickford et al. (The American Ceramic Society, 1988). Dl K.L. Loewenstein, The manufacturing technology of continuous glass fibres (Elsevier, Amsterdam, 1973). [31 J.G. Mohr and W.P. Rowe, Fiber glass (Van Nostrand Reinhold, New York, 1978). (CRC, Boca 141B. Bhushan, Handbook of micro/nanotribology Raton, Florida, 1995).
ELSEVIER
Materials Letters 29 (1996) 215-220
Nanoscale mechanical characterization of glass fibers Xiaodong Li a,*, Bharat Bhushan a, Peter B. McGinnis b ’ Computer Microtribology and Contamination Laboratory, Depurtment of Mechanical Engineering, The Ohio State University Columbus, OH43210-1107, WA b Owens Corning Science nnd Technology Center, 2790 Columbus Rood, Route 16. Granrille, Ohio 43023-1200,
USA
Received 28 May 1996; revised 3 June 1996; accepted 8 June 1996
Abstract The hardness and elastic modulus of E-and S-glass fibers with small diameters (8 to 20 km) have been measured by nanoindentation. As expected, the hardness and elastic modulus of S-glass fibers was found to be greater than those of E-glass fibers. As compared with E-glass fibers, S-glass fibers exhibit higher resistance to plastic deformation. The change in diameter of E-glass fibers does not affect the hardness and elastic modulus. No change in hardness and elastic modulus across diameters was observed for both E-and S-glass fibers. The present work shows that nanoindentation is a very powerful method for studying mechanical properties of small diameter glass fibers or short glass fibers of which the mechanical properties cannot be measured in fiber form using conventional mechanical testing techniques. Keywords: Micromechanical
properties;
Hardness:
Young’s
modulus of elasticity;
1. Introduction Glass fiber insulation is used as a thermal and acoustical barrier and is produced using discontinuous glass fibers. Continuous glass fibers are used as reinforcements in a variety of materials including plastic, rubber, and cement. E-glass and S-glass are two examples of continuous glass fiber formulations. E-glass was originally patented by Owens Coming in 1943 [ l] for applications which required the glass fiber to have a high electrical resistivity. Because of the excellent mechanical properties and water durability, the range of applications for E-glass has grown considerably and is today the most widely used continuous glass fiber formulation. E-glass fibers are
* Corresponding
author.
Glass; Fibers
commonly used as reinforcements in a wide range of applications including, boats, skis, underground storage tanks, asphalt roofing shingles, as well as many aerospace and automotive applications. S-glass was originally developed by Owens Coming for applications requiring higher strengths and elastic moduli and is used in various aerospace and military applications such as armor plating. Continuous glass fibers are manufactured by first melting raw materials into a homogeneous liquid using a recuperative fired furnace. The molten glass is subsequently “pulled” through holes in an electrically heated platinum crucible (or bushing) thus forming glass fibers which are then wound onto a rotating cylinder (or collet). Various texts may be consulted for greater detail on the commercial manufacturing of continuous glass fibers [2,3].
00167-577X/96/$12.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved PII SO 167-577X3(96)001 54. I
Continuous filament glass fibers demonstrate excellent mechanical properties for use as reinforcements. Certain mechanical properties, such as tensile strength and elastic modulus, can easily be measured in fiber form. Other mechanical properties, such as microhardness, need to be measured on larger glass samples. For a small diameter glass fiber, it is impossible to measure its hardness using conventional microhardness techniques. Recent developments in small-scale hardness testing have now made it possible to make hardness indentations in materials and derive meaningful mechanical data from depths as small as a few nanometers. By proper analysis of the load-displacement data, it is also possible to determine a number of material properties which cannot normally be obtained using conventional microhardness testing, for example, the elastic modulus. Nanoindentation has been proven to be a useful analytical tool in the determination of the mechanical properties of thin films and small volumes of material. However, until now there have been no reports on the nanoindentation of glass fibers with diameters less than 20 km. In the present investigation, hardness and elastic modulus of small diameter glass fibers (8 to 20 rJ,m> were measured. Glass fibers made from E-and Sglasses were selected for the present study. We have conducted cyclic nanoindentation experiments to understand the elastic-plastic deformation behavior of the glass fibers. To assess structural and mechanical heterogeneity, hardness and elastic modulus across diameters of the glass fibers have been measured.
