Challenges in accelerated life testing

Accelerated testing typically targets-life estimation and defect or design weakness identification. The intent is to obtain more information from a given test time than would normally be possible. Time compression is typically achieved by acceleration of single or combination of stresses- temperature, vibration, humidity, etc. Short product development schedule, time-to-market requirements and the development timeline often dictate a fixed time under test. In a test-to-fixed life approach, given number of the product are tested to a fixed life, with zero failures allowed. The test demonstrates the product´s minimum reliability, while allowing for a fixed time to conduct testing. In absence of life-test information, the challenge is to decipher if the product may be over-designed or marginally designed. Failure mechanisms and modes observed in accelerated test may not be observed in field life. Accelerated tests such as thermal shock from -55 to 125°C may stress the material beyond the equipment operating range, such as above glass transition temperature, where material properties may be significantly different. In general, failure mechanisms may be accelerated by a various forms of temperature stresses including temperature cycle, time dependent temperature change and spatial gradient of temperature or non-temperature stresses including humidity, shock and vibration. Variability of field use conditions often make the task of developing correlations more difficult.