摘要:

AbstractTorsional and tension‐torsion creep studies have been performed on cellulose acetate butyrate at 65°C. The aging shift factor, μ, at this temperature has been determined to be 0.85. This is somewhat higher than 0.75 which was suggested as a maximum value for cellulose acetate butyrate (5). Axial stresses cause the torsional retardation times to become shorter. The change in retardation time is mainly determined by the magnitude of the axial stress and not by the length of time during which the axial stress is applied. Torsional stresses cause the axial retardation times to shift in a similar manner. The shifting of retardation times follows a maximum shear stress criter

ISSN:0032-3888    

DOI:10.1002/pen.760260402

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effect of ductility on fatigue behavior was studied using two DGEBA‐based (diglycidyl ether of bisphenol A) epoxies: a ductile Epon 815/Versamid 140 and a brittle Epon 828/Epon Z. Failure modes were different although normalized stress‐life relations were similar for both resins. Two competing failure mechanisms were identified: viscoelastic creep, and nucleation and coalescence into a main crack of microcracks. No signs of crazing or fibrillation were detected. The plastic elongation during fatigue was larger in Epon 815/Versamid 140. Fracture sources showed cracked material surrounded by a region of stable growth of the main crack. In the brittle Epon 828/Epon Z cracked material was scarce and the crack initiation region was clean, especially at high stress levels. Discontinuous crack growth bands and striations were seen in the stable crack growth regions. During unstable propagation the crack advanced at different levels joined by deep cleavage steps. Branching of the main crack occurred only in the brittle resin at the final stage of propagat

ISSN:0032-3888    

DOI:10.1002/pen.760260403

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractDraw ratios have been measured for samples of polyethylene andtrons‐polyisoprene, crystallized at various temperatures and at various degrees of orientation. The values obtained range from unity, i. e., no drawing is observed, up to values of about 15X for materials crystallized in the oriented state and then drawn in a perpendicular direction. The results are in rough accord with a simple molecular network model in which network strands are incorporated into crystallites with a number of reversals of direction (folds), and the remainder of a strand between network junctions is randomly arranged. The reduction in draw ratio with increasing temperature of crystallization and with increasing orientation at the time of crystallization is then accounted for in terms of a reduction in the number of reversals (folds) per molecular strand. Differences in natural draw ratio for different polymers are attributed to variations in characteristic sequence length within a crystallite and in the number of folds per network stran

ISSN:0032-3888    

DOI:10.1002/pen.760260404

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractPhysical aging of a network epoxy resin in both the dry and water plasticized state has been investigated using calorimetric methods. Enthalpic retardation (recovery) towards equilibrium below the glass transition temperature (TK) has been qualitatively and quantitatively evaluated over a wide temperature range by following the enthalpy recovered (Er) on re‐heating through to and beyond the glass transition. Results indicate that water, acting as a plasticizer, accelerates aging at any given temperature. However, by using the respectiveTgas a point of reference, a simple comparison of the kinetics of aging in the dry and plasticized state suggests that in the temperature range studied there are no significant differences. These observations, together with observed dilational and relaxational effects of water which appears to erase all accumulated aging effects in dry aged material, are commented upon and their importance in the' context of transport‐phenomena and moisture sorption‐desorption cycles are disc

ISSN:0032-3888    

DOI:10.1002/pen.760260405

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760260406

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractRates of crystallization, stress‐optical coefficients, and melting points were determined for unelongated and elongated polysebacate model networks. For the unelongated networks, the maximum rate of crystallization was found to occur at approximately 0°C. For the elongated networks, the stress‐optical coefficients documented the extent to which strain‐induced crystallization was facilitated by increase in elongation and decrease in temperature. Measurements of stress relaxation due to crystallization at constant elongation indicated that the dimensionality of crystallization growth decreased from 3.0 to 2.5 as the temperature increased Melting points increased significantly with increase in elongation as predicted by theory. Fiber (non‐equilibrium) shrinkage temperatures, as expected, showed no correlation with the meltin

ISSN:0032-3888    

DOI:10.1002/pen.760260407

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractNetworks were prepared from a sample of 1,4‐polybutacliene having an extremely highciscontent (98.5 mol percent) and from other samples having relatively hightranscontents (72 to 80 mol percent). The cross‐linking techniques employed were gamma irradiation, ultraviolet irradiation, and peroxide thermolysis. The resulting elastomers were studied in elongation in the unswollen state at several temperatures, to their rupture points, and in swelling equilibrium in a good solvent. Values of the elasticity constant 2C1obtained from the stress‐strain isotherms at low and moderate elongations gave values of the molecular weight M, between cross‐links in at least approximate agreement with those obtained from the swelling equilibrium data. The other elasticity constant 2C2generally had relatively large values, suggesting inhomogeneous cross‐linking, but approached zero for smallMcas expected from reduced configurational interpenetration. At high elongations, the reduced stress for the high‐cispolymer showed marked upturns due to strain‐induced cr

ISSN:0032-3888    

DOI:10.1002/pen.760260408

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractResidual stresses, generally present in solid polymers, arise as a result of temperature gradients during solidification. These stresses influence the mechanical behavior of polymers and therefore it is important to measure them; most conventional methods are destructive. In the present work, a non‐destructive photoelastic technique is discussed and applied to circular rods of poly(methyl methacrylate) (PMMA). This technique involves the measurement of the distribution of total birefringence across a diameter; the residual stress distribution is obtained numerically from the birefringence distribution. The influence of the birefringence caused by molecular orientation is also investigated. This technique is also applied to a glass rod, in which case the molecular birefringence is minimum. It is seen that the residual stresses obtained in this case are consistent with equilibrium consideration

ISSN:0032-3888    

DOI:10.1002/pen.760260409

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe large deformation behavior of nylon‐6 when subjected to constant loading rate tests has been investigated experimentally. Three types of loadings—tension, torsion, and combined tension‐torsion—have been used and the strain histories for each type analyzed. It is shown that a piecewise power law in time can adequately describe the strain histories up to equivalent strains as high as 30 percent for all cases. This piecewise power law shows well‐defined transitions from one mode to the other while each mode is characterized by a power law exponent valid for all types of loading. On the basis of experimental results, it is also possible to establish the functional form of various kernels involved in the Green‐Rivlin representation of the non‐linear viscoelastic behavior of nylon‐6. This method of finding kernels is much simpler than the conventional method of carrying out a large number of multi‐step creep tests. A comparison is also made between the results of the present work and the well‐known Findley equation, particularly with respect to the instantaneous strain re

ISSN:0032-3888    

DOI:10.1002/pen.760260410

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper explores the concept of continuously extruding reacting polyurethane foams. The control of the process is hampered by the fact that the state of the conversion of the extrudate is not directly observable. We present the general concept, describe an experimental apparatus, present a mathematical model of the process, and report on some initial experimentation. In the experimental work, low density (0.5 g/cc) polyurethane foam was extruded in a cylindrical cross section at a rate of 250 g/min. Maximum run time was thirty minutes. In all cases, the experiment had to be stopped due to problems in the process. Problems requiring further investigation were identified: channelling of uncured liquid foam around the solid cured foam, poor skin quality due to adhesion of the foam to the wall, and the general lack of observability of the conversion field.

ISSN:0032-3888    

DOI:10.1002/pen.760260411

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY