ISSN:0032-3888    

DOI:10.1002/pen.760141002

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe yield stress is a simple function of the deformation ratio in the direction of testing for specimens oriented by uniaxial or biaxial stretching or rolling. Unless the yield stress increases more rapidly than in proportion to the deformation ratio, there will be instability during tensile creep under high loads. The relative merit of various polymers differs for creep and stress relaxation. Fatigue and bend recovery are also related to the molecular structure.

ISSN:0032-3888    

DOI:10.1002/pen.760141003

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractA new kind of acetal fiber has been discovered which has a tensile strength of 1.7 GPa (250,000 psi) and an elastic modulus of 35 GPa (5 × 106psi). This fiber is produced by a special two‐stage drawing process in the solid state which requires careful control of deformation rate and temperature. Previously known drawn fibers are reported to consist of folded‐chain blocks joined by a limited number of tie‐molecules. It is hypothesized that the second stage of the novel drawing process eliminates the lamella (block) surfaces which act as strength‐limiting stress concentrators. A new type of fiber is created in which any remaining chain‐folds are distributed as defects in a continuous crystal matrix. It is the continuity of the crystal matrix which is believed responsible for the remarkable properties of

ISSN:0032-3888    

DOI:10.1002/pen.760141004

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractRigid, glassy plastics differ over a wide range in the amount of energy they can absorb before fracturing under the influence of an applied stress. It is here proposed that molecular structure influences energy absorption more significantly by determining the onset of fracture than by its effect on the energy‐dissipating processes themselves. Emphasis has been placed, therefore, on finding a relationship between molecular structure and the onset of fracture. Since many relationships between molecular structure and bulk mechanical response have already been established, it should be a useful step to relate the onset of fracture to bulk mechanical responses. The hypothesis is developed that the appropriate bulk property is the stress‐deformation function of the material. The observed stress‐deformation function is of such a nature that a highly non‐homogeneous deformation is produced at any point of stress concentration. Typically, this is a narrow region in which the material is highly deformed while the deformation in adjacent material is still slight. Fracture initiation is postulated to occur in such a region of high deformation. Differences among polymers in the shape of the stress‐deformation function are demonstrated experimentally. These differences correlate with tough‐brittle behavior. An explanation is proposed in terms of the probability of fracture

ISSN:0032-3888    

DOI:10.1002/pen.760141005

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractWe wish to investigate the path dependence of yield processes in glassy polymers and to understand this dependence, if any, in terms of molecular mechanisms. To this end the effect of sudden strain‐rate change on the yield behavior of bisphenol‐A polycarbonate has been investigated. In the experiment, a specimen was initially deformed at a constant elongation rateR1; at an elongation Δlcthe rate was suddenly changed to another constant elongation rateR2.R1was either lower or higher thanR2. The yield stress subsequent to the rate change was found to be lower than if the entire deformation was atR1. These results can be satisfactorily explained in terms of Robertson's theory of the yielding of glassy polymers if it is assumed that the “bond flexing” in his theory manifests itself in anelastic def

ISSN:0032-3888    

DOI:10.1002/pen.760141006

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractSpecific volume change and stress‐strain data were obtained simultaneously during tensile deformation on several plastics known to be resistant to impact loading. Tensile deformation rates of 20 percent/minute and 106percent/minute and temperatures of −190° to 55°C were employed. A common sequence of deformation modes was observed in all materials studied (rubber modified acrylics and styrene, ABS materials, polycarbonate, impact grade polypropylenes, and high density polyethylene). In all cases the major mode of deformation to failure at low rates and/or higher temperatures is volume conserving and primarily a shear flow process. At higher rates of deformation or lower temperatures, a transition occurs and the specific volume of the material increases in direct proportionality to the tensile strain above the apparent yield point. Volume increases of 17 to 50% were observed and these were equal to 85 percent or more of the observed tensile strain at failure. These observations indicate that microcavitation may be the major process available for the absorption of mechanical energy at impact rates in plastic mate

