Abstract
We propose a multi-scale modeling approach that can simulate the microstructural and mechanical behavior of metal/alloy parts with complex geometries subjected to multi-axial load path changes. The model is used to understand the biaxial load path change behavior of 316L stainless steel cruciform samples. At the macroscale, a finite element approach is used to simulate the cruciform geometry and numerically predict the gauge stresses, which are difficult to obtain analytically. At each material point in the finite element mesh, the anisotropic viscoplastic self-consistent model is used to simulate the role of texture evolution on the mechanical response. At the single crystal level, a dislocation density based hardening law that appropriately captures the role of multi-axial load path changes on slip activity is used. The combined approach is experimentally validated using cruciform samples subjected to uniaxial load and unload followed by different biaxial reloads in the angular range [27°,90°]. Polycrystalline yield surfaces before and after load path changes are generated using the full-field elasto-viscoplastic fast Fourier transform model to study the influence of the deformation history and reloading direction on the mechanical response, including the Bauschinger effect, of these cruciform samples. Results reveal that the Bauschinger effect is strongly dependent on the first loading direction and strain, intergranular and macroscopic residual stresses after first load, and the reloading angle. The microstructural origins of the mechanical response are discussed.
Highlights
IntroductionEngineering metals and alloys are often subjected to multi-axial load path changes during their fabrication (to form them into the International Journal of Plasticity 108 (2018) 144–168 desired shape) or under service conditions
During load path 1 (LP1) loading, the maximum applied force F1 (40kN) and force rate (80N/s) on all cruciform samples are the same, there is a non-negligible difference in their measured E11 values
At the end of LP1, the largest difference in measured E11 (0.01381) occurs between the cruciform samples subjected to LSA and LSC loadings; note that this difference is one of the key reasons the cruciform tests are not used to fit the hardening law parameters
Summary
Engineering metals and alloys are often subjected to multi-axial load path changes during their fabrication (to form them into the International Journal of Plasticity 108 (2018) 144–168 desired shape) or under service conditions. A load reversal after a uniaxial tension, compression or shear can result in lowering the yield stress i.e. the Bauschinger effect, an extended elastic-plastic transition regime and a different hardening regime. The origin of such macroscopic behavior has to be found in the microstructural response. At the meso-scale or intergranular level, crystallographic texture evolution and anisotropy play a major role, and at the microscale or intra-granular level, heterogeneous dislocation activity combined with latent hardening effects have to be taken into account (Beyerlein and Tomé, 2007; Christodoulou et al, 1986; Rauch et al, 2007; Takahashi and Shiono, 1991)
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