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The use of thin DCB specimens for measuring mode I interlaminar fracture toughness of composite materials
properties in resultant composite laminates was reported in this paper. Weft knitting was stated to be of particular interest to the manufacture of composites because of its potential for the net shape manufacture of preforms. The mechanical properties were discussed with respect to a simple elastic model.
Modelling fracture in resin matrix composites Herakovich, C.T. Polymer Composites Vol 11 N o 6 (1990) pp 322-327 This paper discusses the characteristics of the fracture of resin-matrix composites and the physical parameters necessary for accurate modelling of fracture. The author's normal stress theory was reviewed and was shown to correctly predict the initiation and direction of growth from an existing notch; however, critical stress predictions were less accurate. Optimisation of the bending stiffness and strength of composite sandwich panels Theulen, J.C.M. and Peijs, A.A.J.M. Composite Structures Vo117 No I (1991) pp 87-92 The minimum weight criterion of a sandwich panel with respect to a given bending stiffness and strength is verified. For this purpose a number of sandwich constructions consisting of a foamed PVC core and glass fibrereinforced epoxy faces are tested in fourpoint bending test. An optimum is found for both the bending stiffness and strength as design parameters. Random glass mat reinforced thermoplastic composites. Part 111: Characterization of the tensile modulus Stokes, V.K. Polymer Composites Vo111 No 6 (1990) pp 342-353 The author has previously shown the variability in modulus for random glass mat thermoplastic composites to vary by up to a factor of two over 12.7 mm in ASTM tests. The tensile modulus was characterized by using long, thin, 12.7 mm wide test specimens and averaging the left and right edge moduli. This was shown to be a reliable measure of tensile modulus and fibre density. Random glass mat reinforced thermoplastic composites. Part IV: Characterization of the tensile strength Stokes, V.K. Polymer Composites Vo111 No 6 (1990) pp 354-368 Using long, thin, dog-boned specimens, the left and right edge tensile moduli were obtained and then the specimen was strained to failure to obtain the tensile strength. Tensile strength was found to correlate well with the average tensile modulus (left edge and right edge) and failure occurred in low modulus (low fibre density) regions. Properties were shown to vary between the machine and cross-machine directions.
252
COMPOSITES. MAY 1991
Rate effects on aramid fibre/epoxy (KRP) tubes under hoop loop loading AI-Salehi, F.A.R., AI-Hassani, S.T.S., Bastaki, N.M. and Hinton, M.J. Journal o f Composite Materials Vol 24 No 9 (1990) pp 894-917 The effect of strain rate on the mechanical properties of Kevlar-reinforced plastic, angle-ply, filament wound tubes was investigated. Static and dynamic tests were performed on tubes of various winding angles which were burst under internal radial loading with minimum end constraints. The hoop burst strength was found to rise significantly with increasing strain rate. The effect on failure mechanism of rate and winding angle was also discussed. Some properties of nickel-coated carbon fibre-polypropylene composite at microwave frequencies Ahmad, M.S., Abelazeez, M.K., Zihlif, A., Martuscelli, E., Ragosta, G. and Scafora, E. Journal o f Materials Science Vol 25 No 7 (1990) pp 3083-3088 Composites have been fabricated using isostatic polypropylene and nickel-coated carbon fibres. Fibre concentrations of 0, 5, 10, 16 and 28 wt% were used. The insertion loss, return loss and equivalent input impedance were measured in the microwave frequency range 8 to 12 GHz. These properties were found to be fairly constant at low and high concentrations of fibres, but to go through significant changes at intermediate concentrations. The shielding effectiveness was also calculated and this indicates that the shielding effectiveness would be expected to reach 40 dB for a 5 mm thick specimen with >16 wt% of fibres added. Tensile and fracture properties of epoxy resin filled with fly ash particles Srivastava, V.K. and Shembekar Journal of Materials Science Vol 25 No 8 (1990) pp 3513-3516 Composite materials were formed from epoxy resin and various percentages of fly ash. The mechanical properties of these materials were tested by tensile and threepoint bend tests. Fracture surfaces were examined by SEM.The fracture toughness and the modulus of elasticity were both increased by the presence of the fly ash, the cracks being deflected by the fly ash particles. Thermal conductivity measurements of some glass fibre- and carbon fibre-reinforced plastics Mclvor, S.D., Darby, M.I., Wostenholm, G.H., Yates, B., Banfield, L., King, R. and Webb, A. Journal o f Materials Science Vo125 No 7 (1990) pp 3127-3132 Thermal conductivity specimens were fabri-
cated from glass fibre composites, R-glass and Fiberdux 914 resin and carbon fibre composites, GY-80 and Code 69 resin. Thermal conductivity measurements were then made over the temperature range -150 to 130°C, both parallel and perpendicular to the fibre directions. Standard theories were applied to the results which allowed the variations of the conductivity of the matrix and the resin to be deduced. Measurements were also made on samples of the carbon fibre composite with the fibre direction at 30°, 45° and 60° to the temperature gradient. An analysis of these results was endeavoured using a two-dimensional finite difference model. At higher angles the calculated values were too high by a factor of nearly two, this was improved when the aspect ratio was taken into account. Better agreement was achieved at lower angles.
