Fatigue Failure by Flow-Induced Vibration (Effect of Initial Defect Size on Cumulative Fatigue Damage)

Abstract

A fatigue life prediction method is presented based upon the data obtained due to flow-induced vibration. In the experimental program a small wind tunnel was used to produce flow-induced vibrations of a Styrofoam cylinder. These vibration was transmitted to an attached fatigue specimen. The specimen was made of a medium carbon steel with a small hole drilled into its surface to simulate a defect and to localize the fatigue crack propagation process. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) was used to acquire the service strain histogram and also to measure the variation of natural frequency. Fatigue damage, D, was defined by the Modified Miner's Rule and was determined by using the strain histogram of the early portion of the test record. The values of D were all smaller than 1.0 and ranged from 0.2 to 0.8. The effect of the size of the simulated defect on the values of D was clarified by focusing on the relationship between small crack growth behavior and the strain histogram.