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Theories of failure of filament wound case composite materials
Curing behaviour of conducting polymer composite Radharkrishnan, S. Journal of Materials Science Letters Vol 6 No 2 (Februa~' 1987) pp 145-148 Electrical resistance of conducting carbon black/phenolic composites with a silica filler was monitored with time, and during heating and cooling cycles. There is a large hysteresis during cyclic heating and a change in the temperature coefficient of resistance, possibly due to a change in thermal expansion coefficient as the silica filler content is varied. The resistance-time curves were analysed using reaction kinetics. The curing behaviour of this conductive composite is mainly governed by the cross-linking process in the polymer matrix. The dynamic response of graphite fibre-epoxy laminates at high shear strain rates Werner, S.M. and Dharan, C.K.H. Journal of Composiw Materials Vol 20 (July 1986) pp 365-374 The high strain rate (6000-18000/s) response of graphite/epoxy composites was determined in both interlaminar and transverse shear using the split Hopkinson bar. The effect of strain rate on the interlaminar shear stress was small, while in transverse shear deformation, increasing the strain rate resulted in a decrease in the shear stress. In both cases, at high strain rates, sparks were produced by the specimens during deformation. The effect of the fiber/matarix interface on the flexural fatigue performance of unidirectional fiberglass composites Shih, G.C. and Ebert. L.J. Composites Sciences and Technology Vo128 No 2 (1987) pp 137-161 The results of fatigue tests on oriented glass fibre-reinforced polymer matrix composites in four-point bending with a stress ratio of-0.8 are presented and discussed in detail. It was found that samples containing fibres treated with diamino-functional silane coupling agents exhibited higher flexural fatigue performance that lhose in which coupling agents were not used. It is concluded that a strong interface between fibre and matrix delayed the occurrence of fibre ridgeing and longitudinal matrix cracking, thus improving the fatigue performance. The effect of interiaminar fracture properties on the delamination buckling of composites Donaldson, S . L . Composites Science and Technology Vol 28. No 1 (1987) pp 33-44 Material lYacture toughness data and mixed mode fracture criteria were taken from literature and inserted in the Whitcomb delaminalion buckling model to ascertain the effect of material toughness on the onset of delaminalion growth in compression-loaded delaminated laminates. Two systems were examined: a carbon fibre-reinforced epoxy (T300/1034C) and a carbon fibre-reinforced thermoplastic resin (XAS/PEEK. APC-I). It was found that the critical load is nearly insensitive to the mixed-mode criterion used. A linear fracture criterion between Mode I and Mode II fracture toughness values produced only slightly conservative values for the critical load. Also, for a given laminate, different delamination depths could be critical depending upon the delamination length.
Effect of specimen geometry on the energy absorption capability of composite materials Earley, G.L. Jounlal of Composite Materials
266
Vo120 (July 1986) pp 390-400 The influence of geometry, of chamfered tubular specimens of graphite/epoxy and Kevlar/epoxy composites, on their energy absorption capability was examined. The graphite/epoxy and Kevlar/epoxy tubes were found to exhibit a non-linear and bilinear relation, respectively, between energy absorption and the tube inside diameter to wall thickness ratio (D/t ratio). The energy absorption of Kevlar/epoxy tubes could be geometrically scaled whereas for graphite/epoxy tubes the energy absorption was not scalable.
Epoxy resins: effect of amines on curing characteristics and properties Varma, I.K. and Bharma, P.V.S. Journal of Composite Materials Vol 20 (September 1986) pp 410-422 The thermal stability and mechanical properties of laminates made with glass fabric and a diglycidyl ether of bisphenol-A (DGEBA) resin, cured with m-DDS and p-DDS diamines, have been compared. The curing behaviour of the resins was also evaluated by varying the amounts of diamine, m-DDS was found to be more reactive than p-DDS as a curing agent for DGEBA. The thermal stability of laminates made with both resins were comparable and dependent on the concentration of amine used. The mechanical properties of the DGEBA/pDDS system were slightly superior. The addition of 3 phr of an amino-terminated acrylonitrile butadiene copolymer (ATBN) brought about a significant improvement in strength, although strength retention on thermal ageing was poor.
Hygrothermal behaviour of glass fibre reinfroced nylon 66 composites: a study of the effects of water absorption on their mechanical properties Valentin, D., Paray, F. and Guetta. B.Journalof Materials Science Vol 22 No l (January 1987) pp 46-56 The kinetics of water absorption and the effects of moisture uptake on the residual mechanical properties of three types of thermoplastic were studied. The three materials were pure nylon 66, nylon 66 reinforced with continuous glass fibre and nylon 66 reinforced with short glass fibres. The tests were carried out at three temperatures 4ll°C, 7(l°C and 90°C) and at three humidities (30%. 75% and 100%). At temperatures below 9(1°C. hygrotherma[ behaviour was Fickean for all materials which was not the case at 90°C. Possible explanations for this behaviour are given. An expression relating failure stress to testing temperature is presented. The effects of moisture uptake were found to be most pronounced in the short fibre reinforced composites. Comparisons of the hygrothermal response between thermoplastics and thermosets are made.
