Abstract: Based on the energy density equivalence method, a quasi-static ductile fracture testing method was established for C-shaped Outside Semi-ellipse-notched Compression (COSC) specimens. A finite element analysis was performed to obtain the J-integral distribution along the crack front. Quasi-static fracture toughness tests were conducted on COSC specimens made of 45 steel and of A5083 steel. By integrating the J-integral distribution, the J-resistance curves at different locations along the surface crack front were determined. The experimental results from limited samples show a negative correlation between the initial crack size and the J-resistance curves. Typically, the J-resistance curve is highest at the deepest point of the crack front. However, as the surface crack propagates, the J-integral near the free surface increases significantly. At certain propagation stages, the J-resistance curves near the free surface (φ/π=0.1 and φ/π=0.3) exceed that at the deepest point (φ/π=0.5).