A comparative study of various approaches for CTOD toughness evaluation

A comparative assessment of various methods proposed for CTOD toughness evaluation has been made on two structural steels. CTOD values are obtained from experimental CMOD data by direct extrapolation as given by Wells' method, BS5762 etc. On the other hand the toughness values based on R-curves (multiple specimen method) are also obtained using various proposed blunting lines. An attempt is made in the present work to find a more realistic blunting line from stretch zone width measurement. Two specific geometries, namely compact tension (CT) and three point bending are considered, besides studying the thickness effects on CTOD. The conventional methods (BS5762 etc.) are found to yield more conservative values, while the R-curve approach considered with a blunting line provides a more realistic estimation of toughness. No clear and systematic dependency of thickness could be observed. However, the CT geometry results in higher CTOD toughness than bend geometry apparently because of a lower constraint factor.