The connection and difference between symmetrically single-edge notched loading method and four-point shear loading method

were analyzed based on lab tests and numerical simulations. Tests were carried out for two different types of specimens to study crack

propagation pattern and fracture toughness. Then, the extended finite element method was employed to study the stress distribution near

the crack tip. Results show that for symmetrically single-edge notched specimens, shear stress near crack tip is much larger than

tension stress perpendicular to the predefined notch. Crack propagates along the direction of original predefined notch, and fracture

toughness is independent of initial length of notch, but it may increase with the increase of specimen length and the decrease of

specimen height. Near the crack tip of four-point shear loading beam specimens, the magnitude of shear stress is similar to that of the

maximum principal stress. Near the loading points, fracture toughness is independent of beam size, but it may increase with the increase

of initial crack length and the shortening of distance between predefined crack and near-end loading point.