Stress analysis of a fracture test specimen for cementitious materials

Stress analysis of a compact compression specimen used for the determination of the fracture toughness of cementitious materials is carried out by the finite element method. The specimen, which is based on 100 mm cubes, contains two notches on opposite faces. It is found that the geometry and loading result in large tensile stresses at the root of the notch remote from the load. These stresses are sufficient to propagate the crack in the opening mode of fracture thus enabling the fracture toughness of the material to be determined. The fracture toughness is evaluated from the failure load and the stress intensity factor computed from the finite element results. Several finite element mesh refinements were employed and accurate estimates of the stress intensity factor were obtained by modelling the specimen by a relatively small number of elements. The accuracy of the results was largely independent of the evaluation method which included displacement extrapolation, conic section simulation, strain energy release rate and the J-integral. Whereas the stress intensity factor varied with the notch size, the tests conducted in the present work did not show significant variation in the fracture toughness.