Study Of Ceramic Transformation On Crack-toughening

Possessing excellent physical, chemical and mechanical properties, ceramic phase-transformation materials play an important role in the hi-tech field of energy, aviation and military affairs etc., and show a good prospect for extremely wide use. In recent years, however, the study of transformation toughening on zirconia ceramic is one of the important aspects in the study of ceramic fracture theory.In this paper, transformation toughening of mode I , II, III cracks is studied in the conditions of static and steady-state growing cracks in detail at first. Embarking from the macro-phenomenological theory, the parabola form of the yield function is given combined with the difference of tension and compression yield strength, and an elastic-plastic constitutive model is built according to the plastic potentioal theory. Then by using the constitutive theory and the weight function method the transformation region is drawn. The laws of variations in transformation toughening with each parameter are discussed, and then the accuracy of the result is demonstrated compared with results from other theories. Finally, following the above analysis of simple cracks, the mixed cracks (I -II, I -III,II-III) are studied in the conditions of static and steady-state growing cracks by using the strain energy release rate criterion. The rules of transformation toughening to mixed cracks with parameters are also discussed, results of which show that transformation has negative toughening effect on static cracks, but positive toughening effect on steady-state growing cracks, these are the same as the results of simple cracks. Such conclusions are demonstrated to be consistent with results from other theories after comparison.The results of ceramic transformation generalized in this paper can be helpful and applid as theoretical references in further research on related problems and in practical porjects.