Sharif Digital Repository

This paper investigates the subsurface stress field induced by a rigid cylinder rolling over a functionally graded coating-substrate system. The Fourier transform is employed to extract the stress components within the graded coating and the homogeneous substrate. The distributions of the stresses are given through the depth and along the coating-substrate interface. The contour plots of normalized Von Mises stresses are provided as well. The results indicate that continuous variation of the shear modulus substantially reduces the difference between the in-plane stresses along the interface. Also, the softening coating leads to the minimum value of the stress concentration near the contact... 

In this paper, a simple approach is presented to determine the Muskhelishvili potential function in a generic quasi-static contact problem between two elastically similar half planes. As an example, this approach is applied to the symmetric indentation of a flat surface by a bi-quadratic punch to obtain the interior elastic stress field of the indented lower half plane  

In this paper an analysis is presented to determine the distribution of a residual stress field from a limited incomplete set of measurements obtained from shot-peened round steel bars. Using an Airy stress function as the primary unknown the axisymmetric stress equations are solved directly. In this new method there exists the flexibility to impose physical conditions that govern the behavior of residual stress to achieve a meaningful complete stress field. This new method aims to achieve the best agreement between the model prediction and limited measured stress components in the sense of least squares approximation. The power of this new method is demonstrated by analyzing experimental... 

The overall mechanical properties of composite materials are dependent on the mechanical response of individual constituents and their interactions while they may be relatively easy to determine. This paper represents a simulation process by which the cyclic stresses and fatigue loadings on its constituents could be predicted for an under fatigue loading lamina. Hence, the unidirectional composites fatigue would be studied through its constituents. The proposed model introduces a new coupled stiffness/strength technique by relating lamina stiffness to the stress field in its constituents. Therefore, the stress field and strength considerations in its constituents could be studied when the... 

In this paper a new continuous model for flexural vibration of rotors with an open edge crack has been developed. The cracked rotor is considered in the rotating coordinate system attached to it. Therefore, the rotor bending can be decomposed in two perpendicular directions. Two quasi-linear displacement fields are assumed for these two directions and the strain and stress fields are calculated in each direction. Then the final displacement and stress fields are obtained by composing the displacement and stress fields in the two directions. The governing equation of motion for the rotor has been obtained using the Hamilton principle and solved using a modified Galerkin method. The free... 

The elastic behavior of an edge dislocation located inside the core of a core-shell nanowire which is embedded in an infinite matrix is studied within the surface/interface elasticity theory. The corresponding boundary value problem is solved exactly by using complex potential functions. An important parameter so-called interface characteristic parameter which has the dimension of length and is a combination of the interface moduli enters the formulations. The stress field of the dislocation, image force acting on the dislocation, and the dislocation strain energy is calculated by considering the interface effect. The introduced characteristic parameter allows the examination of the... 

Rock formations are always under in situ stresses due to overburden or tectonic stresses. Drilling a well will lead to stress redistribution around the well. Understanding such a stress redistribution, and adopting a proper failure criterion, play a vital role in predicting any potential wellbore failure. However, most of the published analytical models are based on assumptions that do not satisfy the boundary conditions during production, that is, when the well pressure is less than the pore pressure. This paper is aimed at the modeling of the stress regime around the wellbore through combining the poroelastic model with proper boundary conditions under different flow regimes. As a result,... 

The elastic behaviors of a two-axes dipole of wedge disclinations and an individual wedge disclination located inside the shell of a free standing core-shell nanowire is studied within the surface/interface elasticity theory. The corresponding boundary value problem is solved using complex potential functions, defined through modeling the disclination dipole by two finite walls of infinitesimal edge dislocations. The stress field, disclination strain energies and image forces acting on the disclinations, are calculated and studied in detail. It is shown that the stresses are rather inhomogeneous across the nanowire cross section, change their signs and reach local maxima and minima far from... 

One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis... 

