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Silicon carbide fibre reinforced glass ceramic composite tensile properties at elevated temperature
Itt talx m fvtq Prepared by M. E. Adams, L. Boniface and A. Pryce
CEMENT MA TRICES
CERAMIC FIBRES
Bond of deformed reinforcing bar embedded in steel fibre reinforced concrete Rostfisy, F. S. and Hartwich, K. The
Calorimetric evaluation of the effects of SiC concentration on the precipitation processes in SiC particulate reinforced 7091 aluminium Petty-Gallis, J. L. and Goolsby, R. D.
International Journal o f Cement Composites and Lightweight Concrete Vol 10 No 3 (August 1988) pp 151-158 Tests devised to help identify the role of reinforcing steel fibres in concrete that is also reinforced by a standard hot-rolled bar of irregular shape are described. Two types of commercially-available steel fibre - straight or hooked - were investigated. It was found that the bond strength of the bar to concrete was not enhanced by the presence of steel fibres. However, the post-peak ductility of specimens failing by splitting was greatly improved by fibre addition. Thus, it is concluded that the observed reduction of crack width and deformation of reinforced concrete bending members with steel fibre addition is caused by the transfer of tensile force across primary cracks by the fibres, acting as randomly oriented reinforcing bars. High strength lightweight concrete for use in offshore structures: utilisation of fly ash and silica fume Seabrook, P. I. amd Wilson, H. S. The
International Journal o f Cement Composites and Lightweight Concrete Vol 10 No 3 (August 1988) pp 183-192 The results obtained in the second phase of on-going research into lightweight concrete suitable for use in offshore structures in Arctic conditions are reported. The mixtures comprised fine and coarse aggregates and cementitious materials which included fly ash and silica fume. It was found necessary to introduce the silica fume in a water slurry with superplasticiser as dispersant to obtain a good dispersion in the mixture but that the addition of silica fume significantly improved the strength of the resultant concrete. Load-deformation behaviour of planar and curved microconcrete plates reinforced with melt extract fibres Kearns, C. F. and McConnell, G. M. The
International Journal of Cement Composites and Lightweight Concrete Vol 10 No 3 (August 1988) pp 159-166 The results of static load tests carried out on simply-supported planar and curved microconcrete plates reinforced with melt extract stainless steel fibres are presented. It is shown that the addition of the fibre reinforcement achieves a stable ductile postcracking response in the plates. The beneficial effect of curvature on the structural behaviour of the plates is also indicated.
COMPOSITES
. SEPTEMBER
1989
Journal o f Materials Science Vo124 (1989)pp 1439-1446 Differential scanning calorimetry is a useful technique to tailor thermal and thermomechanical properties of metal matrix composites to produce the required ultimate properties. The present paper characterises the precipitation reactions in the discontinuous SiC reinforced 7091 aluminium composite, paying particular attention to the effect of processing variables such as SiC concentration, temperature, time and sequences. The results indicate that the presence of SiC significantly alters the transformation kinetics of the aluminium alloy, increasing the temperature at which GPI zones revert at their maximum rate. In addition increasing the SiC content decreases the temperature at which GPI and GPII zones precipitate and equilibrium of phase dissolution occurs. Transformation mechanisms have been proposed for these observations. Evidence for a silicon oxycarbide phase in the Nicalon silicon carbide fibre. Porte, L. and Sarte, A. Journal o f Materials
Science Vol 24 (1989) pp 271-275 There is at present considerable interest in the use of silicon carbide fibres as the reinforcement of composite materials in high temperature applications. The Nicalon fibre (trade mark of the Nippon Carbon Company) studied here consists of primary SiC and certain other phases which influence its behaviour. The present paper considers the role of oxygen atoms and how they are incorporated into the fibre network using X-ray photoelectron spectroscopy (XPS). Results indicate that only a small proportion of the total oxygen content exists as SiO2 incorporated in the fibre. Larger quantities are found however in a silicon oxycarbide ternary phase, intermediary to SiC and SiOz. This phase, probably originating from the polymer precursor, could be an important factor governing the thermomechanical properties of the Nicalon fibre.
