摘要:

AbstractFlow of molten epoxide prepolymer (Tg= 303 K,M̄n889,M̄u/M̄n= 1.46) shows stress jumps. A hydrodynamic explanation is forwarded, and a check of the theoretical jump is carried out, with shear viscosites and shear moduli measured at 361 K. The increase in pressure produces a decrease in volume, which increases the rigidity of the polymer, which is then reduced by relaxation of the compressed chain segmen

ISSN:0032-3888    

DOI:10.1002/pen.760230402

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA fatigue crack propagation in an epoxy resin in the presence of organic solvents or water was studied from the viewpoint of fracture mechanics. The fatigue crack growth rate (da/dN) of the resin under various stress‐intensity‐factor ranges (ΔKl) was measured using a tapered double‐cantilever beam specimen. In air environment, plots ofda/dNagainst ΔKlwere found to be represented by the Paris equation:da/dN=C(ΔKl)n, whereCandnare empirical constants. In this case, the constantnwas about 6.5. The fatigue crack growth rate in the presence of organic solvents decreased to 1/10 ∼ 1/4 of that in air environment at the same ΔKl. It was considered that a penetration of the solvent molecules into the resin enlarged a region of plastic deformation near the crack tip. Therefore, more fracture energy was needed for the growth of the fatigue crack. Also, observations of the fatigue fracture surfaces suggested that a large plastic deformation occurred at the crack tip in the presence

ISSN:0032-3888    

DOI:10.1002/pen.760230403

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractIt is shown that the Williams‐Landel‐Ferry equation can be taken to describe the temperature dependence of viscosity of an amine‐cured epoxy resin. Furthermore, for this resin system, the two parameters of the W‐L‐F equation can be expressed simply as functions of hardener concentration. Since the hardener concentration decreases with advancement, and since the reaction rate equation for advancement is readily determined and known, the viscosity can be calculated over any temperature (cu

ISSN:0032-3888    

DOI:10.1002/pen.760230404

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractOur laboratory recently published several analytical equations that can be used to predict the melting rate of fully compacted solid polymers sliding on a heated metal surface, modeling the melting mechanism inside an extruder. These equations were obtained by seeking asymptotic solutions to the differential equations describing the melting mechanism, temperature, and shear‐dependent viscosity of polymer melts. Following the same asymptotic approach, we successfully developed accompanying analytical equations for predicting the stress required to slide fully compacted solid polymers on a heated metal surface. The accuracy of these analytical stress equations was found to be reasonable, although not fully satisfactory, by comparing their predictions to the experimentally measured values. The accuracy of the stress calculation is directly related to the accuracy of the viscosity values at high shear rates. The consideration of the temperature and shear dependencies of melt viscosity is most important for accurate prediction of the stress, just as it is for the melting rate. The stress not only depends on the melt rheological properties of the polymer but also on the thermodynamic propertie

ISSN:0032-3888    

DOI:10.1002/pen.760230405

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractCharpy specimens of a filled‐polymeric system from two partially cured and two completely cured lots obtained from one supplier were stored at selected temperature and relative humidity (RH) conditions to determine the relationship between mobile water content and the fracture toughness of the material. The fracture data showed that specimens from three of the structures exhibited similar ductile‐to‐brittle transition temperatures (DBTT) as a result of exposure to these environments even though samples from one of the three units were subjected to only part of the pure cycle. Samples from the other partially cured structure consistently displayed a more ductile fracture behavior throughout the conditioning range studied. Exposure to 100°F/75 percent RH environments, the highest temperature and RH of this study, appeared to enhance the fracture toughness of the material from all four units, and no evidence of deleterious chemical aging was found. Mobile water contents were measured on Charpy fracture residues, and these results correlate well with DBTTs of the filled polymer, as does RH. Charpy specimens from the partially cured structure with the best fracture performance have essentially the same water concentrations as the others, suggesting that the lower DBTTs associated with this unit may be due to a lesser degree of crossl

ISSN:0032-3888    

DOI:10.1002/pen.760230406

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractStress corrosion cracking of poly(vinylidene fluoride) in sodium hydroxide solution is investigated. Poly(vinylidene fluoride) (PVDF) is embrittled in the presence of solutions of sodium hydroxide. Cracks developed in specimens of PVDF subjected to load and solution of NaOH. Reddish‐brown deposits appear before cracks can be seen. Straining the material slightly above its yield point retards the cracking activity. An explanation for this behavior is provide

ISSN:0032-3888    

DOI:10.1002/pen.760230407

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe rheological behavior of highly filled polymer melts has been examined. At concentrations near the maximum packing fraction, strain‐dependent behavior was observed at strains as low as 1 percent. Selected surface treatments were shown to reduce particle agglomeration. This produced composite melts with lower viscosities and higher maximum loadings. While η* – ω plots provide information on the shear strength of the interparticle network,G′ – ω plots show evidence of phase

ISSN:0032-3888    

DOI:10.1002/pen.760230408

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractSamples of poly(methyl methacrylate) with a central circular hole are compressed, and crazes form on or after unloading, provided that the strain attains or exceeds a threshold value ϵt. Crazes induced in air are transformed rapidly to cracks, but environmental crazes are more stable. These residual stress crazes form at the diameter of the hole on a plane perpendicular to the applied stress direction. In contrast, during loading, crazes form on the vertical plane containing the hole axis. Unloading crazes are relatively insensitive to changes in strain rate, whereas loading erazes have a pronounced rate dependence. Environmental residual stress crazing exhibits an apparent rate sensitivity at constant time, but the critical applied strain ϵtis essentially constant, irrespective of rate, if the sample is in contact with the environment for a sufficiently long time to ensure that the minimum ϵtis obtained. Residual stress crazes appear to initiate at the equator of the hole, and the maximum tensile residual strain, indicated by a strain gauge, occurs in this positi

ISSN:0032-3888    

DOI:10.1002/pen.760230409

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe strength and elongation to break of an acetal copolymer were measured at four elongation rates, from 0.2 to 20 in./min, at temperatures from 239 K to 339 K. Both strength and elongation results could be reduced to master curves by means of time‐temperature superposition. The temperature dependence of the shift factors was given by an equation of the WLF form, with parameters close to those found for most amorphous polymers, at a reference temperature equal to the γ‐transition temperature of the polymer. Extrapolation to much higher testing rates and to much slower creep rates was satisfactory. Similar but less extensive tests were run on two other samples with different molecular weights. The yield stress was independent of molecular weight, but elongation increased with increasing molecular weight at all condit

ISSN:0032-3888    

DOI:10.1002/pen.760230410

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA thermal aging study of carboxyl‐terminated polybutadiene (CTB) and poly(butadiene‐acrylonitrile) (CTBN) reactive liquid polymers has been conducted at 50°, 75°, 100°, and 125°C. All CTB and CTBNs are stable at 50°C aging. On aging at higher temperatures prior to use, viscosities of CTB and CTBNs increase, and terminal carboxylic acid functional groups start disappearing. Rate of viscosity increase and rate of carboxylic acid functional group disappearance increase with higher aging temperature and also with higher cyano group concentration in the polymers. The major cause of rapid viscosity increase and disappearance of carboxylic acid functional groups seems to be crosslinking between terminal carboxylic acid groups and cyano groups, which form imide structures. Crosslinking among the unsaturation in polybutadiene segments may contribute to the slow, steady viscosity increase. No acid‐anhydride formation and decarboxylation reaction, which may also result in viscosity increase and disappearance of carboxylic acid functional groups, are observed during the thermal aging at elevated te

ISSN:0032-3888    

DOI:10.1002/pen.760230411

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY