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Mechanical properties of a glass reinforced plastic naval composite material under increasing compressive strain rates
September 2000
Materials Letters 45 Ž2000. 167–174 www.elsevier.comrlocatermatlet
Mechanical properties of a glass reinforced plastic naval composite material under increasing compressive strain rates M.Z. Shah Khan ) , G. Simpson Maritime Platforms DiÕision, Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, P.O. Box 4331, Melbourne, Victoria 3001, Australia Received 8 February 2000; accepted 15 February 2000
Abstract This paper reports on the mechanical behaviour of a ship structure composite, reinforced by glass fibres of type DF1400, under increasing compressive strain rates ranging from 0.001 to 10 sy1. The constituents of the composites Žreinforcing glass fibres and resin. were similar to those used in the shell and bulkhead structures of The Royal Australian Navy’s minehunter ships. Experiments were carried out using a servo hydraulic testing machine and the application of loading was in the normal Žthrough thickness. and in-plane orientation of the laminated specimens. Properties measured were ultimate strength, elastic modulus and strain at ultimate strength. Post failure analysis of specimens was carried out using optical microscopy in order to understand failure mechanisms. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Glass reinforced plastics; Composite materials; Strain rate; Minehunters Žships.; Royal Australian Navy
1. Introduction Accurate modeling, using finite element ŽFE. codes, of the response of ship structures to dynamic loading rates such as in underwater shock depend on inputs of material property data generated at corresponding rates. For minehunter ships constructed of glass fibre reinforced composites wglass reinforced plastic ŽGRP.x, an underwater mine blast could severely test the structural integrity of a ship by subjecting it to intense loading at strain rates reaching up to 10 sy1 . ) Corresponding author. Tel.: q61-03-9626-8315; fax: q61-039626-8409. E-mail address: [email protected] ŽM.Z. Shah Khan..
The reinforcement in a composite is the glass fibres that bear most of the load, and the matrix provides load transfer support. Failure modes in GRP composites should be influenced by the fracture behaviour of individual constituents and the direction in which the load is applied. Accordingly, failure modes in composites have been identified as fibre dominated w1–4x and matrix dominated w5–8x. The fibre pull-out and fibre fractures are regarded as difficult failure processes occurring predominantly under tension loading, requires greater energy and therefore result in high structural integrity. On the other hand, splitting and delamination occur under compressive loading, require less energy and result in significantly low structural integrity w9x. The delamination and splitting failures are due to stresses concentrated between the laminate plys Žinterfaces..
00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 0 9 9 - 9
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Table 1 Details of the make-up of the composite material Material
No. of ply
Resin
GF content
Fabrication process and ply sequence
Weave
GRP
7 WR Ž1350 g my2 . 1 CSM Ž450 g my2 .
Synolite 0288-T1w
52%
Hand lay-up and successive plys
Plain
Shear failure involves matrix cracking and to some extent failure of the interface. Increasing the delamination resistance is expected to transfer load to the fibres. The delamination resistance has been shown influenced by the stacking sequence in a composite w10x. This paper presents the mechanical properties, at increasing compressive strain rates, of a naval composite containing DF 1400 glass fibre reinforcement in a polyester resin matrix. The specimens were subjected to loading in the normal and in-plane orientations with respect to the laminated composite. The in-plane orientation was further separated to discriminate loading parallel to warp and normal to weft orientations, each of which may influence the mechanical properties of the composite.
warp orientations were normal and parallel, respectively. The fill direction is designated as warp direction. A servo-hydraulic test machine was used and all tests were conducted in displacement control. The test machine was interfaced with a Tektronic w data acquisition system to record load and displacement output signals for each test. The stress on the specimen was calculated by dividing the registered load by the cross-sectional area of the specimen. The modulus was calculated from the linear elastic portion of the stress–strain curves. The machine deflection was accounted in calculating the modulus and specimen strain. Strain rates were estimated from specimen strain versus time data and ranged from 0.001 to 10 sy1 . In figures displaying mechanical properties, each data point corresponds to a single test result.
2. Experimental 3. Results 2.1. Materials The composite consisted of 7 plys of 1350 g my2 woven roving with 1 outer ply of 450 g my2 chopped strand mat ŽCSM. and the resin matrix was isophthalic polyester, Synolite 0288-T1w , see Table 1 for details. The directionality of the woven roving in the composites was 08r908. The composite, following lay-up, was allowed to cure at room temperature and the thickness of the laminated plate measured approximately 10 mm.
The average stress–strain curves of the composite in the normal and in-plane orientations are shown in Figs. 2 and 3, respectively. For clarity the in-plane stress–strain curves are separated into normal-to-weft and parallel-to-warp orientations, Fig. 3a and b, respectively. The linear elastic behaviour in the in-plane
2.2. Compression testing The compression tests were conducted on a 10 mm cubicle specimen geometry and the loading was in the normal Žthrough thickness. and in the in-plane directions, see Fig. 1. In the normal direction of loading, the specimen top and bottom surfaces were woven roving and CSM, respectively. For specimens loaded in the in-plane direction, the weft and the
Fig. 1. Specimen geometry and directions of loading with respect to ply planes; Ža. in-plane loading and Žb. normal loading.
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
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Fig. 2. Average stress–strain curves for the composite with the loading in the normal Žthrough thickness. direction.
orientation ŽFig. 3. was much steeper in comparison with that observed in the normal orientation ŽFig. 2.. Other noticeable differences between the two orientations were in the maximum stress and strain corresponding to the maximum stress. In the following sections, the important features of the stress–strain curves are described and the results are depicted in Figs. 4–6 at increasing compressive strain rates. 3.1. Maximum stress Fig. 4 illustrates the variation of maximum stress with strain rate. When loaded in the normal Žthrough thickness. direction, the maximum stress increased linearly by 16% between strain rates from 0.005 to 10 sy1 , and the maximum stress levels were higher when compared with those obtained in the in-plane direction of loading. In the in-plane direction of loading, with the exception of only a few data points at low strain rates, the maximum stress remained unchanged over the entire strain rate range.
10 sy1 , see Fig. 5. Modulus levels in the in-plane direction of loading were found to be significantly higher than the modulus in the normal direction of loading, see Fig. 3. In the in-plane direction of loading Žnormal to weft direction., there was some scatter of data points at low and intermediate strain rates. Modulus values corresponding to these data points were much lower at low strain rates and significantly higher at intermediate strain rates. With the exception of these, increasing strain rates resulted in negligible change in modulus. 3.3. Maximum strain Maximum strains were significantly higher Žon average five times. in the normal direction of loading than in the in-plane direction of loading, see Fig. 6. In both directions of loading, increasing strain rates had negligible effect on the maximum strains. 4. Discussion
3.2. Modulus
4.1. Normal loading (through thickness)
When loading was normal, the modulus increased linearly by 18% between strain rates from 0.005 to
The effect of increasing strain rate caused increases in the maximum stress and modulus, whereas
170
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
Fig. 3. Average stress–strain curves for the composite with the loading in the in-plane direction; Ža. normal to weft and Žb. parallel to warp.
the effect was insignificant on the maximum strain, see Figs. 4–6. Polymeric matrix materials when
loaded are known to display viscoelastic behaviour. The matrix material used in the composite was shown
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
171
Fig. 4. Variation in maximum stress with strain rate; B — normal direction of loading, I — in-plane Žparallel to warp. and ^ — in-plane Žnormal to weft. direction of loading.
Fig. 5. Variation in modulus with strain rate; B — normal direction of loading and I — in-plane Žparallel to warp. and ^ — in-plane Žnormal to weft. direction of loading.
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M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
Fig. 6. Variation in maximum strain with strain rate; B — normal direction of loading and I — in-plane Žparallel to warp. and ^ — in-plane Žnormal to weft. direction of loading.
in a separate study to be strain rate sensitive, being viscoelastic at low strain rates and brittle at high strain rates w11x. This behaviour resulted in lower strength and modulus of the resin at strain rate of 0.005 sy1 when compared with those achieved at 10 sy1 . The observed behaviour of the composite in this study resembled to that described above for the matrix and may be responsible for the increase in strength and modulus with increasing strain rate. The composite failure process was also observed to be dependent on the strain rate and occurred by a combination of two distinct failure modes, the extent of each mode varying with strain rate, Fig. 7. Given the layered cubicle geometry of the specimen, these modes were identified as a crushing mode where the top of the specimen was crushed and a shearing mode that left a damage trace running diagonally across the specimen. At low strain rates, deformation caused 458 sliding and led to a predominantly shear mode failure, see Fig. 7a. When the strain rate was high, deformation caused crushing of specimen top surface and failure was dominated by the crushing mode, see Fig. 7b.
