Analysis of Mixed-Mode I/II/III Fracture Toughness Based on a Three-Point Bending Sandstone Specimen with an Inclined Crack

Xin Pan,Shiming Dong,Jiuzhou Huang,Zhiqiang Gan,Wen Hua

doi:10.3390/app11041652

Abstract

The crack-propagation form may appear as an arbitrary mixed-mode fracture in an engineering structure due to an irregular internal crack. It is of great significance to research the mixed-mode fracture of materials with cracks. The coupling effect of multiple variables (crack height ratio, horizontal deflection angle and vertical deflection angle) on fracture parameters such as the stress intensity factors and the T-stress are the key points in this paper. A three-point bending specimen with an inclined crack was proposed and used to conduct mixed-mode fracture research. The fracture parameters were obtained by finite element analysis, and the computed results showed that the pure mode I fracture and mixed-mode fractures (mode I/II, mode I/III and mode I/II/III) can be realized by changing the deflection angles of the crack. The pure mode I and the mixed-mode fracture toughness of sandstone were obtained by a series of mixed-mode fracture experiments. The experimental results were analyzed with the generalized maximum tangential strain energy density factor criterion considering T-stress. The results showed that the non-singular term T-stress in the fracture parameters cannot be ignored in any mixed-mode fracture research, and the generalized maximum tangential strain energy density factor criterion considering T-stress can better predict the mixed-mode fracture toughness than other criteria.

Highlights

The pure mode I fracture is a common in-plane open fracture, and the mode I critical stress intensity factor (KIC) is one of the important material properties characterizing material fractures
The influences of the deflection angles and crack length on fracture parameters (i.e., stress intensity factors (SIFs) and T-stress) and the experiments of the three-point bending specimen with inclined crack (TPB-IC) specimen made of sandstone for mixed-mode I/II/III fracture were carried out
It was shown that the generalized maximum tangential strain energy density (GMTSED) criterion can significantly improve the prediction of experimental results by considering the influence of T-stress, in addition to KI, KII and KIII

Summary

Introduction

The pure mode I fracture is a common in-plane open fracture, and the mode I critical stress intensity factor (KIC) is one of the important material properties characterizing material fractures. The GMTS criterion was used to predict and verify the experimental results of threepoint bending specimens in mixed-mode I/II fracture studies, whether SCB or ETC speci-. The mixed-mode I/III fracture experimental results for various materials such as marble [37], asphalt concrete [39] and graphite [40] using ENBD specimens were in good agreement with the theoretical predicted value of the MTSED criterion without considering T-stress. Based on the previous investigations, a mixed-mode fracture test configuration, called the three-point bending specimen with inclined crack (TPB-IC), was proposed in this study. The influences of the deflection angles and crack length on fracture parameters (i.e., SIFs and T-stress) and the experiments of the TPB-IC specimen made of sandstone for mixed-mode I/II/III fracture were carried out. The contribution of mode I, mode II and mode III SIFs in mixed fractures depends on α and β

Numerical Simulation of the TPB-IC Specimen

Experimental Investigation of TPB-IC Specimens

Fracture Toughness and Criterion Analysis

Findings

Conclusions