3. Fracture phenomena (semi-fragile materials)

Experience shows that materials (other than polymers) with high elasticity, i.e. a low E /R _e ratio, break during the tensile test in the elastic deformation range. , but, due to the compressive nature of the stress state generated in the indentation test, they can be plastically deformed in the Vickers hardness test, possibly according to mechanisms different from those of metallic materials, as in the case of glasses. This is particularly true of high-strength metallic materials and tool materials. However, hardness testing also generates tensile stresses and cracks, which provide valuable information for measuring the fracture properties of such materials. According to Irvin-Griffith theory, a material's resistance to crack propagation in mode 1 (stress purely normal to the crack surface) is equivalently characterized by...