ON THE METHOD OF DAMAGE ASSESSMENT IN POROUS CERAMICS

The paper proposes a new method of estimation of the current mechanical characteristics and of damage evolution in porous ceramics subjected to mechanical loading. The essence of the method is the modelling of material damage development both by micromechanical and phenomenological approach. The micromechanical approach requires determination of the initial material structure by SEM. The phenomenological approach needs experimental testing of the material under quasi-static compression with observation of the several repeated cycles of: loading, unloading and subsequent reloading, what enables detailed analysis of changes of the elastic material constants and further damage assessment. Micromechanical description of damage evolution in ceramics comprises the consideration of distributed pores and cracks inside the so called Representative Surface Element and application of averaging procedure in order to get the global material behaviour. In the phenomenological approach we introduce an internal parameter describing macroscopic material damage (the second order tensor) and specify criteria of cracks nucleation, their propagation and final failure of the material sample. Experimental part of the method covers microscopic (SEM) observation of the initial ceramic structure, compressive loading tests with unloading and reloading until the specimen failure, SEM observations of fracture surfaces in order to specify the way o