On the Fatigue Damage Estimation in Multi-axis and Single-Axis Vibration Testing

Random vibration testing is one of the most frequently employed procedures to ensure the durability of a component in operational conditions. Random vibration tests are commonly performed by means of single-axis tests. In particular, it is common practice to test the component multiple times, changing the loading direction. However, real working environments present, in general, multi-axis vibration, and single-axis loads are often incapable of reproducing the response of a component subjected to multi-axis vibration. In this work, the effects of sequential single-axis and multi-axis vibration are compared in terms of fatigue damage. A test campaign has been carried out, exploiting the triaxial shaker system available at the University of Ferrara. In particular, a specifically designed specimen has been tested until failure in different configurations under sequential single-axis and multi-axis uncorrelated vibration. The objective of the test campaign is to quantify the difference in terms of time to failure of the specimen when its dynamic behavior is activated differently. The tests performed with multi-axis vibration resulted always in a significant reduction of the time to failure, compared to sequential single-axis testing. Moreover, it has been found that the S–N curve of the specimen is heavily affected by the activation of the specimen dynamics, resulting in a different fatigue damage accumulation. Finally, the time to failure and the S–N curve of the specimen are used to define a correction factor that quantify the damage inflicted to the specimen by the multi-axis vibration, compared to sequential single-axis testing. The correction factor takes into account the different activation of the specimen dynamics, and it is capable of accurately estimating the time to failure of the specimen under multi-axis loading.