CERAMIC MA TRICES Fibre reinforced glasses Hegeler, H. and Briickner. Journal of Materials Science Vol 24 (1989) 1191-1194. The processing of fibre reinforced glasses can
be achieved by two distinct routes; the slurry method and the sol-gel technique. The present paper proposes a method using the Nicalon fibre reini ~rced borosilicate glass system which combines ideas from both processes, thus eliminating the use of a binder. The resulting prepregs are hot pressed and the influence of a number of processing variables on bend strength is examined. Fracture resistance of a TiB2 particle/SiC matrix composite at elevated temperature. Jenkins, M. G., Salem, J. A. and Seshadri,
S. G. Journal o f Composite Materials Vo123 No 1 (January 1989) pp 77-91 The fracture behaviour of a commercial composite of particulate TiB2 reinforced SiC matrix is studied in the temperature range 20-1400°C. Crack mouth opening displacement (CMOD) is monitored in straightnotched and chevron-notched three-point bend specimens using a laser interferometric strain gauge to determine R-curves, fracture toughness and work of fracture. The chevron-notched configuration is subsequently adopted since the sharper notch gives stable crack growth and more reliable work of fracture results and R-curves. Strength is found to be independent of temperature but the fracture parameters show a decrease with increasing temperature, related to thermally activated mechanisms. Microscopic observations of fracture surfaces, microstructure and oxidation coatings are compared for asreceived samples and samples tested up to 1400°C. In as-received samples, microcracks develop at the TiB2 particle/matrix interface which divert the fracture path around particles, producing a rough surface. At high temperature, the smooth fracture surface indicates that the particles are less effective in resisting crack growth. The change in crack mechanism at elevated temperature is explained in terms of the relief of residual stresses which otherwise enhance microcracking. X-ray analysis of the oxide layer shows TiO2 with SiO2 which increases in thickness with increasing temperature, leading to attack of the material beneath to variable depths. Silicon carbide fibre reinforced glass ceramic composite tensile properties at e l e v a t e d temperature. Prewo, K. M., Johnson, B. and Starrett, S.
Journal o f Materials Science Vo124 (1989) pp 1373-1379 Fibre reinforced glass ceramic composites offer an alternative to light metal alloys in many elevated temperature applications. For this reason there has been much interest in developing such materials as the Nicalon fibre (trade mark of the Nippon Carbon Company) reinforced LAS matrix composite, which is studied in this paper. The
493
investigation concerns the effects test temperature and environment have on the tensile behaviour of simple crossply laminates by testing in tension, fatigue and stress rupture modes. Results indicate that under an inert argon atmosphere tensile strength is maintained to 1300°C. However in air, poor strength and a change in failure mode are observed at high temperature due to an alteration in fibre-matrix bond. Fatigue testing in air causes a further loss in strength which is explained by matrix cracks allowing air to enter the fibre-matrix interfacial region.
