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

Abstract

The method of fatigue life prediction is presented for structures which suffer from flow-induced vibration. A small wind tunnel was made and used to reproduce fatigue failure by flow-induced vibration. A medium carbon steel specimen attached to a larger styrofoam cylinder was fixed to the experimental equipment. A small artificial hole was introduced onto the specimen surface. Fatigue crack initiated from the artificial hole. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) developed in another project of the authors' team was used to acquire the service strain histogram at a critical point of the specimen and to measure the variation of natural frequency. Fatigue damage D defined by the Modified Miner Rule was calculated by using the strain histogram at the initial stage of the operation of the wind turbine. The values of D were all smaller than 1.0 and ranged approximately from 0.2 to 0.8. The reason for small values of D is explained from the behaviour of small crack growth.