Search for: unloading
Total 32 records
Article 2007 ASME Pressure Vessels and Piping Conference, PVP 2007, San Antonio, TX, 22 July 2007 through 26 July 2007 ; Volume 3 , 2008 , Pages 195-201 ; 0277027X (ISSN); 0791842819 (ISBN); 9780791842812 (ISBN) ; Farrahi, G. H ; Hoseini, S. H ; Sharif University of Technology
Real loading- unloading behavior of an A5083 aluminum alloy was recorded experimentally. This real behavior was incorporated in the variable material properties (VMP) numerical algorithm to predict residual stresses resulted from autofrettage and shrink fit in two kinds of autofrettage compound tubes. Using an analytical method, residual stresses induced by bore material removal via machining were calculated. Using developed VMP code and isotropic hardening rule in both autofrettage compound tubes, residual stresses resulted from shrink fit and autofrettage processes and via post machining, were estimated. Machining process simulation was performed for 10 mm bore material removal. ANSYS...
Article Journal of Pressure Vessel Technology, Transactions of the ASME ; Volume 135, Issue 2 , 2013 ; 00949930 (ISSN) ; Voyiadjis, G ; Hoseini, S. H ; Hosseinian, E ; Sharif University of Technology
Recent research indicates that accurate material behavior modeling plays an important role in the estimation of residual stresses in the bore of autofrettaged tubes. In this paper, the material behavior under plastic deformation is considered to be a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. The yield surface is assumed to depend on the first stress invariant and the Lode angle parameter which is defined as a function of the second and the third invariants of the deviatoric stress tensor. Furthermore for estimating the unloading behavior, the Chaboche's hardening evolution equation is modified. These...
A hybrid computer simulation-genetic algorithm for scheduling optimisation of cargo trains with time and queue limitations, Article International Journal of Industrial and Systems Engineering ; Volume 8, Issue 2 , 2011 , Pages 157-174 ; 17485037 (ISSN) ; Izadbakhsh, H. R ; Mohammadhosseinzad, M ; Raissifard, M. R ; Sharif University of Technology
This paper presents the scheduling optimisation of cargo trains by hybrid computer simulation (CS) and genetic algorithm. Scheduling cargo trains is based on the timetable of passenger trains that have priority in relation to cargo trains. System modelling is accomplished by Visual SLAM by considering time limitations, queue priority and limited station lines. Time limitations define that a cargo train is permitted to travel from station i to j if scheduled passenger trains have completed the travel from station i to j. Queue priority means that passenger trains have priority over cargo trains. In addition, each station has a limited storage track. In addition, all repair, maintenance,...
Transient growth of a micro-void in an infinite medium under thermal load with modified Zerilli–Armstrong model, Article Acta Mechanica ; Volume 227, Issue 4 , 2016 , Pages 943-953 ; 00015970 (ISSN) ; Eskandari, A. H ; Zakerzadeh, M. R ; Sharif University of Technology
In this paper, the transient growth of a spherical micro-void under remote thermal load in an infinite medium is investigated. After developing the governing equations in the problem domain, the coupled nonlinear set of equations is solved through a numerical scheme. It is shown that a small cavity can grow rapidly as the temperature increases in a remote distance and may damage the material containing preexisting micro-voids. Conducting a transient thermal analysis simultaneously with a structural one reveals that the material may experience a peak in the radial stress distribution, which is five times larger compared to the steady-state one, and shows the importance of employing a...
Bauschinger effect investigation of an aluminum alloy, and its application in autofrettaged and compound tubes, Article 2007 ASME Pressure Vessels and Piping Conference, PVP 2007, San Antonio, TX, 22 July 2007 through 26 July 2007 ; Volume 6 , 2008 , Pages 629-637 ; 0277027X (ISSN); 0791842843 (ISBN); 9780791842843 (ISBN) ; Farrahi, G. H ; Hoseini, S. H ; Sharif University of Technology
For characterizing Bauschinger effect factor (BEF) and Bauschinger modulus reduction of an A5083 aluminum alloy experimentally, several uniaxial tension- compression tests carried out in different pre-strain levels using INSTRON testing machine. BEF was investigated using both Welter and Milligan's definitions for various offset values. It was observed that Milligan's definition predicts BEF less than Welter's definition for all offset values. In addition, real loading-unloading behavior of such alloy was recorded to predict residual stresses resulting from autofrettage and shrink fit processes. Variable material properties (VMP) method, which is capable of incorporating real unloading...
Article International Journal of Pressure Vessels and Piping ; Volume 98 , 2012 , Pages 57-64 ; 03080161 (ISSN) ; Voyiadjis, G. Z ; Hoseini, S. H ; Hosseinian, E ; Sharif University of Technology
In this paper the effect of the re-autofrettage process on the residual stress distribution at the wall of a thick-walled tube is considered. For accurate material behavior modeling, it is assumed that the yield surface is a function of all the stress invariants. Also for estimating the behavior of the material under loading-unloading process, a modified Chaboche's hardening model is applied. For evaluation of this unloading behavior model a series of loading-unloading tests are conducted on specimens that are made of the high strength steel, DIN1.6959. In addition the finite element simulations are implemented to simulate the re-autofrettage process and to estimate the residual stresses....
