Fundamental Studies on Tensile Fracture and Compressive Fracture of Solid Polymers at Low Temperatures

Abstract

The effect of deep freezing on the fracture behaviors of solid polymers has been investigated experimentally as a fundamental study of industrial cryogenic crushing operation. The apparatus used is shown in Fig. 1, which consists of an universal testing machine and a cryogenic thermostat with liquid nitrogen.
As the temperature drops below the ductile-brittle fracture transition temperature T_c, the material becomes brittle and fracture takes place in the elastic range after a very small elastic deformation (Fig. 3).
At higher temperatures T>T_c, the material stretches elastically until the yield stress is reached, whereupon the nominal stress decreases quite rapidly to a lower value with the appearance of a neck. The strain produced increases with temperature (Fig. 4).
The homologous true breaking stress σ_B/σ_Bc, the reciprocal homologous breaking strain ε_Bc/ε_B, the homologous longitudinal elastic modulus E/E_c, the homologous crushing initiation index CII/CII_c, and the homologous crushing extension index CEI/CEI_c increase with the reciprocal homologous absolute temperature T_c/T as given by Eqs. (5)∼(17) (Figs. 7∼16). The values of T_c, σ_Bc, ε_Bc, CII_c and CEI_c at the ductile-brittle fracture transition temperature are the material-constants.
The true tensile stress-strain curves and the tensile load-elongation curves for solid polymers at several temperature levels are shown in Figs. 9 and 10.