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Thermal response of fire-exposed composites
Literature survey Prepared by M.R. Alexander, C. Barren, J. Colfins, M.D. Glendenning and A.J. Hosty, University of Sheffield, UK GENERAL Analytical and numerical calculation of strain energy release rate during delamination growth in a carbon epoxy laminate Renard, J. and Roudolff, F. Composites Science and Technology Vol 42 No 4 (1991) pp 305-316 The delamination of an infinite laminate under an applied tension stress is investigated. A finite element analysis and an analytical model based on Love-Kirchoff plate theory is employed to study the stress state. During delamination the global strain energy release rate with its Mode I, II and III components are evaluated and a correlation is made between the two formulations. It is shown that the analytical model can be used to analyse various stacking sequences composed of a large number of plies and estimate their capacity for delamination. Evaluation of Mode-1 interlaminar fracture toughness for fibre-reinforced composites materials Ye, L. Composites Science and Technology Vo143 No I (1992)pp 49-54 The basis of applying linear elastic fracture mechanics (LEFM) to composite materials was discussed and found to be valid. Interlaminar Mode I crack growth was examined for unidirectional carbon fibre-reinforced epoxy composites. Orthotropic correction factors were evaluated for double cantilever beam specimens and compared with values obtained from LEFM. The inter-relationship between K and G was explained in terms of LEFM. On modelling of laminates containing freeedge delaminations Harikumar, H.K. and Murty, A.V.K. Composites Science and Technology Vol 42 No 4 (1991) pp 393-411 A modified version of the Whitney-Sun theory has been employed to investigate the stress field in front of the delamination tip and the strain energy release rate in symmetric composite laminates with mid-plane delamination subjected to thermal and mechanical strains. The principle of virtual displacements is used to derive equations which govern this behaviour, and solutions obtained by applying boundary and continuity conditions. Strain energy release rates together with interlaminar normal stresses ahead of the crack tip are shown for various sizes of the delamination and a comparison is made with results available in the literature. Thermal response of fire-exposed composites Milke, J.A. and Vizzini, A.J. Journal o f Composites Technology and Research Vol 13 N o 3 (1991) pp 145-151 The effect of fire on the structural response of a composite component is studied. To do this, the thermal response of that component is
first investigated by developing a threedimensional heat transfer model for an anisotropic composite laminate. The model involves temperature-dependent material properties, arbitrary locations of heat sinks and sources, and a variety of boundary conditions.
A transient stochastic failure model for unidirectional composites under impact loading Xia, Y. and Ruiz, C. Composites Science and Technology Vo143 No I (1992) pp 25-36 This paper presents a method to describe the transient failure processes for some unidirectional composites. Using shear-lag theory, the dynamic stress field ahead of a notch tip and the failure nodes were studied. Then a complete stochastic simulation based on the Monte Carlo method was carried out to obtain fibre length distributions at the fracture surfaces. Predictions from the model were consistent with experimental data.
THERMOSETTING MA TRICES Effects of temperature and rate on fracture toughness of short-alumina-fibre-reinforced epoxies Low, I.-M., Mai, Y.M. and Bandyopadhayay, S. Composites Science and Technology Vo143 No I (1992) pp 3-12 The fracture toughnesses of two toughened epoxies were compared over the temperature range of -70°C to 100°C and rates of 0.05 to 180 000 mm min ~. The epoxy (DGEBA cured with piperidine) was toughened with either 19% alumina fibres or 15% alumina fibres and 15% CTBN rubber. Fracture toughness data (K~c and G~c) were obtained from compact tension and Charpy test specimens, which were examined after fracture by SEM. The alumina fibres were shown to significantly improve the low temperature toughness. High rates and low temperatures promoted brittle fracture whilst the reverse promoted extensive fibre debonding, pull-out and plastic shear deformation of the matrix. The temperature dependence of the toughness was explained in terms of a residual stress model, Measurement of the static compressive strength of carbon-fibre/epoxy laminates Soutis, C. Composites Science and Technology Vo142 No 4 (1991) pp 373-392 A study is made of the compressive failure of T800/924C carbon fibre/epoxy composite laminates. Unidirectional laminates fail by microbuckling at 70% of the tensile strength when loaded in compression parallel to the fibres. In this kind of failure the fibres debond from the matrix and are broken in bending. Multidirectional [(+/--45/02)3k laminates are observed to fail by microbuckling of the 0° plies. It is shown that the failure strain is almost the same in both laminate systems, this indicating that the +/--45° plies have no
significant influence on the failure strength of the 0° plies.
THERMOPLASTIC MA TRICES Failure mechanisms in carbon-fibrereinforced poly(ether sulphone) Hine, P.J., Brew, B., Duckett. R.A. and Ward, 1.M. Composites Science and Technology Vol 43 No I (1992) pp 37-47 The fracture behaviour of unidirectional carbon fibre-reinforced PES matrix composites was compared with that of similar PEEK composites using the double cantilever beam testing geometry in interlaminar and intralaminar orientations. Tests were performed at -61) to 100°C and the resulting fracture surfaces examined by SEM. Interlaminar shear strength was also determined. PES composites had slightly lower fracture toughness than PEEK composites; however, they did exhibit stable fracture independent of the testing temperature. This was shown to be due to ductility in the PES matrix. Interlaminar shear strength was less for PES composites but debonding associated with this was responsible for higher intralaminar toughness than for PEEK composites at longer crack lengths.
