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Verification of laminated plate theory for unsymmetrical laminates
ment was obtained between the model and results from the literature.
ing at the fibre end. The nature of the stress fields and their distributions were discussed.
A progressive failure model for composite laminates containing openings Tan, S.C. Journal o f Composite Materials Vol 25 No 5 (1991) pp 556-577 There are many causes of progressive damage in composites containing stress concentrations (openings) such as matrix cracking, fibre/matrix splitting, fibre breakage and delamination. The wide variety of failure mechanisms were simply modelled using a damaged ply constitutive relationship which was solved using finite element techniques. Residual thermal and hygroscopic stresses are included in the model. Load increment was shown to have little effect on ultimate strength. The model agreed well with experimental results for strength, stress/strain behaviour and damage accumulation.
Strength and fracture of grasses Vincent, J.F.V. Journal o f Materials Science I/ol26 No 7 (1991) pp 1947-1950 The strength and fracture toughness of six grasses have been measured in tension. Increases in strength and toughness are related to the amount of sclerenchyma the grasses contain. Sclerenchyma is normally present as isolated bundles. However, at high volume fractions it is observed that bundles fuse laterally and although the grass is stronger, it becomes more brittle.
Pull-out and fragmentation in model fibre composites Gent, A.N. and Liu, G.L. Journal o f Materials Science Vol26 No 9 (1991) pp 2467-2476 A study was made of the debonding and fibre rupture of model composites (a glass rod embedded in a transparent silicone rubber block). Basic fibre pull-out and fragmentation tests were performed and the results compared with the predictions of a theory based on a fracture energy criterion for debonding. By extrapolating the debonded length to zero the debonding force in the absence of friction is obtained. A further study shows that frictional stress between cast silicone rubber and glass is approximately constant due to a smooth matrix/fibre interface. Reliability analysis of continuous fibre composite laminates Thomas, D.J. and Wetherhold, R.C. Composite Structures Vo117 No 4 (1991) pp 277294 The heterogeneous nature of composites and variability of processing give composites an inherently high variability in material strengths. Rather than using a model adapted from a conventional homogeneous material, this paper uses a probabilistic approach. Two solutions were used, one where the strengths act separately (modal or independent action) and one where they interact through a quadratic interaction criterion. Upper and lower bounds of reliability were derived and their sensitivities to variations in applied load and material strengths illustrated. Singular stress and displacement fields around the corner point of a fibre end in short fibre reinforced composites Kohno, Y. and Ishikawa, H. International Journal o f Engineering Science Vol 29 No 8 (1991) pp 1005-1012 The strength of short fibre-reinforced plastics has been experimentally shown to be determined by either pull-out of the fibre after interface debonding or propagation of debonding cracks at the fibre end. Stress and displacements fields for three types of singular points were obtained using an eigenfunction expansion method. The types of points studied were: (1) debonding at the fibre end and at the interface; (2) complete bonding near the fibre end; and (3) debond-
474
Strength of sandwich beams with interface debondings Zenkert, D. Composite Structures Vol 17 No 4 (1991) pp 311-350 Debonding in the adhesive joints between the faces and core in sandwich beams can reduce both the stiffness and load-carrying capacity of the beam. An analytical model was developed assuming that the cracks/debonding were at the core/face interface. Stress intensities calculated from the model were successfully compared with those from finite d e m e n t models. Using fracture toughness values from simple experimental test-pieces, fracture loads for beams with simulated debonding could be accurately predicted. Verification of laminated plate theory for unsymmetrical laminates Parhizgar, S. Journal o f Composite Materials Vol25 No 5 (1991) pp 578-592 Non-linear laminated plate theory provides a theoretical basis for determining the stiffness properties of unsymmetrical laminated composites from the stiffness properties of their plies. However, previous attempts to verify the theory have used standard test fixtures which couple axial deformations with shearing, bending and twisting. This paper designs a grip system to decouple the deformation modes for a 0/90 laminated strip and introduces a procedure to determine the stiffness constants AI~ and B'~ of the laminate.
METAL MA TRICES Fatigue behaviour of a 2xxx series aluminium alloy reinforced with 15 vol pct SiCp Bonnen, J.J., Allison, J.E. and Jones, J.W. Metallurgical Transactions A Vol 22A No 5 (1991) pp 1007-1020 The addition of particulate reinforcement to an aluminium alloy has been shown to significantly influence fatigue behaviour. This paper compares the fatigue lives of a naturally aged powder metallurgy 2xxx alloy and a composite made with 15% of particulate SiC reinforcement using load-controlled axial testing of unnotched cylindrical samples at stress ratios o f - 1 , 0.1 and 0.7. Fatigue life decreased with increasing mean stress for both alloy and composite but the composite displayed improved resistance to stresscontrolled fatigue at low and intermediate stress levels compared with the alloy. The performance of the composite was inferior on a strain-life basis. Fatigue life was not seen to vary with the specific crack initiation site in the composite or the alloy.
COMPOSITES. NOVEMBER 1991
Fracture mechanism in a SIC,--6061 AI composite Ma, Z.Y., Liu, J. and Yao, C.K. Journal of Materials Science Vol 26 No 7 (1991) pp 1971-1976 Samples of as-extruded SIC,,,/6061 AI composite have been dynamically tested with a tensile stage in an SEM and the process of fracture observed continuously. The off-axis angle was found to have a great effect on the tensile strength of the composite. The SEM observations are compared with brittle fracture and shear fracture models. Influence of lithium on the mechanical properties of the mechanical composite materials based on the entectic AI-5.7% Ni alloy Terao, N. Journal o f Materials Science Vol26 No 8 (1991) pp 2093-2099 Composites consisting of fine particles in a ductile matrix are produced from the eutectic alloy AI-5.7% Ni by casting into a copper mould and subsequent isostatic extrusion. The addition of a small amount of lithium is found to significantly increase the tensile strength. TEM observations showed this to be due to solid-solution hardening up to lithium contents of 1.7 wt% and precipitation hardening above this value. Interface and fracture of carbon fibre reinforced AI-7 wt% Si alloy Yang, M. and Scott, V.D. Journal o f Materials Science Vol26 No 6 (1991) pp 1609-1617 An AI-7 wt% alloy reinforced with carbon fibres has been extensively characterized with optical, scanning electron and analytical electron microscopy. The composite was produced by melt infiltration and the interface between the fibre and the matrix was of particular interest. Mechanical tests in fourpoint bend were carried out and the properties measured are explained in terms of the microstructure observed. The aluminium in the alloy was found to react with the fibre to produce aluminium carbide. This produced a strong fibre/matrix bond, reduced the fibre strength and caused matrix embrittlement. As a result in longitudinal specimens the fibres failed at low stresses, before brittle catastrophic failure. Interface structure in infiltrates composites of aluminium reinforced with alumina-silica fibre preforms Li, Q., Dunand, D.C., Mortensen, D.C. and Cornie, J.A. Metallurgical Transactions A Vo122A No 5 (1991) pp 1126-1128 This paper used TEM techniques to investigate the interface in composites produced by infiltration of alumina fibre preforms containing a silica binder with aluminium. The binder ensured cohesion of the preform but was known to be unstable in liquid aluminium. When infiltrated by aluminium a preform kept at a temperature below the melting point of aluminium yielded intimate fibre/matrix contact and the interface showed no reaction products. The binder was found in patches at the interface and showed limited reaction with the matrix. Mechanical bebaviour of cast particulate SiC/AI (A356) metal matrix composites Wang, Z. and Zhang, R.J. Metallurgical Transactions A Vo122A No 7 (1991) pp 15851594 The deformation behaviour has been studied in both tension and compression of the aluminium-matrix alloy (A356) and its corn-
ing at the fibre end. The nature of the stress fields and their distributions were discussed.
A progressive failure model for composite laminates containing openings Tan, S.C. Journal o f Composite Materials Vol 25 No 5 (1991) pp 556-577 There are many causes of progressive damage in composites containing stress concentrations (openings) such as matrix cracking, fibre/matrix splitting, fibre breakage and delamination. The wide variety of failure mechanisms were simply modelled using a damaged ply constitutive relationship which was solved using finite element techniques. Residual thermal and hygroscopic stresses are included in the model. Load increment was shown to have little effect on ultimate strength. The model agreed well with experimental results for strength, stress/strain behaviour and damage accumulation.
Strength and fracture of grasses Vincent, J.F.V. Journal o f Materials Science I/ol26 No 7 (1991) pp 1947-1950 The strength and fracture toughness of six grasses have been measured in tension. Increases in strength and toughness are related to the amount of sclerenchyma the grasses contain. Sclerenchyma is normally present as isolated bundles. However, at high volume fractions it is observed that bundles fuse laterally and although the grass is stronger, it becomes more brittle.
Pull-out and fragmentation in model fibre composites Gent, A.N. and Liu, G.L. Journal o f Materials Science Vol26 No 9 (1991) pp 2467-2476 A study was made of the debonding and fibre rupture of model composites (a glass rod embedded in a transparent silicone rubber block). Basic fibre pull-out and fragmentation tests were performed and the results compared with the predictions of a theory based on a fracture energy criterion for debonding. By extrapolating the debonded length to zero the debonding force in the absence of friction is obtained. A further study shows that frictional stress between cast silicone rubber and glass is approximately constant due to a smooth matrix/fibre interface. Reliability analysis of continuous fibre composite laminates Thomas, D.J. and Wetherhold, R.C. Composite Structures Vo117 No 4 (1991) pp 277294 The heterogeneous nature of composites and variability of processing give composites an inherently high variability in material strengths. Rather than using a model adapted from a conventional homogeneous material, this paper uses a probabilistic approach. Two solutions were used, one where the strengths act separately (modal or independent action) and one where they interact through a quadratic interaction criterion. Upper and lower bounds of reliability were derived and their sensitivities to variations in applied load and material strengths illustrated. Singular stress and displacement fields around the corner point of a fibre end in short fibre reinforced composites Kohno, Y. and Ishikawa, H. International Journal o f Engineering Science Vol 29 No 8 (1991) pp 1005-1012 The strength of short fibre-reinforced plastics has been experimentally shown to be determined by either pull-out of the fibre after interface debonding or propagation of debonding cracks at the fibre end. Stress and displacements fields for three types of singular points were obtained using an eigenfunction expansion method. The types of points studied were: (1) debonding at the fibre end and at the interface; (2) complete bonding near the fibre end; and (3) debond-
474
Strength of sandwich beams with interface debondings Zenkert, D. Composite Structures Vol 17 No 4 (1991) pp 311-350 Debonding in the adhesive joints between the faces and core in sandwich beams can reduce both the stiffness and load-carrying capacity of the beam. An analytical model was developed assuming that the cracks/debonding were at the core/face interface. Stress intensities calculated from the model were successfully compared with those from finite d e m e n t models. Using fracture toughness values from simple experimental test-pieces, fracture loads for beams with simulated debonding could be accurately predicted. Verification of laminated plate theory for unsymmetrical laminates Parhizgar, S. Journal o f Composite Materials Vol25 No 5 (1991) pp 578-592 Non-linear laminated plate theory provides a theoretical basis for determining the stiffness properties of unsymmetrical laminated composites from the stiffness properties of their plies. However, previous attempts to verify the theory have used standard test fixtures which couple axial deformations with shearing, bending and twisting. This paper designs a grip system to decouple the deformation modes for a 0/90 laminated strip and introduces a procedure to determine the stiffness constants AI~ and B'~ of the laminate.
METAL MA TRICES Fatigue behaviour of a 2xxx series aluminium alloy reinforced with 15 vol pct SiCp Bonnen, J.J., Allison, J.E. and Jones, J.W. Metallurgical Transactions A Vol 22A No 5 (1991) pp 1007-1020 The addition of particulate reinforcement to an aluminium alloy has been shown to significantly influence fatigue behaviour. This paper compares the fatigue lives of a naturally aged powder metallurgy 2xxx alloy and a composite made with 15% of particulate SiC reinforcement using load-controlled axial testing of unnotched cylindrical samples at stress ratios o f - 1 , 0.1 and 0.7. Fatigue life decreased with increasing mean stress for both alloy and composite but the composite displayed improved resistance to stresscontrolled fatigue at low and intermediate stress levels compared with the alloy. The performance of the composite was inferior on a strain-life basis. Fatigue life was not seen to vary with the specific crack initiation site in the composite or the alloy.
COMPOSITES. NOVEMBER 1991
Fracture mechanism in a SIC,--6061 AI composite Ma, Z.Y., Liu, J. and Yao, C.K. Journal of Materials Science Vol 26 No 7 (1991) pp 1971-1976 Samples of as-extruded SIC,,,/6061 AI composite have been dynamically tested with a tensile stage in an SEM and the process of fracture observed continuously. The off-axis angle was found to have a great effect on the tensile strength of the composite. The SEM observations are compared with brittle fracture and shear fracture models. Influence of lithium on the mechanical properties of the mechanical composite materials based on the entectic AI-5.7% Ni alloy Terao, N. Journal o f Materials Science Vol26 No 8 (1991) pp 2093-2099 Composites consisting of fine particles in a ductile matrix are produced from the eutectic alloy AI-5.7% Ni by casting into a copper mould and subsequent isostatic extrusion. The addition of a small amount of lithium is found to significantly increase the tensile strength. TEM observations showed this to be due to solid-solution hardening up to lithium contents of 1.7 wt% and precipitation hardening above this value. Interface and fracture of carbon fibre reinforced AI-7 wt% Si alloy Yang, M. and Scott, V.D. Journal o f Materials Science Vol26 No 6 (1991) pp 1609-1617 An AI-7 wt% alloy reinforced with carbon fibres has been extensively characterized with optical, scanning electron and analytical electron microscopy. The composite was produced by melt infiltration and the interface between the fibre and the matrix was of particular interest. Mechanical tests in fourpoint bend were carried out and the properties measured are explained in terms of the microstructure observed. The aluminium in the alloy was found to react with the fibre to produce aluminium carbide. This produced a strong fibre/matrix bond, reduced the fibre strength and caused matrix embrittlement. As a result in longitudinal specimens the fibres failed at low stresses, before brittle catastrophic failure. Interface structure in infiltrates composites of aluminium reinforced with alumina-silica fibre preforms Li, Q., Dunand, D.C., Mortensen, D.C. and Cornie, J.A. Metallurgical Transactions A Vo122A No 5 (1991) pp 1126-1128 This paper used TEM techniques to investigate the interface in composites produced by infiltration of alumina fibre preforms containing a silica binder with aluminium. The binder ensured cohesion of the preform but was known to be unstable in liquid aluminium. When infiltrated by aluminium a preform kept at a temperature below the melting point of aluminium yielded intimate fibre/matrix contact and the interface showed no reaction products. The binder was found in patches at the interface and showed limited reaction with the matrix. Mechanical bebaviour of cast particulate SiC/AI (A356) metal matrix composites Wang, Z. and Zhang, R.J. Metallurgical Transactions A Vo122A No 7 (1991) pp 15851594 The deformation behaviour has been studied in both tension and compression of the aluminium-matrix alloy (A356) and its corn-