ISSN:0032-3888    

DOI:10.1002/pen.760150402

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractA phenomenological model combining a Weibull distribution function with a kinetic equation for flaw growth has been used to describe the static tensile strengths and fatigue lives of short graphite‐fiber reinforced nylon 66 materials. A simple Weibull function of the form\documentclass{article}\pagestyle{empty}\begin{document}$ P\left( {\sigma _b } \right) = \exp - \left( {{{\sigma _b } \mathord{\left/ {\vphantom {{\sigma _b } {\hat \sigma }}} \right. \kern-\nulldelimiterspace} {\hat \sigma }}} \right)^{9.5} $\end{document}described the distribution of static strengths. The scale factor\documentclass{article}\pagestyle{empty}\begin{document}$ {\hat \sigma } $\end{document}varies with the annealing treatment and, in general, is a function of environmental variables. The cumulative distribution of breaking times in fatigue can be characterized by a translated three parameter Weibull function\documentclass{article}\pagestyle{empty}\begin{document}$ P\left( {t_B } \right) = \exp - \left\{ {\left. {\left( {\frac{{\sigma _{\max } }}{{\hat \sigma }}} \right)^{16} + \frac{{t_B }}{{\hat t}}} \right\}} \right.^{0.59} . $\end{document}The average time to break (which is related to the time scale factor\documentclass{article}\pagestyle{empty}\begin{document}$ {\hat t} $\end{document}), appears to be a function of the flaw growth rate. The distribution equation has been found to predict the number of half cycle failures and is thus a valid model for the proof testing of large populations. An electrical resistivity method was developed to measure flaw growth rates in prenotched cantilever beams. Experimental data fit the following equation: ln (Δa/Δn) = −88.88 + (12.46 ± 5.68) ln (Keff)max. The correlation coefficient was 0.81. From curve fitting of fatigue data it appeared that flaw growth rate varied with the ninth power of flaw length (Δa/Δn) =Ma9. The direct measure of flaw growth rate using electrical resistance gave Δa/Δn=Ma6.23±2.84with 90 percent confidence. The two measurements overlap within the 90 percent confidence bands, but predictions of fatigue life using the flaw propagation data were not good. Scanning electron microscope studies showed that specimens with a short fatigue life have glassy, fibrillated fracture surfaces while specimens with a long fatigue life exhibit a high degree of ductility in portions of the fracture surface. These differences are traced to differences in the size and sha

ISSN:0032-3888    

DOI:10.1002/pen.760150403

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractOne is faced with an interesting challenge when trying to explain the effect of test frequency on polymer fatigue performance. While hysteretic heating arguments appear sufficient to explain adiminutionof fatigue resistance with increasing cyclic frequency inunnotchedtest samples, theenhancementof fatigue resistance in many polymers with increasing cyclic frequency innotchedsamples is still not clearly understood. In large measure, this is due to contradictory trends in fre‐quency‐sensitive material properties which affect the fatigue process. In this paper, a number of proposed fatigue models dealing with the time and strain rate dependence of elastic modulus, yield strength, creep and localized crack tip heating are examined and confronted with available data from the literature. Additional fatigue crack propagation data for poly(methyl methacrylate), poly (vinyl chloride), polystyrene, poly‐carbonate, nylon 66, poly(vinylidene fluoride) and poly(2,6‐dimethylphenylene oxide) were obtained and are reported herein. These data were obtained over a maximum frequency range of 0.1 to 100 Hz and, for selected polymers, with various waveforms. Frequency sensitivity is shown to be greatest in those polymers that show a high tendency for crazing. Relative fatigue behavior is found to reflect a competition between strain rate and creep effects. Where creep effects dominate, the total crack growth rate may be viewed as consisting of the summation of pure fatigue and creep components, respectively. Finally, the β transition appears to have a role, with frequency sensitivity being at a maximum for polymers where the β transition at room temperature occurs in the range of the experimental test

ISSN:0032-3888    

DOI:10.1002/pen.760150404

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe sorption kinetics and equilibria of n‐hexane in glassy polyblends of polystyrene and poly(2,6 dimethyl‐1,4 phenylene oxide) were studied as a function of annealing conditions. Cast film samples were annealed 20°C above their respective glass transition temperatures for two hours and twenty‐four hours. The rate of relaxation‐controlled (Case II) sorption of n‐hexane in these films was reduced markedly consequent to annealing. The effect of annealing on the sorption kinetics and the independently determined film densities was more pronounced for the poly(phenylene oxide)‐rich samples. Although sorption rates were reduced by as much as a factor of 100, the sorption equilibrium was insignificantly affected by annealing. Super Case II transport was observed for the slow absorbing annealed samples whereas the more rapid sorption in the unannealed samples followed ideal Case II kinetics. The more pronounced effects of annealing for the poly(phenylene oxide)‐rich samples on sorption rates and film densities were explained by considering the increasing difference between the filmTgand the drying temperature used in the original film preparation for the poly(phenylene oxide)‐rich samples. These results suggest that glassy polymers, cast and dried well below their glass transition temperatures, will be subject to large long‐term reductions in absorption rates and specific volume. Moreover, residual, excess free volume significantly affects relaxation‐controlled absorption of vapors in partially anne