GENERAL Acoustoelastic response of unidirectional fiber composites Chatterjee, S. N., Journal of Composite Materials Vol 23 No 1 (January 1989) pp 58-76 The theory of acoustoelasticity, relating the change in wave speeds to initial stresses, has been widely applied to homogeneous materials. This paper considers the analytical relationship between wave speeds in a unidirectional composite, the second and third order moduli of the constituents and the residual stresses and applied stresses. The authors obtain acoustoelastic equations of motion for in-plane waves by simple averaging of stress and displacement gradients over a representative volume element and define effective moduli in order to estimate the change in potential energy of the system. They examine published experimental data on wave velocity changes due to thermal cycling in graphite/aluminium composite and obtain reasonable agreement between computed wave velocities and test data after thermal cycling. Analysis of delamination in compressively loaded laminates Shaw, D. and Tsai, M. Y. Composites Science and Technology Vol 34 No 1 (1989) pp 1-17 A combination of post-buckling theory and fracture mechanics is used to present a model describing delamination in one direction. Classical plate theory is used to determine stress distribution and then a finite element model for the crack tip region is used to evaluate the strain energy release rate. It is shown that the influence of fibre orientation on delamination behaviour is significant. Application of reflection orthotropic photoelasticity to laminated composites Friere, J. L. F., Antonelli, R. A., Dror, Y. and Voloshin, A. S. Journal of Composite Materials Vol 23 No 1 (January 1989) pp 42-57 Qualitative observations of fringe patterns in glass/polyester composites are made using a reflection photoelastic technique to obtain information on stress fields in multilayered composites. The technique involves application of a layer of aluminium paint between plies of different orientations in a + 3 0 / - 3 0 / +30 laminate under tensile loading and discs of 0/0/0 and 0/45/0 configuration under diametrical compression. Isochromatic fringes in the surface plies are distorted according to the underlying fibre orientation. Good agreement is obtained between experimental
494
observations of fringe order and predictions made using orthotropic photomechanics combined with finite element analysis to calculate the stress state in the laminate. A continuum damage model of fatigueinduced damage in laminated composites Harris, C. E. and Allen, D. H. S A M P E Journal Vol 24 No 4 (July~August 1988) pp 43-50 A model (based on the concept of continuum damage mechanics) which will predict stress/ strain behaviour of continuous fibrereinforced laminated composites in the presence of microstructural damage is presented. It is shown that predictions from the model are in close agreement with results of fatigue tests obtained experimentally on laminate panels of graphite fibre-reinforced epoxy with different fibre orientations. Decomposition of strain energy density in fiber reinforced composites Theocaris, P. S. Engineering Fracture Mechanics Vol 33 No 3 (1989) pp 335-344 The elliptic paraboloidal failure surface (EPFS) criterion is proposed as a suitable criterion for yielding and failure of heterogeneous composite materials. The criterion is first reviewed in general and then applied to the case of a transtropic composite, the elastic strain energy density, defined as corresponding to a point on the EPFS, can be divided into two independent parts derived from orthogonal state of stress. Expressions for the decomposition of the strain energy density are presented. Delamination from surface cracks in composite materials Thouless, M. D., Cao, H. C. and Mataga, Journal of Materials Science Vo124 (1989)pp 1406-1412 The mechanism for delamination in laminated composite materials normally occurs by the differing elastic properties of the constituent plies inducing interlaminar shear and normal stresses. However for a different type of delamination caused by discontinuities in sample geometry such as surface flaws, a system of an elastically homogeneous material containing aligned interfaces may be used as a model, which is the subject for the present paper. It is shown that when the interface is sufficiently weak the delamination crack will propagate along the interface under simple and mixed loading conditions when considering the fracture mechanics of the process. An explanation is offered based on statistical effects for cracks observed to deviate from the interface. Driving forces for composite interface fatigue cracks Chan, K. S. and Davidson, D. L. Engineering Fracture Mechanics Vo133 No 3 (1989. pp 451-466 Fatigue crack growth at the fibre/matrix interface in a composite material is considered both experimentally and analytically. The local stress intensity factor range (AK) at the crack tip is derived by two methods: by plotting experimentally determined crack opening displacement (COD) as a function of r the distance ahead of the crack tip, or by using a J-integral approach based on the experimental crack tip opening displacement. These methods are compared for fatigue cracks in SEN specimens of compo-
