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epoxy composites
On refined theories of beams, plates and shells Vasil'ev, V.V. and Lur'e, S.A. Journal of Composite Materials Vol 26 No 4 (1992) pp 546 557 Refined beam, plate and shell theories are presented, based on the reduction of the threedimensional elasticity theory, assuming an approximation of the displacements through the thickness. The consistency of the theory is maintained by imposing suitable conditions. The theory is developed for a beam with further generalized results given for plates and shells. An example of a thick isotropic plate is considered. Some relationships and limitations of tensorial polynomials strength theories Wilczynski, A.P. Composites Science and Technology Vo144 No 3 ! 1992) pp 209 213 Malmeister's strength theory for orthotropic materials is used as the basis of this paper. Work by Goldenblat and Kopnov and Tsai and Wu is considered to have established his proposal firmly in theory and application. This study presents new possibilities of using approximate relationships and partial replacement of experimental data. Comparison between the proposed relationships and experimental results for isotropic and anisotropic cases is good. Thermal diffusivities of composites with various types of filler Hatta, H., Taya, M., Kulacki, F.A. and Harder, J.F. Journal ~[" Composite Materials Vo126 No 5 (1992)PlY 612 625 Experimental and theoretical studies were made into the in-plane and out-of-plane thermal diffusivities of Keramid matrix composites. SiO2 particles, short A I~O~ fibres, BN flakes and SigN4 whiskers were used as fillers. The predictions from the theoretical model gave fairly good agreement with the experimental results, except for the BN flake system. It was seen that the overall thermal conductivity of the composites is strongly dependent on the orientation of the filler material.
THERMOSETTING MA TRICES The effect of an interphase on the stress and energy distribution in the embedded single fibre test Di Anselmo, A., Accorsi, M.L. and Di Bcnedetto, A.T. Composites Science and TeehnoIogy l/ol 44 No 3 (1992) pp 215 225 The embedded single fibre test and finite element analysis are used to study the behaviour of the interphase of an E-glass/epoxy system. The effect of interphase thickness and mechanical properties on the stress distribution after fibre breakage is studied. The energy distribution and elastic energy released during crack propagation along the interface are calculated. The results are combined to produce a strain history for this system. The effect of side loads on the energy absorption of composite structures Fleming, D.C. and Vizzini, A.J. Journal o[" Composite Materials Vol 26 No 4 (1992) pp 486-499 Pre-impregnated unidirectional graphite/ epoxy tape was made into slightly tapered truncated cones and loaded in compression. By loading the samples away from the centralaxis, side loads were introduced to the cone.
The energy absorption of the cones subjected to quasi-static crushing was measured. It is shown that for small side loads the energy absorbance was improved; however, it deteriorates for high side loads. A further reduction is caused by the toppling of the cone, which is due to the moment applied to it by the side loads. Effects of hydrostatic pressure on the torsional shear behaviour of graphite/epoxy composites Shin, E.S. and Pae, K.D. Journal of Composite Materials Vo126 No 4 (1992) pp 462 485 A high pressure torsion apparatus has been developed to study the stress/strain behaviour of a graphite/epoxy composite and of the epoxy alone. Uniaxial, press-moulded, continuous fibre composites were machined into thin-walled hollow cylinders to act as samples. It is shown that the linear elastic shear stress/ strain behaviour of the epoxy at atmospheric pressure shifted upwards with pressure and becomes non-linear above 2 kbar. A marked increase is also seen for shear modulus and fracture strength and strain. The shear stress/ strain curves for the composite showed dramatic changes from linear behaviour, exhibiting yielding, work hardening and drawing. The shear strength and strain to failure increased linearly with an abrupt change at 4 to 5 bar, where the mode of failure changed to delamination from shearing. Influence of artificial pre-stressing during curing of CFRP laminates on interfibre transverse cracking Schulte, K. and Marissen, R. Composites Science and Technology Vo144 No 4 (1992) pp 361- 367 It is shown that the residual stresses in the 90 ° plies of a cross-ply laminate were affected by pre-stressing the 0 ° plies during curing. Alter curing and cooling to room temperature the pre-stress was released, putting the 90 ° plies under compressive stress. Under tensile loading this caused the development of transverse cracks to be shifted to high load and strain values. interfaciai shear stress distribution in model composites part 2: fragmentation studies on carbon fibre]epoxy systems Melanitis, N., Galiotis, C.. Tetlow, P.L. and Davies, C.K.L. Journal o/ Composite Materials Vol 26 No 4 (1992) pp 574-610 A single fibre embedded in an epoxy resin was subjected