Research on the Crack Initiation in Precision Cropping Based on Energy Release Rate Theory

Abstract

In the low-stress precision technology, the initiation of crack at the V-shaped notch tip is a complicated process. It is of great significance to improve the quality of the bar cross-section through obtaining the conditions that influence the initiation angle and the critical loading force of the bar. Due to the complexity of the force at V-shaped notch tip, the parameter model of the V-shaped notch tip is established and the stress field of the composite crack is analyzed, thus obtaining the stress component formula of the V-notch tip. The energy release rate theory is used to calculate the crack initiation angle and the critical loading force in the low-stress cropping. The formula for calculating the energy release rate at the maximum initiation angle is established. The calculated results show that when the critical loading force is 1500N, the micro-cracks at the V-shaped notch tip first occur at the initiation angle of 20.28°, and the corresponding energy release rate is 7.539×104Pa.m2. The radial blanking fatigue experiments also prove that when the critical loading force was 1500N, the bifurcate micro-cracks are generated at the tip of V-shaped notch.