1. Introduction

The present study deals with aspects of brittle and quasi-brittle failure of brittle materials on the microscopic and on the continuum level. It refers particularly to ceramics. The significance of microstructural parameters is investigated by a numerical model that progressively accounts for separation of grain interfaces. The microcracking model [DOL 98] requests specification of the material structure which can be subject to variations in conjunction with synthetic Monte Carlo sampling. Beyond the evolution of damage, the strength of the material specimen is estimated by this computational approach which applies fracture mechanics to a microstructure subject to statistical variability as suggested in the literature [DAV 80].

Under tensile actions, the brittle mode of failure by separation of the specimen is predominant, but any structural disorder promotes damage by distributed microcracking prior to ultimate failure. Compressive loading may close microcracks, separation of grain interfaces is mainly by sliding which may be opposed by friction. The quasi-brittle mode of failure prevails, synergies between interacting cracks while damage progresses form localized patterns and lead to ultimate failure. Structural disorder can be introduced by the nature and size of grain phases, thermal eigenstrains stemming from manufacturing, and pores. The presence of pores was found to favour distributed damage as well, but if the loading is by internal pressure in the pores the process of microcracking is such that pores are bridged and failure by separation of the material specimen is quite straightforward [DOD...