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- 저자 : Mojtaba Hejazi (검색결과 2 건)
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Assessment of Various Ductile Damage Criteria in Numerical Simulations of Machining Processes
Mojtaba Hejazi,Farhad Haji Aboutalebi 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.25 No.1
In the machining processes, chip removal can be performed by the applied forces. Therefore, predicting the required forces and energy is an essential challenge to reach the efficient processes. In this research, employing various ductile damage models of the continuum damage mechanics (CDM), a few machining processes such as 3D plane machining, 3D drilling, and turning are numerically simulated. Using the numerical simulations of finite element method (FEM), variations of the applied forces on the workpiece and the maximum force as well as the mechanism of chip formation during the machining processes are estimated. Besides, to assess the ductile damage models, the numerical simulation results are compared with the experimental results. The comparison reveals that the Ayada, Ayada negative, and Johnson–Cook damage criteria can accurately predict the required forces and respectively are the reliable models for numerical simulations of chip removal in the machining processes.
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Mojtaba Rafiee,Hossein Amoushahi,Mehrdad Hejazi 국제구조공학회 2024 Structural Engineering and Mechanics, An Int'l Jou Vol.89 No.2
A numerical method is presented in this paper, for buckling analysis of thin arbitrary stiffened composite cylindrical shells under axial compression. The stiffeners can be placed inside and outside of the shell. The shell and stiffeners are operated as discrete elements, and their interactions are taking place through the compatibility conditions along their intersecting lines. The governing equations of motion are obtained based on Koiter's theory and solved by utilizing the principle of the minimum potential energy. Then, the buckling load coefficient and the critical buckling load are computed by solving characteristic equations. In this formulation, the elastic and geometric stiffness matrices of a single curved strip of the shell and stiffeners can be located anywhere within the shell element and in any direction are provided. Moreover, five stiffened composite shell specimens are made and tested under axial compression loading. The reliability of the presented method is validated by comparing its numerical results with those of commercial software, experiments, and other published numerical results. In addition, by using the ANSYS code, a 3-D finite element model that takes the exact geometric arrangement and the properties of the stiffeners and the shell into consideration is built. Finally, the effects of Poisson's ratio, shell length-to-radius ratio, shell thickness, cross-sectional area, angle, eccentricity, torsional stiffness, numbers and geometric configuration of stiffeners on the buckling of stiffened composite shells with various end conditions are computed. The results gained can be used as a meaningful benchmark for researchers to validate their analytical and numerical methods.
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