Journal ArticleDOI
Effects of the state of stress on the toughness of polycarbonate
TLDR
In this paper, it was shown that the mechanical properties of polycarbonate are controlled by the state of stress of the test specimen and that the tendency of the material to microcavitate is strongly dependent on the residual stresses in the surfaces of a test specimen.Abstract:
It is shown that the mechanical properties of polycarbonate are controlled by the state of stress of the test specimen. Whereas the yield stress of the material is relatively insensitive to the state of stress, the tendency of the material to microcavitate is strongly dependent on the residual stresses in the surfaces of a test specimen. The effects of quenching, annealing, post notching, solvent swelling and rate of testing on the modulus of toughness are all related to the state of compression on the free surfaces. The mechanism of deformation is shown by cinematography to consist of the nucleation of a shear band followed by microcavitation along the propagating band. Maximum toughness is obtained by suppressing microcavitation so as to promote shear yielding. When microcavitation occurs, it is the competition between propagating the microcavitation throughout the material and the generation of microcracks in the advancing shear band that controls the ultimate elongation.read more
Citations
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Journal ArticleDOI
Microstructure, elastic properties and deformation mechanisms of horn keratin.
TL;DR: The structure and mechanical properties of the horns from a desert bighorn sheep, Ovis canadensis, were examined and microscopy of fractured samples revealed several toughening mechanisms: delamination and ligament bridging in bending anddelamination and microbuckling of the lamellae in compression.
Journal ArticleDOI
The effect of physical ageing on the properties of poly(ethylene terephthalate)
TL;DR: Physical ageing of polyethylene terephthalate (PET) is associated with the conventional glass formation process, which occurs at a more rapid rate at higher temperatures as mentioned in this paper, and is accompanied by a marked change in mechanical properties, increased tensile yield stress and drawing stress, more localized yielding of the polymer and a marked decrease in impact strength.
Journal ArticleDOI
Physical factors affecting the impact strength of polycarbonate
TL;DR: In this paper, the effects due to internal stress, physical ageing and thickness have been separated, and it is shown that each of these variables can cause a change from tough to brittle fracture.
Journal ArticleDOI
Macroscopic, microscopic and molecular aspects of fracture in polymers
K. L. Devries,L. E. Hornberger +1 more
TL;DR: In this paper, the combined effects of stress and environmental agents on mechanical strength of nylon, polyethylene, and Kevlar fibers were measured, in conjunction with investigations of bond rupture kinetics, suggest that fracture in these materials involves thermally activated chain scission in which the activation energy is aided by stress and the chemical environment.
Journal ArticleDOI
Hot water aging of polycarbonate
TL;DR: In this article, internal cracking and microvoids are shown to form during room temperature storage of polycarbonate samples that have previously been exposed to boiling water, these microcracks are actually disc-shaped pockets filled with water.
References
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Journal ArticleDOI
Crazing, yielding, and fracture of polymers. I. Ductile brittle transition in polycarbonate
TL;DR: In this article, the authors evaluated the ductile brittle transition in terms of σG (the stress required to propagate the Griffith flaw), and σy, the yield stress for the polymer.
Journal ArticleDOI
The effect of thermal pretreatment on the strength of polycarbonate
TL;DR: In this paper, the effect of preheat treatment at temperatures below the glass transition for various periods of time on selected properties of molded polycarbonate has been studied and changes in tensile and flexural strength as functions of time and preheat temperature (80 −140°C).
Journal ArticleDOI
Residual stresses in polymers and their effect on mechanical behavior
Paul So,L. J. Broutman +1 more
TL;DR: In this article, it was shown that compressive residual stresses at the surface can cause plastic yielding to occur in bending experiments resulting in permanent deformation and greater energy absorption, and that these residual stresses can influence the notched Izod impact strengths for polycarbonates.