COMPARISON OF METHODS FOR CRACK TIP OPENING DISPLACEMENT TOUGHNESS DETERMINATION

The crack tip opening displacement (CTOD) initiation toughness has been obtained by different methods in Cr and Cr-Mo steels at 30, 200 and 400-degrees-C. The crack tip stretching and grain deformation has been investigated by scanning electron microscope and optical microscopic studies and by microhardness measurements. The resistance curve approach is used employing the average and the maximum crack growth and the initiation toughness determined are with respect to 0.2 mm crack growth (delta-0.2), the stretched zone width (SZW) and also using a blunting line approach. In addition, an initiation toughness using stretched zone depth (SZD) measurement is also obtained. The various initiation toughness values have been compared and an attempt has been made to identify the realistic plane strain CTOD toughness amongst the different values. The J-CTOD relationship has also been investigated.