Consistency analysis of degradation mechanism in step-stress accelerated degradation testing

Due to the strong market competition, many newly developed products are highly reliable and long-lifetime, such as light emitting diodes and silicone rubber seals. For these highly reliable products, it turns out to be impractical to make the reliability assessment within a feasible life testing time. Accelerated life testing (ALT) and accelerated degradation testing (ADT) have been widely used in industry to solve this problem. Hirose [11] used the ALT data to estimate the lifetime of insulation film at the normal stress. Cary [5] applied the ADT to the reliability evaluation of an integrated logic family. Tang [22] described the procedure for the reliability prediction of power supplies by nondestructive ADT data. Wang [25, 26] made a research on the lifetime prediction of self-lubricating spherical plain bearings based on the ADT, and he provided an optimal design of the test plan. In an ALT and ADT, the failure times and performance degradation data of samples at accelerated stress levels are recorded respectively. When the failure mechanism for an ALT and the degradation mechanism for an ADT are consistent at all stress levels, the accelerated test results can be extrapolated to estimate the product lifetime at the normal condition. In terms of the sample size and the amount of test time needed, SSADT is more efficient than other accelerated tests. Many reliability analysts recently employ the SSADT to assess the lifetime distribution of highly reliable products. Tseng et al. [23] presented an optimal test plan for the SSADT of carbon-film-resistors, and they performed a sensitivity analysis for the test plan. Cai and Liao [4, 15] established a SSADT model and a test plan for the degradation of light emitting diodes. In order to obtain an accurate lifetime prediction, the design of the test plan should guarantee the failure mechanism and degradation mechanism keep unchanged at all accelerated stress levels. But these researchers mainly focused on the exact statistical inference of test data. They guaranteed the consistent degradation mechanism based on the empirical assumption and standard specifications. Xiang Lu Xun Chen Yashun WAng Yuanyuan TAn