Size scaling of tensile failure stress in boron carbide

Abstract

Weibull strength size scaling in a rotary ground, hot pressed boron carbide is described when strength test coupons sampled effective areas from very small (∼0·001 mm²) to very large (∼40 000 mm²). The testing of this ceramic is relevant because it is a candidate material for use in personnel armour. Equibiaxial flexure and Hertzian testing were used for the strength testing. Characteristic strengths for several different specimen geometries are analysed as a function of effective area. Characteristic strength was found to substantially increase with decreased effective area and exhibited a bilinear relationship. Machining damage limited strength as measured with equibiaxial flexure testing for effective areas greater than ∼1 mm², and microstructural scale flaws limited strength for effective areas <0·1 mm² for the Hertzian testing. The selections of a ceramic strength to account for ballistically induced tile deflection and expanding cavity modelling are uniquely considered in context with the measured strength size scaling.