TWI Industrial Member Report Summary 61/1978
By S J Garwood
The Report is divided into two parts. In the first the crack growth resistance of 20mm thick API 5LX65 pipeline steel in the longitudinal orientation has been measured in both three-point bend and centre-cracked tension (CCT) using the yielding mechanics parameters J and COD.
The values of these parameters at the initiation of cracking for the two geometries were essentially identical. Resistance curves derived for the tension specimens, however, were appreciably steeper than their bend counterparts.
An estimation technique for the evaluation of the J resistance value is presented and compared with existing methods. A simple relationship is also suggested for the determination of COD resistance for the CCT geometry.
In the second part energy balance considerations are extended to describe instability in the elastic-plastic regime. Elastic-rigid plastic J driving force curves are derived for three-point bend and CCT geometries and are compared with measured resistance curves to assess the stability of tearing.
The analysis is extended to derive the Paris instability parameter T and is compared with the existing analysis for the CCT configuration. The applicability of the T parameter to the description of tearing is also discussed.