Surface Cracks In Bars Research Articles

Slow Crack Growth from Controlled Surface Flaws in Hot‐Pressed Si3N4

The elevated‐temperature slow‐crack‐growth behavior of HS‐130 Si3N4 was studied by extending “controlled” surface cracks in bars loaded in 4‐point bending. Several such nonin‐teracting cracks were produced on the tensile surfaces of bend bars by Knoop microhardness indentation. The stress and dimensions of the subcritically growing cracks were used to calculate the stress‐intensity factor, K1, from fracture‐mechanics formulas for semielliptical surface cracks in bending. The crack‐growth velocity, v, was obtained by dividing crack extension by loading time interval. The data indicated very large scatter in measured velocities for given K1 values, which was interpreted as due to the interaction of the small cracks with local material heterogeneities. No simple functional relation between K I and v could be established for HS‐130 Si3N 4 from the v−K1 data.

Strength of Stress Singularities at Crack Tips for Flexural and Torsional Problems

Continuing a series of studies on the fracture analysis of elastic bodies, the present paper provides a complex variable method for evaluating the strength of stress singularities at crack tips encountered in the flexure and torsion of cylindrical bars. As a result of the complex flexure functions being sectionally holomorphic for crack problems, the singular character of the shearing stresses is found to be of the type r−1/2, where r is radial distance from the crack point. Crack-tip stress-intensity-factor solutions are given for problems involving both imbedded and surface cracks in bars. The results suggest the possibility of extending the Griffith-Irwin theory of static fracture to flexural and torsional problems.