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Electrical resistivity of an aluminium-graphite composite between 77 K and 300 K
location of the notch. Midway between the loading points produced crack growth in a direction normal to the applied stress. If located towards one of the loading points, then the initial direction was normal to the stress, but the crack would then turn to grow parallel to the stress. A theoretical treatment of this observation is given in terms of critical tensile force. It is also shown how conventional linear fracture mechanics can account for comparable behaviour in a brittle isotropic material.
Monte Carlo simulation of the strength of composite fibre bundles Manders, P.W., Bader, M.G. and Chou, T-W. Fibre Science and Technology Vol 17 No 3 (November 1982) pp 183-204 Monte Carlo simulations of the failure process in three dimensional fibre composite bundles are used to generate cumulative distribution functions for their strength for the cases of localized and equal sharing of load between unfailed fibres. The model quantifies the influence of the stress transfer properties of the matrix on the strength of the composite and predicts essentially elastic behaviour up to failure.
Moulding influence on the mechanical properties of sheet moulding compounds: Part 1. Elastic properties Berthelot, J.M. Fibre Science and Technology Vol 1 7No 4 (December 1982) pp 235244 The elastic properties of sheet moulding compounds were studied for the case of a simple moulding geometry in which deformation flaw taking place during the moulding process occurred in one direction only. Theoretical expressions for the engineering constants were derived and the results compared with the experimental results obtained for Young's moduli. For small deformation flaws, the model well fitted the experimental results. A new hybrid-stress element for multilayer
laminates Wang, T.K. and Yuan, Y. Journal of Reinforced Plastics and Composites Vol 1 (1982) p 124 The prediction of stress and displacement in multilayer composites becomes both expensive in terms of computer execution time, and storage when there are more than 5 layers. The authors have developed a theory based upon a hybrid stress element SZ-YS. They compare their predictions for 7 and 9 ~ayer composites with those obtained using either an exact elastic solution or classical laminate theory. They claim their equations offer substantial savings both in execution time and computer memory compared with other methods eg ELEMZ.
An optimal design of simple symmetric laminates under the fwst ply failure criterion Park, W.J. Journal o f Composite Materials
Vol 16 (July 1982) pp 341-355 An approach in the design of laminates is proposed which utilizes a first ply failure (FPF) criterion as the objective function in the design. Under the FPF criterion the ply orientation angle, O, is a very sensitive design variable and the optimal laminate designed has the most strength in the sense of first ply failure. Simple symmetric laminates of the composite material T300/5208 are then designed using FPF criteria. It is
COMPOSITES . JULY 1983
concluded that a [ - ¢ , 0, ¢] stacking sequence is best in FFP criteria under maximum longitudinal stress while a [ - 0 , - 4 5 , +45, 0] stacking sequence is best under maximum shear stress. A possible use of bounds on effective moduli of composite materials Phaw-Thien, N. and Milton, G.W. Journal of
Reinforced Plastics and Composites Vol ] (April 1982) p 107 The use of bounds on the effective moduli of two phase composites, to allow predictions of microstructural parameters from experimental measurements of the effective moduli is discussed. Expressions have been derived for the bounds on volume fraction. These are accurate to a second order, and if the ratio of the moduli is less than 10, are recommended for evaluating end products.
Wave propagation in linear viscoelastic composites modelled as interpenetrating solid continua McCarthy, M.F. International Journal of Engineering Sciences Vol 21 No I pp 65-76 The behaviour of shock waves in higher order discontinuities which propagate in a viscoelastic composite is modelled. A mixture of two interpenetrating solid continua is taken as the model. The propagation conditions for shock and higher order waves are derived and it is shown that, in general, six waves of any order may propagate in any direction. It is also shown that the amplitudes of all waves decay as they propagate. Detailed results are presented for isotropic composites.
METAL MA TRICES Pure plastic bending of sheet laminates under plane strain condition Majlessi, S.A. and Dadras, P. International Journal of Mechanical Sciences Vol 25 No 1 pp 1-14 Different deformation zones have been recognized in two- and three-ply laminates. The relevant equations for radial and tangential stress distributions in terms of material parameters have been determined. In each of these cases, a numerical expression for the location of the central axis has been obtained. The influence of laminate geometry has been investigated, as well as the effect of material properties in terms of the core/clad strength differential.
Scanning electron microscopy studies in abrasion of NR/BR blends under different test conditions Mathew, N.M. and De, S.K. Journal of Materials Science Vol 18 (1983) pp 515-524 A comparison of abraded rubber rankings is made using twice abrading machines (Akron, Du Pont, DIN). Carbon black filled vulcanizates were ranked in the same way by all the machines, but for unfilled grades the Akron machine ranked materials differently. It is proposed that in this machine, fatigue and tensile properties account for the loss in abrasion. The fine abrasion patterns for the carbon filled vulcanizates were noted to be different for each machine. The mode of abrasion is discussed and observed as being different for each of the machines. The Du Pont machine gave support for the low abrasion loss of the 50/50 blend from inspection of the abraded surface.
