ISSN:0032-3888    

DOI:10.1002/pen.760270102

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractAn approach to nonlinear viscoelasticity is described which is based on the “coupling model” of relaxation. A brief review of nonlinear viscoelasticity models is given to put the present approach into historical perspective. The physical basis of the coupling model is then described, and the quantitative predictions that the model has made in linear viscoelasticity and other areas of relaxation are discussed. The relaxation function predicted by the coupling model is used as a time‐dependent kernal in a constitutive equation for a description of nonlinear viscoelasticity. The model incorporates the strain history dependence and allows for the evolution of material structure. Simulations are presented showing how the model reproduces the essential features of constant strain‐rate, strain‐rate change, and strain‐step experiments. Experiments are described that can partially characterize the coupling model parameters and lead to quantitative tests o

ISSN:0032-3888    

DOI:10.1002/pen.760270103

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractAlthough yield stress and its dependence upon temperature and strain rate are well characterized for many thermoplastics, there are a number of scientific and engineering situations that require additional information regarding post‐yield deformation behavior. For example, the prediction of formability in plastics will require a quantitative description of constitutive behavior for strains between 40 and 300 percent, depending on the plastic. Data characterizing this behavior now exists for a number of plastics, and an analytical understanding of its effect on mechanical behavior has also been established. The purpose of this investigation is to apply the experimentally measured large‐strain constitutive behavior of polycarbonate to the analysis of several simple forming experiments and illustrate the accuracy of current predictions in comparison to experiment. Analyses of a tensile test, a “bend‐stretch” forming experiment, and the indentation of a circular disc by a hemispherical punch are compared with experiments. Agreement between analysis and experiment is very good for all geometries c

ISSN:0032-3888    

DOI:10.1002/pen.760270104

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractUltrasonic fractography studies were performed on poly(methyl methacrylate) of high molecular weight. The transient fracture velocity change at the slow‐to‐fast transition during discontinuous propagation has been measured precisely. Fast fracture starts with a characteristic velocity which falls in a narrow range between 90 to 150 m/s, nearly independent of the loading speeds and the specimen temperature from −50 to 40°C. Parallel double‐cantilever‐beam specimens exhibited stick‐slip type propagation whose velocity change was also evaluated. In these specimens, the fast fracture abruptly slows down to speeds on the order of 10° m/s. These intermediate velocities have never been obtained in the slow‐to‐fast transition. Velocity measurements under hydrostatic pressure have shown that fracture velocities decrease significantly with increasing pressure, and that the slow‐to‐fast transition tends to disappear at a pressure between 5 and 10 MPa. Models have been presented concerning the mechanism of the slow‐to‐fast transition, crazing and cracking under superposed cyclic stress field, and the relationship between dynamic toughness and fracture

ISSN:0032-3888    

DOI:10.1002/pen.760270105

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractHexcel F185 neat resin and T6T145/F185 graphite fiber‐reinforced composite were subjected to Mode I loading in the compact tension (CT) geometry (fibers parallel to the crack) and the energy per unit area of crack extension,JIC, determined to be 8100 and 1600 J/m2respectively.In‐situfracture studies using scanning electron microscopy on a CT‐type specimen of F185 showed extensive microcracking in a damage zone ahead of the crack tip, which was similar to the microcracking observed in the whitened area ahead of the crack tip in the macroscopic CT specimens. A simple calculation using a rule of mixtures approach suggests that the diminished size of the damage zone and the presence of rigid fibers in the damage zone in the composite are not a sufficient explanation for the significantly lower delamination toughness of the composite compared to the neat resin. From this it may be inferred that the strain to failure locally in the damage zone ahead of the crack in the composite may also be lower than that which can be tolerated in the neat resin. Evidence for this idea comes from the observation that microcrack coalescence seems to occur preferentially at the fiber/resin inte

ISSN:0032-3888    

DOI:10.1002/pen.760270106

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe development of plastic deformation and crazing in the neighborhood of a notch has been studied in connection with nonlinear fracture processes of crystalline ductile polymers, polyethylene, polypropylene, and propylene‐ethylene block copolymers. After revealing the morphology of plastic deformation around the notch and studying the effects of crystalline structure on ductile fracture processes, theJ‐energy analysis was applied to give a criterion for crack initiation in the fracture of these elastic‐plastic materials. The material resistance to stable and unstable cracking was characterized using the curves ofJagainst crack extensi

ISSN:0032-3888    

DOI:10.1002/pen.760270107

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractIn some ductile amorphous polymers, the fatigue lifetime behavior can exhibit two distinct crack propagation modes: a craze dominated sub‐critical discontinuous crack growth mode, which leads to a low stress, short fatigue lifetime branch and a shear fracture mode, which produces a higher stress, long lifetime branch. When both branches coexist, the fatigue lifetimes at higher stress amplitudes are often longer than those at lower stress amplitudes! This unusual lifetime inversion has been explored for a polyestercarbonate at various temperatures, frequencies, degrees of physical aging, and fatigue overload historie

ISSN:0032-3888    

DOI:10.1002/pen.760270108

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractMany of the features that cause the great complexity of the fracture surfaces of thermosets are suggested to have a simple explanation. These features include the “basic longitudinal texture,” “steps,” “welts,” “arrays of skewed cracks,” and the “stacked lamellar texture.” The explanation for their occurrence is based on the hypothesis of an instability of the propagating crack front that produces a “fingerin

ISSN:0032-3888    

DOI:10.1002/pen.760270109

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractAn approach using strain energy‐like potentials to characterize deformation and fracture of inelastic, nonlinear composite materials is described. The inelasticity may be due to various causes, including microcracking, microslipping, and rate processes responsible for fading memory (viscoelasticity). The concept of work potentials is introduced first, and then arguments are given for their existence for inelastic materials. Emphasis in the paper is on elastic composite materials with changing or constant states of distributed damage. Experimental results on polymeric composites are subsequently presented to illustrate this approach to deformation and fracture characterization. Finally, extension to viscoelastic behavior is discusse

ISSN:0032-3888    

DOI:10.1002/pen.760270110

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe mechanisms of resin controlled failure in adhesive joints and composites (delamination and transverse cracking) are examined. An in‐situ failure model based on the fracture mechanics principles is applied here to describe the failure processes involved. The model centers on the crack tip plastic zone developed in the thin resin layer between the fibers or the adherends. The plastic zone in the resin layer is heavily influenced by a dominant slow varying stress distribution, approximated to ber−m/2dependent withm≪ 1 (ris the distance from the crack tip). The adhesive or composite fracture toughnessG*ICcan then be expressed as a function of several resin properties of comparable importance: modulusE, yield stress σy, resinGICand residual stress. The relative significance of the resin properties on the adhesive or composite fracture is discussed. The effects of temperature, loading rate, and resin toughening on such failure as a result of the corresponding variations in resin properties are also add

ISSN:0032-3888    

DOI:10.1002/pen.760270111

出版商:Society of Plastics Engineers    

年代:1987

数据来源: WILEY