Experimental Study on the Caustics of Moving Cracks and Elliptical Curvature under Impact Loading

Haohao Luo,Chengxiao Li,Guoliang Yang,Yanbing Wang,Yuantong Zhang,Renshu Yang,Chen An

doi:10.1155/2021/5524635

Abstract

A dynamic caustics test system was used, and different moving cracks were analysed to study the interaction between the crack growth rate, stress intensity factor, and curvature of the elliptical end of a moving crack under impact loading. Based on the linear elastic fracture mechanics theory, linearly fitting of the crack tip stress intensity factor and the elliptical curvature were employed to obtain the specific functional expressions. ABAQUS software was used to numerically simulate the moving crack fracture process passing through different elliptical curvatures. The crack tip stress intensity factor was calculated by the stress extrapolation method. The stress intensity factor obtained from the numerical calculation and the caustics test was consistent. The test and numerical simulation results showed that the direction of moving cracks entering and passing through the elliptical defects shows a certain regularity. As the ellipse curvature increased, the moving crack stress intensity factor passing through the ellipse gradually decreased, and the moving crack also passed easily through oval defects.

Highlights

During rock excavation, rock masses with joints, cracks, holes, and other defects are often encountered
Zhenhai Zhu [3] used a dynamic photoelastic test to observe the dynamic interaction between the explosion stress wave and the static radial crack produced by an explosion as well as the interaction between the reflected wave from the free boundary and the expanding crack
Camas et al [5] carried out three-dimensional modelling of CT aluminium samples considering the three combinations of different load levels, specimen thicknesses, and crack end curvatures and showed that the plastic zone range depended on the applied load, the specimen thickness, and the crack curvature

Summary

Introduction

Rock masses with joints, cracks, holes, and other defects are often encountered. Renshu Yang et al [1] studied a polymethyl methacrylate (PMMA) directional fracture blasting test with defects and showed that, with increasing curvature on both sides of the specimen defect, the main crack peak propagation velocity and the peak dynamic stress intensity factor (SIF) gradually decreased. Wenfeng Hao et al [14] conducted a dynamic caustics test using fibre bundles of different thicknesses and showed that the fibre bundle shielded the stress intensity factor and crack propagation speed at the crack tip. Chenxi Ding et al found that, as the notch curvature decreases, both the peak value of the dynamic stress intensity factor and the corresponding peak value of the propagation velocity of the crack tip increase significantly after the initiation [22]. The dynamic caustics test system was used to study the prefabricated elliptical crack curvature influence on the stress intensity factor, propagation path, and propagation speed of the moving crack by changing the prefabricated ellipse tip curvature. e crack tip stress intensity factor was calculated by stress extrapolation

Test Principle

Test Plan

Results and Analysis

Conclusions