EXPERIMENTS AND THEORETIC ANALYSIS FOR THE FRACTURE OF BRITTLE MATERIALSUNDER BIAXIAL STRESS
脆性材料在双向应力下的断裂实验与理论分析

The fracture behavior of brittle materials under biaxial plane stress, especially theinfluence of the stress parallel to the crack plane on critical fracture parameters, was investigated by means of thermomechanical method. Biaxial and uniaxial tension tests were performed with thin glass and zirconia disk specimens. The aims of this study is to clarify the fracture dependenceof brittle material in plane stress state and their difference between biaxial and uniaxial tension,baized on experimental and analytical approaches.A though thickness crack was introduced in the center of end disk specimen for measuring the plane stress fracture toughness. Fifty glass specimens and thirty 8YSZ specimens were measuredby using various loading rates. The observation to crack initiation and fracture reveals that thebiaxial stresses do affect the fracture properties of solid material. The fracture toughness of glassunder biaxial tension was about 20% higher than that under uniaxial load. Thus, the fracturecriterion by the stress intensity factor is questioned for the bledal plane stress issues. The studyalso showed that the plane stress fracture toughness of brittle materials increases in a great rangewith increasing loading rate, and the subcritical crack growth in plane stress is much more obviousthan that in plane strain state. Strain dependence of crack growth was discussed to explain theinfluence of biaxial stress, and was demonstrated by the experimental results.As a research conclusion, it was confirmed that the tensile stress parallel to the crack planehas the action of crack arrest, while the compressive stress parallel to the crack plane contributesto crack opening for brittle materials in plane stress state.l) The project supported by A.V. Humboldt Foundation, Germany.