Dynamic splitting tensile behaviors of red-sandstone subjected to repeated thermal shocks: Deterioration and micro-mechanism

Thermal shock (TS) is common for rock engineering where the environment temperature changes sharply. As a typical kind of brittle material, rock fails mainly because that the tensile stress exceeds the tensile strength, which is influenced significantly by strain rate. In this work, physical detection, quasi-static and dynamic splitting tensile tests were carried out on red-sandstone free from and after 10, 20, 30, 40 artificial TS cycles. TS induced deterioration of red-sandstone was obvious, with the rock density reduced, and the porosity increased obviously with the adding-up of TS cycles. Splitting tensile strength (STS) of red-sandstone was influenced by the coupling effects of TS-induced decay and strain rate strengthening. Considering the strain rate effect, deterioration model was built to predict the STS degradation of rock after repeated TS. The model parameters, decay constant (lambda) and half-life (N-1/2) were both expressed as functions of strain rate. Microscopic features of the splitting tensile fracture surface were scanned by SEM techniques to analyze the micro-mechanism of TS-induced deterioration and strain rate effects on the STS. As the SEM results show, trans-grain fracture during the splitting tension increases with the rise of strain rate, leading to the strengthening of STS, and TS cycles reduces the agglutination of cements and the gomphosis between grains and thus reducing the STS of TS weathered red sandstone.