Mehdi Bayat

SECOND-ORDER SHEAR DEFORMATION THEORY TO ANALYZE STRESS DISTRIBUTION FOR SOLAR FUNCTIONALLY GRADED PLATES

Second-order shear deformation theory (SSDT) is applied to evaluate the displacement and stress fields of a solar functionally graded plate (SFGP) due to mechanical loadings. The material properties are graded by a simple power law between Full-ceramic and Full-metal at upper and lower surfaces, respectively. Naviers method is applied to find analytical results for derived equations by using energy method in case of simply supported boundary conditions. The effects of the material grading index of the plate on the stresses and displacements are investigated. It is revealed that the longitudinal stresses in the functionally graded (FG) plates lie between full-metal and full-ceramic plates. It is found that the neutral axes for SFGP move to upper surface and not at the mid-surface as predicted in the homogeneous plates. The SSDT has computed acceptable results for in-plane stresses and displacement fields when compared with the existing literatures.

On the Stress Analysis of Functionally Graded Gear Wheels with Variable Thickness

This paper presents the elastic solutions of the gear wheels made of functionally graded material (FGM) with variable thickness subjected to rotating loads. The material properties and wheel thickness profile are assumed to be represented by two power law distributions. Solid and hollow wheels are considered and the solutions for the stresses and displacements are given under appropriate boundary conditions. The solutions for FGM are compared with that of non-FGM, and for variable thickness and for uniform thickness. The effects of the material grading index, n, and the geometry of the wheel on the stress and displacement are investigated. It is found that a functionally graded wheel with parabolic and hyperbolic convergent thickness profile has smaller stresses and displacements compared with that with uniform thickness. The maximum radial stress for the solid functionally graded wheel with parabolic thickness profile was not at the center, whereas for solid wheel with uniform thickness, the maximum was at the center. The results obtained suggest that an FGM gear wheel with hyperbolic convergent and parabolic concave thickness profile is more suitable compared with that of uniform thickness.

Finite element analysis on longitudinal and radial functionally graded femoral prosthesis

This study focused on developing a 3D finite element model of functionally graded femoral prostheses to decrease stress shielding and to improve total hip replacement performance. The mechanical properties of the modeled functionally graded femoral prostheses were adjusted in the sagittal and transverse planes by changing the volume fraction gradient exponent. Prostheses with material changes in the sagittal and transverse planes were considered longitudinal and radial prostheses, respectively. The effects of cemented and noncemented implantation methods were also considered in this study. Strain energy and von Mises stresses were determined at the femoral proximal metaphysis and interfaces of the implanted femur components, respectively. Results demonstrated that the strain energy increased proportionally with increasing volume fraction gradient exponent, whereas the interface stresses decreased on the prostheses surfaces. A limited increase was also observed at the surfaces of the bone and cement. The periprosthetic femur with a noncemented prosthesis exhibited higher strain energy than with a cemented prosthesis. Radial prostheses implantation displayed more strain energy than longitudinal prostheses implantation in the femoral proximal part. Functionally graded materials also increased strain energy and exhibited promising potentials as substitutes of conventional materials to decrease stress shielding and to enhance total hip replacement lifespan.

Natural frequency of F.G. rectangular plate by shear deformation theory

Natural frequency of functionally graded (F.G.) rectangular plate is carried out by using second-order shear deformation theory (SSDT). The material properties of functionally graded rectangular plates, except the Poissons ratio, are assumed to vary continuously through the thickness of the plate in accordance with the exponential law distribution. The equations of motion are obtained by energy method. Numerical results for functionally graded plates are given in dimensionless graphical forms and the effects of material properties on natural frequency are determined.

Analysis of Functionally Graded Rotating Disks with Parabolic Concave Thickness Applying an Exponential Function and the Mori-Tanaka Scheme

In this paper, a semi-analytical investigation intended to determine the axisymmetric elastic response of functionally graded (FG) disks. The material properties of the disk are assumed to be graded continuously along the radial direction. An exponential function and the Mori-Tanaka scheme are used for estimating the effective material properties. Two kinds of functionally graded materials (FGMs) namely metal-ceramic and ceramic-metal are considered. Hollow disks are considered and the solutions for the displacements and stresses are given under appropriate boundary conditions. The effects of the material grading index n and the geometry of the disk on the displacements and stresses are investigated. The results in metal-ceramic and ceramic-metal FGMs are compared. These results show that radial displacement in Ceramic-Metal functionally graded disks are smaller than those in Metal-Ceramic FG disks. These results suggest that a rotating functionally graded disk with concave thickness profile can be more efficient than the one with uniform thickness.

