摘要:

Sheets of oriented low-density polyethylene possessing transverse symmetry were prepared by simple tensile drawing at room temperature. The degree of anisotropy was varied by varying the draw ratio. Classic elasticity theory shows that five constants are necessary to characterize the deformation behavior of an elastic material possessing such symmetry. The time-dependent equivalents of these constants have been determined from the simultaneous measurement of longitudinal and lateral strain during tensile creep of specimens cut at 0, 45, and 90 deg to the draw direction. Special creep apparatus, able to handle small, flexible specimens, was developed for this study. The shear compliance obtained from the tensile creep studies was in good agreement with the value obtained from torsional creep measurements on a 0-deg specimen, for the entire range of draw ratios. The contraction measurements have been used to provide additional evidence for deformation mechanisms suggested by the longitudinal strain measurements and, when combined with tensile measurements, have allowed the volume changes occurring during tensile creep to be calculated.

ISSN:0022-2348    

DOI:10.1080/00222347108212529

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The influence of secondary low-temperature dispersions on the storage and loss compliances of four poly(β-hydroxyethyl methacry-late) solutions in diethylene glycol was studied by comparing previously published double-transducer data with isochronal torsion pendulum data measured starting from the temperature of liquid nitrogen. It was found that the contribution of the main transition as observed in the storage compliance J'pdecreased with increasing swelling degree of the samples. For a sample swollen to volume fraction of polymer v2= 0.168, log Jp changes only about one decade, from −6 to −7; the further decrease of log J′pfrom −7 to −10.5 corresponds to the secondary low-temperature dispersion characteristic for polar side chains—polar diluent systems. For the latter dispersion the Arrhenius plot obtained using the double-transducer data gave δH = 24 kcal/mole. It was concluded that in some special cases the role of low-temperature secondary dispersions can be of primary importance in influencing the changes of storage and loss compliance. The contribution of the secondary β relaxation (as shown in earlier work on methacrylate polymers) and the influence of the low-temperature dispersion arising in polymethacrylate-diluent systems (β(SW)dispersion) studied in this paper were distinguished.

ISSN:0022-2348    

DOI:10.1080/00222347108212530

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The complex dielectric constant of natural rubber samples cross-linked by sulfur and dicumyl peroxide has been measured over a frequency range from 1.5 to 3.0 × 105cps by the bridge method and from 3.0 to 1.0 × 104cps by the relaxation method. Two dispersion peaks were detected which lay in the measured frequency range at temperatures above the main dispersion zone. Temperature and cross-link density-dependent shift of these peaks were studied and compared with the results obtained by Ferry et al. from complex compliance measurements performed on analogous systems.

ISSN:0022-2348    

DOI:10.1080/00222347108212531

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

For studies of the low-frequency viscoelastic behavior in the rubberlike plateau zone of lightly cross-linked networks, an apparatus based on forced vibrations was developed, working over the frequency range from 2.5 × 10−4to 1 cps. Sandwich-type samples were used, the stress imposed on the samples varied sinusoidally, both stress and strain were registered using an X-Y recorder, and the components of the complex compliance were calculated using a computer from the recorded ellipse. Log J′ ≥ −8 can be measured over the temperature range from −50° to +200°C.

ISSN:0022-2348    

DOI:10.1080/00222347108212532

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The description and analysis of the deformational behavior of material bodies has been a great challenge to scientists interested in this area of studies for many years. This is particularly true in the case of polymeric systems. Under loading a polymer in general exhibits a complex behavior involving deformational characteristics including plastic deformation. The following presentation is an attempt to formulate a constitutive equation to cover this type of behavior with special emphasis on large deformation.

ISSN:0022-2348    

DOI:10.1080/00222347108212533

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

This paper proposes that physically cross-linked amorphous polymer networks can successfully be treated a s reinforced composite solids. The suggested model is based on observations in three different areas of investigation: on the composite solid approach of oriented polymers, on the time-dependent fracture strength of polymer networks, and on the kinetics of chain breakage (free radical formation) in stressed polymers as observed by electron spin resonance (ESR).

ISSN:0022-2348    

DOI:10.1080/00222347108212534

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The influence of elevated temperature on the fatigue behavior of poly-6-caprolactam has been studied. The fatigue behavior is influenced by internal damping. Wohler's curves measured at elevated temperatures correspond to the conditions of kinetic fluctuation theory. If the specimen is fatigued at low stresses and at temperatures lying sufficiently below the glass transition temperature of the amorphous phase of this polymer, the mechanism of fatigue fracture is different from that at elevated temperatures. The apparent activation energy of fatigue failure at temperatures higher than Tgwas calculated. If the specimen is fatigued at elevated temperatures and its lifetime is long enough the monoclinic α-form crystal lattice of the crystalline portion is transformed to the hexagonal γ form.

ISSN:0022-2348    

DOI:10.1080/00222347108212535

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The effect of flaws on the ultimate behavior of poly (β-hydroxyethyl methacrylate) swollen with water to equilibrium has been examined experimentally, by using test pieces containing model defects. For both the defect-free samples and samples with macrodefects the experimental dependences of the time to break on stress have been obtained at various temperatures. The curves corresponding to different temperatures are approximately parallel to each other, the temperature dependence of shift factors obeys the Williams-Landel-Ferry equation. The presence of macrodefects in the test pieces accounts for the change in shape of the time-to-break curves and influences distinctly the value of the characteristic temperature Ts determined from the temperature dependence of the shift factors. This effect has been ascribed to the high orientation in the roots of the macroscopic defects.

ISSN:0022-2348    

DOI:10.1080/00222347108212536

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

For more than a dozen years quite a number of scientists have centered their attention in devising proper representations of material systems by constructing sophisticated constitutive equations. From the use of rheological models to the application of rational mechanics many theories have been published in the literature. However, attempts in incorporating the generally accepted, microscopic, kinetic behavior of the material constituents in the constitutive equation have been lacking. It is toward this end that in this brief report a simple continuum representation of systems involving certain physical phenomena in the microstructure is described.

ISSN:0022-2348    

DOI:10.1080/00222347108212537

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The stress-cracking resistance of thermoplastics can be determined by means of the Oversize Ball Test (DIN 53 449). Figures for critical strain are obtained, which if exceeded cause stress-cracking. They provide a means of assessing the stress-cracking resistance of oriented polystyrenes. It has been found that not only the degree of orientation but also the rate of initiation of the stress-cracking influence the critical strain. The report concludes with further examples of the Oversize Ball Test with polycarbonate, polymethyl methacrylate, and polyethylene.

ISSN:0022-2348    

DOI:10.1080/00222347108212538

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor