Antiplane Shear Fracture Tests (Mode III)

Abstract

Mode III (antiplane) shear fracture energies of concrete and mortar were measured on the basis of the size-effect law. The specimens were cylinders with a circumferential notch at midlength, subjected to pure torsion at zero axial force. The specimens were geometrically similar and their sizes varied as 1:2:4. It was observed that the mortar specimens behave closer to linear elastic fracture mechanics than the concrete specimens. The ratio of Mode III to Mode I (tensile) fracture energies was found to be about 3 for concrete and about 8 for mortar. The results indirectly indicate that a volume expansion of the sheared fracture process zone may be a significant mechanism causing transverse tensile stresses across the ligament. The size effect measurements also yield an estimate of the size of the fracture process zone, which is found to be nearly the same as for Mode I fracture.