Cyclic Deformation at the Tip of Inclined Cracks in Steel Plates

The evaluation of the crack tip deformation is essential to the estimation of crack growth under either static or cyclic loading. A 3-D elastic-plastic finite element analysis was developed to simulate the crack tip deformation along mixed mode inclined edge cracks in a steel plate subjected to either monotonic or cyclic loading at selected R-ratios. Bilinear kinematic hardening model was used to describe the material behavior. The development of the monotonic (Δm) and cyclic (Δc) crack tip plastically deformed zones and opening displacements were traced to find the effect of the crack inclination angle, which significantly affected the size and shape of the crack tip plastic zone. The finite element results compared well with the analytical results based on modified Dugdale’s model. It was observed that Mode II has a significant effect on the plastic zone in the case of equal inclined crack length (EICL), i.e., Mode II increases as the crack angle decreases. Also, it is interesting to note that for the EICL, the magnitude of Δc is delayed to appear with decreasing the inclination angle. Whereas, the variation of monotonic and cyclic plastic zone size in the equal crack horizontal projection (ECHP) case is not affected by the crack inclination angle. Furthermore, it was observed that the static crack tip opening displacement (CTOD) and the cyclic CTOD are independent of the crack inclination angle.

The Effect of Lamb Wave Interaction with Fatigue Crack in Thin Al Sheet

The phenomenon of the Lamb wave interaction with fatigue crack in Al2024-T3 sheet was investigated at cyclic loading. Mentioned effect is associated with the crack open/close that change acoustic impedance of a crack. Analytical simulation of fatigue crack opening using the generalized Dugdale’s model of a crack in thin plate shows good accordance between the intensity of ultrasonic signal and a crack opening.

Etude de l’influence des défauts de petite taille sur le comportement à rupture avec le modèle de Dugdale régularisé

The goal of this work is to prove that, within the framework of Fracture Mechanics with the regularized Dugdale’s model of cohesive forces, the defects the size of which are small compared to the material characteristic length are practically without influence on the limit loads of structures. For that, we treat two examples : the case of a precracked plate, then the case of a plate with a circular hole. The calculations are made with the finite element method.

Electrical Nonlinearity in Fracture of Piezoelectric Ceramics

The structural reliability of piezoelectric ceramics in smart sensors and actuators is hindered by the lack of an appropriate fracture mechanics model. Recent experimental observations of their cracking behavior under combined electrical and mechanical loads contradict predictions made by the linear theory. Evidently, a fracture criterion suitable for piezoelectrics must account for material nonlinearity. Because these materials are typically mechanically brittle, we expect electrical ductility to be the dominant effect. By adopting a multiscale viewpoint, we identify a region of electrical nonlinearity near the crack tip in which the mechanical response of the material remains linear. The equilibrium equations for a fully anisotropic solid have closed-form solutions if the material’s behavior is assumed to be entirely linear outside of the plane of the crack. This approximation is equivalent to Dugdale’s model of the plastic zone in cracked metal sheets. The energy release rate derived using this load for specimens with cracks perpendicular to the poling direction. A remarkable feature of our model is that the energy release rate is strictly independent of the form of the nonlinear electrical constitutive relation. In fact, the material may even experience domain switching in the Dugdale zone without affecting the fracture criterion determined by our formulation.