Effect of support friction on pure mode I, II, and III fracture toughness of cement concrete tested with edge-notched disc bend specimen

In this paper, the effect of friction on the interactions between the supports and test specimen is investigated in the fracture tests under pure mode I, pure mode II, and pure mode III loadings. 3D finite element analyses are performed on the ENDB (edge-notched disc bend) specimen by modeling the friction at the interactions, and SIFs (stress intensity factors) are computed. The results show that friction affects the values of SIFs significantly. Next, mode I, mode II, and mode III fracture tests are performed on the ENDB specimens made of concrete by using three different supports including the R (roller), RG (roller-in-groove), and F (fixed)-supports. Based on the results, mode I, mode II, and mode III fracture toughness are considerably dependent on the type of supports. Such that the F-supports and R-supports show the highest and lowest values of the fracture toughness, respectively due to having the highest and lowest friction coefficients at the interactions. Finally, the friction coefficients at the interactions are computed for the mode I, mode II, and mode III loadings using the FE and experimental data. Accordingly, mode I fracture tests of the concrete are more sensitive to the friction coefficient at the interactions than the mode II and mode III ones.