Design and validation of simple bend beam specimen for covering the full range of I plus II fracture modes

Using short beam specimen containing an edge crack (perpendicular to the beam axis) and subjected to asymmetric three-point bend loading a new test configuration (called ASBB) was suggested for investigating the mixed mode I/II fracture. Despite the conventional beam specimen with high aspect ratio of length to width that is not able to produce mode II or dominantly mode II conditions, complete mode mixities were obtained using the proposed three-point bend asymmetric short beam specimen. The fracture parameters including modes I and II stress intensity factors and T-stress were determined numerically for this test specimen with different crack lengths and bottom rollers distances relative to the crack. The practical ability of the ASBB specimen was examined experimentally by conducting several mixed-mode I/II fracture tests on PMMA material. The critical stress intensity factors, the direction of fracture kinking and the path of fracture trajectory were investigated both experimentally and theoretically using MTS and GMTS criteria. The fracture toughness of PMMA tested with the ASBB specimen was increased by increasing the contribution of mode II component. The effects of beam length aspect ratio, crack type and loading type on the mixed mode fracture of cracked beam samples subjected to threepoint bend loading were also examined.