The notched beam in asymmetric four-point bending for brittle material testing

A reliable test in which the stress state approximates that of pure shear is necessary in order to establish a valid failure criterion for brittle materials. One of the possible tests, the notched beam in asymmetric four-point bending, has been analysed using the finite element method. The results show that for brittle materials a stress concentration at or near the notch tip will cause the specimens to fail in the original configuration. A modified version of the test has been developed, which involves the enlargement of the notch angle and the rotation of the beam so that it is loaded with the notches lying in the direction of the loads. The new configuration was applied to graphite specimens which showed a distinctive mode of fracture.