Fracture analyses of different pre-holed concrete specimens under compression

Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-like material containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement （PPC）, fine sands, and water. The pre-holed Brazilian discs and rectangular specimens are experimentally tested under compression. The breakage load in the ring type disc specimens containing an axial hole with varying diameters is measured and the distribution of the induced lateral stress is obtained. The mechanism of cracks propagation in the wall of the ring type specimens is also stud- ied. In the case of multi-hole Brazilian disc and rectangular specimens, the cracks propagation and cracks coalescence are also investigated. These experiments are numerically modeled by a modified higher order displacement discontinuity method. It has been shown that the corresponding experimental and numerical results are in good agreement with each other. The results presented in this research vali date the accuracy and applicability of these crack analyses procedures.

Tensile and tear-type fracture toughness of gypsum material:Direct and indirect testing methods

In this context,four specimens,i.e.(i)circumferentially notched cylindrical torsion(CNCT),(ii)circum-ferentially notched cylindrical direct tension(CNCDT),(iii)edge notch disc bend(ENDB)and(iv)three-point bend beam(3PBB),were utilized to measure the modesⅠandⅢfracture toughness values of gypsum.While the CNCT specimen provides pure modeⅢloading in a direct manner,this pure mode condition is indirectly produced by the ENDB specimen.The ENDB specimen provided lower KⅢc and a non-coplanar(i.e.twisted)fracture surface compared with the CNCT specimen,which showed a planar modeⅢfracture surface.The ENDB specimen is also employed for conducting pure modeⅠ(with different crack depths)and mixed modeⅠ/Ⅲtests.KIc value was independent of the notch depth,and it was consistent with the RILEM and ASTM standard methods.But the modeⅢfracture results were highly sensitive to the notch depth.While the fracture resistance against modeⅢwas significantly lower than that of modeⅠ,the greater work of fracture under modeⅢwas noticeable.