A Method for Evaluating Superplastic Properties in Ceramics by Means of a Three-Point Bend Test. General Comparison of Bend, Tension and Compression Test Results.

Abstract

A method for evaluating superplastic properties of a material with different stress/strain-rate relations when deformed in tension and in compression was studied by means of a bend test. To begin with, four-point bending of a beam under a constant deflection rate for a case Kt≠Kc and mt = mc in the constitutive equation of superplasticityσ=Kεm was analyzed, where σ, ε, m and K are stress, strain-rate, strain-rate sensitivity index and constant, respectively, and the subscripts t and c refer to tension and compression sides of the beam. Then a compression test of Y-TZP was conducted and the result was discussed and compared as a whole with the previous results of the bend and tension tests on the same material. The normal stress and normal strain-rate on the mean strain-rate points in the tension and compression sides of the beam were calculated by substituting the bend test result into equations derived in this study. The normal stress/strain-rate relations calculated on the tension and compression sides of the beam agreed fairly well with those relations obtained directly from the tension and compression tests, respectively.