Fatigue failure in random vibration and accelerated testing

Accelerated testing involves testing a product at a level higher than the normal usage level. This is important because test time and expenditure for testing can be greatly reduced by accelerated testing. This study involves aluminum beams (bare as well as coated with sprayable damping material) subjected to random vibration. Since most materials fail in fatigue and because accelerated testing is becoming more important due to economic considerations, this paper addresses applicability of various theories for estimation of time failure in normal usage and accelerated condition. Another issue addressed was whether application of damping material makes any difference because many automotive and aerospace applications involve damped materials. Experimentally observed failure time in random vibration for both bare and damped beams under random vibration are compared with various fatigue failure theories. Next the exponent for accelerated testing isobtained for bare and damped beams. This exponent has been studied in terms of both G(2)/Hz and Grms. Even though different failure theories predicted different failure times, the exponent correlated with all theories for undamped beams and in general with Dirlik theory for damped beams.