In the present work, a critical analysis of the most-commonly used analytical models and recently... more In the present work, a critical analysis of the most-commonly used analytical models and recently introduced ANN-based models was performed to evaluate their predictive accuracy within and outside the experimental interval used to generate them. The high-temperature deformation behavior of a medium carbon steel was studied over a wide range of strains, strain rates, and temperatures using hot compression tests on a Gleeble-3800. The experimental flow curves were modeled using the Johnson–Cook, Modified-Zerilli–Armstrong, Hansel–Spittel, Arrhenius, and PTM models, as well as an ANN model. The mean absolute relative error and root-mean-squared error values were used to quantify the predictive accuracy of the models analyzed. The results indicated that the Johnson–Cook and Modified-Zerilli–Armstrong models had a significant error, while the Hansel–Spittel, PTM, and Arrhenius models were able to predict the behavior of this alloy. The ANN model showed excellent agreement between the pre...
Damaging effects of microcracks on the elastic properties of brittle materials (rocks, concrete, ... more Damaging effects of microcracks on the elastic properties of brittle materials (rocks, concrete, ceramics) have been extensively studied through experiments and modelling approaches. In the latter case, the homogenization (up-scaling) technique appears as an effective tool to provide the overall properties from the microstructural features of the material. Especially for microcracks, main difficulties arise from: (i) the anisotropy induced by the oriented nature of defects, (ii) their ability to be open or closed according to tension or compression loading and to influence differently the overall response of the material. Such unilateral behaviour is typical of contact problems related to that kind of defects. Regarding the thermal properties of microcracked media, very few investigations on the effects have been done in the literature, even on the experimental point of view. Some micro-macro modelling works have been proposed to derive effective properties of a given Representative...
Ophthalmic lenses are made of plastic polymeric substrates usually coated with functional treatme... more Ophthalmic lenses are made of plastic polymeric substrates usually coated with functional treatments composed of 5 to 15 layers, ranging from micrometers to nanometers. Each of these interfaces may lead to delamination due to poor adhesion, and therefore affect the vision and comfort of wearers. The interface between the anti-reflective stack and the hardcoat is particularly sensitive because of chemical and mechanical contrast of its materials. To better understand mechanisms that lead to loss of adhesion between the SiO2 anti-reflective layer deposited on the anti-scratch hardcoat, compression experiments are performed to induce buckling of SiO2 layer. A Finite Element Model is developed to refine characterization of interfacial properties. Simulation of buckling phenomenon and delamination of SiO2 layer under compressive stress is proposed. Interfacial properties between SiO2 layer and hardcoat are modeled using cohesive elements following a traction separation law. Geometry of b...
The design and realization of optimized technological systems are increasing through development ... more The design and realization of optimized technological systems are increasing through development and integration of different functions and combining elements of varied nature. Not only in the field of space but also in power electronics, many ceramic parts are linked by various processes to metallic elements of different physical and mechanical properties. When these assemblies are subjected to high levels of thermomechanical loadings, their heterogeneities generate significant over-stresses that can lead to irreversible damage. A damage model for microcracking in brittle materials taking into account the opening or closing of microcracks (unilateral effect) has been developed by Welemane and Cormery under isothermal conditions. This article gives an overview of damage modelling and the progress made in accounting for temperature effects.
Numerical simulation of friction stir welding process is a great deal since high time consuming p... more Numerical simulation of friction stir welding process is a great deal since high time consuming problems are to be solved. Indeed the process is non-linear because of friction condition at tool/workpieces interface and mainly the nonlinear constitutive laws required to describe the elastic and the viscoplastic material far and close to the pin, respectively. The high strain rate generated by the rotating tool involves mesh refining and a strong remeshing rule to solve mesh distortion problems.
A damage evolution law is proposed to consider the frictional behavior within an Eulerian materia... more A damage evolution law is proposed to consider the frictional behavior within an Eulerian material after full damage as a Lagrangian material, where the mesh explicitly describes the newly born interface interactions. This approach is prominent for simulating severe plastic deformation (SPD) processes during which material separation can occur. Among these, orthogonal cutting represents the simplest process for comparison with the simulation because it offers accessibility for measuring physical quantities in situ in the vicinity of the tool. Therefore, a numerical model based on a coupled Eulerian-Lagrangian formulation to simulate segmented chip formation mechanisms during orthogonal cutting was developed. A simple damage initiation criterion was used, and the damage evolution criterion was coded in the ABAQUS subroutine VUSDFLD. The model can simulate both segmented and continuous chip formation, depending on the experimental configuration, while satisfactorily predicting chip morphology and physical quantities such as temperature, primary shear band and cutting forces. Additionally, a non-negligible material side flow observed experimentally was successfully predicted by simulation. The model accuracy in predicting the material plastic behavior is auspicious for its subsequent extension to the three-dimensional model of SPD processes (i.e., milling, friction stir welding, etc.)
The severe deformation and temperature paths in the stir zone, also called weld nugget, of fricti... more The severe deformation and temperature paths in the stir zone, also called weld nugget, of friction stir welded joints result, at very local levels, in significant microstructural variations, such as major differences in grain size or precipitation. One of the most common features of friction stir welds is the presence of successive material layers, known as onion rings; however, little data is available on the mechanical properties of the different regions of the weld nugget, and particularly within the onion ring bands. Such information becomes very important for the integrity of large size friction stir welded structures. In the present study, a comprehensive characterization of onion rings produced during friction stir welding of a 6082-aluminum alloy was carried out. Advanced techniques such as in-situ SEM nanoindentation, EBSD, and high-resolution EDS were used to validate and compare the characteristics of the different bands in the onion rings. The analyses consisted of quan...
