Fatigue in Textile Fibers

Abstract

Creep measurements during fatiguing by cyclic tension have been made on an acrylic fiber and two types of Dacron,² at various strokes and frequencies. The curves for creep extension vs fatiguing time in cycles for the acrylic sample were found to be concave downward, whereas those for the Dacron fibers are concave upward, suggesting basic differences in the original structures and the structural changes occurring during fatiguing. The results indicate that there exists an inverse relationship between the number of cycles to failure and the minimum creep rate in the case of acrylic fibers. Creep extension at break, in a number of fiber samples, was found to decrease as the average lifetime increases as a rsult of reductions in stroke, and also, in the acrylic sample, as a result of increases in cyclic frequency. Simultaneous measurements of creep and force in a number of samples indicate that most of the changes in the geometry and dynamic properties of the fiber specimens occur in a very short initial interval of the fatiguing period. These data are taken to indicate that creep is only an accon ni ment of fatiguing by cyclic tension, and not the immediate cause of final rupture, which is believed to be the result of crack propagation.