2. Experimental 2.1. Test samples The types and diameters of the glass fibers used in this study are presented in Table 1. Fibers A through D were made from the identical E-glass formulation (E-glass #l> and varied only in fiber diameter. Fiber Q was made from a second E-glass formulation (E-glass #2) and fiber S was made from S-glass. E-glass is based on the eutectic composition in the system CaO-Al,O,-SiO, with the total alkali content restricted to less than 2% by weight. S-glass was developed to produce high tensile strengths from
Table I Types and diameters
of the glass fibers used in this study
Fiber
Glass
A B C
E-glass E-glass E-glass E-glass E-glass S-glass
a” S
Diameter (pm) #I #I # 1 #I #2
8 12 16 20 16 16
a composition (of SiO, , Al,O, and MgO) that could be easily melted. The compositions and mechanical properties of E-and S-glasses are shown in Table 2. Fibers were prepared by re-melting glass cullet in a single hole platinum bushing and pulling fibers at various speeds and temperatures to achieve the desired thickness. A “bundle” of fiber was then selected and mounted in epoxy. After the epoxy was allowed to cure, the sample was ground and polished using l/4 micron diamond abrasive. The polished fiber cross sections were subsequently measured using the nanoindenter. 2.2. Mechanical
characterization
Hardness and elastic modulus are calculated from the load displacement data obtained by nanoindentation on each sample at six different indentation loads ranging from 0.1 to 5 mN using a commercially available nanoindenter [4]. This instrument monitors and records the dynamic load and displacement of the three-sided pyramidal diamond (Berkovich) indenter during indentation with a force resolution of about 75 nN and displacement resolution of about 0.1 nm. In the present study, a typical indentation experiment consists of seven successive steps: (1) approaching the surface; (2) loading to peak load; (3) unloading 90% of peak load; (4) holding the indenter after 90% unloading; (5) reloading to peak load; (6) holding the indenter at peak load; and finally (7) unloading completely. Multiple loading and unloading steps are performed to examine the reversibility of the deformation and thereby making sure that the unloading data used for analysis purposes exhibited mostly elastic behavior. The first hold segment is included to incorporate the corrections due to thermal drift. The second hold segment is included to
X. Li et al. /Materials
0.1 and 5 mN peak indentation loads together with the SEM micrographs of 50 mN indentations on fibers C, Q and S are shown in Fig. 1. In load-displacement plots, greater indentation depths indicate a lower hardness. Lower slopes of the unloading curve indicate a lower stiffness (elastic modulus) of the sample. Fiber S exhibits the lowest indentation depths and highest slopes of the unloading curve, followed by fibers Q and C. Load-displacement plots of indentations made at 0.1 mN peak indentation loads on all fibers exhibit
avoid the influence of creep on the unloading characteristics. Indentations were observed using scanning electron microscopy @EM).
3. Results and discussion The hardness and elastic modulus of glass fibers made from two types of glasses with the same diameter were measured and compared. Representative load-displacement plots of indentations made at
(a)
0.1 mN peak load
217
Letters 29 (19961 215-220
5 mN peak load
0.12 ,
6 I
0.12
. Fiber
0
5
I
S
IO
15
20
25
0
Displacement,
50
100
150
200
250
nm
Fig. I. Representative load-displacement plots of indentations made at 0.1 and 5 mN peak indentation micrographs of 50 mN indentations, (b) on fibers C, Q and S.
loads: (a) together
with the SEM
218
X. LI et al. /Materids
300 200
“, s T3
100
% E
~ot------i
300 Fiber S
0
100
200
2 w
300
Depth, nm Fig. 2. Hardness and elastic modulus depth for fibers C, Q and S.
