Maximum resistance rate principle for quasi-brittle fracture

The maximum resistance rate principle (MRRP) is proposed to characterise the unstable of quasi-brittle fracture. Under quasi-static loading conditions, the unstable fracture of quasi-brittle materials occurs when the resistance rate reaches its maximum value. Firstly, the whole fracture process of the single edge cracked specimen was calculated, and the MRRP was elaborated based on the calculated fracture resistance and resistance rate curve. Then, the MRRP was verified by existing experimental data of three-point bending beams of different sizes. Furthermore, the influence of specimen geometry, size and material parameters on the fracture resistance and resistance rate was discussed. The calculation results reveal that the resistance rate and external load reach their maximum values in the critical state simultaneously. Combined with the cohesive crack model, the MRRP can well describe the unstable fracture of quasi-brittle materials, which is an extension of Griffith's theory of brittle fracture.