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Fracture studies of discontinuous fiber reinforced thermoplastic composites
Effect of filler size and matrix properties on fracture toughness of particulate composites Mall, S., Newaz, G.M. and Farhadinia, F.Journal of Reinforced Plastics and. Composites Vol 6 No 2 (April 1987)pp 138-152 The effects of particulate size and matrix ductility on the fracture toughness of sand/polyester composites are examined in this investigation. Two systems were studied: the first system consistedofth reedifferent typesofpolyesterwith different ductilities in conjunction with a constant sand particle size particle size (particle diameter was 300 p,m); in the second system, the polyester matrix remained the same and the sand particle size varied (particles diameters were 100 ~t m, 300 ~t m and 700 ~t m). The fracture toughness (/(if) was measured using single-edge notch beam specimens in three-point bending. The results from tests on the first system show that the fracture toughness of the composite increases with the strain to failure of the matrix up to a strain to failure of about 5.5%,afterwhich there was no significant increase inKic. It was foundthat fracture toughness in the second system was maximized in the composite containing 300 # m particles. Some reasons for this behaviour are suggested.
The effect of fibre orientation on the interfacial shear stress i n short fib re rei nforced polypropylene Mittal, R.K., Gupta, V.B. and Sharma, P.Journal of Materials Science Vo122(1987)pp 1949-1955 The Kevy-Tyson model of stress transfer from matrix to fibre h as been adapted using two methods for an inclined fibre system. The authors have found that for short fibre-reinforced polypropylene the interfacial shear stress varies linearly with the applied tensile stress on the specimens and is not constant for all the strains as assumed in the literature.
Effect of moisture on fatigue and residual strength losses for various composites Hofer, K.E., Skaper, G.N., Bennet, L.C. and Rao, N. Journal of Reinforced Plastics and Composites Vol 6 No 1 (January 1987) pp 53-65 The effects of moisture on the fatigue properties of a glass-fibre cloth/epoxy laminate were studied. The fatigue tests included the following: tension-tension, compression-compression, and a cantilever beam test to introduce interlaminar shear stresses and tensile and compressive bending stresses into the laminate. Results are given in the form of S/N curves and photomicrographs of the development of damage in the cantilever beam coupons. The effects of water on the fatigue properties of the laminates are then discussed.
The falling weight impact test appfied to some glass-fibre reinforced nylons. Part 2: Some results and interpretations Johnson, A.E.,Moore, D.R.,Prediger, R.S.,Reed, P.E. and Turner, S. Journal of Materials Science Vo122 (1987)pp 1724-1732 This paper is the second part of a study in which the results of conventional impact tests undertaken at several laboratories are compared. Flash photography was employed to interpret response curves accurately. Results on injection moulded specimens of five glass fibrereinforced compounds showed that at fibre weight fractions of 0.3 and 0.5, greater resistance to impact was achieved by increasing the mean fibre length. The effect of impact velocity in the 1.5 m s -I range was negligible.
COMPOSITES . NOVEMBER 1987
Fracture studies of discontinuous fiber reinforced thermoplastic composites Crosby, J.M. and Drye, T.R. Journal of Reinforced Plastics and Composites Vol 6 No 2 (April 1987) pp 162-177 Theeffectsofflbrelength,fibretype, flbrevolume and resin/fibre adhesion on the strength and toughness of discontinuous fibre-reinforced composites was investigated. The composite matrix was nylon 6,6 and the reinforcing agents were E- and S-glass, aramid and PAN carbon fibres. There is a discussion of the results and conclusion s are drawn. Hydrothermal ageing of jute-glass fibre-hybrid composites - an acousto-ultrasonic study Phani, K.K. and Bose, N.R. Journal of Materials Science Vo122 (1987)pp 1929-1933 The hydrothermal degradation of untreated and silane-treated jute-glass hybrid composites is studied in flexure and by measurement of the acousto-ultrasonic stress wave factor. It was found that the stress wave factor is a sensitive indicator of strength reduction. The addition of jute in the glass-reinforced plastic decelerated the degradation process. Silanc treatment brought about a marginal improvement in the strength of jute-glass hybrids. Interlaminar fracture morphology of carbon fibre/ PEEK composites Crick, R.A., Leach, D.C., Meakin, PJ. and Moore, D.R. Journal of Composite Materials Vol 22 (1987)pp 2094-2104 This paper presents a study of the interlaminar fracture process in carbon fibre/ polyetheretherketone (APC-2) composites by the use of qualitative and quantitative microscopy and measurements of fracture toughness. Failure processes during interlaminar fracture included fibre breakage, fibre peeling and polymer fracture. Two types of interlaminar fracture were observed: stable fracture (where microfracture was more extensive) and unstable fracture. The authors calculated that the contribution to toughness due to polymer fracture was 44% while the fibre fracture contribution amounted to 10%. The deformation zone was tound to extend to approximately 100 /,tm into the composite for stable fracture and 7 ~ m in unstable fracture.
A micromechanics analysis of the influence of the interface on the performance of polymer-matTix composites Adams, D.F. Journal of Reinforced Plastics and Composites Vol 6 No I (January 1987)pp 66-88 Using a specially developed two-dimensional finite-element micro-mechanics analysis program, in conjunction with experimental results, the author studies the influence of the interface on the performance of carbon fibre-reinforced unidirectional composite materials. Three different polymer matrix materials were used with carbon fibres which had four different sizings applied, ie, 12 material combinations. Samples were tested at room temperature in a dry condition and at elevated temperature in a wet condition. It was found that the sizing used had little effect on th e performance of the composite material, more important was the mode of loading and the type of matrix. The micro-mechanical analysis program was found to be reasonably accurate.
Optimization of composite matrices using acoustic emission analysis
Caldwell, D.L., Steele, D.L. and Guth, LT. Journal of Reinfomed Plasticsand Composites Vol6 No 2 (April 1987)pp 193-206 A series of mechanical tests (0 ° tensile, 0 ° flexural, 90 ° tensile and short beam shear) were used, in conjunction with acoustic emission analysis (AEA), to study the behaviour of a set of unidirectional glass-reinforced epoxy laminates fabricated from nine resin systems. It was proposed that three AE critical strain parameters could be identified, and that a low value of any of these parameters was indicative of a particular type of fabrication fault (ie, flawed laminate, poor bonding between laminae, and poor wetting).
Reduction of flexural properties in an SMC composite due to impact Gu, Z.L. and Sun, C.T. Journal of Reinforced Plastics and Composites Vol 6 No 1 (January 1987) pp 13-24 The change of thickness in SMC-R50composite panels is used to gauge the extent of damage, caused by impact. The relationships between thickness change and reduction in modulus and strength were determined experimentally, and were used in a finite-element program to predict the residual strength of SMC panels. It was found th at theoretically predicted strengths were conservative and quite close to those observed experimentally, whilst the predicted elastic properties showed considerable deviation from the observed results.
Rubber toughening of plastics. Part 2. Effects of rubber particle size and structure on yield behaviour of HIPS Bucknall, C.B., Davies, P. and Partridge, I.K. Journal of Materials Science Vo122(1987)pp 13411346 The effect of rubber particle size and its internal morphology on the Young's modulus, tensile and compressive yield strength and Charpy impact strength of a series of six non-standard HIPS materials has been examined..Two of the polymers were blended with polystyrene to produce materials with lower rubber particle volume contents. Microscopy showed that although all the polymers had the same content ofpolybutadiene, they varied in particle size and volume fraction ( 0 ) of composite rubber particles. It was found that both tensile modulus and yield stress depend on 0. At a given value of 0, smaller particle sizes (<1 /tm) gave lower values ofmoduli and yield stresses, while the tensile yield stress remained unaffected. Particles below 1 btm were also less effective in toughening the HIPS.
