Irregular Time-Varying Stress Degradation Path Modeling: a Case Study on Lithium-ion Cell Degradation

The aim of this paper is to investigate the issue of degradation modeling and reliability assessment for products under irregular time-varying stresses. Conventional degradation models have been extensively used in the relevant literature to characterize degradation processes under deterministic stresses. However, the time-varying stress, which may affect degradation processes, widely exists in field conditions. This paper extends the general degradation-path model by considering the effects of time-varying stresses. The new degradation-path model captures influences of varying stresses on performance characteristics. A nonlinear least square method is used to estimate the unknown parameters of the proposed model. A bootstrap algorithm is adopted for computing the confidence intervals of the mean time to failure and percentiles of the failure-time distribution. Finally, a case study of lithium-ion cells is presented to validate the proposed method. Copyright (C) 2015 John Wiley & Sons, Ltd.