ISSN:0032-3888    

DOI:10.1002/pen.760190202

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe failure behavior of uniaxially‐oriented isotactic polypropylene films has been examined over a wide range of rates and temperatures. Above the glass transition temperature the failure behavior is observed to be a direct function of the initial noncrystalline orientation state of the film. Below the glass transition temperature (−80°C, −196°C), both the crystalline and noncrystalline regions contribute to the

ISSN:0032-3888    

DOI:10.1002/pen.760190203

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractTensile creep measurements at constant load on nonoriented polyethylene have shown a marked transition at a certain stress level from a neck formation followed by instantaneous fracture to the formation of a neck which resists fracture for a considerable time. The transition, which shifts towards shorter time and higher nominal stress with increasing molecular weight, has been studied for 16 polyethylenes of different molecular weights, degrees of branching and crystalline structures. The marked. transition has only been observed for high density polyethylene of high molecular weight. Deformation measurements show a more distinct necking for the high density than for the medium density polyethylenes. This is consistent with current molecular deformation theories. A hypothesis for the transition is proposed based on the distinctness of the neck process in the high density polyethylene and the large difference in strength between the spherulitic structure and the fibrillar structure. The dependence of the transition on molecular weight is expected since the number of tic chains incrcrtses with increasing molecular weight.

ISSN:0032-3888    

DOI:10.1002/pen.760190204

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractExperiments have been conducted employing tapereddouble‐cantilever‐beam joints with different epoxide adhesives. Depending on the adhesive employed, crack propagation occurred either (a) in a continuous stable manner with crack propagation velocities in the range 10−4to 5 m/s and values of the adhesive fracture energy,GIc, being almost independent of the crack velocity, or (b) intermittently in an unstable manner when the initial crack velocity was never less than about 20 m/s and, in some instances, rose to about 450 m/s; values ofGIc(initiation) increased rapidly with increasing velocity. It is proposed that the amount of localized plastic deformation arising from shear yielding that occurs at the crack tip prior to crack propagation is controlling. Secondly, the longterm strength of stressed, structural adhesive joints has been investigated. The fracture of these joints over eight decades of time is uniquely described by a critical plastic zone size developed at the crack tip at fa

ISSN:0032-3888    

DOI:10.1002/pen.760190205

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractRadical generation during tensile deformation of poly‐p‐(2‐hydroxyethoxy) benzoic acid (PEOB) fibers was studied by electron spin resonance techniques under various stretching conditions. Primary phenoxy radicals were detected at room temperature, indicating main‐chain rupture during mechanical loading. The kinetics of phenoxy radical formation were observed at constant strain, constant load, constant strain‐rate, and in constant load rate experiments. The effect of strain rate on the radical formation was found to be larger in this sample than was observed in Nylon 6. These results coupled with other experimental observations have yielded information on a basic structural model and improved insight into the basic molecular mechanism responsible for deformation and

ISSN:0032-3888    

DOI:10.1002/pen.760190206

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractGlassy crosslinked networks were prepared by copolymerization of methyl methacrylate with up to 4.7 mole‐percent ethylene dimethacrylate. These networks were degraded by exposure to γ‐rays and the solubilized fraction estimated by benzene extraction using the analysis of A. R. Schultz. The efficiency of the Crosslinking agent was found to be 0.5 and this value was used to calculate the molecular weight between crosslinks. The molecular weight of the primary molecules in the network,M, was estimatfrom the radiation dose using the known fact that one fracture requires an energy deposition of 59 ev. Crosslinking was found to have little influence on the tensile strength of networks of primary molecular weight>105. In contrast. crosslinking raised, the strength of polymers ofM<105to, a value approaching that of a high molecular weight linear polymer (ca. 70MN/m2). Crosslinking was found to have only a small influence on the gross morphology of fracture surf

ISSN:0032-3888    

DOI:10.1002/pen.760190207

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIt is shown that under conditions of uniaxial creep the fracture of high density polyethylene can be categorized as one of three types, depending upon the magnitude of the applied load, molecular architecture, and environment. When subjected to relatively large loads, the specimens neck and then fracture almost immediately. At the other extreme of very small initial loadings, the specimens fracture in a brittle fashion through crack formation and growth. In the intermediate range of loadings the specimens neck and, depending upon the molecular weight and molecular weight distribution, may then elongate substantially before fracture. It is shown that the uniaxial creep behavior for the region where drawing occurs, when plotted in terms of isochrones, represents a type of phase diagram, one boundary of which describes the fracture enelope. In addition, experiments employing different constant rate of loading histories are described and an additivity of damage criterion used to predict the time to failure under constant load conditions, and visa versa.

ISSN:0032-3888    

DOI:10.1002/pen.760190208

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractBased on a continuum model, a point of instability is predicted for the uniaxial creep of high density polyethylene. From dead load experiments it has been found that the instability occurs for linear polyethylene at around 10–12 percent strain, depending upon molecular weight and molecular weight distribution. It is shown that in the range of applied stresses for which the specimens neck during uniaxial creep, the time required to reach the critical point is related by a constant factor to the time at which the neck appears. A synopsis of theoretical considerations, as well as experimental work in support of this idea, is give

ISSN:0032-3888    

DOI:10.1002/pen.760190209

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA discussion is given of three types of experimental techniques which make use of polymers for the verification of theoretical solutions to three‐dimensional linear fracture mechanics problems. The three techniques discussed are designated as the fatigue method, the photoelastic stress‐freezing method and the static fracture method. These techniques employ poly(methyl methacrylate) sheets which are cut into appropriate fracture mechanics specimen geometries or castable epoxies which may be cast into flat plates or other appropriate shapes for investigation. The suitability of these materials for linear fracture mechanics testing is discussed and the quality of results obtained is descri

ISSN:0032-3888    

DOI:10.1002/pen.760190210

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractMechanical fracture of nylon 6 produces free radicals as a direct result of bond‐breaking; these initial free radicals rapidly decay into secondary free radicals at room temperature. Aromatic nitro‐compounds react with the initial, but not the secondary, free radicals. The rate of reaction is sufficiently fast to compete with the usual initial radical decay process, even at room temperature. Considerations involved in applying high speed (microsecond) electron spin resonance techniques are discus

ISSN:0032-3888    

DOI:10.1002/pen.760190211

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY