Fatigue life of a rocker arm using Calibrated accelerated Life Test Approach

Nagaraju Soma, Ranjith Sr, Pravin Kadekodi Center for Reliability Maintainability Safety, Eaton India Innovation Center, Pune, India somanagaraju@eaton.com Abstract Fatigue life estimation of mechanical components with a complex geometry is generally carried out using statistical methods. The commonly used approach in the industry is the staircase method using ISO12107. Staircase approach requires fifteen samples for exploratory testing to build the S-N Curve, eight of these being used to estimate the S-N curve in the finite fatigue life range (inclined line) and seven for the fatigue strength at the infinite life regime (horizontal line). In this paper staircase approach is compared with another approach to predict the fatigue life of an engine valve train ‘rocker arm’, calibrated accelerated life test (CALT) is discussed, which is very effective in predicting fatigue life, and reduce the test time significantly and quantifying reliability. The CALT test is performed with 3 samples at each of 3 different stress levels till failure, and the expected life time at the normal stress is estimated based on all the test results. The fatigue life prediction of rocker arm is compared with the conventional staircase approach. The comparison of the test results of both approaches shows that the CALT method shows similar results for fatigue life prediction in a shorter test time. This approach not only reduces the test time but also reduces the carbon foot print in using the test resources.