Compressive behavior and deformation-mode map of an open cell alumina

Abstract

Compressive behavior of an open cell, porous ceramic has been examined and compared to a prior theoretical model. The study involved (i) microstructural characterization, (ii) crushing strength and Young's modulus measurements, and (iii) construction of a deformation-mode map. Initially, the crushing behavior was found to be different than predicted theoretically. Weaker struts throughout the material fractured during the loading and this damage was accumulated until a macroscopic crack or cracks propagated through the material at the crushing stress. Further work showed the discrepancy was related to the uniformity of loading in these porous materials. The use of compliant faces on the loading rams improved the loading uniformity, leading to a substantial reduction in the experimental scatter and increasing the likelihood of unstable crack propagation events rather than damage accumulation. Both crushing strength and Young's modulus were found to be dependent on cell size, but this was considered to be a result of strut cracking at the smallest cell size. A deformation-mode map was constructed using the average stress/strain values at critical points such as the onset of crushing, the minimum crushing stress, and the densification stress. Although some of the details of the deformation map were different from that expected theoretically, the map did appear to be a useful guide to the compressive behavior.