1993 Volume 42 Issue 475 Pages 426-430
MgO and MgO-ZrO2 sintered bodies with different grain sizes were prepared by pressureless sintering, and an artificial crack was introduced on the specimen surface by Vickers indentation method. Then the strength was measured by 3-point bending tests to examine the effects of grain size and artificial crack length on the bending strength of MgO sintered body.
In the case of a crack shorter than the critical length, the bending strength was constant, irrespective of the crack length and equal to the strength of the smooth-faced specimen. Above the critical crack length, the bending strength decreased with an increase in crack length, which follows the rule of the linear elastic fracture mechanics, LEFM. The equivalent critical crack length, ac, calculated by means of LEFM, was not proportional to grain size, D, but it increased with an increase in D. The relationship between ac and D is expressed as ac=6.39+0.36D-2.89×10-3D2. Consequently, the bending strength, σ was apparently expressed by an equation, σ=262.2+402.3D-1/2.
