Low-Constraint Toughness Testing of Two Single-Edge Notched Tension Methods in a Single Specimen

Single-edge notched tension (SE(T) or SENT) specimens have been increasingly proposed as a low-constraint toughness test to measure toughness of line pipe materials, as the crack tip constraint approximates a circumferential surface flaw in a pipe under loading. The clamped SE(T) single-specimen procedures recently developed by Shen and Tyson (2008, "Fracture Toughness Evaluation of High Strength Steel Pipe," ASME Paper No. PVP2008-61100; 2008, "Development of Procedure for Low-Constraint Toughness Testing Using a Single-Specimen Technique," CANMET Materials Technology Laboratory, Technical Report No. 2008-18 (TR)) and Tang et al. (2010, "Development of the SENT Test of Strain-Based Design of Welded Pipelines," 8th International Pipeline Conference, IPC 2010, Calgary, AB, Canada) have both used in common the use of a clamped single-specimen of similar geometry and relied on the unloading compliance technique for crack size estimation. In the former case, a single clip gauge is attached to the integral knife edge and the crack-tip opening displacement (CTOD) is estimated by means of a J-integral-to-CTOD conversion, similar to the procedure of ASTM E1820-11. The latter uses a pair of clip gauges mounted on an attachable raised set of knife edges to estimate CTOD at the original crack tip position by a triangulation rule. Consolidating these two sets of clip gauges in a specimen makes direct comparisons of two SE(T) methods under identical test conditions: material, specimen geometry, equipment, test temperature, and operator (Weeks et al., 2013, "Fracture Toughness Instrumentation Techniques for Single-Specimen Clamped SE(T) Tests on X100 Linepipe Steel: Experimental Setup," 6th Pipeline Technology Conference, Ostend, Belgium). In this study, SE(T) testing employing these two SE(T) methods on a single specimen was conducted on B x B shallow-cracked (a/W similar to 0.35) specimens of two X70 pipeline girth welds. This paper discusses details of the two SE(T) methods and techniques on the same specimen.