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Impact induced fracture in a laminated composite
Effect of compounding on the properties of short fibre reinforced injection moldable thermoplastic composites Bigg, D.M. Polymer Composites Vol 6 No 1 (January 1985) pp 20-28 The effect of compounding upon various thermoplastic matrices containing glass, aluminium or carbon fibres was investigated. Considerable breakage of both glass and carbon fibres was found to occur. More damage was done by a counter-rotating twin screw extruder than with a single screw extruder and, in all cases, the injection moulding machine inflicted more damage to the fibres than the extrusion compounders. The fibre aspect ratio was also investigated. Effect of glass-resin interface on the electric breakdown of PET-glass composite Lhymn, C. Journal of Materials Science Letters Vol 4 (June 1985) pp 665-668 The glass/matrix interlace, and particularly its orientation with respect to an applied electric fiekk is critical to the breakdown characteristics of a composite. In this study, specimens were prepared by injection moulding, with good or poorly bonded glass, and tested in two configurations (H and V). If the glass was oriented parallel to the applied electric field, the breakdown characteristics of good and poorly bonded composites were similar. The critical factor was the amount of microbonding along the fibre/matrix interface. The effect of stress concentration on the reliability of composite materials Wetherhold. RC. Journal of Composite Materials Vol 19 No 1 (January 1985) pp 19-28 A macroscopic interactive fracture criterion is used to predict the reliability of brittle composite structures in a state of multiaxial stress. The equations for reliability based on a maximum distortional energy analysis are evaluated using a Monte Carlo method for offaxis and centre-hole off-axis specimens in glass/epoxy and graphite/epoxy of short and long configurations. The general trends of smaller volume giving better reliability and end-induced stresses reducing reliability are modified by the strength and stiffness characteristics of the material For the centrehole specimens, low variability material has a high repeatability of fracture limitation site, and high strength variability materials are less sensitive to stress concentrations. Effects of space environmental conditions on graphite epoxy composites Seehra, S., Benton, D., Rosen. J. and Gounder, R SAMPEJournal Vo121 No2 (March/April1985) pp 18-23 Samples of a quasi-isotropic laminate, constructed from six plies of graphite/epoxy unidirectional tape, were tested in simulated space environment conditions. Samples coated with vapour-deposited aluminium, some of which received coatings of SiO2 or special paints, were also tested and their thermophysical thermo-opticak RF and mechanical properties assessed. Little change in the mechanical properties of the laminate was observed. The material exhibited some property changes which, though not sufficient to degrade the performance of reflectors fabricated from the material, required further examination. Electrical lifetime of a PPS/glass composite Lhymn` C. and Sch ultz, J. M. Journal of Materials Science Letters Vol 4 (June 1985) pp 662-664
COMPOSITES. OCTOBER 1985
The electrical breakdown characteristics of a glass-filled polyphenylene sulphide (PPS) composite have been studied. Three specimen geometries were tested. The results obtained were similar to those for a glass/PET composite, where preferential breakdown channels occur at the fibre/matrix interface. Electrical resistivity behaviour of solution-east metal-filled composites Singh, R R and Roberts, ILR Polymer Composites Vol 6 No 1 (January 1985) pp 58-62 Solvent-cast. metal-filled composites of polymethylmethacrylate and aluminium or copper were found to exhibit electrical resistance behaviour. A precipitous change in volume resistivity which was thermally dependent was found at filler concentrations of 17 to 19.5%. Materials with compositions at this conductive/non-conductive threshold showed semi-conductor behaviour and were found to exhibit memory switching, Environmental and time dependence of fracture toughness and crack growth in glass-reinforced polyester resins Roberts, RC. Journal of Materials Science Vo120 (April 1985) p 1341 The validity of fracture toughness testing of glass fibre-reinforced polyester has been examined for single edge-notched specimens using slow strain-rate tests. The fracture toughness is greatly reduced by the presence of the chemical environment as a result of acidinduced environmental stress cracking. Environmental effects are also found to determine crack growth rates and could be useful in ranking materials. Environmental lifetime of fibrous polymer composites Lhymn, C., Davis, P.K., Tempelmeyer, K.E. and Schultz, J.M. Journal of Materials Science Letters Vol 4 (May 1985) pp 575-579 A study of the stress corrosion failure of short fibre-reinforced (glass and carbon) composites was carried out. Matrix materials were rubber toughened polyethylene terephthalate and unmodified polyphenylene sulphide. Test environments were 10% sodium hydroxide. water and aqueous mineral acids; notched coupon specimens were used. It was found that the alkali predominantly attacked the matrix. especially the rubber/matrix interface, whereas the acid attacked the glass fibre, Equations that qualitatively explain the lifetime behaviour based on Markov statics are also presented,
