The Experts below are selected from a list of 1491 Experts worldwide ranked by ideXlab platform
Guido Berti - One of the best experts on this subject based on the ideXlab platform.
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mathematical definition of the 3d strain field of the ring in the radial axial ring rolling process
International Journal of Mechanical Sciences, 2016Co-Authors: Luca Quagliato, Guido BertiAbstract:Abstract The paper focuses on the radial-axial ring rolling process and details a new mathematical approach for the determination of the evolution of the ring geometry during the deformation process, taking into account separately the sequence of incremental deformations occurring when the ring passes through the mandrel-main roll gap and through the axial rolls gap. Based on the determined geometry of the ring, the three strain components of the strain tensor are estimated and the equivalent plastic strain is computed. The proposed approach, taking into account a third strain in each deformation gap, allows an estimation of the equivalent plastic strain, which is a required parameter for the analytical estimation of the flow stress of the material, needed to compute the forming force. Since a direct validation of the strain components is not possible in the industrial RARR process, authors’ models for the determination of geometry and strain, together with preliminary authors’ models for the estimation of strain rate and temperature drop along the process, have been applied to a literature case for the estimation of the radial forming force in order to obtain a validation of the proposed models. Prediction of radial forming force utilizes a literature model based on Slip Line Theory adapted to the ring rolling process. To extend the validation of the approach and to explore the quality of its predictions to other process configurations, different geometry of the ring have been considered and compared with FEM predictions. These comparisons resulted in good agreement between analytical and FEM results as concerns ring geometry evolution, strain tensor prediction and effective strain estimation.
Gianni Royercarfagni - One of the best experts on this subject based on the ideXlab platform.
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phase field Slip Line Theory of plasticity
Journal of The Mechanics and Physics of Solids, 2016Co-Authors: Francesco Freddi, Gianni RoyercarfagniAbstract:Abstract A variational approach to determine the deformation of an ideally plastic substance is proposed by solving a sequence of energy minimization problems under proper conditions to account for the irreversible character of plasticity. The flow is driven by the local transformation of elastic strain energy into plastic work on Slip surfaces, once that a certain energetic barrier for Slip activation has been overcome. The distinction of the elastic strain energy into spherical and deviatoric parts is used to incorporate in the model the idea of von Mises plasticity and isochoric plastic strain. This is a “phase field model” because the matching condition at the Slip interfaces is substituted by the evolution of an auxiliary phase field that, similar to a damage field, is unitary on the elastic phase and null on the yielded phase. The Slip Lines diffuse in bands, whose width depends upon a material length-scale parameter. Numerical experiments on representative problems in plane strain give solutions with noteworthy similarities with the results from classical Slip-Line field Theory, but the proposed model is much richer because, accounting for elastic deformations, it can describe the formation of Slip bands at the local level, which can nucleate, propagate, widen and diffuse by varying the boundary conditions. In particular, the solution for a long pipe under internal pressure is very different from the one obtainable from the classical macroscopic Theory of plasticity. For this case, the location of the plastic bands may be an insight to explain the premature failures that are sometimes encountered during the manufacturing process. This practical example enhances the importance of this new Theory based on the mathematical sciences.
Luca Quagliato - One of the best experts on this subject based on the ideXlab platform.
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mathematical definition of the 3d strain field of the ring in the radial axial ring rolling process
International Journal of Mechanical Sciences, 2016Co-Authors: Luca Quagliato, Guido BertiAbstract:Abstract The paper focuses on the radial-axial ring rolling process and details a new mathematical approach for the determination of the evolution of the ring geometry during the deformation process, taking into account separately the sequence of incremental deformations occurring when the ring passes through the mandrel-main roll gap and through the axial rolls gap. Based on the determined geometry of the ring, the three strain components of the strain tensor are estimated and the equivalent plastic strain is computed. The proposed approach, taking into account a third strain in each deformation gap, allows an estimation of the equivalent plastic strain, which is a required parameter for the analytical estimation of the flow stress of the material, needed to compute the forming force. Since a direct validation of the strain components is not possible in the industrial RARR process, authors’ models for the determination of geometry and strain, together with preliminary authors’ models for the estimation of strain rate and temperature drop along the process, have been applied to a literature case for the estimation of the radial forming force in order to obtain a validation of the proposed models. Prediction of radial forming force utilizes a literature model based on Slip Line Theory adapted to the ring rolling process. To extend the validation of the approach and to explore the quality of its predictions to other process configurations, different geometry of the ring have been considered and compared with FEM predictions. These comparisons resulted in good agreement between analytical and FEM results as concerns ring geometry evolution, strain tensor prediction and effective strain estimation.