Comparison of various functionally graded femoral prostheses by finite element analysis

This study is focused on finite element analysis of a model comprising femur into which a femoral component of a total hip replacement was implanted. The considered prosthesis is fabricated from a functionally graded material (FGM) comprising a layer of a titanium alloy bonded to a layer of hydroxyapatite. The elastic modulus of the FGM was adjusted in the radial, longitudinal, and longitudinal-radial directions by altering the volume fraction gradient exponent. Four cases were studied, involving two different methods of anchoring the prosthesis to the spongy bone and two cases of applied loading. The results revealed that the FG prostheses provoked more SED to the bone. The FG prostheses carried less stress, while more stress was induced to the bone and cement. Meanwhile, less shear interface stress was stimulated to the prosthesis-bone interface in the noncemented FG prostheses. The cement-bone interface carried more stress compared to the prosthesis-cement interface. Stair climbing induced more harmful effects to the implanted femur components compared to the normal walking by causing more stress. Therefore, stress shielding, developed stresses, and interface stresses in the THR components could be adjusted through the controlling stiffness of the FG prosthesis by managing volume fraction gradient exponent.

Probabilistic finite element stiffness of a laterally loaded monopile based on an improved asymptotic sampling method

AbstractThe mechanical responses of an offshore monopile foundation mounted in over-consolidated clay are calculated by employing a stochastic approach where a nonlinear p–y curve is incorporated with a finite element scheme. The random field theory is applied to represent a spatial variation for undrained shear strength of clay. Normal and Sobol sampling are employed to provide the asymptotic sampling method to generate the probability distribution of the foundation stiffnesses. Monte Carlo simulation is used as a benchmark. Asymptotic sampling accompanied with Sobol quasi random sampling demonstrates an efficient method for estimating the probability distribution of stiffnesses for the offshore monopile foundation.

Preliminary analysis of knee stress in Full Extension Landing

OBJECTIVE: This study provides an experimental and finite element analysis of knee-joint structure during extended-knee landing based on the extracted impact force, and it numerically identifies the contact pressure, stress distribution and possibility of bone-to-bone contact when a subject lands from a safe height. METHODS: The impact time and loads were measured via inverse dynamic analysis of free landing without knee flexion from three different heights (25, 50 and 75 cm), using five subjects with an average body mass index of 18.8. Three-dimensional data were developed from computed tomography scans and were reprocessed with modeling software before being imported and analyzed by finite element analysis software. The whole leg was considered to be a fixed middle-hinged structure, while impact loads were applied to the femur in an upward direction. RESULTS: Straight landing exerted an enormous amount of pressure on the knee joint as a result of the bodys inability to utilize the lower extremity muscles, thereby maximizing the threat of injury when the load exceeds the height-safety threshold. CONCLUSIONS: The researchers conclude that extended-knee landing results in serious deformation of the meniscus and cartilage and increases the risk of bone-to-bone contact and serious knee injury when the load exceeds the threshold safety height. This risk is considerably greater than the risk of injury associated with walking downhill or flexion landing activities.

THE EFFECT OF CERAMIC IN COMBINATION OF TWO SIGMOID FUNCTIONALLY GRADED ROTATING DISKS WITH VARIABLE THICKNESS

This paper presents elastic solutions of a disk made of functionally graded material (FGM) with variable thickness subjected to rotating load. The material properties are represented by combination of two sigmoid FGM (S-FGM) namely aluminum–ceramic–aluminum and the disks different thickness profiles are assumed to be represented by power law distributions. Hollow disks are considered and the solutions for the displacements and stresses are given under appropriate boundary conditions. The effects of the material grading index n and the geometry of the disk on the displacements and stresses are investigated. The results are compared with the known results in the literature on metal–ceramic–metal FGMs. Also the solutions are compared S-FGM versus FGM and non FGM and variable thickness versus uniform thickness. It is found that a sigmoid functionally graded disk with concave thickness profile has smaller displacements and stresses compared with concave or linear thickness profile. It is also observed that an S-FGM rotating functionally graded disk with metal–ceramic–metal combination can be more efficient than the one with ceramic–metal or metal–ceramic.

Thermal Free Vibration Analysis of Temperature-Dependent Functionally Graded Plates Using Second Order Shear Deformation

This research has been conducted to approach second-order shear deformation theory (SSDT) to analysis vibration characteristics of Functionally Graded Plates (FGP’s). Material properties in FGPs were assumed to be temperature dependent and graded along the thickness using a simple power law distribution in term of the volume fractions of the constituents. FGP was subjected to a linear and nonlinear temperature rise. The energy method was chosen to derive the equilibrium equations. The solution was based on the Fourier series that satisfy the simply supported boundary condition (Naviers method). Numerical results indicated the effect of material composition, plate geometry, and temperature fields on the vibration characteristics and mode shapes. The results revealed that, the temperature field and volume fraction distribution had significant effect on the vibration of FGPs. It was observed the second order theory was very close to the other shear deformation theorem as reported in the literature.