ENGINEERING APPROACH FOR CUMULATIVE DAMAGE IN METALS UNDER CREEP LOADING

A concept of cumulative damage is developed for an evaluation of the damage incurred under creep loading at high temperature. The damage is essentially stress-dependent and is a non-linear function of the exposure time. The development results in equations which permit the determination of the creep-rupture curve under loading with constant stress as well as the evaluation of the remaining life under loading with several stress levels. The order effect of creep loading is taken into consideration. The theoretical sum of time-ratios is greater than unity for two decreasing stresses; the reverse is obtained for two increasing levels. This trend is in agreement with observations obtained in cumulative creep damage tests. The correlation between the proposed relations and some available experimental data is discussed. © 1979 by ASME.