The fracture behaviour of an epoxy resin reinforced with a balanced weave glass cloth was investigated. It was found that fracture proceeded by tensile failure of the fibres rather than by shear failure of the matrix or interface. It was also found that fracture mechanics concepts can be applied to these composites when the initial crack is longer than the critical value. Fracture in epoxy resin matrices Robertson, RE., Mindroiu, V.E. and Cheung. M.-F. Composites Science and Technology Vol 22 No 3 (1985) pp 197-207 The fracture surface of a trifunctional aromatic epoxy resin, containing a tertiary amine and cured with an anhydride, was examined in detail. A model is proposed to describe the fracture-energy enhancing steps and welts which are seen to arise from the underlying basic longitudinal texture. The glass fibre/polymer interface. 1 - Theoretical considerations for single fibre pullout tests Chua, P.S. and Piggott, M. R Composites Science and Technology Vo122 No 1 (1985) pp 33-42 The dynamics of the fibre pull-out process were examined. The optimum conditions needed to obtain reliable values of as many parameters as possible in the pull-out process were determined. It was shown that by careful control of conditions the work of fracture of the interface can be determined in a single fibre pull-out test. The glass fibre/polymer interface. 2 - - Work of fracture and shear stress Chua, P.S. and Piggott, M. IL Composites Science and Technology Vo122 No 2 (1985) pp 107-119 Single fibre pull-out tests were carried out under carefully controlled conditions for fibres in both epoxy and polyester matrices, lnterfacial yield stresses and the work of fracture of the interface were determined and compared. The glass fibre/polymer interface. 3 - - Pressure and coefficient of friction Chua, P.S. and Piggott M. R Composites Science and Technology Vo122 No 3 (1985) pp 185-196 Single fibre pull-out from both polyester and epoxy resins was observed under carefully controlled conditions, with external pressure applied to the matrix. Both the coefficient of friction of the interface and the interfacial pressure resulting from cure shrinkage of the resin were obtained. The processes taking place at the interface are also reported.
Failure loads for notched graphite/epoxy laminates with a softening strip Sun. C.T. and Luo, J. Composites Science and Technology Vo122 No 2 (1985)pp 121-133 The strengths of two graphite/epoxy notched laminate systems with a softening strip were investigated. The softening strip was created by replacing the 0° graphite/epoxy plies by a glass/ epoxy composite. The experimental results indicated that the use of softening strips could significantly increase the laminate strength. The classical laminate plate theory was shown to be adequate for analysis of deformation in hybrid laminates with holes and the existence of the softening strip simplified the failure analysis. A simple point-stress failure criterion was shown to be accurate.
The glass fibre/polymer interface. 4 - Controlled shrinkage polymers Ch ua, P.S. and Piggott, M. R Composites Science and Technology Vo122 No 4 (1985) pp 245-258 Experiments were carried out in which production glass fibres were embedded in epoxy homopolymers and spiro-epoxy copolymers. Pulling the fibres out under carefully controlled conditions provided data on the strength of the fibre/matrix bond, the matrix shrinkage pressure and the coefficient of friction at the interface. The spiro reduced the shrinkage pressure by about 70%, but increased the adhesion` and increased the coefficient of friction almost threefold.
Fracture behaviour of glass cloth-reinforced composites AgrawaL D.C., Agarwak B.D. and Banjeri, K. Polymer Composites Vol 6 No 1 (January 1985) pp 29-33
Impact induced fracture in a laminated composite Joshk S.P. and Sun, C.T. Journal of Composite Materials Vol 19 No 1 (January 1985) pp 51-66 Specimens from a (0/90/0~) graphite/epox) laminate have been subjected to impact
339
damage from a hard steel ball travelling at several different velocities, and the cracking patterns obtained studied in conjunction with numerical results from a 2D plane-strain analysis for a wide plate impacted by a cylindrical impactor. The stress field obtained approximates to the local stress field in an impact region, and is useful in identifying areas of stress concentration. Detailed damage observations help to establish the importance of transverse shear stress in crack initiation.
