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Abstract: Effective and accurate experimental measurement of fracture toughness is critical to structural integrity assessment. Fracture testing to characterize toughness often adopts ASTM standard E1820 and the single edge-notched bend (SENB) specimen. For this specimen, the simultaneous measurement of load, load-line displacement (LLD), and crack mouth opening displacement (CMOD) are required in E1820, with CMOD used to obtain the compliance-based crack extension and LLD to evaluate the incremental value of J-integral. In this paper, a direct approach is introduced to determine more accurate J resistance curves for SENB specimens using only load-CMOD records. For constraint-dependent J-R curves obtained from fracture testing, J-A2 fracture constraint theory is used to quantify the constraint effect on fracture toughness, so that laboratory test data can be transferred to practical engineering components.