ISSN:0032-3888    

DOI:10.1002/pen.760150405

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractMuch has been written on the theoretical mechanisms by which the oxidation of polyolefins is believed to proceed and on the role of stabilizers in impeding this process. Relatively little information is available on the effects of some of the interesting, practical considerations—stress, stabilizer stability and the consequences of crystalline content and texture to name a few—which exert a controlling influence on the behavior of these materials in real‐life situations. Data are presented on the aging behavior of low‐ and high‐density polyethylenes at temperatues in the range 50‐110°C in the presence of copper and on the utility and limitations of oxygen absorption and differential thermal analysis as tools for accelerated prediction of t

ISSN:0032-3888    

DOI:10.1002/pen.760150406

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractLong‐term performance of carbonated plastic beverage bottles depends on a number of critical factors. Testing to predict the effects of these factors is expensive and time‐consuming. Many of these factors are interdependent. The presence of more than one critical factor in a given test makes the analysis of data difficult. The separation and prediction of the contribution of any one factor to long‐term performance is complex even for the single composition studied, a rubber‐modified high acrylonitrile resin. In addition to superior gas barrier properties, the container should exhibit a high degree of creep resistance. Visible manifestations of creep are reflected in gross dimensional changes of the bottle and consequent loss in carbonation. The purpose of this paper is to examine creep deformation of the bottle and its implications on bottle performance. Various factors contributing to the creep are also briefly analyzed. Since the ultimate goal is to predict creep, the merits of relevant short‐term tests in this context are discussed. Finally, the data from short‐term tests are compared with creep data obtained on bottles that were subjected to long

ISSN:0032-3888    

DOI:10.1002/pen.760150407

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractIn order to determine the effect of outdoor aging in various areas of the world, poly(vinyl chloride), PVC, compositions were exposed at test sites in Australia, Canada, England, Germany, South Africa, and in Piscataway, New Jersey. These results are related to the climatological data from the different test sites. The data obtained show the effects of a three‐year period of exposure on clear and filled, flexible and rigid PVC compositions. The merits of various types of additives are shown in respect to the outdoor aging properties of PVC compounds. It was observed that the exposure conditions vary from severe for Australia and South Africa to mild for England. However, the general results obtained throughout the world correlate well with those from the exposure site in New Jerse

ISSN:0032-3888    

DOI:10.1002/pen.760150408

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractIt has long been known that interaction of blood with artificial surfaces results in thrombogenic effects. With the increased use of prosthetic cardiovascular appliances, it is becoming more evident that surfaces which are thromboresistant are of utmost importance. A review is presented of the recent research on binding of heparin by ionic, covalent and thermal means, to different polymer surfaces, with the results of in vitro and in vivo tests. Additionally, a survey of theories on the role of heparin surfaces in thromboresistance is given.

ISSN:0032-3888    

DOI:10.1002/pen.760150409

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractABS (acrylonitrile‐butadiene‐styrene) plastics are one of the most common two‐phase commercial polymer systems. They consist of a continuous rigid phase (styrene‐acrylonitrile co‐polymer) in which the elastomer phase (polybutadiene grafted with styrene and acrylonitrile) is finely dispersed in the form of spherical particles. Because of their properties and relatively low cost compared to other engineering thermoplastics, ABS resins are now being used increasingly in fields of application involving severe aging. The polybutadiene content, however, poses a problem in relation to ABS aging resistance, since it is a prime site for degradative attack at double bonds and tertiary carbon atoms. The present paper presents a concise account of the methods used in our labortory for measuring ABS aging. As an example, ABS degradation during processing and during natural and artificial light aging are discussed in mo

ISSN:0032-3888    

DOI:10.1002/pen.760150410

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractFalling Dart Impact, FDI, toughness is used extensively to characterize the response of plastics to potential abuse. A critical study shows FDI toughness is highly variable with only 68 percent of the test pieces of a typical material failing within ±35 percent of the mean break energy, MBE. If no adjustment for this variability is made, the ASTM accepted “up/down” testing procedure leads to erroneous MBE values. A statistical analysis was carried out which defines the confidence which can be placed in measured MBE's as a function of the number of pieces tested. This analysis shows, for example, that 60 pieces must be tested so that a measured 20 percent difference in MBE's will be significant 90 percent of the time; while if 20 pieces are tested, as is suggested by ASTM, a 35 percent difference is needed before the same level of significance is rea

ISSN:0032-3888    

DOI:10.1002/pen.760150411

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY