چكيده به لاتين
Experimental observations of the fracture behavior of hard brittle materials, such as concrete, rocks, bones, and glassy polymers, have shown that the actual situation is much more complex than the idealized one. To apply the effect of crack faces friction in fracture tests, it is necessary to determine the friction coefficient between different materials. Therefore, in this research, a friction testing apparatus based on ASTM D2394-05 standard was constructed, and the friction coefficient between two asphalt cut surfaces was measured. When the contact area is 900 square millimeters and the loading rate (forward speed) is 3 millimeters per minute; the normal stress is directly proportional to the friction coefficient; an increase in the normal stress results in an increase in the friction coefficient. Additionally, increasing the loading rate also leads to an increase in the friction coefficient.
Subsequently, asymmetric semicircular bend (ASCB) specimen were subjected to three-point bending loading. The cracks were created at angles ranging from 0 to 40 degrees with a 10-degree increment, and five specimens were produced and tested for each angle. When the crack angle is zero and 10 degrees, crack propagation occurs in tensile-shear mode, and when the crack angle is 20, 30, and 40 degrees, crack propagation occurs in shear-compressive mode. Numerical simulation was conducted in Abaqus software according to the criteria of maximum tangential stress (MTS) and average strain energy density (ASED), assuming zero friction for angles ranging from 0 to 40 degrees, and non-zero friction for angles of 20, 30, and 40 degrees. The first contact between the crack surfaces occurs at a crack angle of 13.2 degrees, indicating transitioning into the pure Mode II. Additionally, an increase in the friction coefficient at crack angles greater than 13.1 degrees results in a reduction in the Mode II stress intensity factor. Applying friction to crack faces increases the predicted failure load and draws the results closer to experimental outcomes; therefore, it can be inferred that friction presence creates resistance against crack propagation. Additionally, the application of friction to crack faces leads to a slight increase in the predicted critical stress intensity factor and is nearly the same regardless of whether the friction coefficient is zero or non-zero. In the presence of contact between crack faces, the ASED criterion predicts experimental results with higher accuracy; however, when dealing with non-contacting crack faces, the MTS criterion provides higher prediction accuracy.
