The effect of internal temperature rise on the tensile behavior of polymeric materials at subambient temperatures

Abstract

synopsisThe tensile properties of nylon, Dacron, and Nomex yarn are given a t liquid helium temperatures, -450"F, and at two strain rates, 1.67 and 3000%/sec. The data are compared to similar results obtained at -320°, -109O, and 70°F. A theoretical analysis of the thermodynamics of straining under both isothermal and adiabatic conditions is presented, and theoretical maximum temperature rises occurring within both adiabatically and isothermally strained yarns are given for a range of subambient test temperatures. The initial modulus of the yarns increases, the tenacity increases, and the breaking elongation decreases with decreasing temperature a t the lower rate of straining. However, at the higher rate of straining, although the initial modulus of the yarns a t -450'F is considerably greater than the modulus a t -320"F, the nylon yarn shows a lower breaking load and greater breaking elongation a t -450°F than at -320°F. The Dacron follows the expected trend with the breaking load higher and the breaking elongation smaller a t -450°F than a t -320'F.The Nomex has a lower breaking load, but its breaking elongation is also lower a t -450°F than a t -320°F. The calculated yarn internal temperature rises are sufficient to explain these differences in the stressstrain behavior of the yarns.