Determining the fracture toughness of quasi-brittle materials with notched four-point bending tests

Fracture is common failure mode of quasi-brittle materials when suffering tensile loads, the accurate determination of the fracture toughness becomes extremely vital. Notched four-point bending (4-p-b) test is one of main fracture test methods, but is rarely applied in evaluating the fracture behavior of quasi-brittle materials. In this study, on the basis of relevant standards, the specific requirement of 4-p-b fracture test is proposed. Then the closed-form solution is used to establish the relation between the four-point bending test results and fracture toughness on the basis of the Boundary Effect Model. The influence of test conditions, boundary effect and distribution characteristics of fracture properties are discussed in detail. After that, two types of hard rock and concrete are utilized to verify the reliability of proposed methods. The results show that four-point bending test and corresponding analytical solution are suitable for determining the fracture toughness of quasi-brittle materials, regardless of the different initial notch length and material categories.