Correlation between Long and Short Crack R‐curves in Alumina Using the Crack Opening Displacement and Fracture Mechanical Weight Function Approach

Both fine grain sized and coarse grain sized alumina has been used as a model material to correlate short crack R ‐ curves by the surface‐flaw‐in‐flexure method with long crack R ‐curves from a compact tension specimen. The analysis has been made using the crack opening displacement from long cracks combined with the appropriate weight function to compute the crack closure stresses by crack bridging as a function of crack opening displacement. Then the long crack R ‐ curve, the short crack curve, as well as the crack opening displacement for short cracks are computed. The agreement with the experimental data is within an absolute value of about 0.3 MPa and attributed to uncertainties in determining the crack tip toughness and effects due to subcritical crack growth.