Notched M(T) specimen for plane strain studies

Stress state has a major influence on different phenomena, namely, those involving diffusion (hydrogen embrittlement, high temperature fatigue crack growth), plastic deformation (ductile fracture, plasticity induced crack closure) and brittle fracture. The isolated analysis of plane stress and plane strain states is important in fundamental studies of material behaviour. The plane stress state is obtained with thin specimens, while the plane strain state is usually achieved by increasing the thickness or introducing lateral side grooves. The aim of this study is the development of specimen geometries able to isolate the plane strain state at a controlled level. This was carried out by introducing lateral side U-shaped and V-shaped grooves in the standard M(T) specimen to reduce the size of the plane stress surface regions. A three-dimensional numerical model was developed to evaluate the stress triaxiality along the crack front and a limit condition was defined to objectively define the plane strain state. The proposed geometry can be produced using conventional milling tools; can be tested using current laboratory equipment; ensures high reproducibility; and enables the comparison of results with standard geometries. Finally, a sensitivity study of the proposed solution to the main geometrical and material properties was done.