Degradation Analysis in Step-Stress Accelerated Testing

Step-stress testing is a very common type of accelerated testing. It is a good way to obtain failures in a relatively short amount of time. There are many variations of step-stress testing. A common type is one in which the units are tested at a given stress level for a certain amount of time. At the end of that time, if there are units surviving, the stress level is increased and held for another amount of time. The data that result from such tests can be analyzed using the cumulative damage model, which computes the degradation (damage accumulated through time and through the increase of stress), in ReliaSoft's ALTA software. Click here for more information about this type of step-stress testing.

Alternatively, there are step-stress tests in which the degradation or performance data that can be directly related to the presumed failure of the product in question are monitored over the duration of the test. This test is essentially a degradation test in time-varying conditions. In this case, the "cumulative damage" (degradation) is measured over time and there is no need to use the complex cumulative damage model to estimate the reliability of the product. This article suggests an approach for using Weibull++ to estimate reliability from degradation data of a product tested using step-stress accelerated testing.

Reliability Growth Test Planning and Management
An effective reliability growth test planning and management strategy can contribute greatly to successful product design and development through its impact on the ability of the design/development team to meet desired reliability goals on time and within the project budget. An effective reliability growth management program both produces and utilizes important information about the reliability of the product design, such as the demonstrated MTBF through testing, the growth in MTBF that has been achieved through implementation of corrective actions, the maximum potential MTBF that can likely be achieved for the product design and estimates regarding latent failure modes that have not yet been uncovered through testing. 

This article presents a brief conceptual overview of a reliability growth test planning/management strategy and data analysis methodology that provide information that can be instrumental to various management decisions for product design/development. Dr. Larry H. Crow, a leading practitioner in the field of Reliability Growth Analysis for over 30 years, developed the approach described in this article and has cooperated with design/development teams in both the military and the private sector to implement, validate and refine the relevant techniques. This article has been written with cooperation from Dr. Crow based on his lectures on the subject and published standards for reliability growth analysis.