Springback Prediction Using Finite Element Simulation Incorporated With Hardening Data Acquired From Cyclic Loading Tool

Springback Prediction Using Finite Element Simulation Incorporated With Hardening Data Acquired From Cyclic Loading Tool

Jasri Mohamad (Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Pekan, Malaysia) and Mohd Zaidi Sidek (Universiti Malaysia Pahang, Pekan, Malaysia)
DOI: 10.4018/IJMFMP.2019010102

Abstract

The aims of this article are to present the accuracy of springback prediction in U-bending sheet metal forming processes using finite element (FE) simulation incorporated with kinematics or mixed hardening parameters that are derived from cyclic data provided by the developed cyclic loading tool. The FE simulation results in the form of springback angles are compared with the experimental results for validation. It was found that the mixed hardening model provides better simulation results in predicting springback. This is due to the capability of the isotropic hardening part of this model to describe cyclic transient and the kinematic hardening part to improve description of the Bauschinger effect. Kinematic hardening however, on its own is capable of providing relatively good springback simulation illustrated by errors of less than 8 percent. Overall, the data provided by cyclic loading from the newly developed bending-unbending tool is considered valuable for simulating springback prediction.
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2. Literature Review

In sheet metal forming process, cyclic loading occurs due to bending and unbending of material in the die such as when the sheet is drawn over a die corner (Sanchez, 2010; Yoshida, Uemori, & Fujiwara, 2002). This is shown in Figure 1.

Figure 1.

Description of Cyclic Loading (A) Draw-Bend (B) Springback (C) Stress-Strain Path (Yoshida et al., 2002)

IJMFMP.2019010102.f01

Yoshida and Uemori(Yoshida & Uemori, 2003) described this cyclic process as having four distinct features: load reversal and Bauschinger point, transient behaviour, work-hardening stagnation and permanent softening. To improve sheet metal forming simulation, there is a need to incorporate an appropriate constitutive equation capable of describing the Bauschinger effect and so-called cyclic transient, which describes transition between the elastic and elastic-plastic state during repeated loading. A combination of isotropic and nonlinear kinematic hardening has been considered as one of the best material models, as the former has been associated with the capability to improve cyclic transient and the latter with the capability to take care of the Bauschinger effect (Chun, Jinn, & Lee, 2002). The Chaboche nonlinear kinematic hardening model as described by Equation 1 was chosen for kinematic hardening in this work. A combination of this hardening model and Voce isotropic hardening models in Equation 2 was selected to represent the mixed hardening model as shown by Equation 3.

IJMFMP.2019010102.m01
(1)
IJMFMP.2019010102.m02
(2)
IJMFMP.2019010102.m03
(3)

The parameters involved are: Q, b, C and IJMFMP.2019010102.m04. Q defines the maximum change in the size of the yield surface and b is the rate of the changes. C is a kind of kinematic hardening modulus and IJMFMP.2019010102.m05 defines the rate at which the kinematic hardening modulus decreases as the plastic deformation develops. This is a widely accepted model in sheet metal forming simulation (Chun et al., 2002) and has been applied in finite element software, such as Abaqus (Abaqus, 2000). Identification of material parameters in this and other cyclic hardening models requires a proper cyclic loading experiment to be developed and carried out.

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