Time Dependence of Mechanical Breakdown Phenomena

A phenomenological theory of the time dependence of mechanical breakdown phenomena is presented which is applicable to creep failure of oriented polymeric filaments under tensile stresses. In using the theory, one makes assumptions about the distribution of breaking times in ensembles of filaments which are bearing constant loads and then proceeds to calculate the distribution of lifetimes under other stress histories, e.g., loads increasing linearly with time and sinusoidal loads. The a priori assumptions used here permit a calculation of the dependence of observed tensile strengths on both the sample size and the rate of loading. Experiments involving drawn 66 nylon monofilament yarn are cited to illustrate how the parameters which describe the average lifetime under dead load behavior of a yarn may be used to calculate its tensile strength distribution when measured with a constant rate of loading apparatus.