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The mechanical behaviour of PVC short-fibre composites
reaches a maximum at high test temperatures at Vf (glass) = 0.1; higher Vf leads to debonding of the glass particles Hybrid-particulate composites have m u c h higher G[c for Vf(glass) = 0.1 than solely rubber-modified epoxy. Both Klc and Gic are increased by using coupling agents to promote interfacial adhesion between the glass and matrix. Glass particles increase crack resistance by crack-pinning whilst rubber particles enhance the extent of plastic shear deformations in the matrix at the crack tip. Fundamental considerations in the injection processing of fibre reinforced thermoplastics Folkes, M.J. and Kells, D. Plastics and Rubber Processing and Applications Vol 5 (1985) pp 125-131 This paper reports on an improved compounding technique to produce a carbon fibre/ nylon 66 composite with fibre lengths well above the critical length. The longer fibres are shown to significantly improve flexural properties a n d Young's modulL Methods for producing further improvements are also considered. Hardening non-linear behavionr in longitudinal tension of unidirectional carbon composites lshikawa, T., Matsushima, M. and Hayashi, Y. Journal of Materials Science Vol 20 No 11 (November 1985) pp 4075-4083 T300/3601 CFRP coupons are loaded in uniaxial tension and electro-optical displacement indicators are used to measure longitudinal strain. Stress/strain curves are found to be convex downwards (ie, modulus increases with stress or strain) at strains up to 60-70% of the failure strain, as also reported by other workers. This behaviour is modelled using a constitutive equation based on non-linear elasticity theory with two higher-order compliance coefficients estimated from experimental results. An empirical relationship between longitudinal modulus and strain is proposed. These equations are applied to the description of non-linear stress/strain behaviour of 8H satin fabric/epoxy composites. Hygrothermal influence on delamination behaviour of graphite/epoxy laminates Garg, A. and Ishai, O. Engineering Fracture Mechanics Vo122 No 3 (1985) pp 413-427 The effects of temperature and humidity on delamination fracture toughness under Mode I and Mode II loading were investigated on a range of specimen configurations (double cantilever, compact tension, and cracked lap shear) and conditions. The results indicated that moisture had a slightly beneficial influence on fracture toughness or critical strain energy release rate during Mode I delamination but a deleterious effect on Mode II delamination and transverse cracking, Impact fatigue of PPS/glass compositemicroscopy Lhymn, C. Journal of Materials Science Letters Vol 4 (1985) pp 1429-1433 The fracture behaviour of short fibre-reinforced poly(phenylene sulphide) during impact fatigue has been investigated. Several micrographs of specimens with two different fibre orientations are presented and the concept of fracture mechanics is applied to derive impact fatigue lifetime. Impact fatigue of PPS/glass composites. Part 1 theoretical analysis Lhymn, C. Journal of Materials Science Letters Vol 4 (1985) pp 1221-1224
COMPOSITES. APRIL 1986
The lifetime equation of impact fatigue is derived and then analysed statistically to predict the engineering lifetime for design purposes. The model proposed was tested experimentally on three layered specimens of short glass fibre-reinforced polyphenylene sulphene. The author found that the fatigue lifetime of specimens was a function of fibre orientation with respect to the impact load direction and that there was a m i n i m u m impact energy threshold below which no impact failure occurred. Influence of damage on mechanical properties of woven composites at low temperatures Kriz, R.D. Journal of Composites Technology and Research Vol 7 No 2 (Summer 1985) pp 55-58 This work investigates the variability in mechanical and thermal properties in a unit cell of plain weave glass/epoxy laminate caused by crack initiation; crack-tip singularities and stress redistributions are predicted using a generalized plain strain finite element analysis, The effects of warp-fibre curvature and thermal stresses at low temperature are beneficial in reducing stresses at the tip of a fill crack; fill cracks decrease the stiffness more for large curvatures than for small curvatures. Therefore, curvature of warp-fibres should be selected for strength or stiffness properties. Influence of fibre orientation on acoustic emission from filament wound pipes Jerzyk, 1. and Kumosa, M. Journal of Materials Science Vol 20 No 10 (October 1985) pp 36613667 Acoustic emission activity during internal pressurization of filament-wound G R P pipes was correlated with fibre orientation and with calculations of the state of stress at the fibre/ matrix interface. The outset of significant acoustic emission was attributed to cohesive cracking at the interface when a critical value of stress normal to the fibre was reached for all the tested orientations. Transverse cracking in the lamina also contributed to AE activity. The internal pressure, mechanical properties and water absorption of carbon fibre composites with spiro-epoxy copolymer matrices Piggott, M.R., Lam, P.W.K., Lim, J.T. and Won, IV[ S. Composites Science and Technology Vo123 No 4 (1985) pp 247-262 An overview of experiments carried out over four years on epoxy copolymers and on composites made with controlled shrinkage pressures at the interface between fibres and matrix is presented. I t is shown that spiro orthocarbamate monomers copolymerized with epoxy can reduce polymer shrinkage stress at carbon fibre surfaces. Composites made on this principle were tougher, had improved fatigue resistance and slightly better water resistance than normal carbon fibre composites. Jute-reinforced polyester composites Roe, P.J. and Ansell, M.P. Journal of Materials Science Vo120 No 11 (November 1985) pp 40154020 Raw jute fibres have been incorporated in polyester resin to give uniaxial composites with up to 60% Vf Young's modulus, tensile strength, work of fracture (Charpy impact) and interlaminar shear strength are measured as a function of V~ these properties follow rule-ofmixtures predicted values. At Vf> 60% there is insufficient wetting of fibres by the resin. The properties of jute and glass fibre composites are contrasted on a basis of specific gravity and cost per tonne.
