Nonlocal Neumann volume-constrained problems and their application to local-nonlocal coupling

As alternatives to partial differential equations (PDEs), nonlocal continuum models given in integral forms avoid the explicit use of conventional spatial derivatives and allow solutions to exhibit desired singular behavior. As an application, peridynamic models are reformulations of classical continuum mechanics that allow a natural treatment of discontinuities by replacing spatial derivatives of stress tensor with integrals of force density functions. The thesis is concerned about the mathematical perspective of nonlocal modeling and local-nonlocal coupling for fracture mechanics both theoretically and numerically. To this end, the thesis studies nonlocal diffusion models associated with ``Neumann-type'' constraints (or ``traction conditions'' in mechanics), a nonlinear peridynamic model for fracture mechanics with bond-breaking rules, and a multi-scale model with local-nonlocal coupling. In the computational studies, it is of practical interest to develop robust numerical schemes not only for the numerical solution of nonlocal models, but also for the evaluation of suitably defined derivatives of solutions. This leads to a posteriori nonlocal stress analysis for structure mechanical models