Random Vibration Fatigue Analysis with LS-DYNA

Fatigue damage assessment for components under random cyclic loading is an important concern in engineering. A new feature of random vibration fatigue analysis has been implemented to LS-DYNA, to perform the structural fatigue analysis in a random vibration environment. This feature computes cumulative damage ratio and expected fatigue life for structures, based on the Palmgren-Miner’s rule of cumulative damage ratio and material’s S-N fatigue curve. A series of fatigue analysis methods have been implemented. They include the Steinberg’s three band method, Dirlik method, Narrow band method, Wirsching method, Chaudhury and Dover method, Tunna method and Hancock method. Brief introduction of the analysis methods is provided. To facilitate post-processing of the fatigue analysis, a new binary plot file d3ftg has been implemented in LS-DYNA. This binary plot file provides fatigue analysis information including cumulative damage ratio, expected life, zero- crossing frequency, peak-crossing frequency and irregularity factor for the structure, based on the stress index adopted in the analysis and the load period. This file is accessible to LS-PREPOST. Several examples are given to demonstrate the effectiveness of the random vibration fatigue analysis feature with LS-DYNA. Some preliminary discussions on the different fatigue analysis methods are included.