METAL MA TRICES Comparison of some micromechanics models for discontinuously reinforced metal matrix composites Johnson, W.S. and Birt, M.J. Journal of Composites Technology and Research Vol 13 No 3 (1991) pp 161-167 A study is made of the effect of variation in reinforcement type, volume fraction and specimen thickness on the tensile properties of whisker- and particulate-reinforced aluminium matrix composites. The information obtained is employed to predict composite moduli using several micromechanics models. The Paul model underpredicts whisker-reinforced composite moduli but gives a good upper bound value for particulate reinforcement. The Cox model underpredicts the particulate moduli but gives a good value for whisker reinforcement and the Halpin-Tsai model is shown to give good results for both. Finally, a comparison was made between a trigonometrical projection of whisker length to predict the fibre contribution to the modulus in longitudinal and transverse directions with the conventional lamination theory approach. The mechanical properties of the matrix in continuous-fibre 6061 aluminium-alloy metalmatrix composites Li, D.S. and Wisnom, M.R. Composites Science and Technology Vol 42 No 4 (1991) pp 413--427
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first investigated by developing a threedimensional heat transfer model for an anisotropic composite laminate. The model involves temperature-dependent material properties, arbitrary locations of heat sinks and sources, and a variety of boundary conditions.
A transient stochastic failure model for unidirectional composites under impact loading Xia, Y. and Ruiz, C. Composites Science and Technology Vo143 No I (1992) pp 25-36 This paper presents a method to describe the transient failure processes for some unidirectional composites. Using shear-lag theory, the dynamic stress field ahead of a notch tip and the failure nodes were studied. Then a complete stochastic simulation based on the Monte Carlo method was carried out to obtain fibre length distributions at the fracture surfaces. Predictions from the model were consistent with experimental data.
THERMOSETTING MA TRICES Effects of temperature and rate on fracture toughness of short-alumina-fibre-reinforced epoxies Low, I.-M., Mai, Y.M. and Bandyopadhayay, S. Composites Science and Technology Vo143 No I (1992) pp 3-12 The fracture toughnesses of two toughened epoxies were compared over the temperature range of -70°C to 100°C and rates of 0.05 to 180 000 mm min ~. The epoxy (DGEBA cured with piperidine) was toughened with either 19% alumina fibres or 15% alumina fibres and 15% CTBN rubber. Fracture toughness data (K~c and G~c) were obtained from compact tension and Charpy test specimens, which were examined after fracture by SEM. The alumina fibres were shown to significantly improve the low temperature toughness. High rates and low temperatures promoted brittle fracture whilst the reverse promoted extensive fibre debonding, pull-out and plastic shear deformation of the matrix. The temperature dependence of the toughness was explained in terms of a residual stress model, Measurement of the static compressive strength of carbon-fibre/epoxy laminates Soutis, C. Composites Science and Technology Vo142 No 4 (1991) pp 373-392 A study is made of the compressive failure of T800/924C carbon fibre/epoxy composite laminates. Unidirectional laminates fail by microbuckling at 70% of the tensile strength when loaded in compression parallel to the fibres. In this kind of failure the fibres debond from the matrix and are broken in bending. Multidirectional [(+/--45/02)3k laminates are observed to fail by microbuckling of the 0° plies. It is shown that the failure strain is almost the same in both laminate systems, this indicating that the +/--45° plies have no
significant influence on the failure strength of the 0° plies.
THERMOPLASTIC MA TRICES Failure mechanisms in carbon-fibrereinforced poly(ether sulphone) Hine, P.J., Brew, B., Duckett. R.A. and Ward, 1.M. Composites Science and Technology Vol 43 No I (1992) pp 37-47 The fracture behaviour of unidirectional carbon fibre-reinforced PES matrix composites was compared with that of similar PEEK composites using the double cantilever beam testing geometry in interlaminar and intralaminar orientations. Tests were performed at -61) to 100°C and the resulting fracture surfaces examined by SEM. Interlaminar shear strength was also determined. PES composites had slightly lower fracture toughness than PEEK composites; however, they did exhibit stable fracture independent of the testing temperature. This was shown to be due to ductility in the PES matrix. Interlaminar shear strength was less for PES composites but debonding associated with this was responsible for higher intralaminar toughness than for PEEK composites at longer crack lengths.
METAL MA TRICES Comparison of some micromechanics models for discontinuously reinforced metal matrix composites Johnson, W.S. and Birt, M.J. Journal of Composites Technology and Research Vol 13 No 3 (1991) pp 161-167 A study is made of the effect of variation in reinforcement type, volume fraction and specimen thickness on the tensile properties of whisker- and particulate-reinforced aluminium matrix composites. The information obtained is employed to predict composite moduli using several micromechanics models. The Paul model underpredicts whisker-reinforced composite moduli but gives a good upper bound value for particulate reinforcement. The Cox model underpredicts the particulate moduli but gives a good value for whisker reinforcement and the Halpin-Tsai model is shown to give good results for both. Finally, a comparison was made between a trigonometrical projection of whisker length to predict the fibre contribution to the modulus in longitudinal and transverse directions with the conventional lamination theory approach. The mechanical properties of the matrix in continuous-fibre 6061 aluminium-alloy metalmatrix composites Li, D.S. and Wisnom, M.R. Composites Science and Technology Vol 42 No 4 (1991) pp 413--427
COMPOSITES. MARCH 1992
133