摘要:

AbstractAn investigation according to LEFM (Linear Elastic Fracture Mechanics) principles has been carried out to determine impact resistance of PP (polypropylene) containing calcium carbonate in comparison with other types of mineral fillers. The tests have also allowed us to emphasize the strong influence of matrix brittleness or ductility on decreasing or increasing of toughness. In any case, of those materials tested, the calcium‐carbonate‐filled polypropylene is the material with the best performance. Scanning microscope (SEM) analysis and comparison of the results with the theoretical models reported in the literature made it possible to point out some particular aspects of this type of behav

ISSN:0272-8397    

DOI:10.1002/pc.750060102

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractA model for the effect of external loading on diffusion into the bulk resin matrix of unidirectional composite materials is proposed. The model attributes the effect to a change in the free volume of the resin matrix, which is equal to its volume strain. The latter is calculated by substracting the volume strain of the fibers from that of the composite. The ratio of the diffusion coefficients in the stressed and unstressed states is expressed as a function of the stress level, the volume fraction of the fibers, and the angle between the applied stress and the fiber direction. Calculations for a glass‐fiber‐reinforced epoxy composites are presen

ISSN:0272-8397    

DOI:10.1002/pc.750060103

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractAn experimental investigation was conducted into establishing relationships between the processing variables and the mechanical properties of compression‐molded parts of sheet molding compounds (SMC). Emphasis was placed on investigating the effects on the tensile properties, impact strength, and dynamic mechanical properties of composite specimens, of low‐profile additives, and of treating glass fibers (for reinforcement) with sizing chemicals. The processing variables investigated were cure time, mold temperature, and mold pressure. It was found that: (1) An optimum cure time and mold temperature exist for achieving molded SMC composites of the greatest tensile and impact strengths; (2) Of the four different types of low‐profile thermoplastic additives employed, the poly(vinyl acetate) modified with acrylic acid gives rise to molded SMC composites having the greatest tensile and impact strengths; (3) An optimum cure time and mold temperature exist for achieving the highest glass‐transition (Tg) of the low‐profile additive; (4) The values of cure time and mold temperature that have yielded the greatest tensile and impact strengths also yield molded specimens having the highestTgof the low‐profi

ISSN:0272-8397    

DOI:10.1002/pc.750060104

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe mechanical properties of short‐fiber‐reinforced thermoplastic composites depend on the degree of interfacial bond strength between the fibers and polymer matrix. This interfacial bond strength can be increased by appropriate coupling agents. This study shows, for example, that an amino silane coupling agent improves the bond strength of nylon‐aluminum fiber composites, but not polycarbonate‐aluminum fiber composites. For cases where appropriate coupling agents are not available it is important to maintain as high a fiber aspect ratio as possible in a molded part. This study shows that a single screw compounder does less damage to glass or carbon fibers than a twin screw compounder under similar processing conditions when the polymer is in the form of pellets. When the polymer is supplied as a powder, satisfactory dry blends can be produced and the twin screw compounder does less damage to the fibers. In both cases, however, fibers initially 6 mm long are reduced to an average length less than 0.5 mm. The greatest degree of fiber size retention was observed when extrusion coated fiber pellets were used in the injection molding machine. The relationship between a fiber's tensile strength and the interfacial shear strength between a fiber and matrix yields a critical fiber aspect ratio below which the maximum reinforcing capability of the fibers are not being utilized. For the polymers investigated in this program, the critical aspect ratio for carbon fibers was found to be between 16 and 25 to 1. The polymers investigated include flame‐retardant grades of acrylonitrile‐butadiene‐styrene (ABS) and poly(phenylene oxide)/polystyrene blend, nylon 6/6 and poly(pheny

ISSN:0272-8397    

DOI:10.1002/pc.750060105

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe fracture behavior of glass‐cloth‐reinforced composites has been studied. Fracture of these composites proceeds by tensile failure of fibers rather than by the shear failure of the matrix or the interface. Although the spread of damage in these composites is restricted to small distances away from the crack path due to the interweaving of the fibers, this distance is found to be appreciably larger for the samples with smaller initial crack lengths. Characteristic distances associated with the Whitney‐Nuismer criteria are, in turn, found to be smaller for these composites than for the angle ply laminates or randomly oriented short‐fiber composites reported in literature in which the spread of the damage is much greater. Analysis through the crack growth resistance also supports this correlation with the extent of damage spread and indicates that the critical crack length for these composites may be equal to the best fit value of the characteristic distance of the average stress cr

