The research reported in this paper provides validation of a notched disk M(N) specimen geometry for both static and dynamic fracture toughness testing. More specifically, the work verifies the proposed procedure for the determination of the fracture toughness of materials most commonly used in plate-like configurations and extends its application to the dynamic case. The notched disk M(N) specimen has an axisymmetric notch machined on one of its faces, is clamped on its periphery, and is loaded axisymmetrically in a direction normal to its plane for both the precracking and loading-to-failure portions of the test. The advantage of this specimen geometry is that it is free from the adverse edge effects that exist in the standard C(T) specimen. Furthermore, a uniform plane strain state along the crack front induces a triaxial tensile stress and a small plastic zone. Finally, the specimens may be manufactured without difficulty.
Also reported in this paper are the findings of finite element analyses of both the 3-mm and 4-mm notch specimen geometries. Parametric studies emphasize the influence on the stress intensity factors of the notch location with respect to the clamped boundary. Stress intensity factors are evaluated for different crack lengths and orientations by the crack opening displacement method, the modified crack closure integral approach, and the virtual crack extension technique. The results, presented as normalized stress intensity factors, are essential for a reliable reduction of the test data.
Fracture toughness testing of an A17075-T651 aluminum alloy was performed using 3-mm notch depth M(N) plate specimens. For dynamic fracture toughness testing, the 4-mm notch depth specimens, manufactured from polystyrene resins, were used.
Using the procedure fully detailed in the body of this_paper, the static fracture toughness of A17075-T651 was determined as KIc = 31.4 MPa √m, while the dynamic fracture toughnesses of polystyrene using the M(N) specimen geometry were between 0.73 and 0.99 MPa √m. These values indicate that the M(N) specimen geometry testing capabilities are substantiated.