Sharif Digital Repository

The size of the rock specimen affects the stress concentrates in the vicinity of the top/bottom of the rock specimen during the evaluation of the geomechanical parameters in the laboratory, which causes unreliable results. However, the appropriate size for geomechanical evaluation is not well understood yet because of limitations in the sampling and analysis. In this study, a series of numerical simulations using a finite element package was conducted to investigate the effect of sample aspect ratio, fluid saturation, and porosity, on the mechanical behavior of the rock under elastic and poroelastic conditions. In addition, two concepts, stress/strain homogeneity index (SHI) and... 

Single lap-shear (SLS) specimens of 63Sn37Pb solder joints were prepared with three different adherend thicknesses at three varying joint lengths. The fracture force was measured at a shear strain rate of 0.01 s-1 for different geometries. The elastic-plastic fracture mechanics (EPFM) theory was used to find the energy dissipated in each case using a finite element model (FEM), and the fracture energy was obtained by cohesive zone modeling (CZM). Both 2-D and 3-D models were used to explain the variations in fracture energy by the level of constraint on the joint. Also, the plastic zone area and stress distribution along the solder layer were calculated at the moment of fracture. A phase... 

This work aims to calculate interlaminar stress distribution through the thickness of multilayered composite shell structures by employing a novel nonlinear layer-wise shell finite element formulation. Adapting the Mindlin– Reissner theory in each layer, the shear-deformable layer-wise shell element presents the interlaminar shear stress distributions by increasing the number of layers. The interlaminar normal stress distribution is then determined using the finite difference solution of the general form of equilibrium equation in the non-orthogonal curvilinear grid along the Gaussian points. Two boundary conditions at the bottom and the top surfaces are satisfied by adopting the linear... 

Cell survival during the early stages of transplantation and before new blood vessels formation is a major challenge in translational applications of 3D bioprinted tissues. Supplementing oxygen (O2) to transplanted cells via an O2 generating source such as calcium peroxide (CPO) is an attractive approach to ensure cell viability. Calcium peroxide also produces calcium hydroxide that reduces the viscosity of bioinks, which is a limiting factor for bioprinting. Therefore, adapting this solution into 3D bioprinting is of significant importance. In this study, a gelatin methacryloyl (GelMA) bioink that is optimized in terms of pH and viscosity is developed. The improved rheological properties... 

Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at... 

Residual stresses are inherent in parts manufactured using the wire + arc additive manufacturing (WAAM) technique, resulting in unpredictable mechanical response and structural integrity (Colegrove et al.: J Mater Process Technol 213:1782-1791, 2013). An effective post-processing technique, which enhances the mechanical properties of WAAM parts, is rolling. This study investigates the vertical and pinch rolling effects on residual stress distribution in WAAM components. Initially, a WAAM model was created using a thermo-mechanical finite element modelling approach and validated against the experimental results. Subsequent to the validation of the model, the effect of the main parameters... 

The local electric field distorsion induced by a dielectric particle leads to particle–particle interactions and assembly which is very interesting for their useful applications on microfluidic devices. Particles behavior becomes more complicated if several particles interact at the same time. This paper presents a comprehensive numerical analysis of the assembly and particle–particle interactions for two similar and dissimilar dielectric particles immersed in a dielectric fluid using the immersed interface method based on two-dimensional direct-current dielectrophoresis. The immersed interface method is a finite-difference (or finite element) based numerical method which its key advantage... 

In a shell and tube heat exchanger, the failure of tube-to-tubesheet welds results in high-pressure water jet which erodes the refractory in front of the tubesheet. Finite element method was employed to simulate the welding process and post weld heat treatment (PWHT) to find the factors affecting the failure in tube-to-tubesheet weldments. Residual stresses in two different geometries of tube-to-tubesheet weldment were calculated through uncoupled thermal-structural analysis. The results showed that the values of residual stresses are higher in heat exchanger of site 1 than site 2 due to more weld passes and geometry of connection. Also, the maximum stress in site 1 occurs at the shellside... 

In a shell and tube heat exchanger, the failure of tube-to-tubesheet welds results in high-pressure water jet which erodes the refractory in front of the tubesheet. Finite element method was employed to simulate the welding process and post weld heat treatment (PWHT) to find the factors affecting the failure in tube-to-tubesheet weldments. Residual stresses in two different geometries of tube-to-tubesheet weldment were calculated through uncoupled thermal-structural analysis. The results showed that the values of residual stresses are higher in heat exchanger of site 1 than site 2 due to more weld passes and geometry of connection. Also, the maximum stress in site 1 occurs at the shellside... 

In this study, based on multipole expansion method an analytical treatment is presented for the anti-plane scattering of SH-waves by an arbitrarily oriented elliptic cavity/crack which is embedded near the interface between exponentially graded and homogeneous half-spaces. The cavity is embedded within the inhomogeneous half-space. The boundary value problem of interest is solved by constructing an appropriate set of multipole functions which satisfy (i) the governing equation in each half-space, (ii) the continuity conditions across the interface between the two half-spaces, and (iii) the far-field radiation and regularity conditions. The analytical expressions for the scattered... 

