Experimental study of effect of number of heating–cooling cycles on mode I and mode II fracture toughness of travertine

Abstract

Fracture toughness is considered a critical index for measuring the fracture strength of cracked rocks, which is sometimes influenced by the heating–cooling process. This process and its repetition change the physical and mechanical properties of rocks. The façade of buildings bears a larger number of heating–cooling cycles over days and seasons. Accordingly, this study simulated the heating–cooling process and its impact on the mode I and mode II fracture toughness of travertine as a widely used rock in the façade of modern buildings by designing a larger number of low-temperature heating–cooling cycles. Previous researches mostly has been studied the effect of high temperatures on physical and mechanical rock properties but in this study, effect of low temperature in a large number of heating–cooling cycle is investigated. Two types of travertine were considered and studied. The mode I and mode II fracture toughness tests were performed on 160 cracked chevron notched Brazilian disc (CCNBD) specimens after applying 0, 1, 4, 8, 16, 32, 64, and 128 heating–cooling cycles. Mechanical properties were measured, and scanning electron microscope (SEM) images were taken to evaluate and match the results of fracture toughness tests. According to the results, mode I and mode II fracture toughness increased after a heating–cooling cycle and then decreased by increasing the number of cycles. The changes in the fracture toughness were consistent with variations of mechanical properties and SEM images with increasing the number of heating–cooling cycles.