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The toughness of fibre composites with inhomogeneous fibre packing
e p o x y resin r e i n f o r c e d with unidirectionally oriented short fibres is investigated by static and dynamic three-point bending tests, Elastic and ductile fibres were used in volume fraction of 0.05 to 0.3. Composite failure mechanisms and models for predicting composite ultimate flexural strength are reviewed. (Authors' abstract) Stress diffusion in a pull out model Sarma, A.V.S.R:J., Murthy, P.N. and Kushwaha, P.S. Fibre Science and Technology, Vol 12 No 2 (March 1979) pp 129-138 Interfacial shear stress plays an important role in the diffusion of load between the fibre and matrix in a fibre-reinforced plastic. In this paper a pull out model for a single fibre embedded in a resin matrix is analysed in an exact manner satisfying all the boundary conditions. The analysis is elastic. Distributions of interfacial shear, interfacial bonding stress and longitudinal deformation are obtained. The response to a constant pull out load kept for a long time is also analysed using a three element visco-elastic model for the resin. It is shown that any load can be a pull out load if sufficient time is allowed. (Authors'abstract) St r ess
measur ements
in
graphite/epoxy comp~osites by X-ray diffraction from Idlers Predecki, P. and Barrett, C.S. Journal o f Composite Materials, Vol 13 (January 1979) p 61 Internal strains in graphite/epoxy composites can be measured from the shift in the X-ray diffraction peaks from filler particles embedded in the composite. Good stress sens i t i v i e s , f r o m 2--4 x ' 1 0 - 4 degrees/MPa were obtained with Ag, Nb and Cd0 particles, which were used to measure residual, and applied stresses and strains. Theory of fabrication-induced anis-
tropy pf chopped-fibre/resin panels Eisenberg, M.A. Fibre Science and Technology, Vol 12 No 2 (March 1979) pp 83-85
246
A theory is developed for predicting the elasticpropertiesofanisotropic, composite sheet-materials reinforced by chopped fibres which, although randomly oriented initially, are preferentially oriented by compression moulding of the sheet material. The theory is a generalisation of previously developed theories for transversely isotropic sheet-materials with randomly oriented fibres. The analysis shows that the magnitude and direction of preferential stiffeningdependonthe geometry of the charge and mould, and that the anistropy can be controlled by adjusting the charge shape. Predictions of the theory agree, to within experimental accuracy, with the results of tests on glass f i b r e / p o l y e s t e r resin p a n e l s . (Author's abstract)
The thermal conductivity of carbon
fibre-reinforced composites Pillivig, M.W., Yates, B., Black, M.A. and Tattersall, P. Journal of Materials Science, Vol 14 (1979)pp 1326o1338 Measurements of the thermal conductivity between 80 and 270K of a series of unidirectional and bidirectional specimens of epoxy resin DX210/BF3400 reinforced with high modulus and high strength carbon fibres are reported for in-plane and out-of-plane directions. The main features of the results conform with expectations based upon known structural properties of the fibres and predictions based upon current theoretical models. The thermal expansion of carbon fibre-reinforcedplasties. Part5. The influence of matrix curing eharac-
teristics Yates, B., McCalla, B.A., Phillips, L.N., Kingston-Lee, D.M. and Rogers, K.F. Journal o f Materials Science, Vol 14 (1979) pp 12071217 The volume changes which occur during the cure of resins employed as matrices for cfrp have been moni-
t o r e d . A d e s c r i p t i o n of the apparatus is given and detailed results throughout the curing cycles of four resins are reported. In the three cases in which measurements were possible over the entire curing cycle, it was found that the major shrinkage occurs during the early stages of solidification, which suggests that transverse craking in multi-layer cross-ply laminates during cool-down after moulding is caused by thermal expansion and contraction effects rather than by resin shrinkage occurring during the final stages of cure. The thermal expansion of chrysotile
asbestos and its composites Harwood, C.,Yates, B.andBadami, D.V. Journal o f Materials Science, Vol 14 (1979) pp 1126-1140 The principal linear thermal expansion coefficients of chrysotile asbestos were measured over the temperature range 80-270K. Implications of the results on: (i) the influence of thermal strain upon the specific heat capacity, and (ii) the temperature variation of the reduced volume dependence of the lattice vibrational frequencies have been assessed. Specimens prepared from composite bars consisting of phenol formaldehyde resin reinforced with chrysotile fibre in random and preferential orientations were tested and their thermal expansion coefficients measured in the above temperature range. The toughness of fibre composites with inhomogeneous fibre packing Cooper, R.E. Journal o f Materials Science, Vol 14 (1979) p 1256 The author examines the results published by Harris and Ankara on the work of fracture of bunched fibres in cfrp, and concludes that their data supports, rather than contradicts the existing suggestions that fibre bunching can increase the fracture toughness of brittle fibre/brittle matrix composites as well as of brittie fibre/ductile matrix composites.
