International audienceFatigue crack growth tests in mixed-mode II + III were performed on maraging steel and Ti-6Al- 4V. The 3D evolutions of the crack fronts -measured by SEM after interrupted tests- were analyzed, taking into account the reduction in effective crack driving force by the interlocking and friction of the asperities of the crack surface. Under small-scale yielding conditions, the mixed-mode crack growth rates were found to correlate best with Keff2 II + 1.2Keff2 III in maraging steel, while for Ti-6Al-4V, Keff2 II + 0.9Keff2 III appeared suitable. For extended plasticity, a crack growth prediction method is proposed and validated for Ti-6Al-4V. This method is based on elastic-plastic F.E. computations and application, ahead of each node of the crack front, of a shear-dominated fatigue criterion
International audienceFatigue crack growth testswere performed under various mixed-mode loading paths, on maraging steel. The effective loading paths were computed by finite element simulations, in which asperity-induced crack closure and friction were modelled. Application of fatigue criteria for tension or shear-dominated failure after elastic–plastic computations of stresses and strains, ahead of the crack tip, yielded predictions of the crack paths, assuming that the crack would propagate in the direction which maximises its growth rate. This approach appears successful in most cases considered herein
Fine‐grained aluminum (700–1000 nm) was processed by dynamic severe plastic deformation of coarse‐grained (3 mm) pure aluminum (99.999 wt.%). The resulting microstructure was characterized by transmission electron microscopy (TEM) and X‐ray profile analyses. It is observed that the grain size determined by TEM departs from measurements made by X‐ray profile analysis. In the latter case, the average crystallite size determined over the global crystallographic or on the deformation‐induced texture components, namely {123} 〈 751 〉, {100} 〈 011〉, and {223} 〈 154 〉, yields similar values (∼225 nm). By contrast, the dislocation density determined on these texture components is about two times higher than the one measured on the global texture. The difference might be related to the specificities of the induced crystallographic texture.
The variable thickness tube drawing is a new modification in the tube drawing methods which enables production of axially variable thickness tubes faster and easier in comparison with other similar methods like radial forging or indentation forging. The production of this type of tubes can be used in optimum design of mechanical parts which do not necessarily need constant thickness along the axis of tube and this method can strikingly reduce the overall weight of parts and mechanical assemblies like cars. In this paper, the variable thickness tube drawing were parameterized in a MATLAB code and optimized with the Ls-Opt software as an optimization engine and Ls-Dyna as a FE solver. The final objective of this optimization study is to determine the minimum thickness which can be produced in one step by this method with various tube dimensions (tube thickness and outer diameter). For verification of results, some experiments were performed in the tube drawing machine which was fabricated by this research group and acceptable correspondence was observed between numerical and experimental results.
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