Surasak Suranuntchai

Simplified identification of material parameters for Yoshida-Uemori kinematic hardening model

In sheet metal forming process of Advanced High Strength (AHS) steels, springback effect is one of the most critical problems for manufacturer. The springback of a formed part occurs due to residual stress released after deformation. FE simulations were often used to describe both forming and springback behavior of steel sheets. Recently, the Yoshida- Uemori (Y-U) kinematic hardening model has been successfully applied for the springback simulation. The model is capable of reproducing the transient Bauschinger effect, permanent softening and work hardening stagnation during a large deformation. In this work, method for determining materials parameter of the Y-U model was briefly presented. Initially, cyclic tests were performed under both tension and compression loads for the high strength steel grade JSC780Y and JSC980Y. FE simulations of 1-element model were carried in order to investigate predicted cyclic stress strain curves. Both Y-U model and a mixed isotropic-kinematic Barlat2000 model were used in the simulations. Stamping tests of hat shape sample were carried out for verifying the experimental and numerical results. It was found that the Y-U model provided more accurate springback results than the other model.

Investigation of Hot Deformation Characteristics of AISI 4340 Steel Using Processing Map

Uniaxial compression tests at various temperatures from 850°C to 1200°C and strain rates between 0.01 s-1 and 10 s-1 were carried out in order to determine hot working characteristic of the AISI 4340 steel. The plastic stress-strain responses at high temperatures of the steel were provided. Constitutive relationship between the flow stresses and the Zener–Hollomon parameters was primarily established by means of a hyperbolic sine function for the entire range of the investigated conditions. Afterwards, the power dissipation map and instability map were developed on the basis of the Dynamic Materials Model (DMM). The variation of efficiency of the power dissipation calculated as a function of strain rate sensitivity represented material behaviors according to the microstructure evolution. The peak efficiency indicated an optimum processing window for hot working. In this study, processing map was obtained by a superimposition of the power dissipation and the instability criterion. The domains of temperature and strain rate, in which material flow stability occurred, were determined. For the AISI 4340 steel, the processing maps exhibited a distinct domain with its peak efficiency at about 1050-1200°C and 0.01-0.1 s-1, in which the peak efficiencies of about 40-50% were shown for different strains. In combination with microstructure observations after hot deformation, dynamic recrystallization zone could be identified in the processing map at a certain strain.

Determination of Damage Criterion Using a Hybrid Analysis for Advanced High Strength Steel

Advanced High Strength (AHS) steels have been increasingly applied in the automotive industries due to their distinguished mechanical properties. Microstructures of these steels play an important role and are designed by constituent phases with distinct characteristics. AHS steels exhibit sophisticated damage mechanisms that complicate the prediction of material formability. In this work, Ductile Crack Initiation Locus (DCIL) was developed for describing failure behavior of dual phase steel sheet. A hybrid experimental and numerical analysis was used to determine the DCIL. Tensile tests of various sample geometries were experimentally carried out and crack initiation occurred during forming was identified by the Direct Current Potential Drop (DCPD) method. Then, FE simulations of the corresponding tests were performed to evaluate local stress triaxialities and equivalent plastic strains of the critical area. The damage curves for both crack initiation and localized necking were obtained. Additionally, the von Mises, Hill48 and Yld2000-2d yield criterion were defined in the calculations in order to examine effect of yield model on the resulted curves. To verify applicability of the damage curves, Nakazima test of uniaxial sample was taken into account.

Anisotropic Plastic Behavior of TRIP 780 Steel Sheet in Hole Expansion Test

Plastic behavior of advanced high strength steel sheet of grade TRIP780 (Transformation Induced Plasticity) was investigated using three different yield functions, namely, the von Mises’s isotropic, Hill’s anisotropic (Hill’48), and Barlat’s anisotropic (Yld2000-2d) criterion. Uniaxial tensile and balanced biaxial test were conducted for the examined steel in order to characterize flow behavior and plastic anisotropy in different stress states. Additionally, disk compression test was performed for obtaining the balanced r-value. According to the different yield criteria, yield stresses and r-values were calculated for different directions and then compared with experimental data. To verify the modeling accuracy, a hole expansion test was carried out experimentally and numerically by FE simulation. Stress-strain curve from the biaxial test was described using voce and swift hardening models. Punch load and stroke, final hole radius, and strain distribution on specimen surface along the hole circumference and the specimen diameter in rolling and transverse directions were determined and compared with the experimental results. It was found that the simulations applying Yld2000-2d yield function provided an acceptable agreement. Consequently, it is noted that the anisotropic yield potential significantly affects the accuracy of the predicted deformation behavior of sheet metal subjected to hole expanding load.

Finite Element Modeling for Hot Forging Process of AISI 4340 Steel

Hot forging is a common, but important manufacturing process in metal forming industries. Forming at high temperature, flow stress of material decreases and thus lower load is required. Furthermore, mechanical properties of material regarding its microstructure characteristics can be improved according to heating and cooling conditions. Hot forging process for a spacer wheel made of steel AISI 4340 was investigated by means of FE simulation. Initially, hot compression test was performed using a thermo-mechanical simulator for determining flow curves. Different temperatures and strain rates within the process range were considered. A Zener-Hollomon parameter was applied to describe the experimentally obtained flow curves. To verify accuracy of the FE simulations, multi-step hot compression test was carried out at different forming temperatures. Subsequently, force development and final shape calculated for the investigated part were analyzed. Reliability of the FE results was significantly influenced by the defined flow curve or hot deformation behavior of material.

