Accelerated Life Tests versus Design Limit Screens – An Effort Towards Disambiguation

Bhanu Sood

There are two broad categories of tests of engineered products that are used for assessment of reliability of products. The first category is accelerated tests where a sample of products is stressed beyond its specification limits during product development (Design Limit Test) and second category is are used to guard against supplier and manufacturing process variations and remove resulting defects from such variations (Screening). Of these two techniques, screening involves a 100% sampling. There is confusion in the industry regarding the use and applicability of the data generated by the HALT, ESS and HASS tests and how to apply this data in reliability assessment. One common misconception is that if a product passes these tests without failure that would mean that the product is reliable in its application. Another misconception is that one can use the test results from a high accelerated test such as HALT to assess the reliability of the product in field. There is need for theoretical and empirical assessment to show the right use of these tests along with critical review of the value and effectiveness of the tests.