The diametral compression testing method proposed in the previous paper for simple measurement of tensile strength is needed to be modified from the view point of fracture mechanics when it is applied for biaxial stress problems. In this paper, a new macroscopic fracture criterion for brittle materials in biaxial stress states is discussed by considering their strength in the diametral compressive testing where initial cracking arises due to shearing stress in the mode II fracture and then propagation to final fracture occurs due to tensile stress. According to this fracture criterion, tensile strength can be derived from the uniaxial compressive strength and the diametral compressive strength. It is ascertained experimentally that the estimated values agree very well with the usual uniaxial tensile strength in a wide range of brittle materials such as graphite and marble.
