Nonlocal interfaces accounting for progressive damage within continuum-kinematics-inspired peridynamics

In this work, we present a modeling approach to nonlocal material interfaces in the framework of continuumkinematics -inspired peridynamics. The nonlocal model accounts for progressive damage within a finitethickness interface, as opposed to the more common practice of abrupt bond breakage across a zero -thickness interface. Our approach is based on an overlap of the constituents within the interface. Interfacial bonds between initially overlapping partner points are governed by a constitutive law reminiscent of a tractionseparation -law. The governing equations for continuum -kinematics -inspired peridynamics in the presence of an interface are derived using a rate -variational principle. The damage formulation is established using the classical concept of internal variables. Following the notion of a standard dissipative material, thermodynamic consistency of the constitutive laws and the evolution of the internal variables is ensured. The latter results in a straightforward evaluation of a damage function. We give details about the computational implementation comprising a peridynamic discretization and a Newton-Raphson scheme. A sound approach to approximate the interface normal during deformation is presented, which allows to penalize material penetration across the interface. The proposed model is explored in a series of numerical examples, i.e., classical peeling and shearing tests, for a variety of damage functions. A key feature of our interface model are the nonlocal characteristics that are assumed to play a role especially at small scales. We, first, observe that an increasing thickness of the nonlocal interface leads to stronger interfacial bonding and less damage. Second, an increase in horizon size results in stiffer material behavior. When studying the wrinkling and delamination behavior of a compressed bilayer, it is found that an increase in interface stiffness leads to a smaller wrinkling wavelength. Moreover, delamination due to progressive damage of interfacial bonds in the post -wrinkling regime is observed, which, to the best of our knowledge, has not been studied in a nonlocal model before.