Transverse tensile strength of glass/polyester unidirectionally aligned composites determined in diametrai compression Sigley, R.H., Wronski, A.S. and Parry, T.V. Composites Science and Technology Vol 37 N o 3 (1990) pp 233-243 The diametral compression of disc-shaped, 52% Ve, uniaxialty aligned glass fibre/ polyester pultrusions was used to measure their 'indirect' transverse tensile strength. This developed in the vicinity of the disc centre an axial compressive stress, -3o A, thus giving a biaxial test at atmospheric pressure. To identify the failure criteria triaxial testing was carried out by superimposing hydrostatic pressure, yielding the principal stresses. Using these situations hypotheses were formed which produced values for transverse tensile strengths and glass fibre/polyester interface strengths.
The use of thin DCB specimens for measuring mode I interlaminar fracture toughness of composite materials Caprino, G. Composites Science and Technology Vol39 No 2 (1990) pp 147-158 Mode I interlaminar fracture toughness, G~c, of composite laminates is measured using double cantilever beam specimens. The author shows that a formula, based on linear elasticity and commonly used for data reduction, may result in small errors in calculating G~c, even when marked non-linearities in the load/displacement curve are observed because of the use of thin samples. The implications of this result for the design of DCB specimens is discussed. Experimental results for graphite/epoxy composites are also presented which confirm the theoretical predictions.
Modelling fracture in resin matrix composites Herakovich, C.T. Polymer Composites Vol 11 N o 6 (1990) pp 322-327 This paper discusses the characteristics of the fracture of resin-matrix composites and the physical parameters necessary for accurate modelling of fracture. The author's normal stress theory was reviewed and was shown to correctly predict the initiation and direction of growth from an existing notch; however, critical stress predictions were less accurate. Optimisation of the bending stiffness and strength of composite sandwich panels Theulen, J.C.M. and Peijs, A.A.J.M. Composite Structures Vo117 No I (1991) pp 87-92 The minimum weight criterion of a sandwich panel with respect to a given bending stiffness and strength is verified. For this purpose a number of sandwich constructions consisting of a foamed PVC core and glass fibrereinforced epoxy faces are tested in fourpoint bending test. An optimum is found for both the bending stiffness and strength as design parameters. Random glass mat reinforced thermoplastic composites. Part 111: Characterization of the tensile modulus Stokes, V.K. Polymer Composites Vo111 No 6 (1990) pp 342-353 The author has previously shown the variability in modulus for random glass mat thermoplastic composites to vary by up to a factor of two over 12.7 mm in ASTM tests. The tensile modulus was characterized by using long, thin, 12.7 mm wide test specimens and averaging the left and right edge moduli. This was shown to be a reliable measure of tensile modulus and fibre density. Random glass mat reinforced thermoplastic composites. Part IV: Characterization of the tensile strength Stokes, V.K. Polymer Composites Vo111 No 6 (1990) pp 354-368 Using long, thin, dog-boned specimens, the left and right edge tensile moduli were obtained and then the specimen was strained to failure to obtain the tensile strength. Tensile strength was found to correlate well with the average tensile modulus (left edge and right edge) and failure occurred in low modulus (low fibre density) regions. Properties were shown to vary between the machine and cross-machine directions.