Multilayer laser cladding process for the material properties of low carbon steel 1015 for workpiece and nickel alloy with 1.5 wt.% and 3 wt.% nano CeO2 as the powder particles is modeled. Finite Element Method (FEM) solutions of transient heat transfer and mass transfer equations in laser cladding process are presented. Geometry of the deposited material as well as temperature and thermal stress fields across the process area are calculated  

The problem of edge dislocation inside the wall of a multi-walled nanotube accounting for the surface effects is addressed. Within the framework of surface elasticity the stress field is obtained, using complex potentials. Furthermore, the stress field and image forces acting on the dislocation, with and without an account of the surface stress, are compared together and discussed  

A fully analytical solution of the classic coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads is presented. Axisymmetric thermal and mechanical boundary conditions are considered in general forms of arbitrary heat transfer and traction, respectively, at the inner and outer radii of the disk. To solve the governing system of equations, an analytical procedure based on the Fourier-Bessel transform is employed. Closed form formulations are presented for temperature and displacement fields. The results of the present formulations are in good agreement with the numerical results available in the literature. The radial distribution and time history... 

A variable kinematic 1D finite element (FE) method is presented for 3D thermoelastic analysis of rotating disks with variable thickness. The principle of minimum potential energy is used to derive general governing equations of the disks subjected to body forces, surface forces, concentrated forces, and thermal loads. To solve the equations, the 1D Carrera unified formulation (CUF), which enables to go beyond the kinematic assumptions of classical beam theories, is employed. Based on the 1D CUF, the disk is considered as a beam, which can be discretized into a finite number of 1D elements along its axis. The displacement field over the beam’s cross section is approximated by Lagrange... 

The stress field of a screw dislocation inside an embedded nanowire is considered within the theory of strain-gradient elasticity. It is shown that the stress singularity is removed and all stress components are continuous and smooth across the interface, in contrast with the results obtained within the classical theory of elasticity. The maximum magnitude of dislocation stress depends greatly on the dislocation position, the nanowire size, and the ratios of shear moduli and gradient coefficients of the matrix and nanowire materials. © 2009 Acta Materialia Inc  

The noncoaxiality of the principal stress direction and plastic principal strain increment has been broadly recognized as an influencing parameter for design of soil structures. Here we performed a series of systematic hollow cylinder experiments to study the effects of stress anisotropy on the noncoaxiality of dense Babolsar and Toyoura sands. A total of 25 undrained torsional shear tests were carried out under constant mean confining pressure, and fixed principal stress directions, α. We investigated the stress-strain behavior of dense sands for different α-directions, and cyclic stress ratio, CSR, under monotonic and cyclic loading conditions. The results show that the noncoaxiality value... 

The stress fields of cylindrical and spherical multi-phase inhomogeneity systems with perfect or imperfect interfaces under uniform thermal and far-field mechanical loading conditions are investigated by use of the Boussinesq displacement potentials. The radius of the core inhomogeneity and the thickness of its surrounding coatings are arbitrary. The discontinuities in the tangential and normal components of the displacement at the imperfect interfaces are assumed to be proportional to the associated tractions. In this work, for the problems where the phases of the inhomogeneity system are homogeneous, the exact closed-form thermo-elastic solutions are presented. These solutions along with a... 

A modified analytical model is developed for analysis of 3-D elastic stress fields in short fibre composites subjected to an applied axial load. Two sets of exact displacement solutions for the matrix and fibre are derived based on the theory of elasticity. The superposition of these two solutions are then used to obtain the analytical expressions for the 3-D stress field components over the entire composite system including the fibre end region which is modelled by the use of imaginary fibre technique. The main difference with the previous works here is that the stress field is considered to be dependent on both radial and axial directions. Such an assumption made it possible to calculate... 

The elasticity formulation for equations of motion of micro-rotating disks in the presence of angular acceleration as well as the corresponding boundary conditions are developed based on the non-classical continuum theory of couple stress. The system of the boundary value problem is derived on the basis of the variational method. Analytical elasticity solutions to the system of equations are then provided. Based on the elasticity solution, the mechanical responses, including the displacement and stress fields, for varying-speed micro-rotating disks are studied. In a numerical case study, the effect of the couple stresses on the distribution of stress and displacement components are...