Ying Hong Peng

Influence of Dynamic Recrystallization on Tensile Properties of AZ31B Magnesium Alloy Sheet

Dynamic recrystallization (DRX) occurring in tensile deformation of AZ31B magnesium alloy sheet has been investigated. In particular, in order to predict the effect of DRX on tensile properties of AZ31B magnesium alloy sheet, a modified constitutive model is presented and used in the finite element method (FEM) model of the tension. Results from this analysis are compared with the experimental data for tensile tests. The results indicate that the modified DRX model can validly express the effect of DRX on tensile properties of AZ31B magnesium alloy sheet. The softening stage of flow stress simulated by this model can approach that of experiment considerably. In addition, the evolution of DRX grain is examined with increasing temperature. Furthermore, a comparison is made between calculated and tested DRX grain size.

Numerical and Experimental Study on Seam Welding Behavior in Extrusion of Micro-Channel Tube

Micro-channel tube with submillimeter-diameter channels is a kind of newly developed heat transfer tube based on theory of micro-scale heat transfer. As the micro-channel tube has multiple welding points and work under high pressure condition, welding strength is one of the key problems for the extrusion process. This paper presented a new method in evaluation of the seam welding strength formed in the extrusion process. Firstly, FE simulation is carried out for the status of the billet in the welding chamber during the extrusion process. Then, thermo mechanical experiment is done for the relationship between the welding strength and three key factors. Combining the relationship with the numerical results, welding strength of the micro-channel tube can be evaluated. Pressure bearing test shows that the evolution method is reliable. The study is helpful for the optimization the extrusion process and improvement of the seam weld quality.

Extrusion Simulation and Texture Study on Mg-Y Alloy

In order to study the influence of extrusion process on texture development of alloys, numerical simulation methods were used to simulate the round and shape extrusion process and deformation texture. Extrusion of Mg-Y magnesium alloy was carried out at the temperature of 673K with different ram speeds to verify the simulation results. Instead of using the Lagrangian FE method, the Arbitrary Lagrangian-Eulerian (ALE) method was employed in this study so that a more accurate description of the steady-state extrusion process can be achieved. By obtaining strain histories of specified material tracer particles, the coupling of deformation and crystal plasticity theory was applied to simulate the texture evolution in hot extrusion. The results showed that the texture simulation corresponded well with the experimental ones. The study proposes a method to analyze the steady-state extrusion process and texture evolution, and can be used as a useful tool in optimizing the extrusion process.

Simulation of the Extrusion Texture of Magnesium Alloy AZ31 Using Crystal Plasticity Finite Element Method

By using Eulerian adaptive modeling approach, both the round extrusion and sheet extrusion of magnesium alloy AZ31 were simulated. Furthermore, the history strains of material point flowing through the Eulerian domain was extracted and used as the foundation for defining the boundary conditions in the crystal plasticity finite element (CPFE) modeling for the extrusion texture. By virtue of this modeling method, the realistic grain boundaries can be approximated by using a 3D polycrystal generator and the intra-granular interactions can be well described. Both of the simulated round extrusion and sheet extrusion textures of alloy AZ31 show reasonable agreement with experimental results.

Thermo-mechanical coupled simulation of warm stamping of AZ31 magnesium alloy sheet

Uniaxial tensile test of a cross rolled magnesium alloy sheet was conducted under different temperatures and strain rates. The mechanical propriety of AZ31 magnesium alloy sheet was analyzed according to the true strain-stress curves. Then the non-thermal drawing process, during which the temperature of die, blankholder and blank is 200°C while the punch is kept at room temperature, was simulated by the thermo-mechanical coupled finite element method. The deformation behavior and the temperature change in the drawing process was investigated. Due to the heat conduction, there was non-uniform distribution of temperature along flange area, force transfer area and deformation area. Therefore the resistance of the force transfer area is enhanced and the warm formability of magnesium alloy sheet can be further improved. The thermo-mechanical coupled simulation provides a good guide for the development of non-isothermal drawing techniques.

