Hertzian crack growth in ThO2 observed by serial sectioning

The formation and growth of cone cracks during Hertzian indentation with spherical indentors has received considerable attention and a number of analytical treatments describe the phenomenon reasonably well. An equation to describe the relationship between indentation load and crack length is presented. Some difficulties are discussed. In the present work it will be demonstrated that the cone crack path is not very sensitive to the value of r/a (where a = contact area, r = initial radius) at which it is created. Thus the equation can be applied to crack extension at any observed load and crack length using the prevailing instantaneous value of r/a regardless of the previous crack growth history. This conclusion is then made use of in a study of the crack growth in ThO2 by serial sectioning, leading to estimates of the fracture surface energy of this compound. (author)