4.2. In-plane loading The in-plane loading used in this study implies that the loading was actually normal to weft direction or parallel to warp direction. Therefore, data points representing in-plane properties are from tests where loading was either parallel to warp or normal to weft directions. Under in-plane compression loading, the specimen experiences stresses, which concentrate as shear stresses between the plys. Under such conditions, the specimen ideally should deform uniformly over the entire cross section and fracture by delamination, see Fig. 8a and b. This study has shown that when the composite was loaded in the direction normal to weft, it exhibited in some tests at low strain rates deviation from the ideal situation with specimen deforming non-uniformly into a shape of a broom and fracturing by unstable delamination, see Fig. 8c. This behaviour resulted in lower maximum stress and modulus values for the composite but the maximum strain values were unaffected. In few other tests at intermediate strain rates, deformation caused severe fibre buckling ŽFig. 8d. which
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
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resulted in significantly higher modulus values for the composite with the maximum stress and strain values unaffected ŽFigs. 4–6.. Apart from these exceptions, the mechanical properties of the composite, irrespective of weft and warp orientations, were generally observed to be insensitive to strain rates.
5. Conclusions
Fig. 7. Failure modes when specimens loaded in the normal Žthrough thickness. direction; at Ža. 0.005 sy1 and Žb. 10 sy1 . Magnification 3=.
This study has provided key material property data and enhanced the understanding of the behaviour of glass reinforced composite materials under increasing compressive strain rates. The composite was tested in the normal Žthrough thickness. and in-plane directions. The mechanical properties in the normal direction were significantly higher than in the in-plane direction. In the normal direction, the maximum strength and modulus increased by 16% and 18%, respectively, over the strain rate range however, the maximum strain showed no strain rate effect. The composite mechanical properties showed a degree of uncertainty particularly when the loading was in-plane with the weft direction being normal. This uncertainty appeared at low and intermediate strain rates due to non-uniform deformation and fibre
Fig. 8. Failure modes when specimens loaded in the in-plane direction; at 0.005 sy1 Ža and c., 1 sy1 Žd., and 10 sy1 Žb.. Loading in Ža. and Žb. was parallel to warp orientation whereas loading in Žc. and Žd. was normal to weft orientation. Magnification 3 = .
174
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
buckling, respectively. The discrimination between loading normal to weft and loading parallel to warp was noticeable at low and intermediate strain rates and effected the maximum stress and the modulus values and not the maximum strain values. References w1x J. Harding, Science and Engineering of Composite Materials 1 Ž1989. 41. w2x Y. Bai, J. Harding, Fracture initiation in glass reinforced plastics under impact compression, in: J. Morton ŽEd.., Structural Impact and Crashworthiness vol. 2 Elsevier, 1984, pp. 482–493. w3x J. Harding, L. Welsh, Journal of Materials Science 18 Ž1983. 1810. w4x L. Welsh, J. Harding, Effect of strain-rate on the tensile failure of woven-reinforced polyester resin composites, Report OUEL 1578r85, University of Oxford, UK, 1985.
w5x J.W. Gillespie Jr., L.A. Carlsson, A.J. Smiley, Composites Science and Technology 28 Ž1987. 1. w6x S. Mall, G.E. Law, M. Katouzian, Journal of Composite Materials 21 Ž1987. 569. w7x J.H. Starnes, M.D. Rhodes, J.G. Williams, Effect of impact damage and holes on the compressive strength of a graphiterepoxy laminate, in: R.B. Pipes ŽEd.., Nondestructive Evaluation and flaw criticality for composite Materials, ASTM STP 696, American Society for Testing and Materials, 1979, pp. 145–171. w8x V.S. Avva, H.L. Padmanabha, Compressive residual strength prediction in fibre-reinforced laminated composites subjected to impact loads, in: S.R. Valluri, D.M.R. Taplin, P.R. Rao, J.F. Knott, R. Dubey ŽEds.., Advances in Fracture Research, Proceedings of the 6th International Conference on Fracture, 1984, pp. 2897–2907. w9x W.J. Cantwell, J. Morton, Composites 22 Ž5. Ž1991. 347. w10x S. Hong, D. Liu, Experimental Mechanics 13 Ž1989. 115. w11x M.Z.S. Khan, G. Simpson, C.R. Townsend, A Comparison of the Dynamic Mechanical Properties of Neat Resins, DSTOTR,1999, in review.
