Showing 4 results for Stress Triaxiality
Asghar Zajkani, Ali Bandizaki,
Volume 17, Issue 12 (2-2018)
Abstract
In the past decades, for prediction of necking phenomenon, several models such as the vertex theory have been proposed. Here, a vertex model considering strain and stress rate discontinuities in the necking band is extended. This model is based on the J_2 deformation theory of classical plasticity to predict the evolution of a bounded deformation in necking modes. Although consideration of the strain rate hardening effect plays an important role to obtain accurate results, but, usually imposing it leads to emerging, relatively the main complex constitutive equations. Therefore, a delicate connective bridge between the diffuse and localized models is made using the maximum force assumption to overcome on the complexity of the problem. Also, by investigating the strain rate behavior on the plastic instability, the forming limit diagrams are obtained by illustrating more accurate results as compared to existing models. Effect of stress triaxiality is investigated on the localization in bifurcation analysis. Also, a modified maximum force criterion is applied to predict diffuse necking considering loading conditions. The anisotropy effects is studied by application of a quadratic Hill's criteria. The necking band angle will be investigated per different conditions through extending the vertex model coupled with the angle-dependent yield criterion.
Esmaeil Salimpour, ,
Volume 18, Issue 2 (4-2018)
Abstract
Determination of the damage parameters for different materials can be beneficial to the analysis and assessment of rupture during forming of thin metallic plates. The amount of damage depends on the strain amplitude, the state of stress, and also the path and rate of the strain. The state of stress at the damage location is an important and effective parameter which is described by stress triaxilality, load angle and equivalent stress. In this paper, the mechanical behavior and ductile damage properties of Al 2024-O have been investigated. The aim was the determination of the mechanical behavior and development of an expression for correlation between the failure strain and the state of stress at the damage location. Hence, the experimental tests were carried out on both smooth and notched flat specimens. Various levels of stress triaxiality in notched specimens were created by variation of the notch radius. Based on the test results, a new expression has been developed for correlation between the failure strain and the triaxiality ratio for Al 2024-O in the plane strain regime. In order to evaluate the simulation procedure and applicability of the proposed expressions in more complex problems, the process was simulated using ductile damage criterion in the ABAQUS software, and the experimental and numerical results were compared. Very good agreements were observed between the simulation and experimental results.
Maziar Khademi, Hassan Moslemi Naeini, Mohammad Javad Mirnia,
Volume 22, Issue 7 (7-2022)
Abstract
In this paper, fracture prediction accuracy was evaluated by the GTN ductile fracture criterion and the effect of its evolution. To investigate the stress states, three calibration tests, including uniaxial tension, plane strain tension, and In-plane shear tension, were used to calibrate the failure criterion and determine the accuracy of fracture prediction. For simulation of the fracture behavior in Aluminum 6061-T6, the GTN ductile fracture criterion was calibrated using the combined experimental-simulation method. ABAQUS software was used to simulate the forming process, and fracture criteria were implemented to the software by the VUMAT subroutine. The force-displacement values and the fracture displacement in the experimental tests were used to validate the numerical results and evaluate the fracture criterion accuracy. According to the results, calibration using uniaxial tension and In-plane shear tension tests predicts failure with an average error of 6.17%. While the original GTN criterion cannot predict the fracture of the In-plane shear tension test, the error value in the plane strain tension test reaches 24%. A U- bending test was performed to investigate the fracture behavior of Aluminium 6061-T6 sheets and validate the calibrated fracture criterion in a more complex process other than tension tests. The Extended GTN criterion was found to predict the onset of fracture in the U-bending process with an error of 3%.
Mohammad Albonasser, Hojjat Badnava, Sayed Hassan Nourbakhsh,
Volume 24, Issue 12 (11-2024)
Abstract
The accurate prediction of crack initiation and growth in manufacturing processes is crucial for minimizing production costs and enhancing the reliability of components. This study focuses on integrated experimental investigation and fracture modeling approach for ductile metals, particularly addressing the mechanisms of ductile fracture and shear localization. The importance of establishing robust damage criteria for accurate reliable numerical simulations cannot be denied. Current literature reveals a significant lack of data on shear and ductile fracture criteria for materials like stainless steel alloy 304. To address this gap, a series of experimental tests was conducted to extract the necessary coefficients for these criteria. Various sample geometries were analyzed to investigate the effects of different triaxiality stress states and loading rates on fracture initiation. The triaxiality stress states were chosen within a range of 0.2 to 2 and strain rates were applied at values of 0.02 s-1, 4.5 s-1, and 30 s-1. A set of coefficients for modeling ductile and shear fracture was derived, taking into account the effects of loading rate and orientation. This research not only provides critical coefficients for fracture modeling but also supports the optimization of manufacturing processes in the automotive industry and other sectors, ultimately contributing to improved material performance and component reliability
