Simplified Estimation Equations of J-Integral for Surface Crack Under Bending Loads.

Abstract

This paper presents the simplified estimation equations of J-integral at the surface and maximum depth point of a surface crack. These equations are based on finite element analysis with the surface cracked large plate specimen. The equations are expressed as the functions of crack length, crack depth, plate thickness and plate width for bending loads. The J-integral equations are used to develop the analysis given by finite element method for semielliptical surface cracks in finite elastic plastic plate subjected to bending loads. A wide range of configuration parameters was included in the equations. The ratios of crack depth to crack length ranged from 0 to 1 and the ratios of crack depth to plate thickness ranged from 0 to 0.75. The effects of plate width on the J-integral variations along the crack front were also included. Comparing the values of J-integral computed by the equations with those from the finite element analysis, the mean errors are within ±2.6 percent. The equations were used to predict patterns of surface crack propagation under bending fatigue loads for a SUS304 steel at 550°C. The curves of crack length, crack depth vs number of cycles predicted by the equations describe the experimental data well.