Numerical modelling and experimental validation of the Pipe-Ring notched Bend (PRNB) specimen for elasto-plastic fracture mechanics

• Validated FEM model for Pipe Ring Notched Bend (PRNB) specimen with path independent J-integral. • Experimental J-CMOD and CTOD-R curves confirmed via DIC and clip-gauge. • PRNB geometry enables fracture testing of constrained pipe materials. • CTOD values from DIC match ASTM E1820 calculations. • PRNB specimen offers a practical alternative to SENB/CT in pipe applications. This paper presents the development and experimental validation of a finite element model for the Pipe-Ring Notched Bend (PRNB) specimen, a promising and increasingly recognized alternative for evaluating the fracture toughness of pipe materials. The study focuses on the accurate evaluation of the J- integral in elasto-plastic fracture mechanics. The numerical model is constructed in Abaqus using material data derived from tensile tests on boiler steel 16Mo3. Mesh sensitivity analysis identifies an optimal element size of 0.5 mm, ensuring both numerical stability and convergence of the J- integral across integration contours. The third integration path is confirmed as sufficient for path-independent results. Experimental validation is performed via three-point bending tests on PRNB specimens, with crack mouth opening displacement (CMOD) measured using both a COD extensometer and the Digital Image Correlation method (DIC). The numerical and experimental force-displacement curves show excellent agreement, confirming the reliability of the proposed model. Additionally, CTOD measurements support the consistency of the J- integral evaluation. Resistance curves (J–R and CTOD–R) were constructed using normalization technique and the Stretch Zone Width (SZW) method has been applied. The results confirm the PRNB specimen as a practical and reliable alternative for fracture toughness evaluation when standard specimens are not feasible. The validated model provides a robust framework for fracture toughness estimation in pipe materials, particularly where standard specimens (SENB, CT) are impractical due to geometric constraints.