The effect of non-singular term (T-stress) on mode I/III cracking parameters of brittle materials, Numerical and experimental study using different beam and disc shape specimens made of marble rock

This study focuses on less-studied mode I/III fracture cracking behaviour. Seven specimens (ENDC, DNDC, SCB, ENDB, ATPB, TPB-IC, and SENB) were analyzed numerically and experimentally. Results show in pure mode-I, the specimens show identical KIc values (1.22 to 1.54 MPa√m). Especially if the KIc was measured by compressive specimens (ENDC and DNDC with KIc of 1.22 and 1.30 MPa√m, respectively) and was neglected. In these cases, the difference in measured KIc values directly relates to the T-stress value in pure mode-I. So, higher T-stress values increase the KIc and vice versa. In pure mode-III, which can only simulated by ENDB, ENDC, and DNDC specimens, the difference in measured KIIIc values was enormous, as 0.99 MPa√m for ENDB, 2.0 MPa√m for ENDC and 2.53 MPa√m for DNDC. Comparing the trend of KIIIc for specimens shows the same as KIc, KIIIc also has a direct relation with the T-stress. The affectability of fracture toughness from T-stress shows the importance of accounting for it in calculations. The trends show that the ENDB, ENDC, and DNDC specimens have considerably negative T-stress values, with different trends. Moving from pure mode-I to pure mode-III, the ENDB has a low-negative T-stress that becomes high-negative (about -0.32 to -2.5 MPa). Meanwhile, of DNDC, it is the opposite; the T-stress is high-negative for pure mode-I and becomes low-negative for pure mode-III (about -2.54 to -0.77 MPa). For ENDC, the T-stress is almost constant moderate-negative in all the mixed mode I/III conditions (about -2.1 MPa).