Constraint effect in tensile to shear type transition

There are two main fracture types in ductile materials: tensile type and shear type. It is believed that when the loading condition is predominantly tensile (mode I), tensile type fracture occurs and when it is mostly shear (mode II), shear type fracture occurs. Transition from tensile to shear type fracture is considered to occur at a certain proportion of mode I to mode II loading, irrespective of the level of constraint. However, this study reveals that the effects of constraint must be included because, depending on the level of constraint, transition may occur anywhere from mode I to mode II. A theoretical model of tensile to shear type fracture has been developed to include the effect of constraint. To provide experimental evidence for this theoretical model, the extreme case of mode I loading has been examined. It is shown that by reducing the constraint level to a low enough value, a tensile to shear type fracture transition takes place, even in mode I.