ISSN:0032-3888    

DOI:10.1002/pen.760141007

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractPlasticized poly(methyl methacrylate) and methyl methacrylate/acrylate copolymer films were examined by isothermal creep at low loads measured at several temperatures from ∼TgtoTg+ 15°C. Viscosity calculated using η = σ/3\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}was plotted vs temperature giving precise values forTgbased on a viscosity criterion of η = 1013poises. Creep fracture data at various temperatures belowTgwere interpreted using the maximum apparent viscosity measured at the minima of strain rate vs strain curves. Plots of ηmaxVSstress at several temperatures gave values of ΔTg/Δσ of −1° to 2°C/106N/m2in agreement with treatment of ΔTg/Δσ based on free volume. Fracture occurred at low elongations when ηmaxwas ≥1013poises, and at higher elongations when ηmaxwas<1013poises supporting the concept that fracture is related to the lowering ofTgunder stress. Plots of log σVSlog εb(the elongation at fracture) had the same form as that for crosslinked elastomers aboveTgreported by T. L. Smith. Plots of log\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}bVSlog εbalso had the same form supporting proposals on the rate

ISSN:0032-3888    

DOI:10.1002/pen.760141008

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThis is a study of materials which are positive‐temperature‐coefficient resistors. Such materials, composed of conductive particles dispersed in a crystalline polymeric matrix, have been found to be of limited stability. An example is carbon black in high‐density polyethylene. On repeated cycling through the anomaly temperature or on extensive heating at or above the anomaly temperature, the room temperature resistivity rises and the anomaly height falls to zero. This phenomenon has been shown to be caused by the absorption of oxygen by the polymer matrix which alters the structure, reduces the crystallinity, and induces an unusual form of crosslinking of a reversible n

ISSN:0032-3888    

DOI:10.1002/pen.760141009

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractDuring an investigation of the time for ignition of polymeric materials under the influence of radiant heating, it was found that the polymer surface reflectance‐absorptance characteristics were a major factor in the variance of the ignition times. A subsequent research study was made of the reflectance‐absorptance characteristics of those polymers used in the ignition testing. Reflectance values were obtained over the wavelength of 0.3 to 2.5 microns using a double‐beam Cary model 14 spectrophotometer with an integrating sphere reflectometer and over the wavelengths of 1.0 to 10.0 microns using a Gier‐Dunkle Hohlraum with a Perkin‐Elmer spectrophotometer. Absorptance values were obtained by means of Kirchoff's Law,Drawings and graphs are included which illustrate the test apparatus and type of data collected. A table of average absorptances of several polymers are given and listed according to the particular type of heat source used.\documentclass{article}\pagestyle{empty}\begin{document}$$ \alpha _\lambda + r_\lambda = 1 $$\end{document}Average absorptances of the polymers over the monochromatic wavelength span of the heat sources were calculated using the equation\documentclass{article}\pagestyle{empty}\begin{document}$$ \alpha _{{\rm av}} = \frac{{\int_{\lambda _1 }^{\lambda _2 } {\alpha _\lambda e_\lambda d\lambda } }}{{\int_{\lambda _1 }^{\lambda _2 } {e_\lambda {\rm d}\lambda}}} $$\end{document}Mathematical analyses were developed and are presented for both the integrating sphere reflectometer and Gier‐Dunkle Hohlraum unit.Drawings and graphs are included which illustrate the test apparatus and type of data collected. A table of average absorptances of several polymers are given and listed according to the particular type of heat

ISSN:0032-3888    

DOI:10.1002/pen.760141010

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractIt was found after heating that the thermal expansion of polyurethane decreased markedly in several hundred hours at constant temperature; after cooling the thermal contraction decreased with time but more slowly. The role of cross‐linking as a possible cause of this effect is discussed. Creep during the expanded phase after heating is shown to be much greater than creep after thermal expansion has stabilized at the same temperature. Experiments are described which suggest that the effect of temperature on creep results primarily from thermal expansion rather than from thermal oscillatio

ISSN:0032-3888    

DOI:10.1002/pen.760141011

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY