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nylon molecular and particulate composites
posite materials is unable to imbibe metal melts. Interaction of AI203-ZrO z fibres with a Ti-AI matrix during pressure casting Nourbakhsh, S., Liang, F.L. and Margolin, H. Metallurgical Transactions A Vo121A No 1 (1990) pp 213-219 A composite was produced by pressure casting the intermetallic alloy Ti-48.4Al-lMn into a ceramic mould containing a preform of alpha-Al203-20%ZrO 2 continuous fibres. The microstructure was characterized by scanning and transmission electron microscopy in conjunction with energy dispersive X-ray microanalysis. The intermetallic matrix was found to consist of a mixture of TiAI and a lameUar structure of TiAI and Ti3AI. Interdiffusion between the fibres and the matrix was found to have occurred. The nature and origin of these effects were discussed.
A simple flow rule for characterizing nonlinear behaviour of fibre composites Sun, C.T. and Chen, J.L. Journal o f Composite Materials Vol 23 No 10 (1989) pp 10091020 The nonlinear stress-strain behaviour of fibre composites, especially pronounced in metalmatrix systems, was modelled using a oneparameter flow rule. The lack of plasticity in the longitudinal direction made it possible to use a plastic potential containing a single parameter. Experimental test results from the boron/aluminium and graphite/epoxy composite systems agreed fairly well with the model.
ORGANIC FIBRES Deformation processes in a molecular composite Young, R.J., Day, R.J. and Ang, P.P. Polymer Communications Vo131 No 2 (1990) pp 47-49 The deformation of rigid rod poly(pphenylene benzobisthiazole) (PBT) in both a high modulus fibre and a molecular composite is followed using Raman spectroscopy. The molecular composite consists of 30% PBT and 70% poly(2,5(6)benzimidazole). In both PBT fibres and the PBT containing molecular composite, changes in the frequency of the stretch absorption of the heterocyclic linkage of PBT are observed when stress is applied. The results indicate that in both materials the deformation occurs by stretching of the rigid rod molecules giving rise to materials with excellent properties. Rheological and mechanical characteristics of poly-p-phenylene terephthalamide/nylon molecular and particulate composites Park, H-S. and Kyu, T. Polymer Composites Vo110 No 1 (1990) pp 429-438 When heated above the melting point of nylon, molecular composites of poly-pphenylene terephthalamide (PPTA) and nylons (nylon 6, 66, 11 or 12) undergo a phase separation to become two phase particulate composites. Rheological, morphological and mechanical characteristics of the composites were determined by dynamic mechanical thermal analysis, capillary rheometry, extrusion, injection moulding, SEM examination and uniaxial stress-strain measurements. Extrudate swell of around 1 existed for all
composite ranges and shear rates. Mechanical properties of 5% PPTA (long fibrils in a nylon matrix) extrudates showed considerable improvement in tension. Heat treatment further improved properties.
RESIN MA TRICES Characterization of thermoset cure behaviour by differential scanning calorimetry. Part II: Effects of low profile additives Lam, P.W.K. Polymer Composites Vo110 No 6 (1989) pp 439-448 This paper uses an autocatalysed second order kinetic model to compare the isothermal and dynamic cure behaviour of low profile polyester resins. Generally the effect of low profile additives (e.g. polystyrene) was to retard the cure rate and suppress the exothermicity of polyester resins because of dilution effects. However, the effect of compatible low profile additives (e.g., polyurethane) was to substantially enhance the reaction rate. The ultimate conversion of low profile polyester resins was found to be generally slightly greater than neat polyester. Coated glass beads-epoxy composites: influence of the interlayer thickness on preyielding and fracture properties Amdouni, N., Sautereau, H., Gerard, J.F., Fernagnt, F., Coulon, G. and Lefebvre, J.M. Journal o f Materials Science Vol 25 No 2B (1990) pp 1435-1443 Composite materials are prepared from untreated or coated glass beads, and an epoxy matrix. Treated glass beads are prepared by mixing with an adduct based on a liquid rubber, an epoxy prepolymer and a liquid diamine hardener, and curing. The critical stress intensity factor for the composite, K~c , is found to vary linearly with volume fraction of glass beads for the composite containing uncoated glass beads. A maximum KIC is observed at 20% volume fraction of beads for composites with coated beads. The elastomerit layer present in composites containing coated glass beads is found to improve fracture toughness, and effect of layer thickness is investigated. Toughening mechanisms are discussed in terms of crack pinning and plastic deformation. Creep behaviour of woven roving GRP beam in three point bending Shuang-Yin Zhang and Bing Zhao Composite Structures Vo113 No 3 (1989) pp 217-234 This paper describes the experimental and analytical study of the creep and relaxation behaviour of laminated glass fibre reinforced plastics in three point bending. While bending deflexion and creep strains were measured in the creep tests, the load and relaxation strain were recorded in the relaxation tests. Creep effects were seen in the tests carried out at 50°C for 60 min. An attempt was made to predict the creep deflexion and relaxation behaviour and the predicted results compared with the experimental ones. They were found to be in reasonable agreement, but the linearization assumption, upon which the relaxation behaviour is based, appears to lead to inaccuracies in the results.