Laboratory production of discontinuous-aligned fiber composite plates using an autoclave-style •press cure Gibson, R.F., Deobald, LR. and Suarez, S.A. Journal of Composites Technology and Research Vol 7 No 2 (Summer 1985) pp 49-54 A method is described for producing plates of discontinuous, aligned composite from continuous prepreg containing graphite/epoxy, Kevlar/cpoxy and boron/epoxy. This uses a vacuum-bagged mould in a small laboratory press; the procedure is described in detail The quality of these laminates is compared with autoclave-fabricated laminates. Load-deformation behaviour of composite cylinders with integrally-formed braided and with machined circular holes Brookstein, D.S. and Tsiang, T.-H. Journal of Composite Materials (September 1985) pp 476-487 The axial tension and compression bchaviour of braided + 45 ° graphite/epoxy cylinders with integrally formed braided and machined holes have been investigated. Analysis of the strain concentration effects and failure modes haYe shown that the braided holes provide an increased joint bearing strength compared with the machined holes. The mechanical behaviour of PVC short-fibre composites Yuan, J., Hiltner, A., Baer, E. and Rahrig, D. Journal of Materials Science Vol 20 No 12 (December 1985) pp 4377-4386 Short glass fibre-reinforced PVC composites were prepared with good and poor coupling between fibre and matri~ Their tensile behaviour under superimposed hydrostatic pressure was evaluated; the deformation processes in three-point bending were studied in situ in the S E M It was found that brittlefracture stress increased with degree of interfacial adhesion due to the increase in interfacial shear strength preventing early failure at the interface. Good coupling also eliminated the deformation behaviour in which a sharp drop in stress was seen due to interfacial debonding followed by matrix yielding, The upper shear yielding behaviour was apparently unaffected by the degree of coupling, Micromechanics of crack propagation in hybrid particulate composites Kinlocl~ A.J., Maxwell D. and Young, R.S. Journal of Materials Science Letters Vol 4 (1985) pp 1276-1279 A combination of scanning electron microscopy and in situ optical microscopy is employed to identify the m e c h a n i s m of crack propagation in a rubber-toughened epoxy containing glass beads. Two toughening mechanisms were identified: crack p i n n i n g which resulted in the crack bowing between glass particles and characteristic 'steps' on the fracture surface at the rear of the inclusions - and localized shear yielding, This second m e c h a n i s m was identified by the appearance of fine dark lines, associated with rubber particles and glass beads at 45 ° to the principal tensile axis. These lines were resolved as shear bands by the presence of typical "furrows' on the fracture surface. The morphology of shear fracture surfaces of Kevlar fibre reinforced epoxy composites Mittelman, A., Harei, H., Roman, I. and Marom, G. Journal of Materials Science Letters Vol 4 (1985) pp 1361-1363 Two major modes of failure have been reported in this fractographic study on unidirectional
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COMPOSITES. APRIL 1986
The lifetime equation of impact fatigue is derived and then analysed statistically to predict the engineering lifetime for design purposes. The model proposed was tested experimentally on three layered specimens of short glass fibre-reinforced polyphenylene sulphene. The author found that the fatigue lifetime of specimens was a function of fibre orientation with respect to the impact load direction and that there was a m i n i m u m impact energy threshold below which no impact failure occurred. Influence of damage on mechanical properties of woven composites at low temperatures Kriz, R.D. Journal of Composites Technology and Research Vol 7 No 2 (Summer 1985) pp 55-58 This work investigates the variability in mechanical and thermal properties in a unit cell of plain weave glass/epoxy laminate caused by crack initiation; crack-tip singularities and stress redistributions are predicted using a generalized plain strain finite element analysis, The effects of warp-fibre curvature and thermal stresses at low temperature are beneficial in reducing stresses at the tip of a fill crack; fill cracks decrease the stiffness more for large curvatures than for small curvatures. Therefore, curvature of warp-fibres should be selected for strength or stiffness properties. Influence of fibre orientation on acoustic emission from filament wound pipes Jerzyk, 1. and Kumosa, M. Journal of Materials Science Vol 20 No 10 (October 1985) pp 36613667 Acoustic emission activity during internal pressurization of filament-wound G R P pipes was correlated with fibre orientation and with calculations of the state of