Computer estimation of the eutectic point for Ni 3Ta-Ni 3 AI Basu, R. Journal of Reinforced Plastics and Composites Vol I (1982) p 115 A computer simulation using the TERCP program, has been used to evaluate the composition of Ni~ Ta-Ni~ A1, at and around the Te temperature of 1633 K. From the results it appears that the composition of the NiAI undergoes substantial variation. This may produce misaligrtment of the phase boundaries at the matrix/precipitate interface. It is postulated that the addition of a quarternary element may prevent this as well as increasing the elevated temperature corrosion resistance. Electrical resistivity of an aluminiumgraphite composite between 77 K and 300K Jenkins, T.A. and Arajs, S. Fibre Science and Technology Vol 17 No 3 (November 1982) pp 205-209 The electrical resistivity of a composite comprising 28 volume % graphite (Thornel 50) fibres in 6061 aluminium alloy (with the fibres parallel to the direction of the electrical current) was studied as a function of thermal annealing. The results indicated that the fabrication process can cause the resistivity to be different from that calculated from theoretical estimates based on values of the components. High temperature creep behaviour of lead-
base particulate composites Kadam, P.B., Murty, G.S., Upadhyaya, G.S. and Vaidya, M.L. Journal of Materials
Science Vo118 (1983) pp 140-152 Tensile strength of unidirectionally reinforced composites I Batdorf, S.B. Journal of Reinforced Plastics and Composites Vol I (1983) p 153 In an investigation of the failure of a unidirectional composite, by means of a model based upon the formation and growth of multiple fibre fractures, weakest link theory is used to determine the number of isolated, double or multiple fibre fractures occuring as a function of stress. By plotting the logarithm of the number of isolated, double, triple etc fibre fractures against the logarithm of stress, a failure envelope can be obtained. Comparison of this model with those of Harlow and Phoenix shows that the simplifying assumptions made do not significantly affect the predictions.
A powder metallurgical technique was used to prepare three lead-base particle composites, followed by deformation processing. The systems were Pb-5% vol Zn; Pb-5% vol A12 O~ ; Pb-2.5% wt Pb0. Recrystallized testpieces were subjected to isothermal creep testing at 100, 150 and 180°C. In this temperature range, steady state creep is not observed in the Pb/Zn composite, but it is present in the other systems. Two distinct stress exponent regions with different associated activation energies are observed over a wide range of shear strain rates. The lower of these stress exponent regions appears to have grain boundary sliding as a rate controlling mechanism; the high stress exponent region has climb as the controlling mechanism.
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Monte Carlo simulation of the strength of composite fibre bundles Manders, P.W., Bader, M.G. and Chou, T-W. Fibre Science and Technology Vol 17 No 3 (November 1982) pp 183-204 Monte Carlo simulations of the failure process in three dimensional fibre composite bundles are used to generate cumulative distribution functions for their strength for the cases of localized and equal sharing of load between unfailed fibres. The model quantifies the influence of the stress transfer properties of the matrix on the strength of the composite and predicts essentially elastic behaviour up to failure.
Moulding influence on the mechanical properties of sheet moulding compounds: Part 1. Elastic properties Berthelot, J.M. Fibre Science and Technology Vol 1 7No 4 (December 1982) pp 235244 The elastic properties of sheet moulding compounds were studied for the case of a simple moulding geometry in which deformation flaw taking place during the moulding process occurred in one direction only. Theoretical expressions for the engineering constants were derived and the results compared with the experimental results obtained for Young's moduli. For small deformation flaws, the model well fitted the experimental results. A new hybrid-stress element for multilayer
laminates Wang, T.K. and Yuan, Y. Journal of Reinforced Plastics and Composites Vol 1 (1982) p 124 The prediction of stress and displacement in multilayer composites becomes both expensive in terms of computer execution time, and storage when there are more than 5 layers. The authors have developed a theory based upon a hybrid stress element SZ-YS. They compare their predictions for 7 and 9 ~ayer composites with those obtained using either an exact elastic solution or classical laminate theory. They claim their equations offer substantial savings both in execution time and computer memory compared with other methods eg ELEMZ.
An optimal design of simple symmetric laminates under the fwst ply failure criterion Park, W.J. Journal o f Composite Materials
Vol 16 (July 1982) pp 341-355 An approach in the design of laminates is proposed which utilizes a first ply failure (FPF) criterion as the objective function in the design. Under the FPF criterion the ply orientation angle, O, is a very sensitive design variable and the optimal laminate designed has the most strength in the sense of first ply failure. Simple symmetric laminates of the composite material T300/5208 are then designed using FPF criteria. It is
COMPOSITES . JULY 1983
concluded that a [ - ¢ , 0, ¢] stacking sequence is best in FFP criteria under maximum longitudinal stress while a [ - 0 , - 4 5 , +45, 0] stacking sequence is best under maximum shear stress. A possible use of bounds on effective moduli of composite materials Phaw-Thien, N. and Milton, G.W. Journal of
Reinforced Plastics and Composites Vol ] (April 1982) p 107 The use of bounds on the effective moduli of two phase composites, to allow predictions of microstructural parameters from experimental measurements of the effective moduli is discussed. Expressions have been derived for the bounds on volume fraction. These are accurate to a second order, and if the ratio of the moduli is less than 10, are recommended for evaluating end products.
