CMOD COMPLIANCE SOLUTION DETERMINED BY STRESS INTENSITY FACTOR FOR SINGLE EDGE NOTCHED TENSION SPECIMENS IN END-CLAMPED CONDITIONS

The oil and gas industry favors to use single edge notched tension (SENT) specimens in the end-clamped conditions to measure less conservative fracture toughness or resistance curves in low constraint conditions. Usually, single specimen test approach is adopted to measure J-integral or crack tip opening displacement (CTOD) based-resistance curves (simply J-R curves or CTOD- R curves), where the elastic unloading compliance technique is often utilized to monitor crack growth in the quasi-static conditions, and instantaneous crack length is inferred from crack mouth opening displacement (CMOD) compliance measured at each loading step during a single specimen test. Several numerical solutions of CMOD compliance were obtained by finite element analysis for end-clamped SENT specimens. However, these CMOD compliance solutions have varied accuracies and different applicable ranges of crack length ratio a/W. Some of them may be inconsistent with existing solutions of stress intensity factor K for the same clamped SENT specimen because the K factor and the CMOD compliance were determined separately by FEA calculations. Due to this reason, the present paper obtains a more accurate analytical solution of CMOD compliance equation from an accurate full-range K solution for the end-clamped SENT specimens, and thus the proposed analytical solution of CMOD compliance is consistent with the stress intensity factor. Comparisons with different FEA results confirm a higher accuracy of the proposed CMOD compliance solution. Finally, an improved SENT test method is discussed for determining J-R and CTOD-R curves.