Effect of continuum damage mechanics on springback prediction in metal forming processes

Ali Nayebi,Mehdi Shahabi 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5

The influence of considering the variations in material properties was investigated through continuum damage mechanics according to the Lemaitre isotropic unified damage law to predict the bending force and springback in V-bending sheet metal forming processes, with emphasis on Finite element (FE) simulation considerations. The material constants of the damage model were calibrated through a uniaxial tensile test with an appropriate and convenient repeating strategy. Holloman’s isotropic and Ziegler’s linear kinematic hardening laws were employed to describe the behavior of a hardening material. To specify the ideal FE conditions for simulating springback, the effect of the various numerical considerations during FE simulation was investigated and compared with the experimental outcome. Results indicate that considering continuum damage mechanics decreased the predicted bending force and improved the accuracy of springback prediction.

Anisotropic continuum damage analysis of thin-walled pressure vessels under cyclic thermo-mechanical loading

Azam Surmiri,Ali Nayebi,Hojjatollah Rokhgireh,Ahmad Varvani-Farahani 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.1

The present study intends to analyze damage in thin-walled steel cylinders undergoing constant internal pressure and thermal cycles through use of anisotropic continuum damage mechanics (CDM) model coupled with nonlinear kinematic hardening rule of Chaboche. Materials damage in each direction was defined based on plastic strain and its direction. Stress and strain distribution over wall-thickness was described based on the CDM model and the return mapping algorithm was employed based on the consistency condition. Plastic zone expansion across the wall thickness of cylinders was noticeably affected with change in internal pressure and temperature gradients. Expansion of plastic zone over wall-thickness at inner and outer surfaces and their boundaries demarking elastic and plastic regions was attributed to the magnitude of damage induced over thermo-mechanical cycles on the thin-walled samples tested at various pressure stresses.

Springback FE modeling of titanium alloy tubes bending using various hardening models

Mehdi Shahabi,Ali Nayebi 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.56 No.3

In this study, effect of various material hardening models based on Holloman’s isotropic, Ziegler’s linear kinematic, non-linear kinematic and mixture of the isotropic and nonlinear kinematic hardening laws on springback prediction of titanium alloy (Ti-3Al-2.5V) in a tube rotary draw bending (RDB) process was investigated with presenting the keynotes for a comprehensive step by step ABAQUS simulation. Influence of mandrel on quality of the final product including springback, wall-thinning and cross-section deformation of the tube was investigated, too. Material parameters of the hardening models were obtained based on information of a uniaxial test. In particular, in the case of combined iso-nonlinear kinematic hardening the material constants were calibrated by a simple approach based on half-cycle data instead of several stabilized cycles ones. Moreover, effect of some material and geometrical parameters on springback was carried out. The results showed that using the various hardening laws separately cannot describe the material hardening behavior correctly. Therefore, it is concluded that combining the hardening laws is a good idea to have accurate springback prediction. Totally the results are useful for predicting and controlling springback and cross-section deformation in metal forming processes.

Predicting the ratcheting strain of 304 stainless steel by considering yield surface distortion and using a viscoplastic model

Nabi Ahmadi,Ali Nayebi 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.7

Yield surface distortion and its center movement were employed in a unified viscoplastic model to predict the ratcheting behavior ofthe 304 stainless steel. A combination of the Ohno-Wang model and the yield surface distortion model of Baltov and Sawczuk was usedin uniaxial loading. Stress amplitude and the mean stress were varied in the tests to verify the model. Uniaxial loadings were simulatedwith and without consideration of yield surface distortion. Results from both simulations were compared. Yield surface distortion showeda significant effect on the simulation of the ratcheting responses.

Failure analysis of tubes under multiaxial proportional and non-proportional loading paths

Mohammad Hossein Iji,Ali Nayebi 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.47 No.2

The failure of a thin-walled tube was studied in this paper based on three failure models. Both proportional and nonproportional loading paths were applied. Proportional loading consisted of combined tension-torsion. Cyclic non-proportional loading was also applied. It was a circular out-of-phase axial-shear stress loading path. The third loading path was a combination of a constant internal pressure and a bending moment. The failure models under study were equivalent plastic strain, modified Mohr-Coulomb (Bai-Wierzbicki) and Tearing parameter models. The elasto-plastic analysis was conducted using J2 criterion and nonlinear kinematic hardening. The return mapping algorithm was employed to numerically solve the plastic flow relations. The effects of the hydrostatic stress on the plastic flow and the stress triaxiality parameter on the failure were discussed. Each failure model under study was utilized to predict failure. The failure loads obtained from each model were compared with each other. The equivalent plastic strain model was independent from the stress triaxiality parameter, and it predicted the highest failure load in the bending problem. The modified Mohr-Coulomb failure model predicted the lowest failure load for the range of the stress triaxiality parameter and Lode’s angle.

Springback Investigation of a Thick-Walled Tube Under Combined Torsion-Bending and Internal Pressure by Using Continuum Damage Mechanics

Afshin Farhadi,Amir Hosseini-Hooshyar,Ali Nayebi 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.6

The choice of material behavior models, as well as the forming procedures such as loadings and their sequences are essential in plastic flow and springback. In this study, the combined torsion and bending of a thick-walled tube under an internal pressure is simulated to predict bending and torsion springback. Continuum Damage Mechanics and the nonlinear kinematic hardening models are assumed and a numerical tool is developed to predict the springback analytically. The numerical model is verified by comparing the experimental results of simultaneous bending and torsion of a pure aluminum tube conducted by Wu et al. (Int J Mech Sci 131–132:191–204, 2017) with the numerical results. The experimental results of Sorour et al. (Thin-Walled Struct 144:106336, 2019), which studied the bending of a tube with internal pads, are also modelled with the present numerical model. The effects of loading sequences on the springback are also investigated.

In vitro and in vivo evaluation of the mechanisms of citalopraminduced hepatotoxicity

Elham Ahmadian,Aziz Eftekhari,Javad Khalili Fard,Hossein Babaei,Alireza Mohajjel Nayebi,Daryoush Mohammadnejad,Mohammad Ali Eghbal 대한약학회 2017 Archives of Pharmacal Research Vol.40 No.11

Even though citalopram is commonly used inpsychiatry, there are several reports on its toxic effects. So,the current study was designed to elucidate the mechanismsof cytotoxic effects of in vitro and in vivo citalopramtreatment on liver and the following cytolethal events. Forin vitro experiments, freshly isolated rat hepatocytes wereexposed to citalopram along with/without various agents. To do in vivo studies liver function enzyme assays andhistological examination were performed. In the in vitroexperiments, citalopram (500 lM) exposure demonstratedcell death, a marked elevation in ROS formation, mitochondrialpotential collapse, lysosomal membrane leakiness,glutathione (GSH) depletion and lipid peroxidation. In vivo biochemistry panel assays for liver enzymesfunction (AST, ALT and GGTP) and histological examinationconfirmed citalopram (20 mg/kg)-induced damage. citalopram-induced oxidative stress cytotoxicity markerswere significantly prevented by antioxidants, ROS scavengers,MPT pore sealing agents, endocytosis inhibitors,ATP generators and CYP inhibitors. Either enzymeinduction or GSH depletion were concomitant with augmentedcitalopram-induced damage both in vivo andin vitro which were considerably ameliorated withantioxidants and CYP inhibitors. In conclusion, it is suggestedthat citalopram hepatotoxicity might be a result ofoxidative hazard leading to mitochondrial/lysosomal toxicconnection and disorders in biochemical markers whichwere supported by histomorphological studies.