as a function
of indentation
several displacement discontinuities or pop-in marks during the first and second loading steps of the indentation, as shown by arrows in Fig. 1. Pop-in marks in the loading curves result from sudden penetrations of the tip into the sample. Fiber S exhibits the smallest pop-in marks, followed by fibers Q and C. The smallest pop-in marks in fiber S suggest that it probably has the highest resistance to
Table 2 Compositions Material
E-glass S-glass
and mechanical Composition
properties
[ 11 of E- and S-glasses
215-220
plastic deformation as well as crack formation and crack propagation. All fibers do not exhibit an anomalous behavior, i.e. hysteresis in the displacement of the tip in cyclic indentations made at different loads. SEM micrographs (Fig. 1b) show that fiber S has a smaller indentation mark than fibers Q and C, indicating that fiber S is harder than fibers Q and C. No cracks were seen on any fibers at magnifications up to 15000 X , however, deformation bands on the surfaces of the indentations were present. Fiber S exhibits small deformation bands while fibers Q and C exhibit large deformation bands, which are probably consistent with the pop-in marks of the load-displacement plots as shown in Fig. la. We also note that the edges of the indentations of fiber S are not as sharp as those of fibers Q and C. This indicates that the initiation of plastic deformation for fiber S is more difficult than that for fibers Q and C. Hardness and elastic modulus as a function of indentation depth for fibers C, Q and S are shown in Fig. 2. Hardness and elastic modulus data of all samples measured at the lowest and highest indentation depths are summarized in Table 3. Indentation depths at the minimum and maximum indentation loads are also included in Table 3. Fiber S exhibits the highest hardness of about 9 GPa and elastic modulus of about 95 GPa, followed by fibers Q and C. The elastic modulus obtained from the present study is in excellent agreement with the elastic modulus in Table 2. The hardness values for all fibers are about 2 times more than their strengths. The hardness and elastic modulus of all fibers decrease with increasing indentation depths/peak indentation loads. This behavior may be due to hardening of the surface caused by the grinding and polishing steps used during sample preparation. The hardness and elastic modulus across the diameters of fibers C, Q and S are shown in Fig. 3.
o.s
15
o-o
Letters 29 il99hi
a Mechanical
(wt%)
SiO,
Al,O,
B,O,
MgO
CaO
Na,O
K,O
FezO,
F
TiO,
52-56 65
12-16 25
5-10
O-5 10
16-25
o-2
o-2
O-0.8
O-I
o-2
a For reference,
hardness
properties
tensile strength (GPa)
elastic modulus (GPa)
3.8 4.5
75 85
and elastic modulus of bulk glass are 3 to 4 GPa and about 74 GPa. respectively.
X. Li et al. / Materials Letters 29 CI9961 2 15-220
5
100
z o-
Oa” 300 0 200
4
2
10
:
H
0 Ir-_.i -10 -5
0 .rl 2 300 3 u 200
5
16
20
24
Fig. 4 shows the hardness and elastic modulus as a function of the glass fiber diameter for fibers made from E-glass # 1. No change in hardness and elastic modulus occurred with varying diameters. This suggests that, for this type of glass fibers, under the present manufacturing conditions, the change in diameter does not affect their hardness and elastic modulus.
0 0
12
Fig. 4. Hardness and elastic modulus as a function of diameter for E-glass # 1 fibers.
100
PE
0
8
Diameter, pm
3 100 8
5
219
10
Distance from center, pm Fig. 3. Hardness and elastic fibers C, Q and S.
modulus
across
the diameters
of
4. Conclusions
These fibers do not show a change in hardness and elastic modulus as a function of distance from the center of the fiber. This suggests that E-and S-glass fibers with diameters less than 20 pm have homogeneous mechanical properties across the diameter of the fiber.
Table 3 Hardness
and elastic modulus of all samples obtained by nanoindentation
Fiber
Indentation
C
24 235 23 230 21 215
Q s
depth (nm)
S-glass fibers have a higher hardness and elastic modulus than E-glass fibers. This is in good agreement with previous studies. As compared with Eglass fibers, S-glass fibers exhibit higher resistance to plastic deformation. No change in hardness and elastic modulus was observed across the diameters of the fibers examined in the present study. The change
at loads from 0.1 to 5 mN
Load (mN)
Hardness (GPa)
Elastic modulus (GPa)
0.1 5 0.1 5 0.1 5
7.3 I 8 7.5 9 8
80 70 85 15 95 85
220
X. Li et ul./Materinls
in diameter of E-glass #I fibers does not affect the hardness and elastic modulus.
Let&w 29 (19%) 215-220
References [II J.R. Gonterman and W.W. Wolf, in: Advances in the fusion of
Acknowledgements The authors would like to thank John C. Mitchell for experimental assistance with SEM. The authors would also like to thank Timothy Gilbert and Terry Gano for their help in preparing the samples. Financial support for this research was provided by Owens Coming Science and Technology Center, Granville, Ohio, USA.
glass, eds. by D. F. Bickford et al. (The American Ceramic Society, 1988). Dl K.L. Loewenstein, The manufacturing technology of continuous glass fibres (Elsevier, Amsterdam, 1973). [31 J.G. Mohr and W.P. Rowe, Fiber glass (Van Nostrand Reinhold, New York, 1978). (CRC, Boca 141B. Bhushan, Handbook of micro/nanotribology Raton, Florida, 1995).