The performance of two methods, termed Manual and Optimization, for determining the values of the constitutive-model parameters for Yoshida-Uemori (Y-U) isotropic-kinematic hardening model was evaluated. The Y-U parameters were determined for two 6000-series aluminum alloys (AA6XXX-T4 and AA6XXX-T81) and two dual-phase steels (DP 980 and DP 1180) using stress-strain data from tension and tension-compression tests. In the Manual Method the parameters were calculated by sequentially fitting the forward and then the reverse segments of tension-compression stress-strain data. In the Optimization Method, the parameters were calculated by systematically reducing the difference between the data and stress-strain curves computed from a one-element finite element model coupled with the optimization module of the commercial finite-element software package. The performance of the methods was evaluated qualitatively by graphically comparing measured and computed stress-strain curves and quantitatively by evaluating the residual between the measured and computed curves. Although the quality of agreement for the Manual Method was generally good for the aluminum alloy tests, the agreement was inferior for the dual-phase steel tests, especially for the reverse deformation segment. The Optimization Method produced the best results as evaluated by the lowest residual between the measured and computed curves. Of several variants of the Optimization Method, simultaneous optimization against all three replicate curves produced Y-U parameters that best represented the measured stress-strain curves. Statistical analyses conducted in conjunction with optimization studies also established the relative influence for each of the Y-U parameters on the overall agreement between measured and computed curves. A broader implication is that using a finite element model, rather than the manual methods, should be used to determine the Y-U parameters, since those parameters will be eventually used in a finite element model to simulate a forming process. This is especially true when determining a single set of parameters for repeat tests. 

Evaluation of Methods for Determining the Yoshida-Uemori Combined Isotropic/Kinematic Hardening Model Parameters from Tension-Compression Tests of Advanced Lightweighting Materials

The deformation of plastics during production and service means that retired parts often possess different mechanical states, and this can directly affect not only the properties of remanufactured mechanical parts, but also the design of the remanufacturing process itself. In this paper, we describe the stress-strain relationship for remanufacturing, in particular the cyclic deformation of parts, by using the particle swarm optimization (PSO) method to acquire the Yoshida-Uemori (Y-U) hardening model parameters. To achieve this, tension-compression experimental data of AA7075-O, standard PSO, oscillating second-order PSO (OS-PSO) and variable weight PSO (VW-PSO) were acquired separately. The influence of particle numbers on the inverse analysis efficiency was studied based on standard PSO. Comparing the results of PSO variations showed that: (1) standard PSO is able to avoid local solutions and obtain Y-U model parameters to the same degree of precision as the OS-PSO; (2) by adjusting section weight, the VW-PSO could improve local fitting accuracy and adapt to asymmetric deformation; (3) by reducing particle numbers to a certain extent, the efficiency of analysis can be improved while also maintaining accuracy.

Parameter Identification of the Yoshida-Uemori Hardening Model for Remanufacturing

Due to the lack of theoretical basis for the determination of process parameters, there are problems such as incomplete melting and excessive melting in the molten pool for laser processing, which ultimately cause the increase of defects such as air hole and crack. The melting behavior of Ti–Al binary alloy during laser processing is studied on the atomic scale by molecular dynamics simulation. The embedded atom method potential is adopted to establish the melting model of Ti–Al binary alloy. According to the changes of temperature, atomic structure and mean square displacement, the influence of different process parameters on the melting behavior of Ti–Al binary alloy is discussed. The results show that a short temperature drops from initial melting to complete melting. Mean square displacement increases rapidly with the increase of laser time after completely melting. The atoms start to move violently and the atomic structure is completely transformed into other structure. The heating and cooling rate increases with the increase of power. The laser power has little effect on the overall distribution of atoms after completely melting and only affects the variation rate of various physical quantities in melting process. The research results provide a deeper practical and theoretical evidence for the determination and optimization of the 3D printing and laser heat treatment.

Tong Wang

Papers

Parameter Identification of the Yoshida-Uemori Hardening Model for Remanufacturing

A molecular dynamics simulation-based laser melting behavior analysis for Ti–Al binary alloy

Research and Development of Gating and Riser Process Optimization Integrated System for Steel Casting