Novel Specimen Design for Measurement of In-Plane Fracture Toughness of Metals

Standard-compliant measurement of the in-plane fracture toughness of metals is often challenging due to insufficient material in the through-thickness direction to extract a full single edge bending (SEB) or compact tension (CT) fracture specimen. In the present work, we propose a new specimen design methodology to overcome this challenge. A W-shaped SEB specimen (called W-SEB) was developed, and its topology was optimized using finite element simulations. The new specimen design was validated numerically and experimentally on a case study showing excellent agreement with standard ASTM E1820 actual SEB specimen geometry. In view assessing the anisotropy of the fracture toughness (K_Q and crack tip opening displacement (CTOD)) of pipeline steels susceptible to hydrogen-induced cracking (HIC), the W-SEB specimen was tested on X65 and X42 pipeline steel samples taken from the field. Experimental results show an increase in the maximum CTOD along the in-plane direction as compared to the transverse direction for both steel grades. Such experimental results could lead to important considerations with respect to accurate fitness for service assessment of HIC-damaged assets.