Traction-separation relationship for polymer-modified bitumen under Mode I loading: Double cantilever beam experiment with stereo digital image correlation

Analysis of the data obtained for the two slower loading rates that exhibited ductile fracture throughout the entire growth process shows that the energy release rate Gcd = 70 J/m2, and the final separation, δcd = 250 µm for the slowest loading rate of 0.03 mm/min and, Gcd = 120 J/m2, and the final separation, δcd = 250 µm for 0.3 mm/min loading rate. For the highest loading rate, which exhibited nominally brittle fracture, the energy release rate Gcb = 10 J/m2, and the final separation δcd = 1.5 µm. The peak cohesive stresses during ductile and brittle fracture are determined to be σd = 0.7 MPa and σb = 9.6 MPa, respectively, for loading rates of 0.3 mm/min and 3 mm/min, respectively. Finally, COD at the onset of crack growth measured at 1.00 mm behind the moving crack tip for the loading rate of 0.3 mm/min, CODd ≈ 0.30 mm, remaining constant for crack lengths, a, in the range 25 mm ≤ a ≤ 165 mm.