252
COMPOSITES. MAY 1991
Rate effects on aramid fibre/epoxy (KRP) tubes under hoop loop loading AI-Salehi, F.A.R., AI-Hassani, S.T.S., Bastaki, N.M. and Hinton, M.J. Journal o f Composite Materials Vol 24 No 9 (1990) pp 894-917 The effect of strain rate on the mechanical properties of Kevlar-reinforced plastic, angle-ply, filament wound tubes was investigated. Static and dynamic tests were performed on tubes of various winding angles which were burst under internal radial loading with minimum end constraints. The hoop burst strength was found to rise significantly with increasing strain rate. The effect on failure mechanism of rate and winding angle was also discussed. Some properties of nickel-coated carbon fibre-polypropylene composite at microwave frequencies Ahmad, M.S., Abelazeez, M.K., Zihlif, A., Martuscelli, E., Ragosta, G. and Scafora, E. Journal o f Materials Science Vol 25 No 7 (1990) pp 3083-3088 Composites have been fabricated using isostatic polypropylene and nickel-coated carbon fibres. Fibre concentrations of 0, 5, 10, 16 and 28 wt% were used. The insertion loss, return loss and equivalent input impedance were measured in the microwave frequency range 8 to 12 GHz. These properties were found to be fairly constant at low and high concentrations of fibres, but to go through significant changes at intermediate concentrations. The shielding effectiveness was also calculated and this indicates that the shielding effectiveness would be expected to reach 40 dB for a 5 mm thick specimen with >16 wt% of fibres added. Tensile and fracture properties of epoxy resin filled with fly ash particles Srivastava, V.K. and Shembekar Journal of Materials Science Vol 25 No 8 (1990) pp 3513-3516 Composite materials were formed from epoxy resin and various percentages of fly ash. The mechanical properties of these materials were tested by tensile and threepoint bend tests. Fracture surfaces were examined by SEM.The fracture toughness and the modulus of elasticity were both increased by the presence of the fly ash, the cracks being deflected by the fly ash particles. Thermal conductivity measurements of some glass fibre- and carbon fibre-reinforced plastics Mclvor, S.D., Darby, M.I., Wostenholm, G.H., Yates, B., Banfield, L., King, R. and Webb, A. Journal o f Materials Science Vo125 No 7 (1990) pp 3127-3132 Thermal conductivity specimens were fabri-
cated from glass fibre composites, R-glass and Fiberdux 914 resin and carbon fibre composites, GY-80 and Code 69 resin. Thermal conductivity measurements were then made over the temperature range -150 to 130°C, both parallel and perpendicular to the fibre directions. Standard theories were applied to the results which allowed the variations of the conductivity of the matrix and the resin to be deduced. Measurements were also made on samples of the carbon fibre composite with the fibre direction at 30°, 45° and 60° to the temperature gradient. An analysis of these results was endeavoured using a two-dimensional finite difference model. At higher angles the calculated values were too high by a factor of nearly two, this was improved when the aspect ratio was taken into account. Better agreement was achieved at lower angles.
Transverse tensile strength of glass/polyester unidirectionally aligned composites determined in diametrai compression Sigley, R.H., Wronski, A.S. and Parry, T.V. Composites Science and Technology Vol 37 N o 3 (1990) pp 233-243 The diametral compression of disc-shaped, 52% Ve, uniaxialty aligned glass fibre/ polyester pultrusions was used to measure their 'indirect' transverse tensile strength. This developed in the vicinity of the disc centre an axial compressive stress, -3o A, thus giving a biaxial test at atmospheric pressure. To identify the failure criteria triaxial testing was carried out by superimposing hydrostatic pressure, yielding the principal stresses. Using these situations hypotheses were formed which produced values for transverse tensile strengths and glass fibre/polyester interface strengths.
The use of thin DCB specimens for measuring mode I interlaminar fracture toughness of composite materials Caprino, G. Composites Science and Technology Vol39 No 2 (1990) pp 147-158 Mode I interlaminar fracture toughness, G~c, of composite laminates is measured using double cantilever beam specimens. The author shows that a formula, based on linear elasticity and commonly used for data reduction, may result in small errors in calculating G~c, even when marked non-linearities in the load/displacement curve are observed because of the use of thin samples. The implications of this result for the design of DCB specimens is discussed. Experimental results for graphite/epoxy composites are also presented which confirm the theoretical predictions.