Experimental characterization of fracture toughness of X52 pipe steel using CT, SENB, and SENT specimens

This experimental study investigates the fracture toughness of X52 steel pipe using compact tension (CT), Single Edge Notch Bending (SENB), and Single Edge Notch Tension (SENT) specimen geometries at different initial crack length-to-specimen width ratios. The Digital Image Correlation (DIC) technique is utilized to measure crack opening displacement (i.e., CTOD and CMOD) and crack extension. During loading, the new crack tip is defined as the point of maximum strain perpendicular to the crack plane (i.e., longitudinal strain) within a defined area of interest in the cracked zone (i.e., half area of the crack zone). Load-crack opening displacement records and resistance curves for CT, SENB, and SENT specimens are presented at various crack ratios, providing insights into the influence of constraints and initial crack length-to-specimen width ratios. Critical CMOD, CTOD and J-integral values (i.e., values corresponding to the maximum load) obtained in the tests (CT, SENT and SENB) are presented as a measure of single point fracture toughness for each of the specimens, which could reflect the variation in crack tip constrains associated with varying specimen type and crack lengths. The results of the SENB specimens compared well with a typical similar test conducted on X52 pipe steel. The results shed light on the relationship between fracture toughness obtained from different specimen types for the same steel material and contribute to the development of pipeline material fracture toughness database, showing that dependence on a single fracture toughness test is insufficient. Since each specimen geometry and loading condition represents a different level of constraints. Consequently, fracture toughness predictions from different tests are not directly correlated, reducing their reliability for industrial applications.