Gow Yi Tzou

Study of the Titanium Alloy Deformation Behavior in Equal Channel Angular Extrusion

The shear plastic deformation behavior of a material during equal channel angular (ECA) extrusion is governed primarily by the die geometry, the material properties, and the processing conditions. Using commercial DEFORMTM 2D rigid-plastic finite element code, this study investigates the plastic deformation behavior of Ti-6Al-4V titanium alloy during 1- and 2-turn ECA extrusion processing in dies containing right-angle turns. The simulations investigate the distributions of the billet mesh, effective stress and effective strain under various processing conditions. The respective influences of the channel curvatures in the inner and outer regions of the channel corner are systematically examined. The numerical results provide valuable insights into the shear plastic deformation behavior of Ti-6Al-4V titanium alloy during ECA extrusion.

An Investigation into Optimized Ti-6Al-4V Titanium Alloy Equal Channel Angular Extrusion Process

The shear plastic deformation behavior of a material during equal channel angular (ECA) extrusion is governed primarily by the die geometry, the material properties, and the process conditions. This paper employs the rigid-plastic finite element (FE) to investigate the plastic deformation behavior of Ti-6Al-4V titanium alloy during ECA extrusion processing. Under various ECA extrusion conditions, the FE analysis investigates the damage factor distribution, the effective stress-strain distribution, and the die load at the exit. The relative influences of the internal angle between the two die channels, the friction factors, the titanium alloy temperature and the strain rate of billet are systematically examined. In addition, the Taguchi method is employed to optimize the ECA process parameters. The simulation results confirm the effectiveness of this robust design methodology in optimizing the ECA processing of the current Ti-6Al-4V titanium alloy.

Influence of Plastic Anisotropy on Limit Load of Welded Joints with Cracks

The limit load is an important input parameter of many defect assessment procedures. Anisotropy of plastic properties can have a large effect on its magnitude and, therefore, on the accuracy of predictions based on such procedures. In the present paper, a general method for constructing kinematically admissible velocity fields is proposed in the case of highly under-matched welded joints assuming Hill’s quadratic yield criterion. This method is adopted to find an upper bound limit load of a welded plate with the inclined weld subject to tension. An effect of anisotropic properties of the weld on the limit load is demonstrated and discussed. Introduction A review of defect assessment procedures is given in [1]. It follows from this review that the limit load is an essential input parameter of such procedures. The accuracy of predictions based on these procedures significantly depends on the accuracy of limit load solutions. The latter, in turn, depends on the constitutive equations chosen. Compendia of defect assessment procedures for limit load solutions, for example [2], and a review of limit load solutions [3] show that isotropic models are usually adopted to find limit loads. However, plastic anisotropy can have a large effect on the magnitude of limit load. This effect has been shown by means of several limit load solutions for over-matched welded specimens in [4 – 6]. Welding of some modern aluminum alloys leads to highly under-matched joints. In such cases plastic deformation is localized in the thin weld whereas the base material is elastic (for limit load calculations the latter can be treated as rigid [7]). This feature of flow pattern should be taken into account in kinematically admissible velocity fields. For isotropic materials, an appropriate method has been proposed in [8]. This method is based on the singular behavior of the real velocity field in the vicinity of velocity discontinuity surfaces [9]. In the case under consideration, such surfaces coincide with the bi-material interfaces. The available solution for anisotropic materials [10] shows that the same singular velocity fields can occur in rigid perfectly/plastic anisotropic solutions. This fact is used in the present paper to extend the method [8] to highly under-matched anisotropic welded joints. It is assumed that the weld obeys Hill’s yield criterion [11]. The method is applied to find a limit load for highly under-matched specimens subject to tensile loading. It is assumed that the weld is inclined to the line of action of the load at an arbitrary angle. In the case of isotropic over-matched specimens of such geometry and loading conditions, an upper bound solution has been proposed in [12]. Method for Constructing Kinematically Admissible Velocity Fields In the case of isotropic rigid perfectly plastic materials, the equivalent strain rate in the vicinity of velocity discontinuity surfaces found with the use of the real velocity fields is represented by [9] ( ) 1 eq O s ξ = as 0 s→ . (1) Key Engineering Materials Online: 2007-08-15 ISSN: 1662-9795, Vols. 345-346, pp 425-428 doi:10.4028/www.scientific.net/KEM.345-346.425

An Upper Bound Solution for a Two-Layer Cylinder Subject to Compression and Twist

The choice of a kinematically admissible velocity field has a great effect on the predictive capacity of upper bound solutions. It is always advantageous, in addition to the formal requirements of the upper bound theorem, to select a class of velocity fields satisfying some additional conditions that follow from the exact formulation of the problem. In the case of maximum friction law, such an additional condition is that the real velocity field is singular in the vicinity of the friction surface. In the present paper this additional condition is incorporated in the class of kinematically admissible velocity fields chosen for a theoretical analysis of two - layer cylinders subject to compression and twist. An effect of the angular velocity of the die on process parameters is emphasized and discussed.

New Corresponding Relationships between Frictional Coefficient and Frictional Factor in Compression Forming of a Rotating Circular Disk

Abstract. Two analytical models of circular disk compression forming with consideration of the rotation effect are derived by the slab method. The Coulomb friction model ( , Model I) assumes the friction at the interface between die and circular disk to be Coulomb friction; the constant shear friction model ( , Model II) assumes the friction to be constant shear friction. Because the circular disk is compressed under the rotation circumstance, the frictional shear stresses ( ) are not acted in the radial direction. The stresses ( p τ = μ

Study on Rotating Compression Forming of Double-Layer Clad Ring Considering Constant Shear Friction

This study establishes an analysis model based on the slab method assuming constant shear friction. The rotating compression forming of the double-layers bounded clad ring is derived by considering von Mises’ yield criterion with the shear stress. Effects of the frictional factor, shear yield stress ratio, rotating angular speed of the ring, frictional factor ratio, clad ring height ratio etc on compression characteristics are investigated effectively. Moreover, the compression pressure, radial stress for each layer, radial stress of the whole layer, and compression force are also predicted effectively. Finally, the FEM simulation is carried out to compare with the slab method to realize the variations of both models.