sites containing alumina fibres in Mg alloy and boron fibres in Ti alloy. Crack opening displacements are measured by a stereoimaging technique for the alumina/Mg composite. Observations indicate that interpenetrating crack surfaces just behind the crack tip can be ignored and small scale yielding in the interface zone is also indicated by good agreement between the COD and AJ methods. The equivalent AK (defined in terms of the cyclic J-integral or strain energy release rate) is found to be the crack growth driving force for these interface fatigue cracks. Crack growth is slower than predicted for the Ti/B composite due to crack branching which reduces the effective AK. Effect of transverse cracks on the thermomechanical properties of cross-ply laminated composites Lim, S. G. and Hong, C. S. Composites Science and Technology Vol 34 No 2 (1989) pp 145-162 A modified shear lag analysis (which takes into account the concept of an interlaminar shear layer) to evaluate the effect of transverse cracks on the stiffness and coefficient of thermal expansion in cross-ply laminated composites is presented. Predictions of the thermomechanical property changes due to transverse cracks are compared with numerical results and existing experimental data. It is shown that the model represents well the dependence of the degradation of thermomechanical properties on the laminate configuration. Effective fracture toughness of a marbleepoxy two phase composite Sachan, A. K. and Kamesawara Rao, C. V. S. The International Journal of Cement Composites and Lightweight Concrete Vo110 No 3 (August 1988) pp 167-169 The effective fracture roughness of a composite material comprising marble particles distributed in an epoxy sand mortar matrix was determined by testing notched beam specimens of varying volume fractions. It is shown that if the phases are of the same fracture toughness then the resulting composite will have the same fracture toughness irrespective of the volume fractions. End fixity effects on the buckling and post-buckling of delaminated composites Kardomateas, G. A. Composites Science and Technology Vol 34 No 2 (1989) pp 113-128 The effects of end fixity (clamped-clamped versus simply-supported) on the buckling and post-buckling of delaminated composites under compressive loads were investigated. An analytical solution for the case of post-buckling behaviour of delaminated composites with simply-supported ends is presented and the results are compared with the characteristics of the clamped-clamped case. The end-fixity effects were found to be more pronounced for lower values of the foundation modulus. Flexible composites (review) Tsu-Wei Chou Journal of Materials Science Vol 24 (1989) pp 761-783 To examine the current knowledge regarding the modelling of elastic behaviour in flexible composites, this review article considers three categories of materials. These are pneumatic tyres, coated fabrics and flexible composites containing wavy fibres, and are
COMPOSITES. SEPTEMBER 1989
CEMENT MA TRICES
CERAMIC FIBRES
Bond of deformed reinforcing bar embedded in steel fibre reinforced concrete Rostfisy, F. S. and Hartwich, K. The
Calorimetric evaluation of the effects of SiC concentration on the precipitation processes in SiC particulate reinforced 7091 aluminium Petty-Gallis, J. L. and Goolsby, R. D.
International Journal o f Cement Composites and Lightweight Concrete Vol 10 No 3 (August 1988) pp 151-158 Tests devised to help identify the role of reinforcing steel fibres in concrete that is also reinforced by a standard hot-rolled bar of irregular shape are described. Two types of commercially-available steel fibre - straight or hooked - were investigated. It was found that the bond strength of the bar to concrete was not enhanced by the presence of steel fibres. However, the post-peak ductility of specimens failing by splitting was greatly improved by fibre addition. Thus, it is concluded that the observed reduction of crack width and deformation of reinforced concrete bending members with steel fibre addition is caused by the transfer of tensile force across primary cracks by the fibres, acting as randomly oriented reinforcing bars. High strength lightweight concrete for use in offshore structures: utilisation of fly ash and silica fume Seabrook, P. I. amd Wilson, H. S. The
International Journal o f Cement Composites and Lightweight Concrete Vol 10 No 3 (August 1988) pp 183-192 The results obtained in the second phase of on-going research into lightweight concrete suitable for use in offshore structures in Arctic conditions are reported. The mixtures comprised fine and coarse aggregates and cementitious materials which included fly ash and silica fume. It was found necessary to introduce the silica fume in a water slurry with superplasticiser as dispersant to obtain a good dispersion in the mixture but that the addition of silica fume significantly improved the strength of the resultant concrete. Load-deformation behaviour of planar and curved microconcrete plates reinforced with melt extract fibres Kearns, C. F. and McConnell, G. M. The
International Journal of Cement Composites and Lightweight Concrete Vol 10 No 3 (August 1988) pp 159-166 The results of static load tests carried out on simply-supported planar and curved microconcrete plates reinforced with melt extract stainless steel fibres are presented. It is shown that the addition of the fibre reinforcement achieves a stable ductile postcracking response in the plates. The beneficial effect of curvature on the structural behaviour of the plates is also indicated.
COMPOSITES
. SEPTEMBER
1989
Journal o f Materials Science Vo124 (1989)pp 1439-1446 Differential scanning calorimetry is a useful technique to tailor thermal and thermomechanical properties of metal matrix composites to produce the required ultimate properties. The present paper characterises the precipitation reactions in the discontinuous SiC reinforced 7091 aluminium composite, paying particular attention to the effect of processing variables such as SiC concentration, temperature, time and sequences. The results indicate that the presence of SiC significantly alters the transformation kinetics of the aluminium alloy, increasing the temperature at which GPI zones revert at their maximum rate. In addition increasing the SiC content decreases the temperature at which GPI and GPII zones precipitate and equilibrium of phase dissolution occurs. Transformation mechanisms have been proposed for these observations. Evidence for a silicon oxycarbide phase in the Nicalon silicon carbide fibre. Porte, L. and Sarte, A. Journal o f Materials
Science Vol 24 (1989) pp 271-275 There is at present considerable interest in the use of silicon carbide fibres as the reinforcement of composite materials in high temperature applications. The Nicalon fibre (trade mark of the Nippon Carbon Company) studied here consists of primary SiC and certain other phases which influence its behaviour. The present paper considers the role of oxygen atoms and how they are incorporated into the fibre network using X-ray photoelectron spectroscopy (XPS). Results indicate that only a small proportion of the total oxygen content exists as SiO2 incorporated in the fibre. Larger quantities are found however in a silicon oxycarbide ternary phase, intermediary to SiC and SiOz. This phase, probably originating from the polymer precursor, could be an important factor governing the thermomechanical properties of the Nicalon fibre.
CERAMIC MA TRICES Fibre reinforced glasses Hegeler, H. and Briickner. Journal of Materials Science Vol 24 (1989) 1191-1194. The processing of fibre reinforced glasses can
be achieved by two distinct routes; the slurry method and the sol-gel technique. The present paper proposes a method using the Nicalon fibre reini ~rced borosilicate glass system which combines ideas from both processes, thus eliminating the use of a binder. The resulting prepregs are hot pressed and the influence of a number of processing variables on bend strength is examined. Fracture resistance of a TiB2 particle/SiC matrix composite at elevated temperature. Jenkins, M. G., Salem, J. A. and Seshadri,
S. G. Journal o f Composite Materials Vo123 No 1 (January 1989) pp 77-91 The fracture behaviour of a commercial composite of particulate TiB2 reinforced SiC matrix is studied in the temperature range 20-1400°C. Crack mouth opening displacement (CMOD) is monitored in straightnotched and chevron-notched three-point bend specimens using a laser interferometric strain gauge to determine R-curves, fracture toughness and work of fracture. The chevron-notched configuration is subsequently adopted since the sharper notch gives stable crack growth and more reliable work of fracture results and R-curves. Strength is found to be independent of temperature but the fracture parameters show a decrease with increasing temperature, related to thermally activated mechanisms. Microscopic observations of fracture surfaces, microstructure and oxidation coatings are compared for asreceived samples and samples tested up to 1400°C. In as-received samples, microcracks develop at the TiB2 particle/matrix interface which divert the fracture path around particles, producing a rough surface. At high temperature, the smooth fracture surface indicates that the particles are less effective in resisting crack growth. The change in crack mechanism at elevated temperature is explained in terms of the relief of residual stresses which otherwise enhance microcracking. X-ray analysis of the oxide layer shows TiO2 with SiO2 which increases in thickness with increasing temperature, leading to attack of the material beneath to variable depths. Silicon carbide fibre reinforced glass ceramic composite tensile properties at e l e v a t e d temperature. Prewo, K. M., Johnson, B. and Starrett, S.
Journal o f Materials Science Vo124 (1989) pp 1373-1379 Fibre reinforced glass ceramic composites offer an alternative to light metal alloys in many elevated temperature applications. For this reason there has been much interest in developing such materials as the Nicalon fibre (trade mark of the Nippon Carbon Company) reinforced LAS matrix composite, which is studied in this paper. The
493
investigation concerns the effects test temperature and environment have on the tensile behaviour of simple crossply laminates by testing in tension, fatigue and stress rupture modes. Results indicate that under an inert argon atmosphere tensile strength is maintained to 1300°C. However in air, poor strength and a change in failure mode are observed at high temperature due to an alteration in fibre-matrix bond. Fatigue testing in air causes a further loss in strength which is explained by matrix cracks allowing air to enter the fibre-matrix interfacial region.
GENERAL Acoustoelastic response of unidirectional fiber composites Chatterjee, S. N., Journal of Composite Materials Vol 23 No 1 (January 1989) pp 58-76 The theory of acoustoelasticity, relating the change in wave speeds to initial stresses, has been widely applied to homogeneous materials. This paper considers the analytical relationship between wave speeds in a unidirectional composite, the second and third order moduli of the constituents and the residual stresses and applied stresses. The authors obtain acoustoelastic equations of motion for in-plane waves by simple averaging of stress and displacement gradients over a representative volume element and define effective moduli in order to estimate the change in potential energy of the system. They examine published experimental data on wave velocity changes due to thermal cycling in graphite/aluminium composite and obtain reasonable agreement between computed wave velocities and test data after thermal cycling. Analysis of delamination in compressively loaded laminates Shaw, D. and Tsai, M. Y. Composites Science and Technology Vol 34 No 1 (1989) pp 1-17 A combination of post-buckling theory and fracture mechanics is used to present a model describing delamination in one direction. Classical plate theory is used to determine stress distribution and then a finite element model for the crack tip region is used to evaluate the strain energy release rate. It is shown that the influence of fibre orientation on delamination behaviour is significant. Application of reflection orthotropic photoelasticity to laminated composites Friere, J. L. F., Antonelli, R. A., Dror, Y. and Voloshin, A. S. Journal of Composite Materials Vol 23 No 1 (January 1989) pp 42-57 Qualitative observations of fringe patterns in glass/polyester composites are made using a reflection photoelastic technique to obtain information on stress fields in multilayered composites. The technique involves application of a layer of aluminium paint between plies of different orientations in a + 3 0 / - 3 0 / +30 laminate under tensile loading and discs of 0/0/0 and 0/45/0 configuration under diametrical compression. Isochromatic fringes in the surface plies are distorted according to the underlying fibre orientation. Good agreement is obtained between experimental
494
observations of fringe order and predictions made using orthotropic photomechanics combined with finite element analysis to calculate the stress state in the laminate. A continuum damage model of fatigueinduced damage in laminated composites Harris, C. E. and Allen, D. H. S A M P E Journal Vol 24 No 4 (July~August 1988) pp 43-50 A model (based on the concept of continuum damage mechanics) which will predict stress/ strain behaviour of continuous fibrereinforced laminated composites in the presence of microstructural damage is presented. It is shown that predictions from the model are in close agreement with results of fatigue tests obtained experimentally on laminate panels of graphite fibre-reinforced epoxy with different fibre orientations. Decomposition of strain energy density in fiber reinforced composites Theocaris, P. S. Engineering Fracture Mechanics Vol 33 No 3 (1989) pp 335-344 The elliptic paraboloidal failure surface (EPFS) criterion is proposed as a suitable criterion for yielding and failure of heterogeneous composite materials. The criterion is first reviewed in general and then applied to the case of a transtropic composite, the elastic strain energy density, defined as corresponding to a point on the EPFS, can be divided into two independent parts derived from orthogonal state of stress. Expressions for the decomposition