Wave propagation in linear viscoelastic composites modelled as interpenetrating solid continua McCarthy, M.F. International Journal of Engineering Sciences Vol 21 No I pp 65-76 The behaviour of shock waves in higher order discontinuities which propagate in a viscoelastic composite is modelled. A mixture of two interpenetrating solid continua is taken as the model. The propagation conditions for shock and higher order waves are derived and it is shown that, in general, six waves of any order may propagate in any direction. It is also shown that the amplitudes of all waves decay as they propagate. Detailed results are presented for isotropic composites.
METAL MA TRICES Pure plastic bending of sheet laminates under plane strain condition Majlessi, S.A. and Dadras, P. International Journal of Mechanical Sciences Vol 25 No 1 pp 1-14 Different deformation zones have been recognized in two- and three-ply laminates. The relevant equations for radial and tangential stress distributions in terms of material parameters have been determined. In each of these cases, a numerical expression for the location of the central axis has been obtained. The influence of laminate geometry has been investigated, as well as the effect of material properties in terms of the core/clad strength differential.
Scanning electron microscopy studies in abrasion of NR/BR blends under different test conditions Mathew, N.M. and De, S.K. Journal of Materials Science Vol 18 (1983) pp 515-524 A comparison of abraded rubber rankings is made using twice abrading machines (Akron, Du Pont, DIN). Carbon black filled vulcanizates were ranked in the same way by all the machines, but for unfilled grades the Akron machine ranked materials differently. It is proposed that in this machine, fatigue and tensile properties account for the loss in abrasion. The fine abrasion patterns for the carbon filled vulcanizates were noted to be different for each machine. The mode of abrasion is discussed and observed as being different for each of the machines. The Du Pont machine gave support for the low abrasion loss of the 50/50 blend from inspection of the abraded surface.
Computer estimation of the eutectic point for Ni 3Ta-Ni 3 AI Basu, R. Journal of Reinforced Plastics and Composites Vol I (1982) p 115 A computer simulation using the TERCP program, has been used to evaluate the composition of Ni~ Ta-Ni~ A1, at and around the Te temperature of 1633 K. From the results it appears that the composition of the NiAI undergoes substantial variation. This may produce misaligrtment of the phase boundaries at the matrix/precipitate interface. It is postulated that the addition of a quarternary element may prevent this as well as increasing the elevated temperature corrosion resistance. Electrical resistivity of an aluminiumgraphite composite between 77 K and 300K Jenkins, T.A. and Arajs, S. Fibre Science and Technology Vol 17 No 3 (November 1982) pp 205-209 The electrical resistivity of a composite comprising 28 volume % graphite (Thornel 50) fibres in 6061 aluminium alloy (with the fibres parallel to the direction of the electrical current) was studied as a function of thermal annealing. The results indicated that the fabrication process can cause the resistivity to be different from that calculated from theoretical estimates based on values of the components. High temperature creep behaviour of lead-
base particulate composites Kadam, P.B., Murty, G.S., Upadhyaya, G.S. and Vaidya, M.L. Journal of Materials
Science Vo118 (1983) pp 140-152 Tensile strength of unidirectionally reinforced composites I Batdorf, S.B. Journal of Reinforced Plastics and Composites Vol I (1983) p 153 In an investigation of the failure of a unidirectional composite, by means of a model based upon the formation and growth of multiple fibre fractures, weakest link theory is used to determine the number of isolated, double or multiple fibre fractures occuring as a function of stress. By plotting the logarithm of the number of isolated, double, triple etc fibre fractures against the logarithm of stress, a failure envelope can be obtained. Comparison of this model with those of Harlow and Phoenix shows that the simplifying assumptions made do not significantly affect the predictions.
A powder metallurgical technique was used to prepare three lead-base particle composites, followed by deformation processing. The systems were Pb-5% vol Zn; Pb-5% vol A12 O~ ; Pb-2.5% wt Pb0. Recrystallized testpieces were subjected to isothermal creep testing at 100, 150 and 180°C. In this temperature range, steady state creep is not observed in the Pb/Zn composite, but it is present in the other systems. Two distinct stress exponent regions with different associated activation energies are observed over a wide range of shear strain rates. The lower of these stress exponent regions appears to have grain boundary sliding as a rate controlling mechanism; the high stress exponent region has climb as the controlling mechanism.
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