Identification of anisotropic Hill criteria from the channel die compression test. Application to a normal anisotropy of zirconium 702α\alpha

During the last years the study of the plastic deformation modes and the anisotropic mechanical behavior of zirconium alloys have been the subject of many investigations. This paper deals with a phenomenological identification of an anisotropic Hill constitutive equation of zirconium 702$\alpha$ samples using channel die compression at room temperature. Generally, by considering the different possible orientations of the samples in the channel die device, three initial textures, named LD (longitudinal direction X), TD (transverse direction Y) and ND (normal direction Z), were defined with the corresponding stresses $\sigma_{LD}$, $\sigma_{ND}$ and $\sigma_{TD}$. To describe the anisotropy of the material, a quadratic Hill criteria is used. After an analytical description of the plane compression test, the Hill parameters can be expressed as a function of $\sigma_{LD}$, $\sigma_{ND}$ and $\sigma_{TD}$. The variation of these parameters with a proposed equivalent plastic strain, desaibing the deformation history of the material, is analyzed. Finaliy a constitutive equation of the normal anisotropy in the plane of the plate is obtained

Influence du trajet de chargement sur l’évolution de texture de la phase

Cette étude porte sur la caractérisation de l'évolution de texture cristallographique d'une tôle de Ti-6Al-4V dont la phase α présente initialement (i) une forte concentration de pôles {0002} le long de la direction transverse et (ii) un alignement de pôles {1010} le long de la direction de laminage. Différents échantillons prélevés dans la tôle de départ selon un angle θ par rapport à la direction de laminage initiale sont étudiés après déformation plastique par laminage et recuit de recristallisation à 1025 °C. Les orientations préférentielles obtenues sont analysées selon les valeurs de θ. Elles mettent en évidence l'influence de la direction de laminage –repérée par rapport à la texture initiale de la tôle– sur les textures après déformation et traitement thermique

Formability and macroscopic shearing of a titanium alloy Ti-6Al-4V under channel die compression

International audienceThe mechanical behavior of Ti-6Al-4V is analyzed using channel die compression tests at room temperature. Specimens were cut out from a starting sheet in order to consider samples with specific initial crystallographic textures. Three types of specimens are considered in the study using an angle θ defined with the initial directions LD0, TD0 and ND0 of the starting sheet. The following values of θ are considered: 0°, 45° and 90°. Plastic deformations up to 20% are considered. Several experimental techniques are used, namely optical microscopy, SEM and Xray diffraction for texture evolution. The true stress-strain curves are plotted and the shape change of the specimens is analyzed. A macroscopic shearing is observed for one the three types of initial textures considered, notably θ = 45°. To complete the study, the Taylor model is applied in order to compare the activation of the mechanisms of the α phase in the different specimens. © 2017 Author(s)

Anisotropic behavior of a Ti-6Al-4V sheet during cold rolling: evidence of macroscopic shearing

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Final textures in cold rolled Zr702α polycrystalline samples

The ability to access to large plastic deformations in cold rolling is applied here in order to determine the final orientations of different initial textures of Zr702α polycrystalline samples (T1-T4 textures). A distribution of the axes in the vicinity of the normal direction (ND) of the sheets and an isotropic repartition of the {[MATH]} poles, almost in the rolling-transverse plane (RD-TD), appears as a final orientation for most of the analyzed samples. No significant reorientation of the {0002} poles from the (RD-ND) plane or from the vicinity of the ND direction to a stable orientation in the (ND-TD) plane is observed

An optimal forward extrusion device proposed for numerical and experimental analysis of materials tribological properties corresponding to bulk forming processes

International audienceThis paper concerns the design and the analysis of an optimal forward extrusion die used in order to characterize and to identify the tribological properties corresponding to real contact conditions which occur during bulk plastic forming processes. The main idea is to find the friction parameters by a two-step inverse analysis method applied to a Finite Element Model of the extrusion process. A compression test, using a special dumbbell specimen, is also performed in order to describe correctly the real rheological behaviour of the material. Experimental upsetting and extrusion tests are carried out for an AA5083 aluminium alloy and the corresponding rheological and friction coefficients are identified using only the recorded load-stroke curves. Experimental analysis of the contact surfaces, validation of the obtained results and influence of the friction on the local mechanical and microstructural properties of the material are performed via tribometer tests, micro-hardness measurements and EBSD characterization

Deformation twinning and the hall-petch relation in commercial purity ti

The effect of grain size and deformation temperature on the behavior of wire-drawn a-Ti during compression has been examined. At strains of 0.3, the flow stress exhibited a negative Hall&ndash;Petch slope. This is proposed to result from the prevalence of twinning during the compressive deformation. Electron backscattered diffraction revealed that {1012} was the most prolific twin type across all the deformation temperatures and grain sizes examined. Of the twinning modes observed, {1122} twinning was the most sensitive to the grain size and deformation temperature. The range of morphologies exhibited by deformation twins is also described.<br /