Rainflow Counting Based Block Cycle Development for Fatigue Analysis using Nonlinear Stress Approach 2013-01-1206

An accurate representation of proving ground loading is essential for nonlinear Finite Element analysis and component fatigue test. In this paper, a rainflow counting based multiple blocks loading development procedure is described. The procedure includes: (1) Rainflow counting analysis to obtain the relationship between load range and cumulative repeats and the statistical relationship between load range and mean load; (2) Formation of preliminary multiple loading blocks with specified load range, mean load, and the approximate cycle repeats, and construction of the preliminary multiple loading blocks; (3) Calibration and finalization of the repeats for preliminary multiple loading blocks according to the equivalent damage rule, meaning that the damage value due to the block loads is equivalent to that from a PG loading. The multiple loading blocks simplifies the original PG loading into several typical load cases, which could be conveniently implemented in nonlinear stress approach based fatigue life estimations.

An example study is made on a tie-down hook joint in a pickup truck cargo box. Several typical tie-down load cases are obtained after block cycle extraction. These blocking loads are then exploited to conduct the nonlinear analysis on a local joint assembly model, which includes contact interference and nonlinear material property. Fatigue lives are estimated based on nonlinear stresses/strains using linear damage accumulation rule.