In this study, an analytical solution is presented for elastic-plastic pure bending of a linear kinematic hardening curved beam with rectangular cross section both in monotonic loading and unloading. Compared to exact plane plasticity solution (already reported in the literature in loading) which needs solution of a system of equations, the proposed method is based on the hyperbolic strain distribution on the cross section which yields a simple approximate solution. To this end, we employ Winkler's theory, and assume plane cross sections remain plane after loading proved by the exact elasticity and plasticity solutions for pure bending of curved beams with rectangular cross section. At the... 

Influence of gas tungsten arc welding on the thermal responses, residual stress distribution and final mechanical properties of the naturally age-hardened (T4) and artificially age-hardened (T6) AA2024 plates was studied. The results showed that age hardening and over-aging occurred in various sections of the heat-affected zone (HAZ) of T4 sample, depending on their locations, while in the HAZ of T6 sample, over-aging is the governing phenomenon. Also, subsequent natural aging occurred in HAZ, weld metal (WM) and partially melted material (PMM) of both weldments. This recent phenomenon is more obvious in the T4 sample in comparison with the T6 one. In both microstructures, weld metal is the... 

The scattering of in-plane P- and SV-waves by a multi-coated circular nanofiber with deformable interfaces is of interest. To this end, in the present work, after introducing two kinds of interface momenta defined as the derivative of the interface excess kinetic energy with respect to the average and relative velocities at the interface, we extend the elastostatic theory of Gurtin et al. (1998) on deformable interfaces to the elastodynamic theory and derive the interface equations of motion using Hamilton principle. The effects of the generalized interface properties including the interface inertial parameters and interface stiffness towards stretch and slip on the dynamic stress... 

Shot peening is the most common surface treatment employed to enhance the fatigue performance of structural metallic materials and often carried out after other surface treatments. This paper mainly focuses on the effects of initial conditions of surface such as initial stress filed and hardness profile on shot peening residual stress field. The residual stress distribution induced by shot peening is obtained using Hertzian contact theory and elastic–plastic evaluation after yielding occurred during impingement and rebound of shots. Elastic plastic calculations are performed using different hardening models considering Bauschinger effect. The present model is able to predict redistribution... 

Three-dimensional thermo-mechanical stress analysis of composite joints with bi-adhesive bonding is presented using the full layerwise theory. Based on three-dimensional elasticity theory, sets of fully coupled governing differential equations are derived using the principle of minimum total potential energy and are simultaneously solved using the state space approach. Results show that bi-adhesive bonding substantially relieves the edge effects. Moreover, series of parametric studies reveal the nonlinear effects of bonding length ratio and the relative stiffness and coefficient of thermal expansion of the mid- and side-adhesives. It is also concluded that the optimum design of a bi-adhesive... 

A finite element analysis of a double layered shell with a circular hole is carried out with the computer aided engineering software Abaqus (Dassault Systèmes, FR). The model proposed has been used to perform a stress analysis on three pipes with different sized hole. Moreover, thermal expansion has been implemented in the testing. For the purpose of the research, the elastic properties of the materials have been considered and the results compared with the ones previously published in literature. The outcome of the investigation will benefit towards the design of optimal and sustainable pipes with circular cut outs  

This paper presents an analytical model to predict the residual stress distribution induced by Shot peening. The analytical approach is based on the work of Shen and Atluri (2006) [18] with some modifications. The modifications are related to the elasto-plastic unloading of shot impingements, friction coefficient effect and the fraction of kinetic energy transmitted to the treated material. In order to predict more realistic residual stresses, the elasto-plastic unloading phase of shot impacts is modeled using two nonlinear kinematic hardening models considering the Bauschinger effect. Moreover, the effect of the Coulomb friction between target surface and shots is evaluated. For this... 

This paper deals with analytical thermomechanical stress analysis of adhesively bonded composite joints in presence of a structural imperfection in the form of an interfacial void within the adhesive layer based on the full layerwise theory (FLWT). The joints are subjected to mechanical tension, uniform temperature change, or steady-state heat conduction. The proposed adhesive joint is divided into three distinct regions along its length and a large number of mathematical plies through its thickness. Three sets of fully coupled governing equilibrium equations are derived employing the principle of minimum total potential energy. The three-dimensional nonlinear interlaminar stress... 

The inadequacy of traditional theory of elasticity in describing such a phenomenon as dispersion associated to a propagating wave with wavelength comparable to the intrinsic length of the medium of interest is well-known. Moreover, under certain circumstances it is incapable of capturing all the propagating waves. A remedy to such dilemmas is the employment of the more accurate higher order continuum theories which give rise to the appearance of at least one new characteristic length in the formulation. The experimental evidences as well as lattice dynamic analysis suggest that, although higher order continuum theories result in some improvements, but cannot fully overcome the... 

In this paper, decomposition of the total strain into elastic and plastic parts is investigated for extension of elastic-type constitutive models to finite deformation elastoplasticity. In order to model the elastic behavior, a Hookean-type constitutive equation based on the logarithmic strain is considered. Based on this constitutive equation and assuming the deformation theory of Hencky as well as the yield criteria of von Mises, the elastic-plastic behavior of materials at finite deformation is modeled in the case of the proportional loading. Moreover, this elastoplastic model is applied in order to determine the stress distribution in thick-walled cylindrical pressure vessels at finite...