Quantitative Analysis of Fatigue Fracture Surface by X-Ray Fractography

Abstract

A new method was developed for the quantitative X-ray fractographic analysis of fatigue fracture surface. The method was basically assumed that the residual stress under the fracture surface could be adjusted on one master curve in a plot of dimensionless residual stress, σ(Y)/σ_Y, against a dimensionless depth, Y/ω_p, where σ_Y is the yield stress of the material and ω_p is the depth of the plastic zone which is produced under the applied maximum stress intensity factor, K_max. The experimental data for three steels of SM50A, HT80, SNCM815 were analysed in order to obtain such master curves. The residual stress was found to be adjusted perfectly on one master curve in SM50A, while it was found to be adjusted in a limitd range of the stress ratio, probably due to the cyclic softening effect, both in HT80 and SNCM815. The value of K_max could be estimated succcesfully in the present method by using the multiple values of the residual stress at different depths, although it could be estimated in principle by a single value at a certain depth.