of the strain energy density are presented. Delamination from surface cracks in composite materials Thouless, M. D., Cao, H. C. and Mataga, Journal of Materials Science Vo124 (1989)pp 1406-1412 The mechanism for delamination in laminated composite materials normally occurs by the differing elastic properties of the constituent plies inducing interlaminar shear and normal stresses. However for a different type of delamination caused by discontinuities in sample geometry such as surface flaws, a system of an elastically homogeneous material containing aligned interfaces may be used as a model, which is the subject for the present paper. It is shown that when the interface is sufficiently weak the delamination crack will propagate along the interface under simple and mixed loading conditions when considering the fracture mechanics of the process. An explanation is offered based on statistical effects for cracks observed to deviate from the interface. Driving forces for composite interface fatigue cracks Chan, K. S. and Davidson, D. L. Engineering Fracture Mechanics Vo133 No 3 (1989. pp 451-466 Fatigue crack growth at the fibre/matrix interface in a composite material is considered both experimentally and analytically. The local stress intensity factor range (AK) at the crack tip is derived by two methods: by plotting experimentally determined crack opening displacement (COD) as a function of r the distance ahead of the crack tip, or by using a J-integral approach based on the experimental crack tip opening displacement. These methods are compared for fatigue cracks in SEN specimens of compo-
sites containing alumina fibres in Mg alloy and boron fibres in Ti alloy. Crack opening displacements are measured by a stereoimaging technique for the alumina/Mg composite. Observations indicate that interpenetrating crack surfaces just behind the crack tip can be ignored and small scale yielding in the interface zone is also indicated by good agreement between the COD and AJ methods. The equivalent AK (defined in terms of the cyclic J-integral or strain energy release rate) is found to be the crack growth driving force for these interface fatigue cracks. Crack growth is slower than predicted for the Ti/B composite due to crack branching which reduces the effective AK. Effect of transverse cracks on the thermomechanical properties of cross-ply laminated composites Lim, S. G. and Hong, C. S. Composites Science and Technology Vol 34 No 2 (1989) pp 145-162 A modified shear lag analysis (which takes into account the concept of an interlaminar shear layer) to evaluate the effect of transverse cracks on the stiffness and coefficient of thermal expansion in cross-ply laminated composites is presented. Predictions of the thermomechanical property changes due to transverse cracks are compared with numerical results and existing experimental data. It is shown that the model represents well the dependence of the degradation of thermomechanical properties on the laminate configuration. Effective fracture toughness of a marbleepoxy two phase composite Sachan, A. K. and Kamesawara Rao, C. V. S. The International Journal of Cement Composites and Lightweight Concrete Vo110 No 3 (August 1988) pp 167-169 The effective fracture roughness of a composite material comprising marble particles distributed in an epoxy sand mortar matrix was determined by testing notched beam specimens of varying volume fractions. It is shown that if the phases are of the same fracture toughness then the resulting composite will have the same fracture toughness irrespective of the volume fractions. End fixity effects on the buckling and post-buckling of delaminated composites Kardomateas, G. A. Composites Science and Technology Vol 34 No 2 (1989) pp 113-128 The effects of end fixity (clamped-clamped versus simply-supported) on the buckling and post-buckling of delaminated composites under compressive loads were investigated. An analytical solution for the case of post-buckling behaviour of delaminated composites with simply-supported ends is presented and the results are compared with the characteristics of the clamped-clamped case. The end-fixity effects were found to be more pronounced for lower values of the foundation modulus. Flexible composites (review) Tsu-Wei Chou Journal of Materials Science Vol 24 (1989) pp 761-783 To examine the current knowledge regarding the modelling of elastic behaviour in flexible composites, this review article considers three categories of materials. These are pneumatic tyres, coated fabrics and flexible composites containing wavy fibres, and are
COMPOSITES. SEPTEMBER 1989