Mechanics of Edge-Cracking and Toughness Determination for Strain Locking Composite Materials

Abstract

In this paper, we describe the mechanics of edge cracking and methods for determining the fracture toughness of strain locking materials using homogenized constitutive models for strain locking materials. We implemented a thermodynamically consistent constitutive model for a strain locking material into a plane stress finite element model and determined the energy release rate for a single-edge cracked configuration. Using material parameters suitable for a copper-clad polymer flexible circuit board and for a biological material, we determined the relationship between the strain energy release rate and the crack length for an applied load history using crackadvance methodology. The change of total potential energy (П = - (U-W)) as an edge crack propagates through a prismatic bar loaded in tension is determined. A polynomial is fitted to П where U is the total strain energy stored and W is the work done by the external loads for the purpose of differentiating with respect to the crack length, a. The energy release rate, G, is derived from the slope Π as a function of crack length from these numerical results. Additionally, an additively manufactured strain locking composite material specimen is produced and tensile tested. The results are used to fit the material constants to a previously derived implicit nonlinear elastic model.