A model for non-linear mechanical behaviour of refractories

It has been observed that many ceramic materials, and in particular refractories, show some non-linear stress-strain behaviour accompanied by a small amount of permanent deformation. This looks like a work hardening plastic response, qualitatively similar to a 'high strength aluminium alloy. This behaviour has, however, been attributed to many mechanisms including: microcracking with debris preventing crack closure; release of residual stresses by microcracking; and plasticity in constituent materialS. In the present paper, the results of bend tests on two commercial refractories are reported and the differences in stress-strain behaviour of these are discussed. These results are shown to be entirely consistent with the hypothesis that the release, by microcracking, ofmicroscale residual stresses in the fired ceramic is the major cause of permanent macroscopic strainS. A simple constitutive model, which has been successfully applied to bending data for the refractories tested, is presented which is capable of predicting the stress-strain behaviour of the material both during cooling and mechanical loading.