Measurement of tensile strength by diametral compression of discs and annuli

Abstract

In the first part of the paper, the validity of diametral compression tests for indirect measurement of tensile strength is investigated theoretically and experimentally. Linear elastic theory for diametral compression of discs and annuli by opposed strip loads is reviewed, and the significance of failure criteria in fracture initiation and test interpretation is considered. Results of careful tests are given for three types of rock, two plastics, glass, and ice, and the experimental results are compared with theoretical expectations. Close consideration of the conflicts between theory and experiment leads to the conclusion that, while there are very serious objections to the ring test, the Brazil test is capable of giving a good measure of uniaxial tensile strength for Griffith-type materials. In the second part of the paper, practical problems involved in diametral compression testing are considered in some detail. Special attention is given to contact stresses under the applied loads, and a design is given for a loading jig that reduces contact stresses. Specimen dimensions, size effects, loading rate, force readout, and specimen preparation are discussed, and some recommended practical procedures for Brazil tests are outlined.