Imperfection sensitivity of fibre-reinforced, composite, thin cylinders Simitses, G.J., Shaw, D, Sheinman, I. and Girl, J. Composites Science and Technology Vol22 No4 (1985) pp 259-276 The imperfection sensitivity of thin cylindrical shells made from composite material and subjected to uniform axial compression, and the effects upon it of certain parameters, were investigated mathematically. The effect of inplane transverse boundary conditions and load eccentricity on the imperfection sensitivity of boron/epoxy laminated cylindrical shells was investigated. The influence of stacking sequence on the strength of bonded CFRP single lap joints Matthews, F.L and Tester, T.T. International Journal of Adhesion and Adhesives Vol 5 No 1 (January 1985) pp 13-18 The effect of changing the stacking sequence in 0/+45 ° lay-up carbon fibre-reinforced plastic adherends on the joint strength of bonded single lap joints is discussed. The results of a limited experimental study are presented and it is found that both lay-up and stacking sequence influence strength. A correlation between experiment and theory is found to exist for 8-ply laminates but not for 6-ply laminates. Matrix cracking and stiffness reduction during the fatigue of a (0/90)s GFRP laminate Ogin, S.L, Smith, P.A. and Beaumont. P.W.R. Composites Science and Technology Vol 22 No l (1985) pp 25-31 Stiffness reduction due to matrix cracking in (0/90)s glass fibre-reinforced plastic (GFRP) laminate was studied under both quasi-static and fatigue loading, The stiffness reduction is shown to be directly proportional to the density of cracks which accumulate in the transverse ply. A model for the transverse ply crack growth during fatigue gives good agreement with the experimentally determined stiffness reduction curves. (Authors' abstract). Melt processible fluoropolymer composites Altland, R., Carreno, C. and Tebay, J. Materials Engineering Vol 101 (May 1985) p 41 Copolymerization technology has enabled fluorocarbons to become processible by conventional melting techniques. The range of fluorinated polymers retain the unique properties of their higher viscosity precursors, and have the advantage of attractive fibre reinforcements. The melt-processible matrices (fluorinated ethylene, propylene and perfluorinated alkoxy polytetrafluorethylene) achieve higher bond strengths with reinforcing fibres. The thermal, mechanical and chemical resistance properties of these composites are discussed. Mierostruetural efficiency and fracture toughness of short fibre/thermoplastic matrix composites Friedrich, K. Composites Science and Technology 11o122 No 1 (1985) pp 43-74 The fracture behaviour of composites with
340
thermoplastic matrices of differing fracture toughness was examined in detail, particularly with regard to the effect of volume fraction, orientation and distribution of the reinforcing short glass fibres. In general, it was found that an increase in composite toughness can be expected with increasing extent of reinforcement if the matrix is in a brittle condition and if the fibres are well bonded and mostly oriented perpendicular to the crack front.
Polypruylene composites: fracture mechanical analysis of impact strength Bramuzzo, M., Savadori, A. and Bacci, D. Polymer Composites Vol 6 No 1 (January 1985) pp 1-8 An investigation using linear elastic fracture mechanics principles was carried out to determine the impact resistance of polyproylene (PP) containing various fillers. A homopolymer PP containing differing amounts of calcium carbonate, talc or glass spheres and a block copolymer PP modified with EP rubber and containing fillers were tested and compared. An SEM analysis of the fractured surfaces was made. The best results were obtained with calcium-carbonate filled PP. Processing-property relationships in compression molding of sheet molding compounds Oh, S.Y. and Han, C.D. Polymer Composites Vol 6 No I (January 1985) pp 13-19 An experimental investigation was carried out to determine the relationships between processing variables and the mechanical properties of compression moulded sheet moulding compounds (SMC). The polyester resin matrix remained the same throughout the investigation; types of glass fibre and thermoplastic low-profile additives were varied, as were the cure time. mould temperature and mould pressure. Tensile properties, impact strength and dynamic mechanical properties of the resulting composites were examined. It was found, interalia~ that an optimum cure time and mould temperature existed for achieving composites of the greatest tensile and impact strengths. Response of polymeric materials to thermal radiation Share, S. and Baba, A. SAMPE Journal Vo121 No 2 (March~April 1985) pp 7-11 The response of polymeric materials to concentrated solar radiation was investigated. Various plastics, elastomers and composites including graphite/polyimide, graphite/epoxy, graphite/PPQ, glass/epoxy and polyaramid/ epoxy were investigated. Most were found to char. Results are compared and discussed. Rubber toughening of plastics. Part 8 Effects of glass beads on the kinetics of creep in ABS Bucknall, C.B. and Reddock, S.E, Journal of Materials Science Vo120 (April 1985) p 1434 Creep measurements were made on ABS blends containing 0 to 20% by volume of g0 p,m glass beads. At low strains the beads reinforce ABS. Upon increasing the strain and bead content, however, debonding occurs resulting in a rapid drop in composite modulus. The presence of stress concentrations results in increases in creep rate which can be correlated using the Eyring equation. It is concluded that debonded glass beads accelerate multiple crazing by increasing stresses in the matrix(and this resembles rubber particles). It is shown that debonded beads drastically reduce the impact strength of the composite.
