Fatigue Crack Growth Measurement Based on Changes in Transverse Natural Frequency

A method to estimate fatigue crack extension in three point bend (TPB) testing based on changes in transverse natural frequency is presented. The theoretical formulation for the transverse free vibration of the specimen is given to relate natural frequency to the specimen dimensions and crack size employing the Timoshenko beam theory and representing crack as a rotational spring. Experimental studies are presented considering three steels, viz. SA333, 20Mn and En47, to demonstrate the accuracy of the proposed method and compare it with the conventional compliance method. The results clearly indicate that the vibration method can be an alternative to the compliance method. The Paris law constants for the materials are presented.