Quasistatic Fracture using Nonliner-Nonlocal Elastostatics with Explicit Tangent Stiffness Matrix

We apply a nonlinear-nonlocal field theory for numerical calculation of quasistatic fracture. The model is given by a regularized nonlinear pairwise (RNP) potential in a peridynamic formulation. The potential function is given by an explicit formula with and explicit first and second derivatives. This fact allows us to write the entries of the tangent stiffness matrix explicitly thereby saving computational costs during the assembly of the tangent stiffness matrix. We validate our approach against classical continuum mechanics for the linear elastic material behavior. In addition, we compare our approach to a state-based peridynamic model that uses standard numerical derivations to assemble the tangent stiffness matrix. The numerical experiments show that for elastic material behavior our approach agrees with both classical continuum mechanics and the state-based model.The fracture model is applied to produce a fracture simulation for a ASTM E8 like tension test. We conclude with an example of crack growth in a pre-cracked square plate. For the pre-cracked plate, we investigated {\it soft loading} (load in force) and {\it hard loading} (load in displacement). Our approach is novel in that only bond softening is used as opposed to bond breaking. For the fracture simulation we have shown that our approach works with and without initial damage for two common test problems.

Conservation laws in dynamic fracture tasks

Two fracture model under elastic wave action are considered: with energy dissipation while fracturing and without energy dissipation. The conservation of integrals of the complete mechanical energy and the quantities of motion of the fragments of the rod is investigated. For the model of fracture without energy dissipation, the complete mechanical energy is stored. For a fracture model involving energy dissipation, the complete mechanical energy decreases, although the motion of the inertia center remains. Therefore, dynamic fracture occurs due to the dissipation of the energy of the wave process in the rod. The application of the models is illustrated by an example of a study of quasistatic fracture by the propagation of a brittle crack. The dependence of the fracture energy on the crack size as well as the complete fracture energy were obtained.