Comparison between continuous and periodic inspections in step-stress tests

Accelerated life test is currently the main method of assessing product reliability rapidly, and the design of efficient test plans is a critical step to ensure that accelerated life tests can assess the product reliability accurately, quickly and economically. In these tests, the samples are tested at stress levels higher than normal. Then, the product life at the normal stress level can be estimated by extrapolating the life information of samples at high stress levels to the normal level based on the stress-life relationship. In this paper, optimal k-level step-stress accelerated life tests are considered for the Weibull failure data under progressive Type-I censoring. There are two strategies for performance inspection of the test unit, which include continuous inspection and periodic inspection. These two strategies generate the life data and group data, respectively. In this paper, these two inspection modes are compared and the efficiencies of these are obtained. This paper investigates the optimal design based on five optimality criteria under the constraint that the total experimental cost does not exceed a pre-specified budget. Finally, based on the simulation study and a real data set, the advantages of using the continuous inspection relative to periodic inspection are investigated.