to an incremental tensile load up to full fragmentation. The strain in the fibre was measured using laser Raman spectroscopy. After the first fracture the strain in the sample was seen to build from the tips of the fibre breaks and reach a maximum at the centre of each fragment. The shape of the load transfer profiles at the fibre tips indicated that the fracture process had affected the stress transfer efficiency. The load transfer profiles were used to calculate interfacial shear stress, and the shape of these profiles confirms that interracial debonding was initiated at fibre tips. The standard fragmentation test was performed to measure the interracial shear stress at full fragmentation. This was found to be half the value measured by laser Raman spectroscopy. Micromechanics prediction of the shear strength of carbon fibre/epoxy matrix composites: the influence of the matrix and interface strengths King, T.R., Blackketter, D.M., Walrath, D.E. and Adams, D.F. Journal o[" Composite
Materials Vo126 No 4 (1992) pp 558-573 This study investigates the effect of the matrix and interfacial bond strengths in carbon fibre/ epoxy systems on the composite shear strength. A finite element technique has been performed to analytically study these effects. It is shown that numerical results agree well with experimental results, suggesting a micromechanics approach to predicting interfacial effects on composite shear strength is a potentially valuable technique. Process-induced stress and deformation in thick-section thermoset composite laminates Bogetti, T.A. and Gillespie, J.W. Journal ~?f Composite Materials Vol 26 No 5 (1992) pp 626 660 A theory is presented for predicting the residual stress evolved during curing. The theory combines a one-dimensional cure simulation and an incremental laminated plate theory. Models are included to describe the mechanical properties and thermal and chemical strains developed during curing. A comparison is made between experimental and model evaluation of cure-dependent epoxy modulus and curvature in unsymmetric graphite/epoxy laminates. How process-induced stress and deformation are affected by process histoy is studied and it is seen that the residual stress is sufficient to induce transverse cracks and delaminations. Strain-relief inserts for composite fasteners - an experimental study Herrera-Franco, P.J. and Cloud, G.L. Journal ¢t/Composite Matermls Vo126 No 5 (1992) pp 751 768 A theoretical and experimental study is made of the stress/strain distributions around single-pin lap joints in a glass/epoxy laminate. The possibility of obtaining stress concentration release by the addition of isotropic material inserts is investigated. Surface strains were measured by Moir+ interferometry and strain rosette equations were used to calculate maximum shear strains. Measurements were made for no insert, a hard insert and a soft insert in an isotropic material and in a composite. The stiffer insert was seen to confer the greatest advantage and stress reductions were observed at bearing and ligament areas for both types of insert. A study of the effects of oxygen plasma treatment on the adhesion behaviour of polyethylene fibres Tissington, B., Pollard, G. and Ward, 1.M. Composites Science and Technology Vo144 No 3 (1992) pp 185 195 A study of the effects of oxygen plasma treatment on ultra-high modulus polyethylene filaments has been made, concentrating particularly on their adhesion to epoxy resins. Pullout tests, contact angle measurements, determination of gel point and scanning electron microscopy were used to chacracterize the fibres. It is concluded that longer plasma treatment times give rise to different mechanisms of adhesion. Short treatments lead to general oxidation, intermediate to cross-linking of the suface and long treatments to pitting of the suface and thus a mechanical keying effect. A study of the impact behavior of ultra-highmodulus polyethylene fibre composites Tissington, B., Pollard, G. and Ward, I.M. Composites Science and Technology Vo144 No 3 (1992) pp 19~208
COMPOSITES
. NOVEMBER
1992
463
THERMOSETTING MA TRICES The effect of an interphase on the stress and energy distribution in the embedded single fibre test Di Anselmo, A., Accorsi, M.L. and Di Bcnedetto, A.T. Composites Science and TeehnoIogy l/ol 44 No 3 (1992) pp 215 225 The embedded single fibre test and finite element analysis are used to study the behaviour of the interphase of an E-glass/epoxy system. The effect of interphase thickness and mechanical properties on the stress distribution after fibre breakage is studied. The energy distribution and elastic energy released during crack propagation along the interface are calculated. The results are combined to produce a strain history for this system. The effect of side loads on the energy absorption of composite structures Fleming, D.C. and Vizzini, A.J. Journal o[" Composite Materials Vol 26 No 4 (1992) pp 486-499 Pre-impregnated unidirectional graphite/ epoxy tape was made into slightly tapered truncated cones and loaded in compression. By loading the samples away from the centralaxis, side loads were introduced to the cone.