C O M P O S I T E S . O C T O B E R 1979
measur ements
in
graphite/epoxy comp~osites by X-ray diffraction from Idlers Predecki, P. and Barrett, C.S. Journal o f Composite Materials, Vol 13 (January 1979) p 61 Internal strains in graphite/epoxy composites can be measured from the shift in the X-ray diffraction peaks from filler particles embedded in the composite. Good stress sens i t i v i e s , f r o m 2--4 x ' 1 0 - 4 degrees/MPa were obtained with Ag, Nb and Cd0 particles, which were used to measure residual, and applied stresses and strains. Theory of fabrication-induced anis-
tropy pf chopped-fibre/resin panels Eisenberg, M.A. Fibre Science and Technology, Vol 12 No 2 (March 1979) pp 83-85
246
A theory is developed for predicting the elasticpropertiesofanisotropic, composite sheet-materials reinforced by chopped fibres which, although randomly oriented initially, are preferentially oriented by compression moulding of the sheet material. The theory is a generalisation of previously developed theories for transversely isotropic sheet-materials with randomly oriented fibres. The analysis shows that the magnitude and direction of preferential stiffeningdependonthe geometry of the charge and mould, and that the anistropy can be controlled by adjusting the charge shape. Predictions of the theory agree, to within experimental accuracy, with the results of tests on glass f i b r e / p o l y e s t e r resin p a n e l s . (Author's abstract)
The thermal conductivity of carbon
fibre-reinforced composites Pillivig, M.W., Yates, B., Black, M.A. and Tattersall, P. Journal of Materials Science, Vol 14 (1979)pp 1326o1338 Measurements of the thermal conductivity between 80 and 270K of a series of unidirectional and bidirectional specimens of epoxy resin DX210/BF3400 reinforced with high modulus and high strength carbon fibres are reported for in-plane and out-of-plane directions. The main features of the results conform with expectations based upon known structural properties of the fibres and predictions based upon current theoretical models. The thermal expansion of carbon fibre-reinforcedplasties. Part5. The influence of matrix curing eharac-
teristics Yates, B., McCalla, B.A., Phillips, L.N., Kingston-Lee, D.M. and Rogers, K.F. Journal o f Materials Science, Vol 14 (1979) pp 12071217 The volume changes which occur during the cure of resins employed as matrices for cfrp have been moni-
t o r e d . A d e s c r i p t i o n of the apparatus is given and detailed results throughout the curing cycles of four resins are reported. In the three cases in which measurements were possible over the entire curing cycle, it was found that the major shrinkage occurs during the early stages of solidification, which suggests that transverse craking in multi-layer cross-ply laminates during cool-down after moulding is caused by thermal expansion and contraction effects rather than by resin shrinkage occurring during the final stages of cure. The thermal expansion of chrysotile
asbestos and its composites Harwood, C.,Yates, B.andBadami, D.V. Journal o f Materials Science, Vol 14 (1979) pp 1126-1140 The principal linear thermal expansion coefficients of chrysotile asbestos were measured over the temperature range 80-270K. Implications of the results on: (i) the influence of thermal strain upon the specific heat capacity, and (ii) the temperature variation of the reduced volume dependence of the lattice vibrational frequencies have been assessed. Specimens prepared from composite bars consisting of phenol formaldehyde resin reinforced with chrysotile fibre in random and preferential orientations were tested and their thermal expansion coefficients measured in the above temperature range. The toughness of fibre composites with inhomogeneous fibre packing Cooper, R.E. Journal o f Materials Science, Vol 14 (1979) p 1256 The author examines the results published by Harris and Ankara on the work of fracture of bunched fibres in cfrp, and concludes that their data supports, rather than contradicts the existing suggestions that fibre bunching can increase the fracture toughness of brittle fibre/brittle matrix composites as well as of brittie fibre/ductile matrix composites.
C O M P O S I T E S . O C T O B E R 1979