Materials Letters 45 Ž2000. 167–174 www.elsevier.comrlocatermatlet
Mechanical properties of a glass reinforced plastic naval composite material under increasing compressive strain rates M.Z. Shah Khan ) , G. Simpson Maritime Platforms DiÕision, Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, P.O. Box 4331, Melbourne, Victoria 3001, Australia Received 8 February 2000; accepted 15 February 2000
Abstract This paper reports on the mechanical behaviour of a ship structure composite, reinforced by glass fibres of type DF1400, under increasing compressive strain rates ranging from 0.001 to 10 sy1. The constituents of the composites Žreinforcing glass fibres and resin. were similar to those used in the shell and bulkhead structures of The Royal Australian Navy’s minehunter ships. Experiments were carried out using a servo hydraulic testing machine and the application of loading was in the normal Žthrough thickness. and in-plane orientation of the laminated specimens. Properties measured were ultimate strength, elastic modulus and strain at ultimate strength. Post failure analysis of specimens was carried out using optical microscopy in order to understand failure mechanisms. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Glass reinforced plastics; Composite materials; Strain rate; Minehunters Žships.; Royal Australian Navy
1. Introduction Accurate modeling, using finite element ŽFE. codes, of the response of ship structures to dynamic loading rates such as in underwater shock depend on inputs of material property data generated at corresponding rates. For minehunter ships constructed of glass fibre reinforced composites wglass reinforced plastic ŽGRP.x, an underwater mine blast could severely test the structural integrity of a ship by subjecting it to intense loading at strain rates reaching up to 10 sy1 . ) Corresponding author. Tel.: q61-03-9626-8315; fax: q61-039626-8409. E-mail address: [email protected] ŽM.Z. Shah Khan..
The reinforcement in a composite is the glass fibres that bear most of the load, and the matrix provides load transfer support. Failure modes in GRP composites should be influenced by the fracture behaviour of individual constituents and the direction in which the load is applied. Accordingly, failure modes in composites have been identified as fibre dominated w1–4x and matrix dominated w5–8x. The fibre pull-out and fibre fractures are regarded as difficult failure processes occurring predominantly under tension loading, requires greater energy and therefore result in high structural integrity. On the other hand, splitting and delamination occur under compressive loading, require less energy and result in significantly low structural integrity w9x. The delamination and splitting failures are due to stresses concentrated between the laminate plys Žinterfaces..
00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 0 9 9 - 9
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
168
Table 1 Details of the make-up of the composite material Material
No. of ply
Resin
GF content
Fabrication process and ply sequence
Weave
GRP
7 WR Ž1350 g my2 . 1 CSM Ž450 g my2 .
Synolite 0288-T1w
52%
Hand lay-up and successive plys
Plain
Shear failure involves matrix cracking and to some extent failure of the interface. Increasing the delamination resistance is expected to transfer load to the fibres. The delamination resistance has been shown influenced by the stacking sequence in a composite w10x. This paper presents the mechanical properties, at increasing compressive strain rates, of a naval composite containing DF 1400 glass fibre reinforcement in a polyester resin matrix. The specimens were subjected to loading in the normal and in-plane orientations with respect to the laminated composite. The in-plane orientation was further separated to discriminate loading parallel to warp and normal to weft orientations, each of which may influence the mechanical properties of the composite.
warp orientations were normal and parallel, respectively. The fill direction is designated as warp direction. A servo-hydraulic test machine was used and all tests were conducted in displacement control. The test machine was interfaced with a Tektronic w data acquisition system to record load and displacement output signals for each test. The stress on the specimen was calculated by dividing the registered load by the cross-sectional area of the specimen. The modulus was calculated from the linear elastic portion of the stress–strain curves. The machine deflection was accounted in calculating the modulus and specimen strain. Strain rates were estimated from specimen strain versus time data and ranged from 0.001 to 10 sy1 . In figures displaying mechanical properties, each data point corresponds to a single test result.
2. Experimental 3. Results 2.1. Materials The composite consisted of 7 plys of 1350 g my2 woven roving with 1 outer ply of 450 g my2 chopped strand mat ŽCSM. and the resin matrix was isophthalic polyester, Synolite 0288-T1w , see Table 1 for details. The directionality of the woven roving in the composites was 08r908. The composite, following lay-up, was allowed to cure at room temperature and the thickness of the laminated plate measured approximately 10 mm.
