TWI Industrial Member Report Summary 98/1979
By S J Garwood
Elastic-plastic resistance curves have been measured on 20mm thick plate to API 5LX65 specifications for the three point bend and centre-cracked tension geometries in the transverse orientation and a comparison made with their longitudinal counterparts. An additional series of tests employing side grooving, in order to eliminate shear lips for these geometries, was also conducted. The results from these tests indicate that a dramatic decrease in the slope of the resistance curve results from the removal of the shear lips. However, toughness values relating to the initiation of tearing appear little affected by the side grooving.
A distinct geometry effect between the tension and bend configuration is evident even with the absence of shear lips. The tension geometry would appear to display a consistently higher resistance to crack growth than the equivalent bend configuration. However, the difference between the crack growth curves for the bend and tension geometries is small when compared to the effect that the shear lips have on the propagation resistance. This would lead to the possibility of employing bend specimens to provide conservative estimates for the equivalent structural resistance curves.
Ductile instabilities were induced on side grooved centre-cracked plates. A ductile instability analysis for this geometry was deduced and good correlation between theory and practice achieved. The importance of the compliance of the test machine is emphasised in this analysis.
Calculations have also been made concerning the tearing instability parameter T and estimates made of the crack opening angles for the various configurations based on the initial slope of the resistance curve.