摘要:

AbstractThe dependence of stress‐strain curves on temperature and extension rate is first discussed qualitatively along with aspects of the fracture process. Considered thereafter are the strength and extensibility, measured over broad ranges of temperature and extension rate, of elastomers in several classes: (a) singlephase non‐crystallizable; (b) crystallizable, both unfilled and containing a reinforcing filler; and (c) block copolymers which contain plastic domains. It is shown that all single‐phase noncrystallizable elastomers lack toughness except under restricted test conditions and that toughness necessitates a dispersed phase. Data are presented on crystallizable rubber vulcanizates and on polyurethane and poly(urea‐urethane) block copolymers to show that plastic domains are highly effective sources of strength. The properties of these block copolymers are examined in detail, and their strengths are compared with those of other segmented copolymers and triblock elastomers. Factors responsible for strength are del

ISSN:0032-3888    

DOI:10.1002/pen.760170302

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractA review of fracture mechanics and its relevance to designing with plastics is given. The basic philosophy of assuming the presence of flaws is developed, and the relevant equations are given. Data is presented for several polymers illustrating thickness and viscoelastic effects. A method of analysis for impact testing is then described together with some data. The unity of the data from a wide range of tests is emphasized.

ISSN:0032-3888    

DOI:10.1002/pen.760170303

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe effects of hydrostatic pressure on the shear, compressive, and tensile stress‐strain behavior of both amorphous and crystalline polymers are reviewed and illustrated. For polymers with Tgnear to but below ambient temperature, there is a steep increase of modulus with pressure and, above some critical pressure, there is a lower rate of increase. The critical pressure is a linear function of the test temperature and, from its slope, one can deduce the pressure coefficient of Tg. For many other polymers, there is a linear increase, over a wide pressure range, of elastic and shear moduli with pressure, and this is in accord, to a first approximation, with predictions of finite strain theory. Most all polymers investigated show a strong pressure coefficient of yield stress and in many cases this variation is linear over a wide pressure range, in accord with several pressure dependent yield criteria. To a considerable extent, the yield stress rise with pressure parallels that of the modulus, and this behavior is predicted by some yield theories. The effects of pressure on fracture stress and fracture strain are discussed. The results obtained depend on the polymer composition and structure and on the pressure medium. Consideration is also given to the effects of pressure on crazing and stress‐whiten

ISSN:0032-3888    

DOI:10.1002/pen.760170304

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThis paper surveys the basic aspects of physical aging. It shows that aging i s a general and important phenomenon found in all organic and inorganic glasses and in some metals as well. Moreover, the behavior of all these materials is very similar. It further shows that aging cannot be ignored in the testing of plastics, particularly in the prediction of their long‐term behavio

ISSN:0032-3888    

DOI:10.1002/pen.760170305

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractMassachusetts Institute of Technology Cambridge, Massachusetts 02.139 The phenomenology of plastic deformation in glassy polymers is described, and a theory based on a molecular model for such deformation is presented and contrasted with other published theories. A phenomenological yield criterion is presented which is consistent with the theory. It is shown that the theory is in very good accord with experimental results on the temperature dependence of the plastic shear resistance of a large group of glassy polymers with widely different molecular structures. Finally, the formation and growth of shear deformation bands is described, based purely on the mechanics of localization processes in inelastically deforming continua.

ISSN:0032-3888    

DOI:10.1002/pen.760170306

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractUnder uniaxial tensile load, the plastic deformation of unoriented crystalline polymers first transforms the lamellae into a fibrous structure. Usually the drawing is inhomogeneous with a neck propagating through the sample. The higher the draw ratio, the higher the axial elastic modulus as a consequence of the larger fraction of taut tie molecules in amorphous layers connecting the crystalline blocks of each microfibril. As a consequence of the almost 1/(1 − α) times higher strain of amorphous layers under tensile load, the taut tie molecules are much more strained than the chains in crystal blocks. Hence, their contribution to elastic modulus is substantially higher than one would guess from their fraction β. This is more so in polyethylene with higher crystallinity (α = 0.8) than in nylon 6 with low crystallinity (α = 0.5). Even for the highest modulus polyethylene E = 70 GPa ∼ 0.3 × Ec, one needs less than 7.5 percent of taut tie molecules. The plastic deformation of the fibrous structure markedly enhances the number of interfibrillar tie molecules in nylon 6 and to a lesser extent in polyethylene and polypropylene. Homogeneous drawing without a neck transforms the whole sample into a fibrous structure rather uniformly so that for a long while one has the lamellar and fibrillar morphology side by side. The end effect on the structure obtained does not differ appreciably from inhomogeneous drawing with neck propagation. The drawing of polymers with a liquid crystal structure yields a highly aligned fibrous structure with very few chain folds and an exceptionally high elastic modulus and strength. But the axial connection of individual highly oriented and ordered domains is affected by a relatively small fiaction of tie molecules, and this is responsible for reduction of the elastic modulus below the value of the ideal crystal

