Low-medium loading rate effect on dynamic fracture toughness of sandstone scaled model

To investigate the effects of loading rate on the dynamic fracture toughness of rock in a scaled system, a multi-scale experimental and numerical study is carried out with a single cleavage semicircle (SCSC) specimen based on a new scaled modeling method. The loading curves of the scaled models are obtained by using the data recorded by an oscilloscope. The fracture time is monitored by the fracture propagation gauge (FPG) to calculate the propagation velocity of fracture. The dynamic fracture toughness of the propagation fracture can be obtained by combining experimental data with a finite-element method. The results show that the effects of loading amplitudes and model size on fracture toughness can be significantly eliminated by the scaled modeling method applied in this paper, which provides a prerequisite for a thorough analysis of the loading rate effect on scaled models. Furtherly, by introducing a new proportional coefficient factor, the scaled modeling method is confirmed to predict the dynamic fracture toughness effectively. The dynamic fracture toughness exhibits a non-linear increase with loading rate in both the fracture initiation and propagation stages. This increase is characterized by a rapid-growth in some middle range of loading rates, with a relatively slow-growth below or above that range. Furthermore, the propagation toughness is greatly affected by loading rate at low rates, whereas the initiation toughness is more significantly influenced by medium loading rates.