Finite Element Simulation of Hot Forging Process for KVBM Gear

In this study, the forging operations of gear has been modeled. This gear is a part which is manufactured with the help of hot forging industry for reduce the cost. The authors propose to reduce the initial billet volume of AISI 4340 steel for the forged through process optimization using the Finite Element (FE)method. The object of this research was to predict the effect of several parameters, such as effective stress, effective plastic strain, temperature and die contact, on the forming of the gear, utilizing computer simulation and experimental results. For this purpose, Solidworks CAD and Simufact Forming FE software were used for the modeling and analysis of the forging process. The billet volume and the preform design were predefined in order to reduce scrap by using preform type C. The experimental results showed that the initial billet volume was reduced at 32 %, which compared favorably with the simulation result of a 40 % reduction. The maximum preforming force of simulation result was diferent with the experiment result at 18 along with the maximum finishing force of simulation result was different with the experiment result at 11 %. It was also found that the effective stress decreased with increasing the temperature, and the press force decreased when the initial billet volume was decreased, which resulted in a decrease of effective plastic strain as well.

Finite Element Simulation of Deep Drawing Processes for Shell Bar RR Impact RH/LH

Finite Element Method (FEM) is one of the most useful techniques to analyze problems in metal forming process because of this technique can reduce cost and time in die design and trial step [1]. This research is aimed to predict the optimal parameters in order to eliminate cracks and wrinkles on automotive deep drawing product “Shell Bar RR Impact RH/LH”. The material was made from high strength steel JSC440W sheet with thickness 1.8 mm. The parameters that had been investigated were blank holder force (BHF) and drawbead restraining force (DBRF). In order to simplify the process, punch and die in the simulation were assumed to be a rigid body, which neglected the small effect of elastic deformation. The material properties assumed to be anisotropic, behaved according to the constitutive equation of power law and deformed elastic-viscoplastic, which followed Barlat 3 components yield function. Most of the defects such as cracks and wrinkles were found during the processes on the parts. In the past, the practical productions were performed by trial and error, which involved high production cost, long lead time and wasted materials. From the results, when decreased blank holder force to 30 tons, cracks on the part were removed but wrinkles had a tendency to increase in part area because of this part is the asymmetrical shape. Finally, applying about drawbead restraining force at 154.49 and 99.75 N/mm could improve product quality. In conclusion, by using the simulation technique, the production quality and performance had been improved.

Use of Deep Cryogenic Treatment to Reduce Particle Contamination Induced Problem in Hard Disk Drive

In this study, the effect of deep cryogenic treatment on the generation of stainless steel particles in screw tightening process in hard disc drive assembly was investigated. During the cryogenic treatment, the specimens of both stainless steel screw and contacting tool (called as “bit”) material were quenched in a chamber containing liquid nitrogen at-196 oC with the soaking times of 33 hr. The specimens were then subjected to sliding wear tests under normal loading conditions. The experiments used for simulating dry sliding wear mechanisms were carried out by TriboGear machine. The machine consists of a stationary bit loaded against the plate containing screw. The screws used were made of martensitic 410 stainless steel and the bit was made of S2 tool steel. The experiments were carried out under both under single and multiple loading cycles under the normal load corresponding to the effective stresses higher and lower than the yield strength of screw material. The results showed that the deep cryogenic treatment led to more homogeneous distribution of fine size carbide particles in both martensitic 410 stainless steel and S2 tool steel. This lead to different failure mechanism of the stainless steel resulting in smaller and slender stainless steel particles generated. This was expected due to the effect of the change in the dimension of carbide, the stress distribution in the material and the crack propagation path.

Tension-Compression Tests for Springback Prediction of AHS Steel Using the Yoshida-Uemori Model

In sheet metal formingprocess of automotive parts, springback effect is crucial, in particular, foradvanced high strength (AHS) steels. Most structural components of new vehiclesshow very complex shapes that require multi–step forming procedures.Therefore, finite element (FE)simulation has been often used to describe plasticdeformation behavior and springback occurrence of formed metal sheets.Recently, the kinematic hardening Yoshida–Uemorimodel has showed great capability for predicting elastic recovery of material. In this work, the AHSsteel grade JSC780Y wasinvestigated, in which tension–compressiontests were carried out. From resulted cyclic stress–strainresponses, material parameters were identified using different fitting methods.Determined model parameters were firstly verified by using simulations of 1–elementmodel. The most appropriate parameter set was thenobtained. Finally, a Hat-Shape forming test was performed and springback waspredicted and compared with experimental results.

Effects of temperature and strain rate during hot compression of manganese aluminum bronze

Manganese Aluminum Bronze or MAB alloy has been extensively used for applications under sea water such as marine propellers because this alloy exhibits high strength as well as excellent corrosion resistance behavior. In this work, microstructures and hardness properties of an annealed MAB alloy after hot deformation at different temperatures of 973 K 1123 K and strain rates between 0.1s and 1 swere investigated. During the tests, stress-strain responses of the alloy were determined, and effects of temperature and strain rate on the flow behavior of the MAB alloy were subsequently examined. Furthermore, microstructures of deformed MAB alloy were characterized by both optical microscopy and scanning electron microscopy. Effect of microstructure on stress-strain curves was illustrated for various forming conditions. The results showed at different temperature and strain was found dynamic recovery and dynamic recrystallization.