The energy absorption of the cones subjected to quasi-static crushing was measured. It is shown that for small side loads the energy absorbance was improved; however, it deteriorates for high side loads. A further reduction is caused by the toppling of the cone, which is due to the moment applied to it by the side loads. Effects of hydrostatic pressure on the torsional shear behaviour of graphite/epoxy composites Shin, E.S. and Pae, K.D. Journal of Composite Materials Vo126 No 4 (1992) pp 462 485 A high pressure torsion apparatus has been developed to study the stress/strain behaviour of a graphite/epoxy composite and of the epoxy alone. Uniaxial, press-moulded, continuous fibre composites were machined into thin-walled hollow cylinders to act as samples. It is shown that the linear elastic shear stress/ strain behaviour of the epoxy at atmospheric pressure shifted upwards with pressure and becomes non-linear above 2 kbar. A marked increase is also seen for shear modulus and fracture strength and strain. The shear stress/ strain curves for the composite showed dramatic changes from linear behaviour, exhibiting yielding, work hardening and drawing. The shear strength and strain to failure increased linearly with an abrupt change at 4 to 5 bar, where the mode of failure changed to delamination from shearing. Influence of artificial pre-stressing during curing of CFRP laminates on interfibre transverse cracking Schulte, K. and Marissen, R. Composites Science and Technology Vo144 No 4 (1992) pp 361- 367 It is shown that the residual stresses in the 90 ° plies of a cross-ply laminate were affected by pre-stressing the 0 ° plies during curing. Alter curing and cooling to room temperature the pre-stress was released, putting the 90 ° plies under compressive stress. Under tensile loading this caused the development of transverse cracks to be shifted to high load and strain values. interfaciai shear stress distribution in model composites part 2: fragmentation studies on carbon fibre]epoxy systems Melanitis, N., Galiotis, C.. Tetlow, P.L. and Davies, C.K.L. Journal o/ Composite Materials Vol 26 No 4 (1992) pp 574-610 A single fibre embedded in an epoxy resin was subjected to an incremental tensile load up to full fragmentation. The strain in the fibre was measured using laser Raman spectroscopy. After the first fracture the strain in the sample was seen to build from the tips of the fibre breaks and reach a maximum at the centre of each fragment. The shape of the load transfer profiles at the fibre tips indicated that the fracture process had affected the stress transfer efficiency. The load transfer profiles were used to calculate interfacial shear stress, and the shape of these profiles confirms that interracial debonding was initiated at fibre tips. The standard fragmentation test was performed to measure the interracial shear stress at full fragmentation. This was found to be half the value measured by laser Raman spectroscopy. Micromechanics prediction of the shear strength of carbon fibre/epoxy matrix composites: the influence of the matrix and interface strengths King, T.R., Blackketter, D.M., Walrath, D.E. and Adams, D.F. Journal o[" Composite
Materials Vo126 No 4 (1992) pp 558-573 This study investigates the effect of the matrix and interfacial bond strengths in carbon fibre/ epoxy systems on the composite shear strength. A finite element technique has been performed to analytically study these effects. It is shown that numerical results agree well with experimental results, suggesting a micromechanics approach to predicting interfacial effects on composite shear strength is a potentially valuable technique. Process-induced stress and deformation in thick-section thermoset composite laminates Bogetti, T.A. and Gillespie, J.W. Journal ~?f Composite Materials Vol 26 No 5 (1992) pp 626 660 A theory is presented for predicting the residual stress evolved during curing. The theory combines a one-dimensional cure simulation and an incremental laminated plate theory. Models are included to describe the mechanical properties and thermal and chemical strains developed during curing. A comparison is made between experimental and model evaluation of cure-dependent epoxy modulus and curvature in unsymmetric graphite/epoxy laminates. How process-induced stress and deformation are affected by process histoy is studied and it is seen that the residual stress is sufficient to induce transverse cracks and delaminations. Strain-relief inserts for composite fasteners - an experimental study Herrera-Franco, P.J. and Cloud, G.L. Journal ¢t/Composite Matermls Vo126 No 5 (1992) pp 751 768 A theoretical and experimental study is made of the stress/strain distributions around single-pin lap joints in a glass/epoxy laminate. The possibility of obtaining stress concentration release by the addition of isotropic material inserts is investigated. Surface strains were measured by Moir+ interferometry and strain rosette equations were used to calculate maximum shear strains. Measurements were made for no insert, a hard insert and a soft insert in an isotropic material and in a composite. The stiffer insert was seen to confer the greatest advantage and stress reductions were observed at bearing and ligament areas for both types of insert. A study of the effects of oxygen plasma treatment on the adhesion behaviour of polyethylene fibres Tissington, B., Pollard, G. and Ward, 1.M. Composites Science and Technology Vo144 No 3 (1992) pp 185 195 A study of the effects of oxygen plasma treatment on ultra-high modulus polyethylene filaments has been made, concentrating particularly on their adhesion to epoxy resins. Pullout tests, contact angle measurements, determination of gel point and scanning electron microscopy were used to chacracterize the fibres. It is concluded that longer plasma treatment times give rise to different mechanisms of adhesion. Short treatments lead to general oxidation, intermediate to cross-linking of the suface and long treatments to pitting of the suface and thus a mechanical keying effect. A study of the impact behavior of ultra-highmodulus polyethylene fibre composites Tissington, B., Pollard, G. and Ward, I.M. Composites Science and Technology Vo144 No 3 (1992) pp 19~208
COMPOSITES
. NOVEMBER
1992
463