ISSN:0272-8397    

DOI:10.1002/pc.750060106

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractStructural changes of chlorinated paraffin (CP) have been studied using UV‐visible absorption spectroscopy in the 180 to 220°C temperature range. Formation and further reaction of conjugated polyene sequence with and without MgO is of major concern. It was found that CP dehydrochlorinated at normal processing temperatures of polypropylene in the absence of MgO. A mixture of various polyene sequences was formed. Unlike a stabilizing effect on poly(vinyl chloride), MgO showed a catalytic effect for dehydrochlorination of CP. As a result, longer conjugation was formed with MgO at the same conditions except for the absence of MgO. The longer polyenes were selectively reacted at the conditions studied. A possible chemical bond formation at the particulate filler/polypropylene matrix interface was suggested as one of the reinforcement mechanisms of the composi

ISSN:0272-8397    

DOI:10.1002/pc.750060107

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractA simple and new technique for direct determination of the short fibers orientation in polymer composites is described. It is based on the fact that the shape of the fibers' cross section in the plane perpendicular to the desired direction (e.g., orientation direction) depends on the orientation angle ϕ with respect to this direction. For an eliptical shape with minor and major radiirandR, the cosϕ =r/R. Using micrographs from the polished samples' cross section and assuming a planar fiber distribution, it is possible to calculate for a part or entire cross section area: (i) the ϕ‐values; (ii) the orientation parameterfp; (iii) the angular distribution (by histograms); and (iv) the number and the sizes of the layers with more uniform fiber orientation as well as the transition zones between them. It is demonstrated for commercial poly(ethylene terephthalate) (PET) reinforced with 45 percent (by weight) short E‐glass fibers (Rynite®) that each surface layer (A) takes ca. 3/16 of the sample thickness (b), the core (C)—3/16band the boundary (B) between them occupies 3/16b. These layers are characterized, respectively, byA= 28°,B= 38°,C= 64°, andf Ap= 0.51,f pB= 0.18,f Cp= −0.15. For the entire thickness (A+B+C) theA+B+C= 44° andf pA+B+C= 0.17. The method described is applicable to any kind of fiber‐reinforced composites from which it is possible to obtain micrographs of a desired cross section. The thickness of the cross section studied, as well as the number of the layers, does not affect

ISSN:0272-8397    

DOI:10.1002/pc.750060108

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThis study focuses on the processing‐structure‐property relations for salicylic acid modified high performance epoxy matrix systems for carbon fiber composites. Differential scanning calorimetry and dynamic mechanical data have shown that as the concentration of salicylic acid increases, the degree of cure first increases, reaches a maximum, and then decreases steadily. Analysis of the results indicated that small amounts of salicyclic acid accelerates the amine‐epoxide reactions resulting into crosslinked networks with increased degree of cure; increasing amounts, however, give rise to networks with reduced crosslinking by reducing the net available diaminodiphenyl sulfone (DDS) content in the system by a reaction of the DDS with salicylic acid. Overall, this study has demonstrated that salicyclic acid modification offers the potential for monitoring and controlling amine‐epoxide reactions that may influence the application and usage of epoxy matrices in composite

ISSN:0272-8397    

DOI:10.1002/pc.750060109

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe effect of gage length and temperature on tensile strength of aramid monofilaments, yarns, and strands has been studied in view of statistical models of the theory of strength. The tensile strength of monofilaments and yarns is found to decrease as the gage length is increased. The strength of strands remains constant. The temperature resistance of strands is determined by the glass transition temperature of a polymeric matrix.

ISSN:0272-8397    

DOI:10.1002/pc.750060110

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractSolvent‐cast metal‐filled composites made of polymethyl methacrylate and aluminum or copper exhibited electrical resistance behavior as is predicted by the percolation and tunneling mechanisms. A precipitous change in volume resistivity of about 1010ohm‐cm was found to be thermally dependent at volume concentration of filler in the range from 17 to 19.5 percent. Materials with compositions at the conductive‐non‐conductive threshold showed semi‐conductor behavior and exhibited memor

ISSN:0272-8397    

DOI:10.1002/pc.750060111

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY