Elastic-plastic characterization of cracks on ductile bimaterial interfaces

In this study, linear elastic and elastic plastic finite element computations are performed to characterize nonlinear fracture behavior on ductile bimaterial interfaces. Nonlinear behavior is obtained directly from finite element computations without utilizing any pre-defined embedded singularity at the crack tip. Analytic expressions obtained for linear elastic fracture mechanics are employed to define boundary conditions in both linear elastic and elastic-plastic analyses. Ramberg-Osgood nonlinear material model is embedded into a finite element source code to characterize uniaxial stress-strain behavior. This nonlinear material model is employed in all elastic plastic analyses to determine the nonlinear stress strain fields at the interface crack tip.; The analytic solution for a finite homogeneous crack in an infinite medium obtained in 1968 by Hutchinson-Rice-Rosengren, which is also called the HRR solution, is reproduced by employing a fourth-order Runge-Kutta method. The problem formulated was a fourth order nonlinear eigenvalue problem. The computed solution is employed in the comparison of elastic plastic finite element results computed at the homogeneous crack tip. Two different finite element meshes are developed for finite element computations and they are employed in the homogeneous fracture problem. Only the second mesh is utilized in the interface fracture computations. The computed linear elastic finite element results are compared to linear elastic analytic results, and elastic plastic results are compared to the HRR results. The comparisons conducted for both analyses were sufficiently close to proceed with a detailed examination of the elastic-plastic interface fracture problem.; Finally, J integral computations at the interface crack tip were performed to characterize the nonlinear interface fracture behavior for different combinations of material variables and loading values. Two important parameters, phase angle and strain energy release rate, are employed to characterize linear elastic fracture behavior. Similarly nonlinear interface fracture behavior can be characterized by two similar variables, plastic phase angle and J integral.