In the recent years, the studies on the mechanical behaviors of various materials subjected to biaxial loading have been worked since they are more complicated and intrinsically different from those under the simple uniaxial condition. The cruciform specimen without any slots has been commonly used for the goal so far. We prepare improved biaxial specimen with slots and make sure its validity by means of finite element analysis and photoelastic experiment. Even though the equal load biaxiality was applied to the specimens, as the results, we found that the stress biaxiality ratios in central region of specimen differ according to the position from the center of them, the specimen with slots in the arms is more effective to make state stress uniform than the specimen without slot.

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The effect of electromechanical loadings including their sequence, which was motivated by the property of crack energy density for piezoelectric material, was experimentally investigated. Three-point bending fracture test was performed for two piezoelectric ceramics under different electromechanical loading conditions. It was found that the fracture loads under closed circuit condition are greater than those under open circuit condition. Effect of applied electric field on fracture load in the test varied with materials. Applied electric field always enhanced crack extension in C-21 ceramics regardless of their directions, while it produced very little effect on crack extension under negative electric fields in C-2 ceramics. It was also found that electromechanical loading sequence clearly affects fracture strength, although its effect varies also with materials.

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