L. Signor

Physically-Based Simulations of the Cyclic Behavior of FCC Polycrystals

Two homogeneization approaches are used in order predict the cyclic elastic-plastic behaviour of 316L(N) polycrystals, either

Influence of Microtexture on Early Plastic Slip Activity in Ti-6Al-4V Polycrystals

Microtextured regions are known to influence the fatigue performance of titanium alloys. Previous studies revealed that crack initiation, accounting for most of the fatigue life, is triggered by slip activity. The influence of microtextured regions on the early plastic slip activity was presently investigated by means of an in situ tensile test performed inside a scanning electron microscope on a bimodal Ti-6Al-4V polycrystalline specimen. A slip trace analysis was carried out in several regions with different crystallographic textures to highlight potentially different deformation behaviors. Significant stress heterogeneities were revealed through an early slip activation in microtextured regions with a predominant [0001] orientation. This point was shown to be related to a locally increased resolved shear stress. Consequences on behavior under cyclic loadings are finally discussed.

Plastic Slip and Early Stage of Fatigue Damage in Polycrystals: Comparison between Experiments and Crystal Plasticity Finite Elements Simulations

For conventional materials with solid solution, fatigue damage is often related to microplasticity and is largely sensitive to microstructure at different scales concerning dislocations, grains and textures. The present study focuses on slip bands activity and fatigue crack initiation with special attention on the influence of the size, the morphology and the crystal orientation of grains and their neighbours. The local configurations which favour - or prevent - crack initiation are not completely identified. In this work, the identification and the analysis of several crack initiation sites are performed using Scanning Electron Microscopy and Electron Back-Scattered Diffraction. Crystal plasticity finite elements simulation is employed to evaluate local microplasticity at the scale of the grains. One of the originality of this work is the creation of 3D meshes of polycrystalline aggregates corresponding to zones where fatigue cracks have been observed. 3D data obtained by serial-sectioning are used to reconstruct actual microstructure. The role of the plastic slip activity as a driving force for fatigue crack initiation is discussed according to the comparison between experimental observations and simulations. The approach is applied to 316L type austenitic stainless steels under low-cycle fatigue loading.

TRANSITION FROM SOLID TO LIQUID SPALL IN TIN UNDER LASER SHOCKS OF INCREASING INTENSITY

When a shock‐loaded target is melted on compression or on release, the tensile stresses generated upon reflection of the pressure pulse from a free surface are induced in a liquid state. Instead of the well‐known spallation process occurring in solid targets, cavitation takes place in the melted material and liquid fragments are ejected from the free surface. Although increasing interest is manifested on the subject, related data are still scarce. In a recent paper, we have reported an exploratory investigation of liquid spall in tin targets submitted to intense laser shocks. Here, we present new results obtained over a lower pressure range, where we focus on the progressive transition from the ductile fracture behaviour of solid tin to the cavitation expected above melting. Both time‐resolved free surface velocity measurements and post‐test examination of the recovered samples clearly indicate this transition. Incipient melting produces a decrease in tensile strength that can be evaluated from the veloci...