Salicylic acid modified high performance epoxy matrices Ibrahim, A.M. and Seferis, J.C. Polymer Composites Vol 6 No 1 (January 1985) pp 47-53 The effect of the presence of salicylic acid on the cure of epoxy systems which may be used as matrices for carbon fibre composites is reported. Stress dependence of the coefficient of moisture diffusion in composite materials Neumann, S. and Marom, G. Polymer Composites Vol 6 No 1 (January 1985) pp 9:-12 A model to express the effect of external loading on diffusion into the bulk resin matrix of unidirectional composite materials is proposed and confirmed for calculations made for glass fibre-reinforced epoxy composites, Structural repair systems for thermoplastics composites Welder, S.M., Lause, H.J. and Fountain, R. SAMPE Quarterly Vol 16 No 2 (January 1985) pp 33-36 The advantages of using thermoplastic composites as replacement materials for aluminium alloys in structural components in aerospace systems are briefly described. One advantage, the possibility of on-site repairs, is further discussed. Candidate methods of achieving repairs - - magnetic heat induction, adhesive bonding, ultrasonic welding, spin/vibration welding, and inert gas welding-- are described. Thermophysical properties of asbestos reinforced rubbers Loftus, P., O'Donnell, J., Wostenholm, G.H., Yates, B., Badami, D.V, and Green, D.Journalof Materials Science Vol 20 (March 1985) p 1093 An experimental study has been made into the sealing characteristics of gaskets made from asbestos-reinforced rubber. The work contains three separate investigations of the thermal properties of the material Two of these were associated with optimizing the moisture uptake for sealing characteristics; and the third was concerned with the composite cure. The measurements provide information which is relevant to thermally induced structural changes in these composite components. Ultrasonic inspection of carbon-epoxy composites Hagemaier, D.J, and Fassbender, 1LH.Materials Evaluation Vo143 No 5 (April 1985) p 556 Laminate and honeycomb structures are subjected to various ultrasonic techniques. Reference standards, with built-in defects, were used which establish test sensitivity and defect detectability. In addition, it is urged meaningful acceptance/rejection criteria must be established for an efficient inspection. Steps are taken to clarify this process for both fabrication and in-service defects. Use of statical identntion laws in the impact analysis of laminated composite plates Tan, T.M. and Sun, C.T. Transactions of the ASME: Journal of Applied Mechanics Vo152 No 1 (March 1985) pp 6-12 The low-velocity impact response of graphite/ epoxy laminates was investigated theoretically and experimentally. A nine-mode isoparametric plate finite element in conjunction with an empirical contact law was used for the theoretical investigation. The theoretical results were in good agreement with strain-gauge experimental data, indicating that the theoretical procedure adequately describes the impact response of graphite/epoxy laminates for low impact velocities.
