Experimental investigations of fracture toughness and crack initiation in marble under different freezing and thermal cyclic loading

Marble specimens were used to investigate the effects of freezing and thermal cyclic loading on crack initiation and propagation and fracture modes. To this end, four loading types of freezing-cooling (F-C), heating-cooling (H-C), freezing-cooling- heating (F-C-H) and heating-cooling-saturating-freezing (H-C-F (sat.)) were considered. Forty-four toughness tests were carried out, and changes in the fracture mechanism in the marble were analyzed at −30 °C and 160 °C. The fracture toughness parameters, load-displacement curves, crack initiation angle for mode II and the mixed mode (I-II) were measured and then predicted using the conventional criteria. Crack initiation angles for the mixed mode (I-II) and mode II fracture toughness in different loading conditions were calculated to be about 58° and 78°, respectively. The F-C-H loading condition seemed to reduce mode I fracture toughness in the tested samples. The experimental data on fracture toughness for H-C, F-C-H and H-C-F (sat.) loading conditions were well predicted by the modified maximum tangential stress (MMTS), maximum tangential stress (MTS) and G-criterion. The results indicated that very good predictions are obtained by the extended maximum tangential strain (EMTSN) for the fracture toughness of marble envelopes in the entire range of mode mixities from pure mode I to pure mode II. Load-displacement curves for different loading conditions were monitored, indicating that the peak load significantly decreased for F-C-H and H-C-F (sat.) cycles.