In the present work, a critical analysis of the most-commonly used analytical models and recently... more In the present work, a critical analysis of the most-commonly used analytical models and recently introduced ANN-based models was performed to evaluate their predictive accuracy within and outside the experimental interval used to generate them. The high-temperature deformation behavior of a medium carbon steel was studied over a wide range of strains, strain rates, and temperatures using hot compression tests on a Gleeble-3800. The experimental flow curves were modeled using the Johnson–Cook, Modified-Zerilli–Armstrong, Hansel–Spittel, Arrhenius, and PTM models, as well as an ANN model. The mean absolute relative error and root-mean-squared error values were used to quantify the predictive accuracy of the models analyzed. The results indicated that the Johnson–Cook and Modified-Zerilli–Armstrong models had a significant error, while the Hansel–Spittel, PTM, and Arrhenius models were able to predict the behavior of this alloy. The ANN model showed excellent agreement between the pre...
Damaging effects of microcracks on the elastic properties of brittle materials (rocks, concrete, ... more Damaging effects of microcracks on the elastic properties of brittle materials (rocks, concrete, ceramics) have been extensively studied through experiments and modelling approaches. In the latter case, the homogenization (up-scaling) technique appears as an effective tool to provide the overall properties from the microstructural features of the material. Especially for microcracks, main difficulties arise from: (i) the anisotropy induced by the oriented nature of defects, (ii) their ability to be open or closed according to tension or compression loading and to influence differently the overall response of the material. Such unilateral behaviour is typical of contact problems related to that kind of defects. Regarding the thermal properties of microcracked media, very few investigations on the effects have been done in the literature, even on the experimental point of view. Some micro-macro modelling works have been proposed to derive effective properties of a given Representative...
Ophthalmic lenses are made of plastic polymeric substrates usually coated with functional treatme... more Ophthalmic lenses are made of plastic polymeric substrates usually coated with functional treatments composed of 5 to 15 layers, ranging from micrometers to nanometers. Each of these interfaces may lead to delamination due to poor adhesion, and therefore affect the vision and comfort of wearers. The interface between the anti-reflective stack and the hardcoat is particularly sensitive because of chemical and mechanical contrast of its materials. To better understand mechanisms that lead to loss of adhesion between the SiO2 anti-reflective layer deposited on the anti-scratch hardcoat, compression experiments are performed to induce buckling of SiO2 layer. A Finite Element Model is developed to refine characterization of interfacial properties. Simulation of buckling phenomenon and delamination of SiO2 layer under compressive stress is proposed. Interfacial properties between SiO2 layer and hardcoat are modeled using cohesive elements following a traction separation law. Geometry of b...
The design and realization of optimized technological systems are increasing through development ... more The design and realization of optimized technological systems are increasing through development and integration of different functions and combining elements of varied nature. Not only in the field of space but also in power electronics, many ceramic parts are linked by various processes to metallic elements of different physical and mechanical properties. When these assemblies are subjected to high levels of thermomechanical loadings, their heterogeneities generate significant over-stresses that can lead to irreversible damage. A damage model for microcracking in brittle materials taking into account the opening or closing of microcracks (unilateral effect) has been developed by Welemane and Cormery under isothermal conditions. This article gives an overview of damage modelling and the progress made in accounting for temperature effects.
Numerical simulation of friction stir welding process is a great deal since high time consuming p... more Numerical simulation of friction stir welding process is a great deal since high time consuming problems are to be solved. Indeed the process is non-linear because of friction condition at tool/workpieces interface and mainly the nonlinear constitutive laws required to describe the elastic and the viscoplastic material far and close to the pin, respectively. The high strain rate generated by the rotating tool involves mesh refining and a strong remeshing rule to solve mesh distortion problems.
A damage evolution law is proposed to consider the frictional behavior within an Eulerian materia... more A damage evolution law is proposed to consider the frictional behavior within an Eulerian material after full damage as a Lagrangian material, where the mesh explicitly describes the newly born interface interactions. This approach is prominent for simulating severe plastic deformation (SPD) processes during which material separation can occur. Among these, orthogonal cutting represents the simplest process for comparison with the simulation because it offers accessibility for measuring physical quantities in situ in the vicinity of the tool. Therefore, a numerical model based on a coupled Eulerian-Lagrangian formulation to simulate segmented chip formation mechanisms during orthogonal cutting was developed. A simple damage initiation criterion was used, and the damage evolution criterion was coded in the ABAQUS subroutine VUSDFLD. The model can simulate both segmented and continuous chip formation, depending on the experimental configuration, while satisfactorily predicting chip morphology and physical quantities such as temperature, primary shear band and cutting forces. Additionally, a non-negligible material side flow observed experimentally was successfully predicted by simulation. The model accuracy in predicting the material plastic behavior is auspicious for its subsequent extension to the three-dimensional model of SPD processes (i.e., milling, friction stir welding, etc.)
The severe deformation and temperature paths in the stir zone, also called weld nugget, of fricti... more The severe deformation and temperature paths in the stir zone, also called weld nugget, of friction stir welded joints result, at very local levels, in significant microstructural variations, such as major differences in grain size or precipitation. One of the most common features of friction stir welds is the presence of successive material layers, known as onion rings; however, little data is available on the mechanical properties of the different regions of the weld nugget, and particularly within the onion ring bands. Such information becomes very important for the integrity of large size friction stir welded structures. In the present study, a comprehensive characterization of onion rings produced during friction stir welding of a 6082-aluminum alloy was carried out. Advanced techniques such as in-situ SEM nanoindentation, EBSD, and high-resolution EDS were used to validate and compare the characteristics of the different bands in the onion rings. The analyses consisted of quan...
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