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In this work, a novel optimization approach is introduced to extract combined hardening parameters from the cyclic stress-strain data obtained from the initial hardening cycles of isothermal, low-cycle fatigue tests. The incremental elastic-limit (IEL) concept is proposed due to the often-undiscernible elastic range of a stabilized stress-strain cycle, that increases the complexity of hardening parameters optimization. The optimization process is implemented by taking an iterative search for the elastic range by a fixed elastic limit increment, and the corresponding hardening parameters are obtained using the nonlinear fitting algorithms in the MATLAB™ Software. An implicit stress-update function is introduced to simulate the cyclic stress and strain with a given set of hardening parameters and yield strength. The fitness of the optimization is calculated based on the least square difference between the experimental and simulated stress-strain data. Furthermore, the IEL concept is incorporated to optimize the cyclic hardening parameters. In the final step, finite element (FE) analysis using the optimized hardening parameters is applied to demonstrate the effectiveness of the IEL approach. The proposed methodology is applied to pressure vessel steels and Ni-based weld metals. 

Flange wrinkling is often seen in deep-drawing process when the applied blankholding force is too small. This paper investigates the plastic wrinkling of flange under a constant blankholding force. A series of deep-drawing experiments of AA1100-O blanks are conducted with different blankholding forces. The critical cup height and wrinkling wave numbers for each case is established. A reduced-order model of flange wrinkling is developed using the energy method, which is implemented to predict the flange wrinkling of AA1100-O sheet by incrementally updating the flange geometry and material hardening parameters during the drawing process. A deep-drawing finite element model is developed in ABAQUS/standard to simulate the flange wrinkling of AA1100-O blanks under constant blankholding force. The predicted cup height and wave numbers from the finite element model and reduced-order model are compared with the experimental results, which demonstrates the accuracy of the reduced-order model, and its potential application in fast prediction of wrinkling in deep-drawing process. 

Abstract In this paper, results for SS316 L microtube experiments under combined inflation and axial loading for single and multiloading segment deformation paths are presented along with a plasticity model to predict the associated stress and strain paths. The microtube inflation/tension machine, utilized for these experiments, creates biaxial stress states by applying axial tension or compression and internal pressure simultaneously. Two types of loading paths are considered in this paper, proportional (where a single loading path with a given axial:hoop stress ratio is followed) and corner (where an initial pure loading segment, i.e., axial or hoop, is followed by a secondary loading segment in the transverse direction, i.e., either hoop or axial, respectively). The experiments are designed to produce the same final strain state under different deformation paths, resulting in different final stress states. This difference in stress state can affect the material properties of the final part, which can be varied for the intended application, e.g., biomedical hardware, while maintaining the desired geometry. The experiments are replicated in a reasonable way by a material model that combines the Hill 1948 anisotropic yield function and the Hockett–Sherby hardening law. Discussion of the grain size effects during microforming impacting the ability to achieve consistent deformation path results is included.