• Tensile behaviour of multilayer thermoplastic composites Sigmann, A. and Bcn-Tzur, M. Journal of Materials Science Vo122 (1987)pp 1405-1412 The tensile behaviour and synergistic deformation behaviour of three and five layer composite sheets moulded with alternating layers of brittle or semi-brittle and ductile thermoplastics have been investigated. The materials were PPO and polystyrene, and PVC and a blend of PVC and ethylene vinyl acetate/vinyl chloride copolymer. The more ductile material of the pairwas chosen as the outer layer. The laminates were moulded at high temperature (175 and 165°C) to obtain interlayer adhesion. The results demonstrated that provided good interlayer adhesion was achieved, the failure of the brittle component is postponed to an appreciable extent.
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The effect of fibre orientation on the interfacial shear stress i n short fib re rei nforced polypropylene Mittal, R.K., Gupta, V.B. and Sharma, P.Journal of Materials Science Vo122(1987)pp 1949-1955 The Kevy-Tyson model of stress transfer from matrix to fibre h as been adapted using two methods for an inclined fibre system. The authors have found that for short fibre-reinforced polypropylene the interfacial shear stress varies linearly with the applied tensile stress on the specimens and is not constant for all the strains as assumed in the literature.
Effect of moisture on fatigue and residual strength losses for various composites Hofer, K.E., Skaper, G.N., Bennet, L.C. and Rao, N. Journal of Reinforced Plastics and Composites Vol 6 No 1 (January 1987) pp 53-65 The effects of moisture on the fatigue properties of a glass-fibre cloth/epoxy laminate were studied. The fatigue tests included the following: tension-tension, compression-compression, and a cantilever beam test to introduce interlaminar shear stresses and tensile and compressive bending stresses into the laminate. Results are given in the form of S/N curves and photomicrographs of the development of damage in the cantilever beam coupons. The effects of water on the fatigue properties of the laminates are then discussed.
The falling weight impact test appfied to some glass-fibre reinforced nylons. Part 2: Some results and interpretations Johnson, A.E.,Moore, D.R.,Prediger, R.S.,Reed, P.E. and Turner, S. Journal of Materials Science Vo122 (1987)pp 1724-1732 This paper is the second part of a study in which the results of conventional impact tests undertaken at several laboratories are compared. Flash photography was employed to interpret response curves accurately. Results on injection moulded specimens of five glass fibrereinforced compounds showed that at fibre weight fractions of 0.3 and 0.5, greater resistance to impact was achieved by increasing the mean fibre length. The effect of impact velocity in the 1.5 m s -I range was negligible.
COMPOSITES . NOVEMBER 1987
Fracture studies of discontinuous fiber reinforced thermoplastic composites Crosby, J.M. and Drye, T.R. Journal of Reinforced Plastics and Composites Vol 6 No 2 (April 1987) pp 162-177 Theeffectsofflbrelength,fibretype, flbrevolume and resin/fibre adhesion on the strength and toughness of discontinuous fibre-reinforced composites was investigated. The composite matrix was nylon 6,6 and the reinforcing agents were E- and S-glass, aramid and PAN carbon fibres. There is a discussion of the results and conclusion s are drawn. Hydrothermal ageing of jute-glass fibre-hybrid composites - an acousto-ultrasonic study Phani, K.K. and Bose, N.R. Journal of Materials Science Vo122 (1987)pp 1929-1933 The hydrothermal degradation of untreated and silane-treated jute-glass hybrid composites is studied in flexure and by measurement of the acousto-ultrasonic stress wave factor. It was found that the stress wave factor is a sensitive indicator of strength reduction. The addition of jute in the glass-reinforced plastic decelerated the degradation process. Silanc treatment brought about a marginal improvement in the strength of jute-glass hybrids. Interlaminar fracture morphology of carbon fibre/ PEEK composites Crick, R.A., Leach, D.C., Meakin, PJ. and Moore, D.R. Journal of Composite Materials Vol 22 (1987)pp 2094-2104 This paper presents a study of the interlaminar fracture process in carbon fibre/ polyetheretherketone (APC-2) composites by the use of qualitative and quantitative microscopy and measurements of fracture toughness. Failure processes during interlaminar fracture included fibre breakage, fibre peeling and polymer fracture. Two types of interlaminar fracture were observed: stable fracture (where microfracture was more extensive) and unstable fracture. The authors calculated that the contribution to toughness due to polymer fracture was 44% while the fibre fracture contribution amounted to 10%. The deformation zone was tound to extend to approximately 100 /,tm into the composite for stable fracture and 7 ~ m in unstable fracture.
