Strain History Effects on Fracture Mechanics Parameters: Application to Reeling

Abstract

It is now well accepted that welded structures may contain flaws, and that these do not necessarily affect structural integrity or service performance. This is implicitly recognized by most welding fabrication codes that specify weld flaw tolerance, or acceptance, levels based on experience and workmanship practice. However, these levels are somewhat arbitrary and do not provide a quantitative measure of structural integrity, i.e. how “close” a particular structure containing a flaw is to the failure condition. This concept is of special interest in cases in which the pipe is subjected to loads that produce important deformations. In particular the reeling process, used to install offshore lines, produce large cyclic plastic deformation on the pipes. In this work the method to perform a structural reliability analysis (SRA) for a tube subject to reeling is considered in detail. A fracture mechanics based methodology is reviewed and the points that need to be resolved before extending the methods to include reeling are clearly identified. The effect of the strain history on the applied and material fracture mechanics parameters were studied. A theoretical model was developed to describe the crack driving force evolution through strain cycles. A criterion was proposed and corroborated to represent material fracture resistance behavior. An experimental program was carried out. The material analyzed was a X65 - tube 355.4 × 22.2 mm. Monotonic and cyclic fracture mechanic tests were performed on single edge notch in tension (SENT) specimens. The material fracture resistance curve was determined based on the monotonic tests. The cyclic tests were used to determine experimentally the applied fracture mechanic parameters evolution. A very good agreement between predicted and measured CTOD values was obtained for the cases analyzed. A methodology to perform a SRA for tube subjected to reeling is proposed.

Numerical simulation of prestrain history effect on ductile crack growth in mismatched welded joints

“…So far, some related prestrain models have been proposed among previous research studies. 7,12,41 According to Fig. 1a, it can be found that the fracture resistance curve of the loss of memory model 7 does not change to a new origin stage from the first cycle to another and the crack driving force of different cycles is independent of loading memory.…”

“…Prestrain effect models are applied to show the prestrain history on the fracture toughness including the process of reeling and re‐tension. So far, some related prestrain models have been proposed among previous research studies . According to Fig.…”

“…Prestrain effect models on fracture toughness: (a) loss of memory model, (b) history‐independent memory model and (c) history‐dependent memory model . [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Ernst et al 41 conducted monotonic and cyclic fracture mechanic tests to describe the crack force driving evolution and develop the history-independent memory model, which is shown in Fig. 1b.…”

Large Scale Tests of Strain Capacity of Pipe Sections With Circumferential Defects Subjected to Installation-Induced Plastic Strain History

“…This is based on prior testing that showed that R-curves were not significantly altered by cyclic loading [2][3][4]. More recent papers, however, conclude that plastic deformation influences, in a detrimental manner, the local failure mechanisms [5][6][7][8][9][10][11][12][13][14]. Somewhat in contradiction to DNV-RP-F108, DNV-OS-F101 [15] states that for ECA of pipelines that have been subject to plastic strains, fracture mechanics testing shall be performed on pre-strained material.…”