MODIFIED FORMULAS FOR 3-DIMENSIONAL DIRECT STRESS-INTENSITY FACTOR COMPUTATION

The popularity of R.S. Barsoum's collapsed quarter-point isoparametric element is due to its simplicity in execution, which does not require new subroutines to available 3-D finite-element codes and their extension to fracture mechanic analysis. In fact, A.R. Ingraffea and C. Manu have pointed out, for this singular element, some remarkable formulae giving stress intensity factors directly, in terms of the nodal displacements. It appears that in general these formulae do not satisfy the rigid modes. On the other hand, these formulae may lead to some drawbacks when loadings are imposed by temperature. The present paper develops improved formulae with additional terms which satisfy the rigid modes and give good results for thermal loading. Numerical tests demonstrate the accuracy of the new and correct formulae.