Service Load Histories Analyzed by the Local Strain Approach
by
Thomas F. Fugger, Jr.
Departments of Theoretical and Applied Mechanics
Abstract
Design of ground vehicle components has become increasingly dependent on the ability to predict the service fatigue life accurately. The local strain approach is one fatigue design method which has been employed to predict fatigue life of a component subject to service conditions.
Evaluation of the accuracy of the local strain approach and the influence of mean stresses was achieved in the present study by analyzing the behavior of smooth specimens subjected to three service strain histories. These histories were used to obtain the corresponding block stress history and number of blocks to failure. Stress response was analytically predicted to allow comparison to the actual recorded stress response. Predicted and actual mean stresses were incorporated into the analysis to investigate the sensitivity of the local strain approach to mean stresses.
Mean stresses determined from the predicted stress response were found to be nonconservative with regard to the damage calculation when compared to the actual stress response. Predicted fatigue lives incorporating either measured or predicted mean stresses were found to be within a factor of two of the experimental data. Lives obtained by ignoring mean stresses were up to a factor of three higher in comparison to the mean stress correction values.
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