LOAD SEQUENCE ANALYSIS IN FATIGUE LIFE PREDICTION

Abstract

In this work, the load sequence effect is analyzed in fatigue test. One of the assumptions of the Miner’s rule is that the total damage is equal to the sum of the damages absorbed; however, different models have been proposed to take the effect of the load sequences under two load levels into account. To analyze this effect, a case study of a rear axle mounting bracket has been performed, analyzing six different sequences of three load levels, defined as Low, Medium and High. A Finite Element Analysis was also performed using MSC Tools. With these results and a series of test at constant amplitude, the component S-N curve was made. 24 tests at room temperature were performed in order to evaluate the damage process. It was found that, under a block of three load levels, the sequence of each block has an effect in the total amount of damage under the same number of cycles. With this information it is possible to improve the life prediction through the modification of the damage rule. The proposed model uses a factor which depends on the ultimate strength and yield point. This is an advantage over other approaches, as the other models need additional dynamic tests to obtain coefficients to perform the life prediction.