COMPOSITES. OCTOBER 1985
COMPOSITES. OCTOBER 1985
The electrical breakdown characteristics of a glass-filled polyphenylene sulphide (PPS) composite have been studied. Three specimen geometries were tested. The results obtained were similar to those for a glass/PET composite, where preferential breakdown channels occur at the fibre/matrix interface. Electrical resistivity behaviour of solution-east metal-filled composites Singh, R R and Roberts, ILR Polymer Composites Vol 6 No 1 (January 1985) pp 58-62 Solvent-cast. metal-filled composites of polymethylmethacrylate and aluminium or copper were found to exhibit electrical resistance behaviour. A precipitous change in volume resistivity which was thermally dependent was found at filler concentrations of 17 to 19.5%. Materials with compositions at this conductive/non-conductive threshold showed semi-conductor behaviour and were found to exhibit memory switching, Environmental and time dependence of fracture toughness and crack growth in glass-reinforced polyester resins Roberts, RC. Journal of Materials Science Vo120 (April 1985) p 1341 The validity of fracture toughness testing of glass fibre-reinforced polyester has been examined for single edge-notched specimens using slow strain-rate tests. The fracture toughness is greatly reduced by the presence of the chemical environment as a result of acidinduced environmental stress cracking. Environmental effects are also found to determine crack growth rates and could be useful in ranking materials. Environmental lifetime of fibrous polymer composites Lhymn, C., Davis, P.K., Tempelmeyer, K.E. and Schultz, J.M. Journal of Materials Science Letters Vol 4 (May 1985) pp 575-579 A study of the stress corrosion failure of short fibre-reinforced (glass and carbon) composites was carried out. Matrix materials were rubber toughened polyethylene terephthalate and unmodified polyphenylene sulphide. Test environments were 10% sodium hydroxide. water and aqueous mineral acids; notched coupon specimens were used. It was found that the alkali predominantly attacked the matrix. especially the rubber/matrix interface, whereas the acid attacked the glass fibre, Equations that qualitatively explain the lifetime behaviour based on Markov statics are also presented,
The fracture behaviour of an epoxy resin reinforced with a balanced weave glass cloth was investigated. It was found that fracture proceeded by tensile failure of the fibres rather than by shear failure of the matrix or interface. It was also found that fracture mechanics concepts can be applied to these composites when the initial crack is longer than the critical value. Fracture in epoxy resin matrices Robertson, RE., Mindroiu, V.E. and Cheung. M.-F. Composites Science and Technology Vol 22 No 3 (1985) pp 197-207 The fracture surface of a trifunctional aromatic epoxy resin, containing a tertiary amine and cured with an anhydride, was examined in detail. A model is proposed to describe the fracture-energy enhancing steps and welts which are seen to arise from the underlying basic longitudinal texture. The glass fibre/polymer interface. 1 - Theoretical considerations for single fibre pullout tests Chua, P.S. and Piggott, M. R Composites Science and Technology Vo122 No 1 (1985) pp 33-42 The dynamics of the fibre pull-out process were examined. The optimum conditions needed to obtain reliable values of as many parameters as possible in the pull-out process were determined. It was shown that by careful control of conditions the work of fracture of the interface can be determined in a single fibre pull-out test. The glass fibre/polymer interface. 2 - - Work of fracture and shear stress Chua, P.S. and Piggott, M. IL Composites Science and Technology Vo122 No 2 (1985) pp 107-119 Single fibre pull-out tests were carried out under carefully controlled conditions for fibres in both epoxy and polyester matrices, lnterfacial yield stresses and the work of fracture of the interface were determined and compared. The glass fibre/polymer interface. 3 - - Pressure and coefficient of friction Chua, P.S. and Piggott M. R Composites Science and Technology Vo122 No 3 (1985) pp 185-196 Single fibre pull-out from both polyester and epoxy resins was observed under carefully controlled conditions, with external pressure applied to the matrix. Both the coefficient of friction of the interface and the interfacial pressure resulting from cure shrinkage of the resin were obtained. The processes taking place at the interface are also reported.
Failure loads for notched graphite/epoxy laminates with a softening strip Sun. C.T. and Luo, J. Composites Science and Technology Vo122 No 2 (1985)pp 121-133 The strengths of two graphite/epoxy notched laminate systems with a softening strip were investigated. The softening strip was created by replacing the 0° graphite/epoxy plies by a glass/ epoxy composite. The experimental results indicated that the use of softening strips could significantly increase the laminate strength. The classical laminate plate theory was shown to be adequate for analysis of deformation in hybrid laminates with holes and the existence of the softening strip simplified the failure analysis. A simple point-stress failure criterion was shown to be accurate.
The glass fibre/polymer interface. 4 - Controlled shrinkage polymers Ch ua, P.S. and Piggott, M. R Composites Science and Technology Vo122 No 4 (1985) pp 245-258 Experiments were carried out in which production glass fibres were embedded in epoxy homopolymers and spiro-epoxy copolymers. Pulling the fibres out under carefully controlled conditions provided data on the strength of the fibre/matrix bond, the matrix shrinkage pressure and the coefficient of friction at the interface. The spiro reduced the shrinkage pressure by about 70%, but increased the adhesion` and increased the coefficient of friction almost threefold.