The durability of controlled matrix shrinkage composites. Part 3. Measurement of damage during fatigue Lam, P.K.W. and Piggot, M.R. Journal of Materials Science Vol 25 No 2B (1990) pp 1197-1202 Testing of aligned carbon fibre/epoxy pultrusions is performed to clarify the causes of fatigue failure. Experiments are carried out on pultrusions made with differing amounts of expanding monomer or, instead, nonreactive plasticizer. Damage appears to develop continuously during testing. Holes grow in size in a direction at right angles to the applied stress, and Poisson's ratio and the energy absorbed during the fatigue cycle also increase continuously. The origin of damage is proposed to be imperfections in the composite, such as misaligned fibres which may generate off-axis stresses high enough to cause interracial failure and ultimately composite failure. The use of expanding, monomers is proposed to reduce microstresses present in the matrix, and thus reduce the rate of damage growth. The effect of aging conditions on the mechaniicai properties of wood fibre/polystyrene composites I. Chemithermomechanical pulp as reinforcing filler Maldas, D. and Kokta, B.V. Composites Science and Technology Vol 36 No 2 (1989) pp 167-182 Composites consisting of hardwood aspen pulp in polystyrene are subjected to ageing conditions such as boiling in water. The effects of various ageing conditions on mechanical properties and dimensional stability are evaluated. Composites prepared with chemical modification are also considered, such as the inclusion of 3% poly(methylene(polyphenyl isocyanate)) coupling agent, and coating and grafting onto the wood pulp surface. It is found that the chemically modified composites have superior mechanical properties and better mechanical stability compared with non-treated composites. Results suggest the existence of an efficient interfacial area between the fibre and the polymer matrix in a chemically modified composite. The influence of varying projectile mass on the impact response of CFRP Cantwell, W.J. and Morton, J. Composite Structures Vo113 No 2 (1989)pp 101-114 This paper reports on the results of high and low velocity impact tests on CFRP laminates as a function of projectile mass. The analyses the effect of projectile mass on the impact response and the subsequent load bearing capability of a composite structure. Results obtained from C-scans and optical micrographs indicated that, for a given impact energy, decreasing the impactor mass resulted in the greater levels of damage and consequently, poorer post impact properties. The authors explain their result by proposing that light, fast moving projectiles induce a very localized form of target response in which most of the incident energy of the projectile is dissipated immediately adjacent to the point of impact, essentially by shearing the fibres. Internal state variable approach for predicting stiffness reductions in fibrous laminated composites with matrix cracks Lee, J-W., Allen, D.H. and Harris, C.E.
COMPOSITES. JULY 1990
359
A simple flow rule for characterizing nonlinear behaviour of fibre composites Sun, C.T. and Chen, J.L. Journal o f Composite Materials Vol 23 No 10 (1989) pp 10091020 The nonlinear stress-strain behaviour of fibre composites, especially pronounced in metalmatrix systems, was modelled using a oneparameter flow rule. The lack of plasticity in the longitudinal direction made it possible to use a plastic potential containing a single parameter. Experimental test results from the boron/aluminium and graphite/epoxy composite systems agreed fairly well with the model.
ORGANIC FIBRES Deformation processes in a molecular composite Young, R.J., Day, R.J. and Ang, P.P. Polymer Communications Vo131 No 2 (1990) pp 47-49 The deformation of rigid rod poly(pphenylene benzobisthiazole) (PBT) in both a high modulus fibre and a molecular composite is followed using Raman spectroscopy. The molecular composite consists of 30% PBT and 70% poly(2,5(6)benzimidazole). In both PBT fibres and the PBT containing molecular composite, changes in the frequency of the stretch absorption of the heterocyclic linkage of PBT are observed when stress is applied. The results indicate that in both materials the deformation occurs by stretching of the rigid rod molecules giving rise to materials with excellent properties. Rheological and mechanical characteristics of poly-p-phenylene terephthalamide/nylon molecular and particulate composites Park, H-S. and Kyu, T. Polymer Composites Vo110 No 1 (1990) pp 429-438 When heated above the melting point of nylon, molecular composites of poly-pphenylene terephthalamide (PPTA) and nylons (nylon 6, 66, 11 or 12) undergo a phase separation to become two phase particulate composites. Rheological, morphological and mechanical characteristics of the composites were determined by dynamic mechanical thermal analysis, capillary rheometry, extrusion, injection moulding, SEM examination and uniaxial stress-strain measurements. Extrudate swell of around 1 existed for all
composite ranges and shear rates. Mechanical properties of 5% PPTA (long fibrils in a nylon matrix) extrudates showed considerable improvement in tension. Heat treatment further improved properties.
RESIN MA TRICES Characterization of thermoset cure behaviour by differential scanning calorimetry. Part II: Effects of low profile additives Lam, P.W.K. Polymer Composites Vo110 No 6 (1989) pp 439-448 This paper uses an autocatalysed second order kinetic model to compare the isothermal and dynamic cure behaviour of low profile polyester resins. Generally the effect of low profile additives (e.g. polystyrene) was to retard the cure rate and suppress the exothermicity of polyester resins because of dilution effects. However, the effect of compatible low profile additives (e.g., polyurethane) was to substantially enhance the reaction rate. The ultimate conversion of low profile polyester resins was found to be generally slightly greater than neat polyester. Coated glass beads-epoxy composites: influence of the interlayer thickness on preyielding and fracture properties Amdouni, N., Sautereau, H., Gerard, J.F., Fernagnt, F., Coulon, G. and Lefebvre, J.M. Journal o f Materials Science Vol 25 No 2B (1990) pp 1435-1443 Composite materials are prepared from untreated or coated glass beads, and an epoxy matrix. Treated glass beads are prepared by mixing with an adduct based on a liquid rubber, an epoxy prepolymer and a liquid diamine hardener, and curing. The critical stress intensity factor for the composite, K~c , is found to vary linearly with volume fraction of glass beads for the composite containing uncoated glass beads. A maximum KIC is observed at 20% volume fraction of beads for composites with coated beads. The elastomerit layer present in composites containing coated glass beads is found to improve fracture toughness, and effect of layer thickness is investigated. Toughening mechanisms are discussed in terms of crack pinning and plastic deformation. Creep behaviour of woven roving GRP beam in three point bending Shuang-Yin Zhang and Bing Zhao Composite Structures Vo113 No 3 (1989) pp 217-234 This paper describes the experimental and analytical study of the creep and relaxation behaviour of laminated glass fibre reinforced plastics in three point bending. While bending deflexion and creep strains were measured in the creep tests, the load and relaxation strain were recorded in the relaxation tests. Creep effects were seen in the tests carried out at 50°C for 60 min. An attempt was made to predict the creep deflexion and relaxation behaviour and the predicted results compared with the experimental ones. They were found to be in reasonable agreement, but the linearization assumption, upon which the relaxation behaviour is based, appears to lead to inaccuracies in the results.
The durability of controlled matrix shrinkage composites. Part 3. Measurement of damage during fatigue Lam, P.K.W. and Piggot, M.R. Journal of Materials Science Vol 25 No 2B (1990) pp 1197-1202 Testing of aligned carbon fibre/epoxy pultrusions is performed to clarify the causes of fatigue failure. Experiments are carried out on pultrusions made with differing amounts of expanding monomer or, instead, nonreactive plasticizer. Damage appears to develop continuously during testing. Holes grow in size in a direction at right angles to the applied stress, and Poisson's ratio and the energy absorbed during the fatigue cycle also increase continuously. The origin of damage is proposed to be imperfections in the composite, such as misaligned fibres which may generate off-axis stresses high enough to cause interracial failure and ultimately composite failure. The use of expanding, monomers is proposed to reduce microstresses present in the matrix, and thus reduce the rate of damage growth. The effect of aging conditions on the mechaniicai properties of wood fibre/polystyrene composites I. Chemithermomechanical pulp as reinforcing filler Maldas, D. and Kokta, B.V. Composites Science and Technology Vol 36 No 2 (1989) pp 167-182 Composites consisting of hardwood aspen pulp in polystyrene are subjected to ageing conditions such as boiling in water. The effects of various ageing conditions on mechanical properties and dimensional stability are evaluated. Composites prepared with chemical modification are also considered, such as the inclusion of 3% poly(methylene(polyphenyl isocyanate)) coupling agent, and coating and grafting onto the wood pulp surface. It is found that the chemically modified composites have superior mechanical properties and better mechanical stability compared with non-treated composites. Results suggest the existence of an efficient interfacial area between the fibre and the polymer matrix in a chemically modified composite. The influence of varying projectile mass on the impact response of CFRP Cantwell, W.J. and Morton, J. Composite Structures Vo113 No 2 (1989)pp 101-114 This paper reports on the results of high and low velocity impact tests on CFRP laminates as a function of projectile mass. The analyses the effect of projectile mass on the impact response and the subsequent load bearing capability of a composite structure. Results obtained from C-scans and optical micrographs indicated that, for a given impact energy, decreasing the impactor mass resulted in the greater levels of damage and consequently, poorer post impact properties. The authors explain their result by proposing that light, fast moving projectiles induce a very localized form of target response in which most of the incident energy of the projectile is dissipated immediately adjacent to the point of impact, essentially by shearing the fibres. Internal state variable approach for predicting stiffness reductions in fibrous laminated composites with matrix cracks Lee, J-W., Allen, D.H. and Harris, C.E.
COMPOSITES. JULY 1990
359