On the Origin of the Anisotropic Damage of X100 Line Pipe Steel: Part I—In Situ Synchrotron Tomography Experiments

Abstract

In this study, anisotropic ductility and associated damage mechanisms of a grade X100 line pipe steel previously studied at the macroscopic scale, were investigated using in-situ synchrotron-radiation computed tomography (SRCT) of notched round bars. Line pipe materials have anisotropic mechanical properties, such as tensile strength, ductility and toughness. Specimens were tested for loading along both rolling (L) and transverse (T) directions. The in-situ data collected allowed quantifying both specimen deformation (evolution of the cross section) and microscopic damage parameters such as porosity, void shape and void orientation. Nucleation at small particles (CaS/TiO 2) aligned along the L direction was observed during plastic deformation. It was shown that only very few anisotropic particle clusters are present in the material. However, these clusters led to substantial early void growth for loading normal to the loading direction, thereby explaining the toughness anisotropy in this material. Significant void growth was observed at the beginning of load decrease for a relatively limited diameter reduction (about 10%). Coalescence of voids within clusters along L-direction (Necklace) clearly explained anisotropic rupture.

Edge tracing technique to study post‐necking behavior and failure in Al alloys and anisotropic plasticity in line pipe steels

“…The lower maximum strain for testing along the T direction is due to the lower ductility of the material when tested in that direction. This behavior is often observed in line pipe steels 49,50 . The Lankford coefficient is lower than 1 for L and T loadings whereas it is close to 1 for D loading.…”

“…This behavior is often observed in line pipe steels. 49,50 The Lankford coefficient is lower than 1 for L and T loadings whereas it is close to 1 for D loading. These trends are commonly observed for UOE pipes.…”

Influence of stress triaxiality on hydrogen assisted ductile damage in an X70 pipeline steel

“…Figure 12 reports the average D eq of the 20 largest voids per sample, which is regularly used to evaluate void growth [25,34,37,48]. By focusing on the 20 largest voids, there is no significant influence of the X-ray micro-CT resolution on the following quantifications [48].…”

“…This is typically done using two-dimensional metallographic sections [13,30,31]. More recently, High-Resolution X-115 ray Computed Tomography (micro-CT) has been utilized for investigating ductile damage in a quantitative way [32][33][34][35]. It has the advantage of providing threedimensional information in a non-destructive manner.…”

In situ 4D mechanical testing of structural materials: The data challenge

“…The non-destructive nature of this type of observation, except for biological material that are very sensitive to radiation, allows material inspection directly under mechanical testing. In situ 3D imaging has been used in many cases to improve our understanding of damage and failure mechanisms in many kinds of structural materials [1][2][3][4][5][6]. With synchrotron tomography techniques maturing, measurements that previously required tens of minutes are now routinely performed in tens of seconds, and in many cases, in much less than 1 s [7].…”