The average stress–strain curves of the composite in the normal and in-plane orientations are shown in Figs. 2 and 3, respectively. For clarity the in-plane stress–strain curves are separated into normal-to-weft and parallel-to-warp orientations, Fig. 3a and b, respectively. The linear elastic behaviour in the in-plane
2.2. Compression testing The compression tests were conducted on a 10 mm cubicle specimen geometry and the loading was in the normal Žthrough thickness. and in the in-plane directions, see Fig. 1. In the normal direction of loading, the specimen top and bottom surfaces were woven roving and CSM, respectively. For specimens loaded in the in-plane direction, the weft and the
Fig. 1. Specimen geometry and directions of loading with respect to ply planes; Ža. in-plane loading and Žb. normal loading.
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
169
Fig. 2. Average stress–strain curves for the composite with the loading in the normal Žthrough thickness. direction.
orientation ŽFig. 3. was much steeper in comparison with that observed in the normal orientation ŽFig. 2.. Other noticeable differences between the two orientations were in the maximum stress and strain corresponding to the maximum stress. In the following sections, the important features of the stress–strain curves are described and the results are depicted in Figs. 4–6 at increasing compressive strain rates. 3.1. Maximum stress Fig. 4 illustrates the variation of maximum stress with strain rate. When loaded in the normal Žthrough thickness. direction, the maximum stress increased linearly by 16% between strain rates from 0.005 to 10 sy1 , and the maximum stress levels were higher when compared with those obtained in the in-plane direction of loading. In the in-plane direction of loading, with the exception of only a few data points at low strain rates, the maximum stress remained unchanged over the entire strain rate range.
10 sy1 , see Fig. 5. Modulus levels in the in-plane direction of loading were found to be significantly higher than the modulus in the normal direction of loading, see Fig. 3. In the in-plane direction of loading Žnormal to weft direction., there was some scatter of data points at low and intermediate strain rates. Modulus values corresponding to these data points were much lower at low strain rates and significantly higher at intermediate strain rates. With the exception of these, increasing strain rates resulted in negligible change in modulus. 3.3. Maximum strain Maximum strains were significantly higher Žon average five times. in the normal direction of loading than in the in-plane direction of loading, see Fig. 6. In both directions of loading, increasing strain rates had negligible effect on the maximum strains. 4. Discussion
3.2. Modulus
4.1. Normal loading (through thickness)
When loading was normal, the modulus increased linearly by 18% between strain rates from 0.005 to
The effect of increasing strain rate caused increases in the maximum stress and modulus, whereas
170
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
Fig. 3. Average stress–strain curves for the composite with the loading in the in-plane direction; Ža. normal to weft and Žb. parallel to warp.
the effect was insignificant on the maximum strain, see Figs. 4–6. Polymeric matrix materials when
loaded are known to display viscoelastic behaviour. The matrix material used in the composite was shown
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
171
Fig. 4. Variation in maximum stress with strain rate; B — normal direction of loading, I — in-plane Žparallel to warp. and ^ — in-plane Žnormal to weft. direction of loading.
Fig. 5. Variation in modulus with strain rate; B — normal direction of loading and I — in-plane Žparallel to warp. and ^ — in-plane Žnormal to weft. direction of loading.
172
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
Fig. 6. Variation in maximum strain with strain rate; B — normal direction of loading and I — in-plane Žparallel to warp. and ^ — in-plane Žnormal to weft. direction of loading.
in a separate study to be strain rate sensitive, being viscoelastic at low strain rates and brittle at high strain rates w11x. This behaviour resulted in lower strength and modulus of the resin at strain rate of 0.005 sy1 when compared with those achieved at 10 sy1 . The observed behaviour of the composite in this study resembled to that described above for the matrix and may be responsible for the increase in strength and modulus with increasing strain rate. The composite failure process was also observed to be dependent on the strain rate and occurred by a combination of two distinct failure modes, the extent of each mode varying with strain rate, Fig. 7. Given the layered cubicle geometry of the specimen, these modes were identified as a crushing mode where the top of the specimen was crushed and a shearing mode that left a damage trace running diagonally across the specimen. At low strain rates, deformation caused 458 sliding and led to a predominantly shear mode failure, see Fig. 7a. When the strain rate was high, deformation caused crushing of specimen top surface and failure was dominated by the crushing mode, see Fig. 7b.