stress at the fibre/ matrix interface. The outset of significant acoustic emission was attributed to cohesive cracking at the interface when a critical value of stress normal to the fibre was reached for all the tested orientations. Transverse cracking in the lamina also contributed to AE activity. The internal pressure, mechanical properties and water absorption of carbon fibre composites with spiro-epoxy copolymer matrices Piggott, M.R., Lam, P.W.K., Lim, J.T. and Won, IV[ S. Composites Science and Technology Vo123 No 4 (1985) pp 247-262 An overview of experiments carried out over four years on epoxy copolymers and on composites made with controlled shrinkage pressures at the interface between fibres and matrix is presented. I t is shown that spiro orthocarbamate monomers copolymerized with epoxy can reduce polymer shrinkage stress at carbon fibre surfaces. Composites made on this principle were tougher, had improved fatigue resistance and slightly better water resistance than normal carbon fibre composites. Jute-reinforced polyester composites Roe, P.J. and Ansell, M.P. Journal of Materials Science Vo120 No 11 (November 1985) pp 40154020 Raw jute fibres have been incorporated in polyester resin to give uniaxial composites with up to 60% Vf Young's modulus, tensile strength, work of fracture (Charpy impact) and interlaminar shear strength are measured as a function of V~ these properties follow rule-ofmixtures predicted values. At Vf> 60% there is insufficient wetting of fibres by the resin. The properties of jute and glass fibre composites are contrasted on a basis of specific gravity and cost per tonne.
Laboratory production of discontinuous-aligned fiber composite plates using an autoclave-style •press cure Gibson, R.F., Deobald, LR. and Suarez, S.A. Journal of Composites Technology and Research Vol 7 No 2 (Summer 1985) pp 49-54 A method is described for producing plates of discontinuous, aligned composite from continuous prepreg containing graphite/epoxy, Kevlar/cpoxy and boron/epoxy. This uses a vacuum-bagged mould in a small laboratory press; the procedure is described in detail The quality of these laminates is compared with autoclave-fabricated laminates. Load-deformation behaviour of composite cylinders with integrally-formed braided and with machined circular holes Brookstein, D.S. and Tsiang, T.-H. Journal of Composite Materials (September 1985) pp 476-487 The axial tension and compression bchaviour of braided + 45 ° graphite/epoxy cylinders with integrally formed braided and machined holes have been investigated. Analysis of the strain concentration effects and failure modes haYe shown that the braided holes provide an increased joint bearing strength compared with the machined holes. The mechanical behaviour of PVC short-fibre composites Yuan, J., Hiltner, A., Baer, E. and Rahrig, D. Journal of Materials Science Vol 20 No 12 (December 1985) pp 4377-4386 Short glass fibre-reinforced PVC composites were prepared with good and poor coupling between fibre and matri~ Their tensile behaviour under superimposed hydrostatic pressure was evaluated; the deformation processes in three-point bending were studied in situ in the S E M It was found that brittlefracture stress increased with degree of interfacial adhesion due to the increase in interfacial shear strength preventing early failure at the interface. Good coupling also eliminated the deformation behaviour in which a sharp drop in stress was seen due to interfacial debonding followed by matrix yielding, The upper shear yielding behaviour was apparently unaffected by the degree of coupling, Micromechanics of crack propagation in hybrid particulate composites Kinlocl~ A.J., Maxwell D. and Young, R.S. Journal of Materials Science Letters Vol 4 (1985) pp 1276-1279 A combination of scanning electron microscopy and in situ optical microscopy is employed to identify the m e c h a n i s m of crack propagation in a rubber-toughened epoxy containing glass beads. Two toughening mechanisms were identified: crack p i n n i n g which resulted in the crack bowing between glass particles and characteristic 'steps' on the fracture surface at the rear of the inclusions - and localized shear yielding, This second m e c h a n i s m was identified by the appearance of fine dark lines, associated with rubber particles and glass beads at 45 ° to the principal tensile axis. These lines were resolved as shear bands by the presence of typical "furrows' on the fracture surface. The morphology of shear fracture surfaces of Kevlar fibre reinforced epoxy composites Mittelman, A., Harei, H., Roman, I. and Marom, G. Journal of Materials Science Letters Vol 4 (1985) pp 1361-1363 Two major modes of failure have been reported in this fractographic study on unidirectional
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