Evaluation of Crack Tip Constraint in Pipes Subjected to Combined Loading

Abstract

Single edge cracked under tension (SENT) specimens appear as an alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The similarities of stress and strains fields between SENT specimens and cracked pipes are now well known. However, these similarities are not so well established for the case of circumferentially cracked pipes under combined loading conditions (i.e. internal pressure plus tension, internal pressure plus bending, etc.). This work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed crack configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads.

Investigation of strain measurements in (curved) wide plate specimens using digital image correlation and finite element analysis

“…Noteworthy hereby is that the flaw tip constraint (Q-stress) in a CWP specimen is highly similar to that in a girth weld of a pressurized pipe. 4,5 The principal result of a (C)WP test for a strainbased assessment is the relation between crack driving force and the remotely applied longitudinal strain (further called 'remote strain'), whose proper measurement is key to obtaining a valid test result. Note that remote strain can significantly differ between both welded plates due to the abovementioned plate-to-plate heterogeneity in terms of yield strength and/or post-yield behaviour.…”

“…Journal of Strain Analysis 47 (5) pronounced in the experiment WP3), and/or the assumption of isotropical yielding behaviour in the simulations. As such, the differences between Figure 8 Finally it can be noted that, for both simulations and experiments, shear strains have been found negligible with respect to the longitudinal strain level in the zones of optimal uniformity.…”