Mechanical behavior of porous alumina under quasi-static and dynamic loading

Abstract

The sensitivity of porous ceramics’ mechanical behavior to strain rate is often attributed, in micromechanical models, to a competition between the loading rate and the crack propagation speed initiated at microstructural defects. However, direct experimental evidence for this phenomenon remains limited. In this study, this competition was investigated by conducting compression and tensile tests across a range of strain rates using Split Hopkinson Pressure Bar set-up on alumina ceramics with precisely controlled microstructures. Porosity was introduced into the alumina matrix with well-defined pore size, morphology, and volume fraction. Three porosity levels (1%, 20%, and 60%) and two pore types (microscopic tortuous and mesoscopic isolated spherical) were used to assess the influence of microstructure on mechanical response under dynamic loading. Results indicate that strain rate sensitivity increases with porosity. However, due to the wide dispersion of results, it is challenging to conclude precisely on the specific effect of pore size. The size of the fragments was then used an indicator of the fragmentation mechanisms occurring during sample fracture. The increase in strain rate leads to an overall reduction in fragment size, reflecting the competition between strain rate and crack propagation velocity introduced by micromechanical models.