Robust Design of UOE Forming Process Based on Support Vector Machine

Fluctuations in material properties of the incoming steel for UOE forming process are widespread. According to the statistics, the fluctuation range of the yield strength of the same grade pipeline steel is around 80MPa. Robust optimization methods have been widely applied in sheet metal forming area. In this paper, experiments were conducted to investigate how a stochastic material behavior of noise factors affected UOE forming quality. Robust design models integrated with response surface method for UOE forming process were established to minimize impact of the variations and improve the qualified rate of UOE pipe ovality. Support vector machine in both classification and regression was adopted to map the relation between input process parameters and forming qualities. The deterministic and robust optimization results are presented and compared, demonstrating increased process robustness and decreased number of product rejects by application of the robust optimization approach.

Experimental and Numerical Study on Dieless Bending of 2-Piece Parallel Flow Microchannel Heat Exchanger

Parallel flow microchannel heat exchangers have been increasingly applied in HVAC (Heating, Ventilation and Air Conditioning) field due to their characteristics, such as high efficient heat transfer performance, compact form and low cost. Production rationalization of the heat exchanger is required for realization of a competitive, light-weight and easy-to-assemble product. The heat exchanger is usually bent to L-shape so as to decrease the volume of air conditioner. To correspond with design changes for multi-generation use and to achieve good forming quality, a dieless forming technique is developed to offer flexible manufacturing. Using this method, heat exchangers can be formed with variable bending radius conveniently, which can reduce the mold cost and obtain high productivity. Meanwhile, product defects such as fin damage can also be reduced because there is no physical contact against tools in the bending portion. In the present study, the forming principle of dieless bending process is first stated by theoretical analysis. Then to verify the proposed forming mechanism, a NC dieless bending machine is manufactured to implement the bending experiment. Finally, based on the verified FE model, the bending process for the 2-piece heat exchanger has been improved. As a result, the dieless bending process has been successfully developed and can be applied to produce square-shape heat exchanger with variable bending radius.

Analysis and Simulation of the UOE Pipe Production Processing by Finite Element Method

Large-diameter pipes used in offshore applications are commonly manufactured through the UOE process. The plate is crimped along its edges, formed into a U-shape and then pressed into an O-shape between two semicircular dies. The pipe is welded closed and then circumferentially expanded to obtain a highly circular shape. In this study, the two-dimensional finite element model of the whole processing of the UOE pipe production has been established, including large deformation and complex contact. The deformed geometries of different steps and distribution of the equivalent plastic strain and variation in load are analyzed. This research is helpful in UOE forming process design and evaluating the capability of the pipe mill.

Numerical analysis of nano-or micro-crystalline materials during ECAP by dislocation evolution method

By the severe plastic deformation, the equal channel angular pressing method (ECAP) has been used for producing metal materials with the ultra-fine grain size and specific mechanical properties, in particular high yield strength. Analytical approaches have also been studied by few researchers. However, none of the previous analyses have taken into account the strain hardening of the material by considering the microstructure evolution. In this paper, the deformation behavior and the strain harden of aluminum during equal channel angular pressing was calculated on the basis of a dislocation evolution model. Then simulated stress, strain and strain distribution and strain hardening were analyzed. The strain is seen to rapidly increase when the material passes the shear area. This makes a maximum value of stress. And for the congregation of dislocation density, the maximal value of strain increase with the process continuing.

Experimental Research on Warm Deep Drawing of Magnesium Alloy Sheet by Variable Blank Holder Force Control

A process of warm deep drawing of magnesium alloy with variable blank holder force has been presented in this study. A hydraulic press that can realize adjustable blank holder forces was developed and its working principle and control system introduced. A warm deep drawing mould was fixed and warm deep drawing experiments are conducted on the hydraulic press. Different variation schemes of the blank holder force with the stroke of the punch was tested, and compared with experiment results. The experimental results show that adopting the variable blank holder force technique can remarkably improve the forming performance and decrease the reduction ratio of thickness from 15.21% to 12.35%. It is further demonstrated that the suitable blank holder force variation scheme is an inverted V curve with the punch stroke.