Impact resistant hybrid composite for aircraft leading edges Nolet. S.C. and Sandusky, P.M. SAMPE Quarterly Vol 17 No 4 (July 1986) pp 46-53 The development and testing of a design for aircraft wing leading edges which will overcome the effects of damage due to bird strikes is described. The design comprises numerous plies of span-wise oriented graphite tape at the outer surface of the leading edge and chordwise oriented graphite tape at the inner surface surrounding a core of Kevlar tape and fabric.
Influence of filler chemistry on the glass transition behaviour of a polymer matrix composite material Greenberg, A.R. Journal of Materials Science Letters Vol 6 No 1 (January 1987) pp 78-80 DMTA was used to measure Tg of composites containing polyacrylic acid (PAA) filled with different ceramics, i.e. silica, alumina and calcium silicate. An increase in Tg of 15°C over the Tg of unfilled PAA is found only in the calcium silicate filled material. This shift in Tg was analysed with reference to existing emipirical mathematical relationships previously proposed to explain the phenomenon. The composite system is considered as comprising the polymer matrix and a boundary layer around the filler particles in which the mobility of the polymer chains was reduced; the Tg shift observed in the PAA composites was attributed to a stronger reaction between the calcium silicate and the matrix than between the silica and alumina fillers. The influence of quality of adhesion on the damping characteristics of a two layer compound beam Theocaris, P.S. Journal of Composite Materials Vol 20 (November 196'6) pp 558-578 Two-phase compound bars made from unplasticized epoxy resin and the same resin plasticized with 20% Thiokol LP3 polysulphide were fabricated with good and poor adhesion between the two layers and then subjected to forced extensional vibrations. The influence of adhesion on the values of storage and loss moduli of the compound bar was investigated. It was found that the compound specimens with good adhesion behaved exactly as if they consisted of a unique material whose properties could be predicted by the law of mixtures. In the case of bad adhesion, a further reduction in the values of loss moduli and loss factors occurred. The positions and extent of these quantities could be satisfactorily explained by the two term unfolding model fot the mesophase, valid for forced-vibrating bodies. Interfacial shear stress in a short glass fibrereinforced polypropylene sheet Gupta, V.B., Mittal. R.K., Sharma. P.K. and Gupta, B.S. Composites Science and Technology Vo128 No 1 (1987) pp 45-56 The interfacial shear stress (ISS) in an extruded short glass fibre-reinforced polypropylene sheet was evaluated using two approaches. In the first the ISS is taken to increase linearly with the composite strain, while in the second, this assumption is made up to 8% composite strain, when the rate of increase is then taken to be smaller. Experimental results show that the dependence of ISS on composite strain is very similar to the tensile stress/strain behaviour of the composite sheet. This is indicative of good adhesion between fibre and matrix. lnterlaminar fatigue growth crack in random short fibre SMC composites Wang, S.S. and Miyase, A.Journal of Composite Materials Vo120 (September 1986) pp 439-456 Double cantilever beams were employed to investigate the interlaminar fatigue crack growth (1FCG) in random, short fibre SMC-R50 composites under displacement controlled cyclic loading. A geometrically nonlinear fracture mechanics analysis was used to determine the cyclic strain-energy release rate. The rate of IFCG was found to follow a power law and the value of the exponent was found to be much higher than the value obtained for inplane fatigue crack growth in the same com-
COMPOSITES. JULY 1987
Effect of specimen geometry on the energy absorption capability of composite materials Earley, G.L. Jounlal of Composite Materials
266
Vo120 (July 1986) pp 390-400 The influence of geometry, of chamfered tubular specimens of graphite/epoxy and Kevlar/epoxy composites, on their energy absorption capability was examined. The graphite/epoxy and Kevlar/epoxy tubes were found to exhibit a non-linear and bilinear relation, respectively, between energy absorption and the tube inside diameter to wall thickness ratio (D/t ratio). The energy absorption of Kevlar/epoxy tubes could be geometrically scaled whereas for graphite/epoxy tubes the energy absorption was not scalable.
