Abstract
Relation between three point bending strength of mullite ceramics and their defects is studied. From SEM analysis of specimens after three point bending test, origin of fracture was mainly due to pores exsisting in specimens. Position of pores depended on specimens and shapes of pores were irregular shapes.Stresses loaded on defects are about 80-90% of bending strengths. Experimental equation of the relation between stress and defect is σ=1420/C1/2, while σ= 1070/C1/2 is obtained by Griffith's theoretical equation in case of sphere defect . Maximum mainstress is calculated by FEM on the assumption that shape of defect are oval (radius ratio: a/b). The maximum main stress of oval defect changed about ± 30% in comparison with that of sphere defect in the range of a/b = 0.5-2.0.