Jeffrey W Kysa - One of the best experts on this subject based on the ideXlab platform.
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cylindrical void in a rigid ideally plastic single crystal ii experiments and simulations
International Journal of Plasticity, 2006Co-Authors: Jeffrey W Kysa, Timothy L MorseAbstract:Abstract Experimental results and finite element simulations of plastic deformation around a cylindrical void in single crystals are presented to compare with the analytical solutions in a companion paper: Cylindrical void in a rigid-ideally plastic single crystal I: Anisotropic Slip Line Theory solution for face-centered cubic crystals [Kysar, J.W., Gan, Y.X., Mendez-Arzuza, G., 2005. Cylindrical void in a rigid-ideally plastic single crystal I: Anisotropic Slip Line Theory solution for face-centered cubic crystals, International Journal of Plasticity, 21, 1481–1520]. In the first part of the present paper, the theoretical predictions of the stress and deformation field around a cylindrical void in face-centered cubic (FCC) single crystals are briefly reviewed. Secondly, electron backscatter diffraction results are presented to show the lattice rotation discontinuities at boundaries between regions of single Slip around the void as predicted in the companion paper. In the third part of the paper, the finite element method has been employed to simulate the anisotropic plastic deformation behavior of FCC single crystals which contain cylindrical voids under plane strain condition. The results of the simulation are in good agreement with the prediction by the anisotropic Slip Line Theory.
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cylindrical void in a rigid ideally plastic single crystal part i anisotropic Slip Line Theory solution for face centered cubic crystals
International Journal of Plasticity, 2005Co-Authors: Jeffrey W Kysa, Gilberto MendezarzuzaAbstract:Abstract The fracture toughness of ductile materials depends upon the ability of the material to resist the growth of microscale voids near a crack tip. Mechanics analyses of the elastic–plastic deformation state around such voids typically assume the surrounding material to be isotropic. However, the voids exist predominantly within a single grain of a polycrystalLine material, so it is necessary to account for the anisotropic nature of the surrounding material. In the present work, anisotropic Slip Line Theory is employed to derive the stress and deformation state around a cylindrical void in a single crystal oriented so that plane strain conditions are admitted from three effective in-plane Slip systems. The deformation state takes the form of angular sectors around the circumference of the void. Only one of the three effective Slip systems is active within each sector. Each Slip sector is further subdivided into smaller sectors inside of which it is possible to derive the stress state. Thus the Theory predicts a highly heterogeneous stress and deformation state. In addition, it is shown that the in-plane pressure necessary to activate plastic deformation around a cylindrical void in an anisotropic material is significantly higher than that necessary for an isotropic material. Experiments and single crystal plasticity finite element simulations of cylindrical voids in single crystals, both of which exhibit a close correspondence to the analytical Theory, are discussed in a companion paper.
Timothy L Morse - One of the best experts on this subject based on the ideXlab platform.
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cylindrical void in a rigid ideally plastic single crystal ii experiments and simulations
International Journal of Plasticity, 2006Co-Authors: Jeffrey W Kysa, Timothy L MorseAbstract:Abstract Experimental results and finite element simulations of plastic deformation around a cylindrical void in single crystals are presented to compare with the analytical solutions in a companion paper: Cylindrical void in a rigid-ideally plastic single crystal I: Anisotropic Slip Line Theory solution for face-centered cubic crystals [Kysar, J.W., Gan, Y.X., Mendez-Arzuza, G., 2005. Cylindrical void in a rigid-ideally plastic single crystal I: Anisotropic Slip Line Theory solution for face-centered cubic crystals, International Journal of Plasticity, 21, 1481–1520]. In the first part of the present paper, the theoretical predictions of the stress and deformation field around a cylindrical void in face-centered cubic (FCC) single crystals are briefly reviewed. Secondly, electron backscatter diffraction results are presented to show the lattice rotation discontinuities at boundaries between regions of single Slip around the void as predicted in the companion paper. In the third part of the paper, the finite element method has been employed to simulate the anisotropic plastic deformation behavior of FCC single crystals which contain cylindrical voids under plane strain condition. The results of the simulation are in good agreement with the prediction by the anisotropic Slip Line Theory.