Experimental Investigation and FEM Simulation on Material Behaviors of Cylinder with the Rotating Flat Die

The study aims at exploring the effects of rotating compression forming on the material behaviors of cylinder. The experiments have been carried out under various angular velocities to realize the flow stress, the compression force, the rotating torque, the grain size, and the hardness. Furthermore, the FEM simulation is also performed to compare with the experiments. From the experimental results, as the angular velocity increases, the compression force and the grain size decrease, but the rotating torque and the hardness increase. The results can provide the industry as the reference.

Slab Analysis and FEM Simulation on Rotating Compression Forming of Double-Layer Clad Cylinder under Constant Shear Friction

The friction caused power losses and bulging deformation are always inevitable. The rotating compression forming can reduce the compression force and bulging deformation in metal forming. Furthermore, the bounded double-layer metal material is able to have advantage in proper material cost saving and meeting the required strength for customer. Accordingly, this present study proposes the analysis based on Slab Method (SM) and Finite Element Method (FEM) under constant shear friction to predict the compression force and the rotating moment in the rotating compression forming. Moreover the bulging deformation profiles, the effective stress, the effective strain, the velocity field, the compression force, the rotating moment, and the twist angle can be obtained from FEM simulations. It is also shown that the predicted results have the same trend to verify the acceptance of analysis models.

FEM Simulation on Rotating Piercing Process with Coulomb Friction

This study proposes a new piercing technology with rotating punch; it carries out an FEM simulation on rotating piercing process using DEFORM-3D commercial software. Frictions among the punch, the blank holder, the dies and the work-piece material are assumed as Coulomb friction, but can be different. The surface of the inner diameter, the effective stress, the effective strain, velocity field, damage, burr and the shearing force can be determined form the FEM simulation. In this study, effects of various piercing conditions such as the clearance, the punch nose angle, the frictional coefficient, the rotating angular velocity, the shearing force, and burr on shearing characteristics are explored effectively to realize the feasibility of FEM model.

A New Analytical Approach to the Cold and Hot Bond Rolling of Unbounded Clad Sheet with Constant Shear Friction

A new analytical model for cold and hot bond rolling of clad sheet unbounded before rolling is derived to investigate the stress field of the clad sheet at the roll gap by using the direct formulation without the Runge Kutta numerical method. Constant shear friction between the rolls and the clad sheet is assumed. Due to the clad sheet unbounded before rolling, double-layer sheets are not bonded at the entrance of the roll gap. Thus the stress field of the roll gap for this model is different from that for clad sheet bonded firmly before rolling. In this study, the neutral point between the rolls and the clad sheet, the rolling pressure distribution along the contact interface between the rolls and the clad sheet, the horizontal stresses in the component layers of the clad sheet, the rolling force, and the rolling torque etc., can be easily and rapidly calculated by using the developed analytical model. In addition, it is a valuable result from this study to obtain the bonding point of the interface and the thickness ratio of clad sheet at the exit. Furthermore, the bonding conditions for the unbounded clad sheet are found to offer useful knowledge in performing bond rolling to avoid manufacturing defects. Introduction Studies regarding clad sheet rolling can be classified into experimental [1,2] and theoretical studies [3-9]. S.H. Lee et al. [2] performed the cold roll bonding for silver and phosphor bronze sheets, and analysis assuming Coulomb friction together with the Runge Kutta numerical method to obtain the rolling pressure and thickness ratio of clad sheet at the exit. The CPU time required is too long to get the more detailed information. Suzuki et al. [3,4] used the slab method and Runge Kutta method to obtain the stress field, assuming friction as Coulomb friction. Kiuchi et al. [5,6] used the upper bound method to explore the plastic deformation of clad sheet, assuming constant shear friction. However the stress field of clad sheet cannot be obtained by the upper bound method. Hamauzu [7] and Shiyouya [8] utilized FEM to investigate the effect of thickness ratio and shear yield stress ratio on the effective stress and strain, as well as rolling force. The CPU time required by foregoing methods is too great to be suitable for on-line rolling industry applications to predict rolling force and torque. For predicting the rolling pressure, the rolling force and the rolling torque, the slab method is a good technique if it is used without the Runge Kutta method. Although Suzuki used the slab method to establish analytical model, the Runge Kutta method was still used to solve the solution. Therefore, a new analytical approach to the cold and hot bond rolling of clad sheet unbounded before rolling is developed to calculate the various stress distributions easily and rapidly without the Runge Kutta numerical method under constant shear friction. Formulations Fig.1 shows the schematic illustration of unbounded clad sheet bond rolling. Assuming the same roll radii and roll speeds for two rolls, the single neutral point ( n x ) is generated at the roll gap. Due to the clad sheet unbounded before rolling, and after being bitten into the roll gap, the soft sheet (layer 1) is yielded, however, the hard sheet (layer 2) is not yet yielded. Thus, the first region (zone I) belongs to the region of the unbounded clad sheet. The slab stress state in zone I is Key Engineering Materials Online: 2004-10-15 ISSN: 1662-9795, Vols. 274-276, pp 999-1004 doi:10.4028/www.scientific.net/KEM.274-276.999