A micromechanics analysis of the influence of the interface on the performance of polymer-matTix composites Adams, D.F. Journal of Reinforced Plastics and Composites Vol 6 No I (January 1987)pp 66-88 Using a specially developed two-dimensional finite-element micro-mechanics analysis program, in conjunction with experimental results, the author studies the influence of the interface on the performance of carbon fibre-reinforced unidirectional composite materials. Three different polymer matrix materials were used with carbon fibres which had four different sizings applied, ie, 12 material combinations. Samples were tested at room temperature in a dry condition and at elevated temperature in a wet condition. It was found that the sizing used had little effect on th e performance of the composite material, more important was the mode of loading and the type of matrix. The micro-mechanical analysis program was found to be reasonably accurate.
Optimization of composite matrices using acoustic emission analysis
Caldwell, D.L., Steele, D.L. and Guth, LT. Journal of Reinfomed Plasticsand Composites Vol6 No 2 (April 1987)pp 193-206 A series of mechanical tests (0 ° tensile, 0 ° flexural, 90 ° tensile and short beam shear) were used, in conjunction with acoustic emission analysis (AEA), to study the behaviour of a set of unidirectional glass-reinforced epoxy laminates fabricated from nine resin systems. It was proposed that three AE critical strain parameters could be identified, and that a low value of any of these parameters was indicative of a particular type of fabrication fault (ie, flawed laminate, poor bonding between laminae, and poor wetting).
Reduction of flexural properties in an SMC composite due to impact Gu, Z.L. and Sun, C.T. Journal of Reinforced Plastics and Composites Vol 6 No 1 (January 1987) pp 13-24 The change of thickness in SMC-R50composite panels is used to gauge the extent of damage, caused by impact. The relationships between thickness change and reduction in modulus and strength were determined experimentally, and were used in a finite-element program to predict the residual strength of SMC panels. It was found th at theoretically predicted strengths were conservative and quite close to those observed experimentally, whilst the predicted elastic properties showed considerable deviation from the observed results.
Rubber toughening of plastics. Part 2. Effects of rubber particle size and structure on yield behaviour of HIPS Bucknall, C.B., Davies, P. and Partridge, I.K. Journal of Materials Science Vo122(1987)pp 13411346 The effect of rubber particle size and its internal morphology on the Young's modulus, tensile and compressive yield strength and Charpy impact strength of a series of six non-standard HIPS materials has been examined..Two of the polymers were blended with polystyrene to produce materials with lower rubber particle volume contents. Microscopy showed that although all the polymers had the same content ofpolybutadiene, they varied in particle size and volume fraction ( 0 ) of composite rubber particles. It was found that both tensile modulus and yield stress depend on 0. At a given value of 0, smaller particle sizes (<1 /tm) gave lower values ofmoduli and yield stresses, while the tensile yield stress remained unaffected. Particles below 1 btm were also less effective in toughening the HIPS.
• Tensile behaviour of multilayer thermoplastic composites Sigmann, A. and Bcn-Tzur, M. Journal of Materials Science Vo122 (1987)pp 1405-1412 The tensile behaviour and synergistic deformation behaviour of three and five layer composite sheets moulded with alternating layers of brittle or semi-brittle and ductile thermoplastics have been investigated. The materials were PPO and polystyrene, and PVC and a blend of PVC and ethylene vinyl acetate/vinyl chloride copolymer. The more ductile material of the pairwas chosen as the outer layer. The laminates were moulded at high temperature (175 and 165°C) to obtain interlayer adhesion. The results demonstrated that provided good interlayer adhesion was achieved, the failure of the brittle component is postponed to an appreciable extent.
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