4.2. In-plane loading The in-plane loading used in this study implies that the loading was actually normal to weft direction or parallel to warp direction. Therefore, data points representing in-plane properties are from tests where loading was either parallel to warp or normal to weft directions. Under in-plane compression loading, the specimen experiences stresses, which concentrate as shear stresses between the plys. Under such conditions, the specimen ideally should deform uniformly over the entire cross section and fracture by delamination, see Fig. 8a and b. This study has shown that when the composite was loaded in the direction normal to weft, it exhibited in some tests at low strain rates deviation from the ideal situation with specimen deforming non-uniformly into a shape of a broom and fracturing by unstable delamination, see Fig. 8c. This behaviour resulted in lower maximum stress and modulus values for the composite but the maximum strain values were unaffected. In few other tests at intermediate strain rates, deformation caused severe fibre buckling ŽFig. 8d. which
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
173
resulted in significantly higher modulus values for the composite with the maximum stress and strain values unaffected ŽFigs. 4–6.. Apart from these exceptions, the mechanical properties of the composite, irrespective of weft and warp orientations, were generally observed to be insensitive to strain rates.
5. Conclusions
Fig. 7. Failure modes when specimens loaded in the normal Žthrough thickness. direction; at Ža. 0.005 sy1 and Žb. 10 sy1 . Magnification 3=.
This study has provided key material property data and enhanced the understanding of the behaviour of glass reinforced composite materials under increasing compressive strain rates. The composite was tested in the normal Žthrough thickness. and in-plane directions. The mechanical properties in the normal direction were significantly higher than in the in-plane direction. In the normal direction, the maximum strength and modulus increased by 16% and 18%, respectively, over the strain rate range however, the maximum strain showed no strain rate effect. The composite mechanical properties showed a degree of uncertainty particularly when the loading was in-plane with the weft direction being normal. This uncertainty appeared at low and intermediate strain rates due to non-uniform deformation and fibre
Fig. 8. Failure modes when specimens loaded in the in-plane direction; at 0.005 sy1 Ža and c., 1 sy1 Žd., and 10 sy1 Žb.. Loading in Ža. and Žb. was parallel to warp orientation whereas loading in Žc. and Žd. was normal to weft orientation. Magnification 3 = .
174
M.Z. Shah Khan, G. Simpsonr Materials Letters 45 (2000) 167–174
buckling, respectively. The discrimination between loading normal to weft and loading parallel to warp was noticeable at low and intermediate strain rates and effected the maximum stress and the modulus values and not the maximum strain values. References w1x J. Harding, Science and Engineering of Composite Materials 1 Ž1989. 41. w2x Y. Bai, J. Harding, Fracture initiation in glass reinforced plastics under impact compression, in: J. Morton ŽEd.., Structural Impact and Crashworthiness vol. 2 Elsevier, 1984, pp. 482–493. w3x J. Harding, L. Welsh, Journal of Materials Science 18 Ž1983. 1810. w4x L. Welsh, J. Harding, Effect of strain-rate on the tensile failure of woven-reinforced polyester resin composites, Report OUEL 1578r85, University of Oxford, UK, 1985.
w5x J.W. Gillespie Jr., L.A. Carlsson, A.J. Smiley, Composites Science and Technology 28 Ž1987. 1. w6x S. Mall, G.E. Law, M. Katouzian, Journal of Composite Materials 21 Ž1987. 569. w7x J.H. Starnes, M.D. Rhodes, J.G. Williams, Effect of impact damage and holes on the compressive strength of a graphiterepoxy laminate, in: R.B. Pipes ŽEd.., Nondestructive Evaluation and flaw criticality for composite Materials, ASTM STP 696, American Society for Testing and Materials, 1979, pp. 145–171. w8x V.S. Avva, H.L. Padmanabha, Compressive residual strength prediction in fibre-reinforced laminated composites subjected to impact loads, in: S.R. Valluri, D.M.R. Taplin, P.R. Rao, J.F. Knott, R. Dubey ŽEds.., Advances in Fracture Research, Proceedings of the 6th International Conference on Fracture, 1984, pp. 2897–2907. w9x W.J. Cantwell, J. Morton, Composites 22 Ž5. Ž1991. 347. w10x S. Hong, D. Liu, Experimental Mechanics 13 Ž1989. 115. w11x M.Z.S. Khan, G. Simpson, C.R. Townsend, A Comparison of the Dynamic Mechanical Properties of Neat Resins, DSTOTR,1999, in review.