Three-dimensional contact fracture problems using enriched finite elements

In this study, three-dimensional fracture problems are solved, with coupled contact behavior included in the finite element analysis. Linear elastic fracture mechanics theory is applied to analyze three-dimensional curved cracks in isotropic/anisotropic materials and three-dimensional interface cracks on bimaterial interfaces. Fracture mechanics parameters, such as stress intensity factors, strain energy release rates, and phase angles, are calculated using the enriched finite element method. Special enriched elements are embedded in the crack front region, so that three-dimensional crack tip singular fields are properly included along the crack front. Contact constraints, which transform the linear problems to a nonlinear one, are imposed by using the penalty function method. Coulomb friction conditions are handled using the tangent force method.; Two typical contact fracture mechanics problems are considered: (1) "crack face contact" problems, and (2) "cracked components loaded through contact with another component" problems. The effect of crack face closure on fracture behavior for a three dimensional crack is studied in detail and it is shown that even partial crack face contact can have a great effect on the stress intensity factor solutions. Special attention is given to interface crack problems, since these problems are known to exhibit unusual contact behavior. The interface crack problem is analyzed using enriched finite elements for various material combinations and loading conditions. The results are compared with both Comninou's asymptotic solution and the classical oscillatory solution that ignores the contact effects. Three-dimensional interface corner crack problems, with full crack face closure, are evaluated and the results are compared with the equivalent reversed loading case, where the crack faces are fully open. It is shown that crack face closure, with frictionless contact, results in strain energy release rates that are just as severe as when crack face opening occurs. The effect of friction is also studied to some extent. Friction between crack faces is shown to have a great effect on the strain energy release rate of an interface crack. In addition, the effect of the unilateral contact and tangential (frictional) contact on the stress intensity factors variation for a three-dimensional crack is investigated. It is shown that contact conditions can completely change the nature of the stress intensity factor variation along the crack front, even though the contact region is very localized.; A general mixed-mode fatigue crack growth simulation methodology, using a fracture mechanics computer program, FRAC3D, is given in detail. Example three-dimensional crack growth simulations are presented. A three-dimensional fatigue simulation, which includes crack face contact, is presented. The effect of crack face contact on fatigue behavior is demonstrated. Thermal fatigue for a three-dimensional corner interface crack is studied under fluctuating thermal loads in order to emphasize the effect of on/off cycles, on fatigue behavior of electronic packages.; Finally, application of multi-point constraint methodology in fracture problems is demonstrated. It is shown that mesh distortion and fine meshes due to the crack insertion into a model can be eliminated by global/local analyses using multi-point constraint methodology.