Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology
In this paper, a new procedure is developed for the solution of a general two-dimensional uncoupl... more In this paper, a new procedure is developed for the solution of a general two-dimensional uncoupled symmetric double contact problem with smooth contact zones in which the indenter geometry is described by a piecewise biquadratic function. This procedure gives an approximate closed-form solution for any smooth indenter profile. In order to evaluate the accuracy of this approach, it is applied to the symmetric indentation of a flat surface by two rigidly interconnected parabolic indenters and results are compared with the exact unclosed-form solution. Moreover, this procedure is applied to the symmetric indentation of a flat surface by two rigidly interconnected cylinders to compare the results with the finite element solution obtained by the finite element method software, ABAQUS. The results showed that in comparison with the finite element method, this procedure is a fast and highly accurate method with low complexity that makes feasible the possibility of determining approximate ...
Smart materials are being utilized in many fields and different external stimuli are used to chan... more Smart materials are being utilized in many fields and different external stimuli are used to change specific properties of these materials. In this research, a novel method was developed to design a structure with the desired nonlinear effective Young’s modulus. This method is geometric based where the structures are designed with a gap between them. These structures exhibit nonlinear elastic response. Wide range of structures with desired stress–strain curve can be generated using this approach. First, a unit cell was designed and later used to create a periodic structure. Numerical simulations have been exploited to prove the efficiency of the method. A prototype was manufactured by the Fused Deposition Modeling (FDM) 3D printing method. The compression test was performed on the structure. Both simulations and experimental results proved that the effective Young’s modulus of the structure can be increased up to 142%. Second, the designed unit cell was optimized using Genetic Algor...
The development of a predictive model for bone remodeling is becoming increasingly important for ... more The development of a predictive model for bone remodeling is becoming increasingly important for medical applications such as bone surgery or bone substitutes like prostheses. However, as bone remodeling is a complex multiphysics phenomenon and difficult to quantify experimentally, predictive numerical models remain, at best, phenomenologically driven. Patient dependency is often ignored as its influence is usually considered secondary, although it is known to play an important role over long periods of time. Another difficulty to study this patient dependency is the availability of experimental samples to carry out extensive analyses. Using our recently developed statistical reconstruction framework, a set of “bone like” microstructures with variety of distributions has been created to study pseudo “patient variabilities.” The method provides similar effective stiffness tensor, equivalent stresses, and strain energy distributions for the original and the statistically reconstructed...
ABSTRACT In this study, microstructure of a porosity-graded lanthanum strontium manganite (LSM) c... more ABSTRACT In this study, microstructure of a porosity-graded lanthanum strontium manganite (LSM) cathode of solid oxide fuel cells (SOFCs) has been characterized using focused ion beam (FIB) and scanning electron microscopy (SEM) combined with image processing. Two-point correlation functions of the two-dimensional (2D) images taken along the direction of porosity gradient are used to reconstruct a three-dimensional (3D) microstructure. The effective elastic modulus of the two-phase porosity-graded cathode is predicted using strong contrast (SC) and composite inclusion (CI) homogenization techniques. The effectiveness of the two methods in predicting the effective elastic properties of the porosity-graded LSM cathode is investigated in comparison with the results obtained from the finite element model (FEM).
ABSTRACT In situ tensile tests show damage initiates in polymer nanocomposites mainly by interfac... more ABSTRACT In situ tensile tests show damage initiates in polymer nanocomposites mainly by interfacial debonding. In this paper a hierarchical multiscale model is developed to study the damage initiation in the graphite nanoplatelets (GNP) reinforced polymer composites. The cohesive zone model was adopted to capture the nanofillers deboning. The results of atomic simulations of GNP pullout and debonding tests were used to obtain the traction–displacement relation for the cohesive zone model (CZM). The effects of volume fraction and aspect ratio of the GNP and the strength of the interfacial adhesion on the overall stress–strain response of the nanocomposite have been investigated. Results show that debonding has a significant effect on the overall stress–strain response of the nanocomposite when volume fraction and aspect ratio increase. The results also indicate that GNP/polymer interfacial strength plays a key role in the damage mechanism of the polymer nanocomposites.
ABSTRACT 3-D reconstruction of Halloysite nanotube (HNT) polypropylene composite has been perform... more ABSTRACT 3-D reconstruction of Halloysite nanotube (HNT) polypropylene composite has been performed using two different methods. In the first method, several slices of the composite material were obtained using focused ion beam (FIB), and scanning electron microscopy (SEM). A representative volume element (RVE) of the real material’s micro/nanostructures was then constructed by stacking these morphological images using VCAT® software. In the second method, SEM images of the nano-composite were used to extract statistical two-point correlation function (TPCF), for reconstruction of an RVE of the nano-composite.The resulting RVEs obtained from both methods were meshed for finite element (FE) simulation of deformation under tension and shear loadings. The FE results were then used to compute the stiffness tensor of the nano-composite.In the statistical approach, the TPCF was obtained from a none-Eigen microstructure which can partially reflect statistical information of the microstructure. The mechanical constants obtained from statistical RVEs using FEM approach shows a 5.7% error compared with those obtained from real RVE, which could be attributed to the approximation using TPCF [1].It is concluded that the statistical method using TPCF alone can produce an approximate microstructure that should be modified using other statistical descriptor such as two-point cluster function and lineal path function to have better reconstruction of heterogeneous nano-composites [2].
