Parametric Study of the Formation of Cone Cracks in Brittle Materials

Brittle materials such as ceramics and oxide glasses are widely employed because they possess a variety of useful properties including hardness, strength, wear resistance and/or transparency. Normal and oblique impacts of spherical projectiles on brittle materials are similar to the classical Hertzian sphere indentation problem, yet different in significant ways. In the case of oblique impacts, these differences can result in the formation of unique damage patterns, including cone cracks, which are not axisymmetric, and they are distinct from partial cone cracks formed by sliding indentation. Some selected results of oblique sphere impacts on brittle targets are shown and discussed, identifying unique features. A parametric study of the factors contributing to the differences between normal and oblique impacts is reported. The effects of normal and tangential velocity, friction, and softening are investigated as factors influencing the peak principal stresses produced by oblique impacts. Friction and projectile softening were found to have a significant impact on peak maximum principal stress values. An obliquely impacting projectile's lateral motion and its interaction with the sides of the cone crack were also found to have a significant effect on the stress field and the shape of the resulting cone crack.