Blunt scratch strength of polycrystalline alumina

A model for the fracture strength of brittle materials controlled by blunt (spherical) scratches is developed and compared with measurements on a polycrystalline alumina. The model is based on a residual stress-intensity factor for median cracks at scratches that include a localized plastic deformation zone formed by dragged spherical contacts. The stress-intensity factor depends nonlinearly on the normal contact load P, resulting in a predicted strength variation of P-3/4. The strength result validates previous claims and extends the overall indentation-strength framework. However, the result has only limited effectiveness in describing experimental measurements, pertaining only to ideal blunt scratches formed over a limited load domain.