Springback prediction of sheet metal forming is always an important issue in the industry, because it greatly affects the final shape of the product. The accuracy of simulation prediction depends on not only the forming condition but also the chosen material model, which determines the stress and strain redistributions in the formed parts. In this paper, a newly proposed elastoplastic constitutive model is used, in which the initial and induced anisotropies, combined nonlinear isotropic and kinematic hardenings, as well as isotropic ductile damage, are taken into account. The aluminum alloy sheet metal AA7055 was chosen as the studied material. In order to investigate springback under non-proportional strain paths, three-point bending tests were conducted with pre-strained specimens, and five different pre-straining states were considered. The comparisons between numerical and experimental results highlighted the hard effect of both kinematic hardening and ductile damage on the springback prediction, especially for a changed loading path case.

In this paper, a multiscale model of ductile damage and its effects on the inelastic behavior of face centered cubic polycrystalline metallic materials, such as the evolution of their crystallographic textures, are investigated. The constitutive equations are written in the framework of rate-dependent polycrystalline plasticity at the microscopic scale. Plasticity and damage are coupled through a ductile damage variable introduced at the scale of the crystallographic slip systems of each grain. When homogenized to the macro-scale, this becomes an approximate phenomenological measure of the macroscopic ductile damage which can describe the material degradation by initiation, growth, and coalescence of micro-defects. In this paper, thermally activated intergranular (or creep) damage is not taken into account. Both theoretical and numerical aspects of the model are presented. The model is implemented into a general-purpose finite element code in order to analyze the effects of texture evolution and ductile damage initiation in the grains with favorably oriented slip systems. The capability of the proposed model to predict the plastic strain localization and the induced textural evolution, as well as the effects of the ductile damage and its evolution up to the final macroscopic failure are studied for a classical tensile loading path, applied to a representative volume element and to a 3D tensile specimen on which a parametric study has been carried out.

The trimodal grain-structured (TGS) carbon nanotube-reinforced aluminum matrix composites (CNT/Al) exhibit better strength–ductility synergy compared to bimodal grain-structured (BGS) composites. The addition of fine grain (FG) to the TGS composites effectively facilitates strain hardening and reduces strain/stress concentrations. In order to address the strain incompatibility in TGS composites, a significant accumulation of geometrically necessary dislocations (GNDs) occurs at the hetero-zone boundaries. This accumulation serves as the key factor in generating additional strengthening and work hardening. By utilizing a multi-mechanism strain gradient model, a quantitative analysis of the contributions made by Hall–Petch, Taylor, and back stress strengthening was conducted. Furthermore, effects of each domain volume fraction on the GND density at the boundaries between heterogeneous domains were carefully and extensively investigated and compared. It is found that the strengthening effect of back stress significantly surpasses that of the Hall–Petch and Taylor strengthening accounting. Compared to BGS composites, the TGS composites are more effective in facilitating strain hardening and reducing strain/stress concentrations, which may lead to a better balance between strength and ductility.

This chapter is dedicated to the presentation of an advanced fully adaptive numerical methodology for virtual sheet and/or bulk metal forming simulation to predict any defects occurrence. First, the detailed formulation of thermodynamically consistent fully coupled, nonlocal constitutive equations is given. Formulated in the framework of the generalized micromorphic continua, the proposed nonlocal constitutive equations account for the main material nonlinearities as the isotropic and kinematic hardening, the thermal exchanges, and the isotropic ductile damage under large inelastic strains. Second, the related numerical aspects required to solve the initial and boundary value problem (IBVP) are presented in the framework of a fully adaptive finite element method. First, the strong and weak forms for the multifunctional IBVP are posed. The well-known static implicit (SI) and dynamic explicit (DE) global resolution schemes are summarized, followed by the detailed presentation of the local integration scheme of the fully coupled constitutive equations. The numerical treatment of the contact and friction is reviewed in the framework of master/slave surfaces method. Finally, some typical examples of sheet and bulk metal forming processes are numerically simulated using the proposed fully adaptive methodology.