Fracture behaviour of glass cloth-reinforced composites AgrawaL D.C., Agarwak B.D. and Banjeri, K. Polymer Composites Vol 6 No 1 (January 1985) pp 29-33
Impact induced fracture in a laminated composite Joshk S.P. and Sun, C.T. Journal of Composite Materials Vol 19 No 1 (January 1985) pp 51-66 Specimens from a (0/90/0~) graphite/epox) laminate have been subjected to impact
339
damage from a hard steel ball travelling at several different velocities, and the cracking patterns obtained studied in conjunction with numerical results from a 2D plane-strain analysis for a wide plate impacted by a cylindrical impactor. The stress field obtained approximates to the local stress field in an impact region, and is useful in identifying areas of stress concentration. Detailed damage observations help to establish the importance of transverse shear stress in crack initiation.
Imperfection sensitivity of fibre-reinforced, composite, thin cylinders Simitses, G.J., Shaw, D, Sheinman, I. and Girl, J. Composites Science and Technology Vol22 No4 (1985) pp 259-276 The imperfection sensitivity of thin cylindrical shells made from composite material and subjected to uniform axial compression, and the effects upon it of certain parameters, were investigated mathematically. The effect of inplane transverse boundary conditions and load eccentricity on the imperfection sensitivity of boron/epoxy laminated cylindrical shells was investigated. The influence of stacking sequence on the strength of bonded CFRP single lap joints Matthews, F.L and Tester, T.T. International Journal of Adhesion and Adhesives Vol 5 No 1 (January 1985) pp 13-18 The effect of changing the stacking sequence in 0/+45 ° lay-up carbon fibre-reinforced plastic adherends on the joint strength of bonded single lap joints is discussed. The results of a limited experimental study are presented and it is found that both lay-up and stacking sequence influence strength. A correlation between experiment and theory is found to exist for 8-ply laminates but not for 6-ply laminates. Matrix cracking and stiffness reduction during the fatigue of a (0/90)s GFRP laminate Ogin, S.L, Smith, P.A. and Beaumont. P.W.R. Composites Science and Technology Vol 22 No l (1985) pp 25-31 Stiffness reduction due to matrix cracking in (0/90)s glass fibre-reinforced plastic (GFRP) laminate was studied under both quasi-static and fatigue loading, The stiffness reduction is shown to be directly proportional to the density of cracks which accumulate in the transverse ply. A model for the transverse ply crack growth during fatigue gives good agreement with the experimentally determined stiffness reduction curves. (Authors' abstract). Melt processible fluoropolymer composites Altland, R., Carreno, C. and Tebay, J. Materials Engineering Vol 101 (May 1985) p 41 Copolymerization technology has enabled fluorocarbons to become processible by conventional melting techniques. The range of fluorinated polymers retain the unique properties of their higher viscosity precursors, and have the advantage of attractive fibre reinforcements. The melt-processible matrices (fluorinated ethylene, propylene and perfluorinated alkoxy polytetrafluorethylene) achieve higher bond strengths with reinforcing fibres. The thermal, mechanical and chemical resistance properties of these composites are discussed. Mierostruetural efficiency and fracture toughness of short fibre/thermoplastic matrix composites Friedrich, K. Composites Science and Technology 11o122 No 1 (1985) pp 43-74 The fracture behaviour of composites with
340
thermoplastic matrices of differing fracture toughness was examined in detail, particularly with regard to the effect of volume fraction, orientation and distribution of the reinforcing short glass fibres. In general, it was found that an increase in composite toughness can be expected with increasing extent of reinforcement if the matrix is in a brittle condition and if the fibres are well bonded and mostly oriented perpendicular to the crack front.
