Stress transfer by shear in carbon fibre model composites. Part 1. Results of single fibre fragmentation tests with thermosetting resin

Journal of Composite Materials Vo123 No 12 (1989) pp 1273-1291 Cracking in cross-ply laminates is mathematically modelled utilizing the internal state variable concept to predict the upper bound of the reduced axial stiffness. The axial crack opening displacement was explicitly expressed in terms of the observable axial strain and the undamaged material properties. For glass/epoxy and graphite/epoxy material systems a crack parameter was calculated representing the effect of matrix cracks on their observable axial Young's moduli. It was shown that the matrix crack opening displacement, and consequently the effective Young's modulus depends, not on the crack length, but on its ratio to the crack spacing. These results compared well with experimental data and other published models confirming applicability to [0p/90r] type laminates. New glassy precipitates of PEEK and PEK obtained from dilute solution Waddon, A.J., Brookes, L.C., Heyderman, L.J. and Hill, M.J. Polymer Communications Vo131 No 1 (1990) pp 5-7 Solutions of the polyaryls PEEK and PEK in organic solvents at 250°C are quenched rapidly into cold non-solvent solutions. The morphologies thus produced are examined by transmission electron microscopy, differential scanning calorimetry and X-ray diffraction. Results show that a two-phase morphology is obtained, consisting of lath crystals and amorphous beads, which may be crystallized on annealing. The production of amorphous polyaryl entities from dilute solution is thus clearly established. Stress transfer by shear in carbon fibre model composites. Part 1. Results of single fibre fragmentation tests with thermosetting resin Favre, J.P. and Jaques, D. Journal of Materials Science Vo125 No 2B (1990) pp 1373-1380 Dog-bone resin specimens containing single carbon fibre filaments are tensile tested in

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order to determine the ability of the interface to transfer shear stresses at the fibre-matrix interface. For brittle resins the 'coaxial' specimen configuration is employed where the fibre is coated in a sheath of brittle resin, then embedded in a tough resin. The influence of carbon fibre surface treatment, as well as resin properties, are conclusively shown to have an influence on stress transfer. A study of glass fibre-epoxy composite interfaces Liad, Y.T. Polymer Composites Vo110 No 6 (1989) pp 424-428 The interfacial bonding in E-glass reinforced epoxy matrix composites was studied using Fourier transform infrared spectroscopy. The pH of the coupling agent used was found to significantly affect the interfacial bonding, deviations away from the natural pH promoted side reactions which reduced bonding strength. Cure temperature had very little effect upon interracial bond strength. The amount of silane needed for hygrothermal conditions was different to that required for dry conditions. Study of interfaces of high performance glass fibres and DGEBA based epoxy resins using single-fibre-composite test Netravali, A.N., Schwartz, P. and Phoenix, S.L. Polymer Composites Vo110 No 6 (1989) pp 385-388 The interfacial strength of flexible epoxy glass fibre composites was studied using the single-fibre-composite test. Specimens were prepared using two blends of D G E B A based epoxy and polyglycol epoxide cured with TEPA and one of three types of glass fibre in order to give differing moduli and strain to failure. Single filament 'dog bone' test pieces were prepared at two different gauge lengths. Data from fragment length distributions, fibre strength data and a Monte Carlo simulation of a Poisson/Weibull model for fibre strength and flaws were used to obtain interfacial shear strength values. The composites

were shown to fail by transverse cracking and have interracial shear strengths many times higher than the yield shear strength of the epoxy itself. Thermal expansivity and bulk modulus of polymer composites: Experiment verses theory Simha, R., Papazoglou, E. and Maurer, F H.J. Polymer Composites Vol 10 No 6 (1989) pp 409-413 The authors have explored the correlations between thermal expansivity and bulk compressibility for polymer composites. Two alternative theories were presented - an interlayer approach based upon micromechanics (IM) and a molecular one starting from a statistical account of the thermodynamics of mixtures (MM). Experimental results from particulate filled composites (polyurethane and rock salt or epoxy and glass beads) were compared with the theories. Both theories predicted filler/matrix interactions. The prediction of thermal expansivity from bulk compressibility was found to be always possible using MM but IM required a knowledge of the expansivity and compressibility relationships in the composite's constituents. Time dependent behaviour of laminated composites at elevated temperatures Ha, S.K. and Springer, G.S. Journal o f Composite Materials Vo123 No 11 (1989) pp 1159-1197 The exposure of unidirectional fibre reinforced thermoset matrix composites and the effect this has on the time dependent viscoelastic and viscoplastic stress-strain relationships has been modelled. Four point bend tests were carried out on Fiberite T300/976 carbon/epoxy composites over the range 75 to 350°F to determine the constants in the stress-strain relationships. A method of calculating stresses and strains in loaded multidirectional laminates at high temperatures was also proposed. A good agreement was found between experimental and analytical results.