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology
In this paper, a new procedure is developed for the solution of a general two-dimensional uncoupl... more In this paper, a new procedure is developed for the solution of a general two-dimensional uncoupled symmetric double contact problem with smooth contact zones in which the indenter geometry is described by a piecewise biquadratic function. This procedure gives an approximate closed-form solution for any smooth indenter profile. In order to evaluate the accuracy of this approach, it is applied to the symmetric indentation of a flat surface by two rigidly interconnected parabolic indenters and results are compared with the exact unclosed-form solution. Moreover, this procedure is applied to the symmetric indentation of a flat surface by two rigidly interconnected cylinders to compare the results with the finite element solution obtained by the finite element method software, ABAQUS. The results showed that in comparison with the finite element method, this procedure is a fast and highly accurate method with low complexity that makes feasible the possibility of determining approximate ...
Smart materials are being utilized in many fields and different external stimuli are used to chan... more Smart materials are being utilized in many fields and different external stimuli are used to change specific properties of these materials. In this research, a novel method was developed to design a structure with the desired nonlinear effective Young’s modulus. This method is geometric based where the structures are designed with a gap between them. These structures exhibit nonlinear elastic response. Wide range of structures with desired stress–strain curve can be generated using this approach. First, a unit cell was designed and later used to create a periodic structure. Numerical simulations have been exploited to prove the efficiency of the method. A prototype was manufactured by the Fused Deposition Modeling (FDM) 3D printing method. The compression test was performed on the structure. Both simulations and experimental results proved that the effective Young’s modulus of the structure can be increased up to 142%. Second, the designed unit cell was optimized using Genetic Algor...
The development of a predictive model for bone remodeling is becoming increasingly important for ... more The development of a predictive model for bone remodeling is becoming increasingly important for medical applications such as bone surgery or bone substitutes like prostheses. However, as bone remodeling is a complex multiphysics phenomenon and difficult to quantify experimentally, predictive numerical models remain, at best, phenomenologically driven. Patient dependency is often ignored as its influence is usually considered secondary, although it is known to play an important role over long periods of time. Another difficulty to study this patient dependency is the availability of experimental samples to carry out extensive analyses. Using our recently developed statistical reconstruction framework, a set of “bone like” microstructures with variety of distributions has been created to study pseudo “patient variabilities.” The method provides similar effective stiffness tensor, equivalent stresses, and strain energy distributions for the original and the statistically reconstructed...
ABSTRACT In this study, microstructure of a porosity-graded lanthanum strontium manganite (LSM) c... more ABSTRACT In this study, microstructure of a porosity-graded lanthanum strontium manganite (LSM) cathode of solid oxide fuel cells (SOFCs) has been characterized using focused ion beam (FIB) and scanning electron microscopy (SEM) combined with image processing. Two-point correlation functions of the two-dimensional (2D) images taken along the direction of porosity gradient are used to reconstruct a three-dimensional (3D) microstructure. The effective elastic modulus of the two-phase porosity-graded cathode is predicted using strong contrast (SC) and composite inclusion (CI) homogenization techniques. The effectiveness of the two methods in predicting the effective elastic properties of the porosity-graded LSM cathode is investigated in comparison with the results obtained from the finite element model (FEM).
ABSTRACT In situ tensile tests show damage initiates in polymer nanocomposites mainly by interfac... more ABSTRACT In situ tensile tests show damage initiates in polymer nanocomposites mainly by interfacial debonding. In this paper a hierarchical multiscale model is developed to study the damage initiation in the graphite nanoplatelets (GNP) reinforced polymer composites. The cohesive zone model was adopted to capture the nanofillers deboning. The results of atomic simulations of GNP pullout and debonding tests were used to obtain the traction–displacement relation for the cohesive zone model (CZM). The effects of volume fraction and aspect ratio of the GNP and the strength of the interfacial adhesion on the overall stress–strain response of the nanocomposite have been investigated. Results show that debonding has a significant effect on the overall stress–strain response of the nanocomposite when volume fraction and aspect ratio increase. The results also indicate that GNP/polymer interfacial strength plays a key role in the damage mechanism of the polymer nanocomposites.
ABSTRACT 3-D reconstruction of Halloysite nanotube (HNT) polypropylene composite has been perform... more ABSTRACT 3-D reconstruction of Halloysite nanotube (HNT) polypropylene composite has been performed using two different methods. In the first method, several slices of the composite material were obtained using focused ion beam (FIB), and scanning electron microscopy (SEM). A representative volume element (RVE) of the real material’s micro/nanostructures was then constructed by stacking these morphological images using VCAT® software. In the second method, SEM images of the nano-composite were used to extract statistical two-point correlation function (TPCF), for reconstruction of an RVE of the nano-composite.The resulting RVEs obtained from both methods were meshed for finite element (FE) simulation of deformation under tension and shear loadings. The FE results were then used to compute the stiffness tensor of the nano-composite.In the statistical approach, the TPCF was obtained from a none-Eigen microstructure which can partially reflect statistical information of the microstructure. The mechanical constants obtained from statistical RVEs using FEM approach shows a 5.7% error compared with those obtained from real RVE, which could be attributed to the approximation using TPCF [1].It is concluded that the statistical method using TPCF alone can produce an approximate microstructure that should be modified using other statistical descriptor such as two-point cluster function and lineal path function to have better reconstruction of heterogeneous nano-composites [2].
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Papers by Azadeh Sheidaei