Polypruylene composites: fracture mechanical analysis of impact strength Bramuzzo, M., Savadori, A. and Bacci, D. Polymer Composites Vol 6 No 1 (January 1985) pp 1-8 An investigation using linear elastic fracture mechanics principles was carried out to determine the impact resistance of polyproylene (PP) containing various fillers. A homopolymer PP containing differing amounts of calcium carbonate, talc or glass spheres and a block copolymer PP modified with EP rubber and containing fillers were tested and compared. An SEM analysis of the fractured surfaces was made. The best results were obtained with calcium-carbonate filled PP. Processing-property relationships in compression molding of sheet molding compounds Oh, S.Y. and Han, C.D. Polymer Composites Vol 6 No I (January 1985) pp 13-19 An experimental investigation was carried out to determine the relationships between processing variables and the mechanical properties of compression moulded sheet moulding compounds (SMC). The polyester resin matrix remained the same throughout the investigation; types of glass fibre and thermoplastic low-profile additives were varied, as were the cure time. mould temperature and mould pressure. Tensile properties, impact strength and dynamic mechanical properties of the resulting composites were examined. It was found, interalia~ that an optimum cure time and mould temperature existed for achieving composites of the greatest tensile and impact strengths. Response of polymeric materials to thermal radiation Share, S. and Baba, A. SAMPE Journal Vo121 No 2 (March~April 1985) pp 7-11 The response of polymeric materials to concentrated solar radiation was investigated. Various plastics, elastomers and composites including graphite/polyimide, graphite/epoxy, graphite/PPQ, glass/epoxy and polyaramid/ epoxy were investigated. Most were found to char. Results are compared and discussed. Rubber toughening of plastics. Part 8 Effects of glass beads on the kinetics of creep in ABS Bucknall, C.B. and Reddock, S.E, Journal of Materials Science Vo120 (April 1985) p 1434 Creep measurements were made on ABS blends containing 0 to 20% by volume of g0 p,m glass beads. At low strains the beads reinforce ABS. Upon increasing the strain and bead content, however, debonding occurs resulting in a rapid drop in composite modulus. The presence of stress concentrations results in increases in creep rate which can be correlated using the Eyring equation. It is concluded that debonded glass beads accelerate multiple crazing by increasing stresses in the matrix(and this resembles rubber particles). It is shown that debonded beads drastically reduce the impact strength of the composite.
Salicylic acid modified high performance epoxy matrices Ibrahim, A.M. and Seferis, J.C. Polymer Composites Vol 6 No 1 (January 1985) pp 47-53 The effect of the presence of salicylic acid on the cure of epoxy systems which may be used as matrices for carbon fibre composites is reported. Stress dependence of the coefficient of moisture diffusion in composite materials Neumann, S. and Marom, G. Polymer Composites Vol 6 No 1 (January 1985) pp 9:-12 A model to express the effect of external loading on diffusion into the bulk resin matrix of unidirectional composite materials is proposed and confirmed for calculations made for glass fibre-reinforced epoxy composites, Structural repair systems for thermoplastics composites Welder, S.M., Lause, H.J. and Fountain, R. SAMPE Quarterly Vol 16 No 2 (January 1985) pp 33-36 The advantages of using thermoplastic composites as replacement materials for aluminium alloys in structural components in aerospace systems are briefly described. One advantage, the possibility of on-site repairs, is further discussed. Candidate methods of achieving repairs - - magnetic heat induction, adhesive bonding, ultrasonic welding, spin/vibration welding, and inert gas welding-- are described. Thermophysical properties of asbestos reinforced rubbers Loftus, P., O'Donnell, J., Wostenholm, G.H., Yates, B., Badami, D.V, and Green, D.Journalof Materials Science Vol 20 (March 1985) p 1093 An experimental study has been made into the sealing characteristics of gaskets made from asbestos-reinforced rubber. The work contains three separate investigations of the thermal properties of the material Two of these were associated with optimizing the moisture uptake for sealing characteristics; and the third was concerned with the composite cure. The measurements provide information which is relevant to thermally induced structural changes in these composite components. Ultrasonic inspection of carbon-epoxy composites Hagemaier, D.J, and Fassbender, 1LH.Materials Evaluation Vo143 No 5 (April 1985) p 556 Laminate and honeycomb structures are subjected to various ultrasonic techniques. Reference standards, with built-in defects, were used which establish test sensitivity and defect detectability. In addition, it is urged meaningful acceptance/rejection criteria must be established for an efficient inspection. Steps are taken to clarify this process for both fabrication and in-service defects. Use of statical identntion laws in the impact analysis of laminated composite plates Tan, T.M. and Sun, C.T. Transactions of the ASME: Journal of Applied Mechanics Vo152 No 1 (March 1985) pp 6-12 The low-velocity impact response of graphite/ epoxy laminates was investigated theoretically and experimentally. A nine-mode isoparametric plate finite element in conjunction with an empirical contact law was used for the theoretical investigation. The theoretical results were in good agreement with strain-gauge experimental data, indicating that the theoretical procedure adequately describes the impact response of graphite/epoxy laminates for low impact velocities.
COMPOSITES. OCTOBER 1985