Modeling the evolution of anisotropy in Al–Li alloys: application to Al–Li 2090-T8E41

Abstract

It is widely reported in current literature that the precipitation hardened Al-Li sheet alloys exhibit extremely high anisotropy in yield (and ultimate tensile) strength, which is well beyond what can be explained as purely a consequence of the strong crystallographic texture in the material (e.g. J. Mater. Sci. Eng. A265, 1999, 100). This paper presents a crystal plasticity based modeling framework that will (i) facilitate the segregation of the contributions to the overall anisotropy from crystallographic texture and precipitation hardening, and (ii) correlate the contribution from precipitate hardening to either co-planar slip activity or the noncoplanar slip activity in the cold-working step prior to the aging heat treatment. More specifically, a Taylor-type (fully-constrained) crystal plasticity model was formulated to predict the yield strength of the fully processed sheet and its anisotropy, while accounting for the initial texture in the hot-worked sheet, its evolution during the cold-working step prior to aging, and the inhomogeneous nucleation of the T 1 phase platelets (these are known to form on {111} planes, but not usually in equal amounts on the different {111} planes in a given crystal). In an effort to illustrate the methodology developed in the study, a limited set of experiments was conducted on Al-Li 2090-T8E41 alloy sheet. Off-axis stretches were applied on the sheet at room temperature prior to the aging treatment, and the mechanical anisotropy in the fully processed sheets was characterized by performing tension tests on coupons cut from the sheet at 0, 30, 45, 60 and 90 to the original rolling direction (RD). Both the initial texture in the sheet and its evolution during the different off-axis stretches were characterized. The alloys processed in this study showed pronounced anisotropy. The application of the methodology developed in this study revealed that much of the observed anisotropy in this particular data set could be explained by accounting for the texture in the sample in the processed condition. Although the data set available was inadequate to establish clear correlations of the anisotropy with preferential hardening mechanisms arising from either co-planar or non-co-planar slip activity during the off-axis stretch, there were indications favoring the latter. This case study, however, illustrates the application of the methodology developed in this study to obtain better insight into the nature of the anisotropy in these sheets and its physical origin. #

Investigation of subsequent viscoplastic deformation of austenitic stainless steel subjected to cyclic preloading

“…Mollica et al (2001) developed a general three dimensional model, which can reproduce the stress-strain response at loading reversals and can be applied to more general changes in loading direction. Deformation induced anisotropy, which leads to different subsequent deformations depending on the loading direction has also been investigated (Ishikawa, 1997;Ishikawa and Sasaki, 1998;Kalidindi, 2001;Yao and Cao, 2002;Tuğcu et al, 2002;Garmestani et al, 2002;Wu, 2002;Chiang et al, 2002;Geng et al, 2002;Wu et al, 2003;Kowalczyk and Gambin, 2004;Tsakmakis, 2004;Häusler et al, 2004;Bron and Besson, 2004;Vincent et al, 2004;Cazacu and Barlet, 2004;Kuwabara et al, 2005;Wu et al, 2005;Barlet et al, 2005). Kalidindi (2001) reviewed and summarized models of anisotropic strain hardening and deformation textures in low stacking fault energy fcc metals and reported a new approach in modeling the deformation behavior of the materials.…”

“…Kalidindi (2001) reviewed and summarized models of anisotropic strain hardening and deformation textures in low stacking fault energy fcc metals and reported a new approach in modeling the deformation behavior of the materials. Garmestani et al (2002) presented a crystal plasticity based modeling framework for the evolution of anisotropy in Al-Li alloys. Loadings with stain path changes are also an important issue in subsequent deformation (Hiwatashi et al, 1997;Hiwatashi et al, 1998;Kuwabara et al, 2000;Hoc and Forest, 2001;El-Danaf et al, 2001).…”

Anisotropic elasto-plastic finite element analysis using a stress–strain interpolation method based on a polycrystalline model

“…This section does not introduce the refined micro-macro models focused on material behavior. For instance, how to recover the Hall Patch effect (Evers et al, 2002), or precipitation hardening (Garmestani et al, 2002) or how to accurately take into account grain interactions (Crumbach et al, 2001a,b;Delannay et al, 2002).…”

A physical mechanism based investigation on the elasto-plastic-damage behavior of anisotropic aluminum alloys under finite deformation

“…In addition, great progress has been made in the microscopic perspective of crystal plasticity theory. For example, the Taylor-type crystal plasticity developed by Garmestani et al [8] and the crystal plasticity model with anisotropic strain hardening rule proposed by Zamiri et al [9]. For the damage stage, continuum damage mechanics (CDM) and microscopic damage mechanics are intended to study the anisotropic damage from different viewpoints, and damage variable is an important base to describe the damage for many models.…”