Epoxy resins: effect of amines on curing characteristics and properties Varma, I.K. and Bharma, P.V.S. Journal of Composite Materials Vol 20 (September 1986) pp 410-422 The thermal stability and mechanical properties of laminates made with glass fabric and a diglycidyl ether of bisphenol-A (DGEBA) resin, cured with m-DDS and p-DDS diamines, have been compared. The curing behaviour of the resins was also evaluated by varying the amounts of diamine, m-DDS was found to be more reactive than p-DDS as a curing agent for DGEBA. The thermal stability of laminates made with both resins were comparable and dependent on the concentration of amine used. The mechanical properties of the DGEBA/pDDS system were slightly superior. The addition of 3 phr of an amino-terminated acrylonitrile butadiene copolymer (ATBN) brought about a significant improvement in strength, although strength retention on thermal ageing was poor.
Hygrothermal behaviour of glass fibre reinfroced nylon 66 composites: a study of the effects of water absorption on their mechanical properties Valentin, D., Paray, F. and Guetta. B.Journalof Materials Science Vol 22 No l (January 1987) pp 46-56 The kinetics of water absorption and the effects of moisture uptake on the residual mechanical properties of three types of thermoplastic were studied. The three materials were pure nylon 66, nylon 66 reinforced with continuous glass fibre and nylon 66 reinforced with short glass fibres. The tests were carried out at three temperatures 4ll°C, 7(l°C and 90°C) and at three humidities (30%. 75% and 100%). At temperatures below 9(1°C. hygrotherma[ behaviour was Fickean for all materials which was not the case at 90°C. Possible explanations for this behaviour are given. An expression relating failure stress to testing temperature is presented. The effects of moisture uptake were found to be most pronounced in the short fibre reinforced composites. Comparisons of the hygrothermal response between thermoplastics and thermosets are made.
Impact resistant hybrid composite for aircraft leading edges Nolet. S.C. and Sandusky, P.M. SAMPE Quarterly Vol 17 No 4 (July 1986) pp 46-53 The development and testing of a design for aircraft wing leading edges which will overcome the effects of damage due to bird strikes is described. The design comprises numerous plies of span-wise oriented graphite tape at the outer surface of the leading edge and chordwise oriented graphite tape at the inner surface surrounding a core of Kevlar tape and fabric.
Influence of filler chemistry on the glass transition behaviour of a polymer matrix composite material Greenberg, A.R. Journal of Materials Science Letters Vol 6 No 1 (January 1987) pp 78-80 DMTA was used to measure Tg of composites containing polyacrylic acid (PAA) filled with different ceramics, i.e. silica, alumina and calcium silicate. An increase in Tg of 15°C over the Tg of unfilled PAA is found only in the calcium silicate filled material. This shift in Tg was analysed with reference to existing emipirical mathematical relationships previously proposed to explain the phenomenon. The composite system is considered as comprising the polymer matrix and a boundary layer around the filler particles in which the mobility of the polymer chains was reduced; the Tg shift observed in the PAA composites was attributed to a stronger reaction between the calcium silicate and the matrix than between the silica and alumina fillers. The influence of quality of adhesion on the damping characteristics of a two layer compound beam Theocaris, P.S. Journal of Composite Materials Vol 20 (November 196'6) pp 558-578 Two-phase compound bars made from unplasticized epoxy resin and the same resin plasticized with 20% Thiokol LP3 polysulphide were fabricated with good and poor adhesion between the two layers and then subjected to forced extensional vibrations. The influence of adhesion on the values of storage and loss moduli of the compound bar was investigated. It was found that the compound specimens with good adhesion behaved exactly as if they consisted of a unique material whose properties could be predicted by the law of mixtures. In the case of bad adhesion, a further reduction in the values of loss moduli and loss factors occurred. The positions and extent of these quantities could be satisfactorily explained by the two term unfolding model fot the mesophase, valid for forced-vibrating bodies. Interfacial shear stress in a short glass fibrereinforced polypropylene sheet Gupta, V.B., Mittal. R.K., Sharma. P.K. and Gupta, B.S. Composites Science and Technology Vo128 No 1 (1987) pp 45-56 The interfacial shear stress (ISS) in an extruded short glass fibre-reinforced polypropylene sheet was evaluated using two approaches. In the first the ISS is taken to increase linearly with the composite strain, while in the second, this assumption is made up to 8% composite strain, when the rate of increase is then taken to be smaller. Experimental results show that the dependence of ISS on composite strain is very similar to the tensile stress/strain behaviour of the composite sheet. This is indicative of good adhesion between fibre and matrix. lnterlaminar fatigue growth crack in random short fibre SMC composites Wang, S.S. and Miyase, A.Journal of Composite Materials Vo120 (September 1986) pp 439-456 Double cantilever beams were employed to investigate the interlaminar fatigue crack growth (1FCG) in random, short fibre SMC-R50 composites under displacement controlled cyclic loading. A geometrically nonlinear fracture mechanics analysis was used to determine the cyclic strain-energy release rate. The rate of IFCG was found to follow a power law and the value of the exponent was found to be much higher than the value obtained for inplane fatigue crack growth in the same com-
COMPOSITES. JULY 1987