ISSN:0032-3888    

DOI:10.1002/pen.760170307

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractIn spite of the importance of fatigue behavior in engineering plastics, relatively few fundamental studies have been made of the effects of polymer structure, molecular weight, composition, and morphology on fatigue crack propagation (FCP). As, part of a broad program for the study of such effects, the role of molecular weight and internal plasticization has been studied in poly(methyl methacrylate) (PMMA) which had been specially prepared and characterized with respect to molecular weight, dynamic mechanical behavior, and, in some cases, stress‐strain response. As expected, values of fracture toughness,Kc, varied considerably as the molecular weight was rai ed, from 0.7 MPa, √matMv= 1.0 × 105to 1.1 atMv, = 4.8 × 106. However, a specific effect of fatigue was noted: over the same range ofKc, values of FCP rate decreased by two orders of magnitude as molecular weight was; increased. It is proposed that this high sensitivity is due to differences in the degree of chain disentanglement effected by the cyclic loading, with consequent differences in the strength of the craze preceding the crack. With PMMA plasticized internally with a low level (10 percent) of n‐butyl acrylate (nBA), the FCP rate andKc, were similar to those of controls, with very high rates shown. At higher nBA levels (up to 30 percent), the sensitivity of FCP rate to stress intensity factor range decreased considerably,Kc, increased by 30 percent and the pre‐exponential constant in the growth rate law increased. Plasticization weakens the polymer but at high degrees leads to enough hysteretic heating to induce local creep and crack

ISSN:0032-3888    

DOI:10.1002/pen.760170308

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe deformation and fracture behavior of injection molded plaques have been determined, and the results interpreted in terms of the effect of molecular orientation on the crazing and shear yielding behavior. The molecular orientation was characterized by optical birefringence. A range of injection molding conditions and two mold thicknesses were Used and this resulted in a large variation in the molecular orientation, particularly through the sheet thickness. Tensile tests were made on samples cut at different angles to the injection molding direction. The moldings are considered to consist of a composite of layers of material with different orientation, and the properties of the samples cut from the molding are analyzed in terms of the properties of each layer. Results from material oriented unidirectionally by hot drawing have been used to predict the composite properties, and good agreement has been obtained.

ISSN:0032-3888    

DOI:10.1002/pen.760170309

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe properties of mixtures of poly(2, 6‐dimethyl p‐phenylene oxide) and poly(styrene) have been measured by DSC, density gradient, dynamic mechanical response, and tensile testing. The mixtures are found to have single glass trasitions that vary continuously with the composition. They also have small negative excess volumes of mixing, indicative of strong polymerpolymer interaction. The dynamic mechanical response of the mixtures shows that the low temperature secondary relaxations are suppressed whereas those at high temperatures are enhanced. These observations imply that mixing on the segmental levc l has occurred. A plot of tensile strength vs composition at different strain rates reveals two regions of failure behavior. The high PS, high strain rate region is brittle, and the high PM2PO, low strain rate region is ductile. When the tensile yield data are treated according to the Ree‐Eyring equation, the addition of PS to PM2PO is found to reduce the flow volum, e of the mixture. The overall effect on mechanical properties of adding small amounts of one component to the other is similar to that of anti‐plasticization. Our experimental observations are consistent with the shifting of the relaxation mechanisms to longer times due to the negative excess volume of

ISSN:0032-3888    

DOI:10.1002/pen.760170310

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760170301

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY