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Autoclave curing—comparisons of model and test results
stress concentration near the fibre ends, as well as the effects of adhesion and fibre characteristics. Comparison is made with experimental data.
Thermomechanical stress fields in high temperature fibrous composites I: unidirectional laminates Dvorak, G.J., Chert, T. and Teply, J. Composites Science and Technology Vo143 No 4 (1992) pp 34~358 A closed-form method for evaluating local thermomechanica! stress fields in two-phase fibrous composites and laminates is presented. It is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Exact solutions cannot be obtained for a real system, instead estimates are made from a modified Mori Tanaka approximation. SiC/ Ti AI Nb composites are presented as examples, and local stresses of interest are found on cooling from fabrication to room temperature. An examination is made of the influence of coupling terms on local stress magnitude and on the presence of local yielding. Thermomechanical stress fields in high temperature fibrous composites II: laminated plates Dvorak, G.J., Chen, T. and Teply, J. Composites Science and Technology Vo143 No 4 (1992) pp 35~368 The work presented in a previous paper on this subject is extended to laminated plates. It is assumed that the plates are subjected to uniform temperature changes, in-plane mechanical loads and that they are macroscopically orthotropic. Average and microstress fields are calculated for each layer of the plate, and failure envelopes are constructed for the SiC/Ti A1 Nb system described in Part I. Transient waves in six-ply and eight-ply fibre composite plates Green, W.A., Rogerson, G.A. and Milosavljevic, D.I. Composites Science and Technology Vol44 No 2 (1992) pp 151 158 Integral transform techniques and the propagator matrix method are combined to investigate the transient response of fibre composite laminates to a line-load impact acting on the upper surface. The composite is modelled in layers as a transversely isotropic elastic continuum which is inextensible in the fibre direction. The results show the variation with distance from the impact line of the normal displacement at the top and bottom surfaces of each laminate at a fixed point in time. A comparison is made with earlier work on four-ply laminates and reveals the existence of an anomalous surface wave in the six-ply and eight-ply plates which is not observed in the four-ply results. Vibration and low frequency acoustic analysis of piecewise-activated adaptive composite panels Anders, W.S., Rogers, C.A. and Fuller, C.R. Journal o[ Composite Materials Vol 26 No 1 (1992) pp 103 120 The Ritz method, classical laminated plate theory and finite panel acoustic radiation theory are employed to predict the modal and structural acoustic behaviour of locally activated, shape memory alloy, hybrid composite panels. The study concentrates on the application of this technique to the
structural analysis of laminated plates. The information gained from this technique is used to determine the structural acoustic response as a function of frequency for a laminated plate with material non-iinearities. Results are given for balanced symmetric adaptive panels to show how various localized activation scenarios affect modal and structural acoustic behaviour.
THERMOSETTING MA TRICES Autoclave curing---comparisons of model and test results Ciriscioli, P.R., Wang, Q. and Springer, G.S. Journal ~[" Composite Materials Vol 26 No I (1992) pp 90 102 The temperature, ionic conductivity and compaction in 16 to 200 ply thick graphite/ epoxy laminates made of T300/976 (tape or fabric) or Hercules AS/3501-6 (tape) were measured. A comparison of results was made with calculations from the Loos Springer cure model. Good agreement was found, suggesting that the technique can be used to select the cure cycle. It is shown that manufacturers' recommended cure cycles may lead to excessive temperatures and incomplete compaction and cannot be used to make thick or even moderately thick composites. The effect of damage on the durability of a sand-filled GRP sewer lining under acidic stress corrosion conditions Tsui, S.W. and Jones, F.R. Composites Science and Technology Vo144 No 2 (1992) pp 137 143 An investigation of the effect of damage on the durability of a commercial sand-filled glass fibre sewer lining in 0.5 M H~SO4 under load has been made. The damage was sinmlated by inducing pre-cracks into the resin-rich barrier layer. Pre-stressing to a 1% strain at the surface of the barrier layer was used to simulate internal damage such as microcracking of the glass fibre/sand particle laminae. A comparison is made between the short- and long-term acidic stress corrosion results and their undamaged counterparts. Estimation of thermal properties in carbon/ epoxy composite materials during curing Scott, E.P. and Beck, J.V. Journal q[ Composite Materials Vol 26 No 1 (1,)92) pp 20 36 A technique for estimating the thermal response properties of thermoset composites during curing is given. The technique involves the minimization of a least-squares function made up of measured and calculated transient temperatures. An experimental model is presented to determine the relationships between the thermal properties, temperature and degree of cure. Hypothetical data obtained from the experimental design are used to demonstrate the estimation procedure. Excellent agreement was found between the thermal properties estimated using simulated data and those used to generate this data. Estimation of thermal properties in epoxy matrix/carbon fibre composite materials Scott, E. P. and Beck, J.V. Journal of Composite Materials Vol 26 No 1 (1992) pp 132 149 In any non-isothermal environment accurate knowledge of the thermal characteristics of composites is of prime importance as these characteristics are related to the thermal
properties of the material. This investigation concentrates on the estimation of the thermal conductivity and volumetric heat capacity of AS4 surface-treated carbon fibre/DGEBAmPDA composites. A Gauss minimization technique was used at different temperatures and stacking orientations to estimate the properties perpendicular to the fibre axis. Over the temperature range studied the magnitudes of the thermal properties were found to increase with temperature, and a significant difference was seen between the estimated thermal conductivities of samples with different stacking orientations.
THERMOPLASTIC MA TRICES Tensile, fiexnral and impact properties of a thermoplastic matrix reinforced by glass fibre and glass bead hybrids Yilmazer, U. Composites Science and Technology Vo144 No 2 (1992) pp 119-125 A study has been made of the tensile and flexural properties and unnotched and notched impact strengths of acrylonitril~ butadiene-styrene (ABS), glass fibre (GF) and glass bead (GB) ternary composites. Using a model developed in this study, the strength of hybrid composites was predicted using the strengths of ABS/GB and ABS/GF composites alone. It is shown that the addition of any amount of glass fibre to ABS or an ABS/GB composite changes to the mode of deformation from vacuole growth and crazing to brittle failure. It is concluded that the elongation at break, the area under the stress/strain curve and the impact energy decrease sharply with the introduction of glass fibre to ABS or ABS/GB composites.
INORGANIC MA TRICES Fabrication of SiC whisker reinforced AI203 composites Yang, M. and Stevens, R. Journal qfMaterials Science Vo125 No 11 (1990) pp 4658--4666 The conditions required for the wet mixing of SiC whiskers and alumina are described such that the slip can be cast to a high green density. Subsequent sintering was found to be difficult due to the formation of whisker networks and differential sintering stresses. Densification could be achieved by hot pressing and the effects of pressure, temperature and whisker content on the densification rate were studied. Fibre reinforced glasses: influence of thermal expansion of the glass matrix on strength and fracture toughness of the composites H~geler, H. and Briickner Journal o[" Materials Science Vol 25 No 11 (1990) pp 4836~4846 A number of glasses with different thermal expansion coefficients have been reinforced with Nicalon SiC fibres and the bend strength of the resulting composites measured. A correlation was found between the strength and bendover stress and the difference in thermal expansion coefficients of the fibre and the matrix. It was found possible to tailor the properties of the composite by varying the thermal expansion of the glass.
COMPOSITES
. SEPTEMBER 1992
377
Thermomechanical stress fields in high temperature fibrous composites I: unidirectional laminates Dvorak, G.J., Chert, T. and Teply, J. Composites Science and Technology Vo143 No 4 (1992) pp 34~358 A closed-form method for evaluating local thermomechanica! stress fields in two-phase fibrous composites and laminates is presented. It is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Exact solutions cannot be obtained for a real system, instead estimates are made from a modified Mori Tanaka approximation. SiC/ Ti AI Nb composites are presented as examples, and local stresses of interest are found on cooling from fabrication to room temperature. An examination is made of the influence of coupling terms on local stress magnitude and on the presence of local yielding. Thermomechanical stress fields in high temperature fibrous composites II: laminated plates Dvorak, G.J., Chen, T. and Teply, J. Composites Science and Technology Vo143 No 4 (1992) pp 35~368 The work presented in a previous paper on this subject is extended to laminated plates. It is assumed that the plates are subjected to uniform temperature changes, in-plane mechanical loads and that they are macroscopically orthotropic. Average and microstress fields are calculated for each layer of the plate, and failure envelopes are constructed for the SiC/Ti A1 Nb system described in Part I. Transient waves in six-ply and eight-ply fibre composite plates Green, W.A., Rogerson, G.A. and Milosavljevic, D.I. Composites Science and Technology Vol44 No 2 (1992) pp 151 158 Integral transform techniques and the propagator matrix method are combined to investigate the transient response of fibre composite laminates to a line-load impact acting on the upper surface. The composite is modelled in layers as a transversely isotropic elastic continuum which is inextensible in the fibre direction. The results show the variation with distance from the impact line of the normal displacement at the top and bottom surfaces of each laminate at a fixed point in time. A comparison is made with earlier work on four-ply laminates and reveals the existence of an anomalous surface wave in the six-ply and eight-ply plates which is not observed in the four-ply results. Vibration and low frequency acoustic analysis of piecewise-activated adaptive composite panels Anders, W.S., Rogers, C.A. and Fuller, C.R. Journal o[ Composite Materials Vol 26 No 1 (1992) pp 103 120 The Ritz method, classical laminated plate theory and finite panel acoustic radiation theory are employed to predict the modal and structural acoustic behaviour of locally activated, shape memory alloy, hybrid composite panels. The study concentrates on the application of this technique to the
structural analysis of laminated plates. The information gained from this technique is used to determine the structural acoustic response as a function of frequency for a laminated plate with material non-iinearities. Results are given for balanced symmetric adaptive panels to show how various localized activation scenarios affect modal and structural acoustic behaviour.
THERMOSETTING MA TRICES Autoclave curing---comparisons of model and test results Ciriscioli, P.R., Wang, Q. and Springer, G.S. Journal ~[" Composite Materials Vol 26 No I (1992) pp 90 102 The temperature, ionic conductivity and compaction in 16 to 200 ply thick graphite/ epoxy laminates made of T300/976 (tape or fabric) or Hercules AS/3501-6 (tape) were measured. A comparison of results was made with calculations from the Loos Springer cure model. Good agreement was found, suggesting that the technique can be used to select the cure cycle. It is shown that manufacturers' recommended cure cycles may lead to excessive temperatures and incomplete compaction and cannot be used to make thick or even moderately thick composites. The effect of damage on the durability of a sand-filled GRP sewer lining under acidic stress corrosion conditions Tsui, S.W. and Jones, F.R. Composites Science and Technology Vo144 No 2 (1992) pp 137 143 An investigation of the effect of damage on the durability of a commercial sand-filled glass fibre sewer lining in 0.5 M H~SO4 under load has been made. The damage was sinmlated by inducing pre-cracks into the resin-rich barrier layer. Pre-stressing to a 1% strain at the surface of the barrier layer was used to simulate internal damage such as microcracking of the glass fibre/sand particle laminae. A comparison is made between the short- and long-term acidic stress corrosion results and their undamaged counterparts. Estimation of thermal properties in carbon/ epoxy composite materials during curing Scott, E.P. and Beck, J.V. Journal q[ Composite Materials Vol 26 No 1 (1,)92) pp 20 36 A technique for estimating the thermal response properties of thermoset composites during curing is given. The technique involves the minimization of a least-squares function made up of measured and calculated transient temperatures. An experimental model is presented to determine the relationships between the thermal properties, temperature and degree of cure. Hypothetical data obtained from the experimental design are used to demonstrate the estimation procedure. Excellent agreement was found between the thermal properties estimated using simulated data and those used to generate this data. Estimation of thermal properties in epoxy matrix/carbon fibre composite materials Scott, E. P. and Beck, J.V. Journal of Composite Materials Vol 26 No 1 (1992) pp 132 149 In any non-isothermal environment accurate knowledge of the thermal characteristics of composites is of prime importance as these characteristics are related to the thermal
properties of the material. This investigation concentrates on the estimation of the thermal conductivity and volumetric heat capacity of AS4 surface-treated carbon fibre/DGEBAmPDA composites. A Gauss minimization technique was used at different temperatures and stacking orientations to estimate the properties perpendicular to the fibre axis. Over the temperature range studied the magnitudes of the thermal properties were found to increase with temperature, and a significant difference was seen between the estimated thermal conductivities of samples with different stacking orientations.
THERMOPLASTIC MA TRICES Tensile, fiexnral and impact properties of a thermoplastic matrix reinforced by glass fibre and glass bead hybrids Yilmazer, U. Composites Science and Technology Vo144 No 2 (1992) pp 119-125 A study has been made of the tensile and flexural properties and unnotched and notched impact strengths of acrylonitril~ butadiene-styrene (ABS), glass fibre (GF) and glass bead (GB) ternary composites. Using a model developed in this study, the strength of hybrid composites was predicted using the strengths of ABS/GB and ABS/GF composites alone. It is shown that the addition of any amount of glass fibre to ABS or an ABS/GB composite changes to the mode of deformation from vacuole growth and crazing to brittle failure. It is concluded that the elongation at break, the area under the stress/strain curve and the impact energy decrease sharply with the introduction of glass fibre to ABS or ABS/GB composites.
INORGANIC MA TRICES Fabrication of SiC whisker reinforced AI203 composites Yang, M. and Stevens, R. Journal qfMaterials Science Vo125 No 11 (1990) pp 4658--4666 The conditions required for the wet mixing of SiC whiskers and alumina are described such that the slip can be cast to a high green density. Subsequent sintering was found to be difficult due to the formation of whisker networks and differential sintering stresses. Densification could be achieved by hot pressing and the effects of pressure, temperature and whisker content on the densification rate were studied. Fibre reinforced glasses: influence of thermal expansion of the glass matrix on strength and fracture toughness of the composites H~geler, H. and Briickner Journal o[" Materials Science Vol 25 No 11 (1990) pp 4836~4846 A number of glasses with different thermal expansion coefficients have been reinforced with Nicalon SiC fibres and the bend strength of the resulting composites measured. A correlation was found between the strength and bendover stress and the difference in thermal expansion coefficients of the fibre and the matrix. It was found possible to tailor the properties of the composite by varying the thermal expansion of the glass.
COMPOSITES
. SEPTEMBER 1992
377