Specimen for Fracture Characterization of Material under Biaxial Stress Fields

The simple circular notched specimen was originally proposed by Arcan to characterize the elastic properties of fiber-reinforced composites. Unfortunately, its optimized geometry does not allow to measure with reasonable accuracy both the material shear strength and the conditions of failure under a generic biaxial stress state, since the effects of stress concentration on the fillets of the two V-grooves and on the inner circular edges are responsible of premature fractures due to the uniaxial stress states of the notches edges. To improve the performance of this kind of specimen, an extensive FEM analysis has been carried out by a two-dimensional parameterized model, in order to identify those geometries that make possible the fracture to occur in the minimum strength section under the action of a uniform pure shear stress state. Furthermore, the parametric analysis has been extended to the 3D field to define alternative geometries, having variable thickness, that are able to produce with an higher probability material fracture in the minimum strength section.