Article International Journal of Pressure Vessels and Piping ; Volume 87, Issue 7 , July , 2010 , Pages 396-401 ; 03080161 (ISSN) ; Farrahi, G. H ; Haghpanah Jahromi, B ; Hosseinian, E ; Sharif University of Technology
In this study, residual stress distributions in autofrettaged homogenous spherical pressure vessels subjected to different autofrettage pressures are evaluated. Results are obtained by developing an extension of variable material properties (VMP) method. The modification makes VMP method applicable for analyses of spherical vessels based on actual material behavior both in loading and unloading and considering variable Bauschinger effect. The residual stresses determined by employing finite element method are compared with VMP results and it is demonstrated that the using of simplified material models can cause significant error in estimation of hoop residual stress, especially near the...
Experimental measurement and analytical determination of shot peening residual stresses considering friction and real unloading behavior, Article Materials Science and Engineering A ; Volume 657 , 2016 , Pages 309-321 ; 09215093 (ISSN) ; Farrahi, G. H ; Mahmoudi, A. H ; Ghasemi, A ; Sharif University of Technology
Elsevier Ltd 2016
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)  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...
Article International Journal of Solids and Structures ; Volume 46, Issue 9 , 2009 , Pages 1925-1936 ; 00207683 (ISSN) ; Abdolhosseini Qomi, M. J ; Kazemi, M. T ; Khoei, A. R ; Sharif University of Technology
The Cauchy-Born hypothesis (CB) provides a hierarchical approach in the molecular theory of crystal elasticity to relate the continuum and atomic deformations. This kinematic theory has been extensively used as the constitutive law of continuum regions in multi-scale models. In these models, the fine scale is proposed to describe the real behavior of crystalline structure wherever the continuum description fails. The main objective of this article is to investigate the stability and size-dependency of CB hypothesis in three-dimensional applications by direct comparison of information between atomistic and continuous description of a medium. The Sutton-Chen many-body potential is used for the...
On the modeling of human intervertebral disc annulus fibrosus: Elastic, permanent deformation and failure responses, Article Journal of Biomechanics ; Volume 102 , 2020 ; Shirazi Adl, A ; Baghani, M ; Eskandari, A. H ; Sharif University of Technology
Elsevier Ltd 2020
As a primary load-resisting component, annulus fibrosus (AF) maintains structural integrity of the entire intervertebral disc. Experiments have demonstrated that permanent deformation and damage take place in the tissue under mechanical loads. Development of an accurate model to capture the complex behaviour of AF tissue is hence crucial in disc model studies. We, therefore, aimed to develop a non-homogenous model to capture elastic, inelastic and failure responses of the AF tissue and the entire disc model under axial load. Our model estimations satisfactorily agreed with results of existing uniaxial (along fiber, circumferential and axial directions) and biaxial tissue-level tests. The...
An analytical framework for the solution of autofrettaged tubes under constant axial strain condition, Article ASME 2008 Pressure Vessels and Piping Conference, PVP2008, Chicago, IL, 27 July 2008 through 31 July 2008 ; Volume 5 , July , 2008 , Pages 71-80 ; 0277027X (ISSN); 9780791848289 (ISBN) ; Farrahi, G. H ; Movahhedy, M. R ; Pressure Vessels and Piping ; Sharif University of Technology
Autofrettage is a technique for introducing beneficial residual stresses into cylinders. Both analytical and numerical methods are used for analysis of the autofrettage process. Analytical methods have been presented only for special cases of autofrettage. In this work, an analytical framework for the solution of autofrettaged tubes with constant axial strain conditions is developed. Material behavior is assumed to be incompressible and two different quadratic polynomials are used for strain hardening in loading and unloading. Clearly, elastic-perfectly plastic and linear hardening materials are special cases of this general model. This material model is convenient for description of the...
An enhanced continuum modeling of the ideal strength and the angle of twist in tensile behavior of single-walled carbon nanotubes, Article Journal of Applied Physics ; Volume 114, Issue 5 , 2013 ; 00218979 (ISSN) ; Shodja, H. M ; Sharif University of Technology
By utilizing the fourth-, sixth-, eighth-, and tenth-order elastic moduli tensors of graphene a highly nonlinear constitutive model for it is proposed. Subsequently, an accurate analytical formulation, describing the entire tensile behavior of single-walled carbon nanotubes (SWCNTs) from their initial unloaded states through their ideal strengths, is made possible. The angle of twist which is a critical parameter that varies with the tensile loading is also calculated within the current framework. The estimated value of the theoretical strength of SWCNTs with different chiralities and radii as well as that of graphene ranges from 0.39 to 0.44 TPa. Some peculiarities associated with chirality...
Swelling and mechanical behavior of nanoclay reinforced hydrogel: single network vs. full interpenetrating polymer network, Article Polymer Bulletin ; Volume 72, Issue 7 , March , 2015 , Pages 1663-1681 ; 01700839 (ISSN) ; Bagheri, R ; Kabiri, K ; Sharif University of Technology
Springer Verlag 2015
Despite the various uses of hydrogels, one of their weaknesses is the poor gel strength. To overcome this restriction, the current study has focused on simultaneously employing an interpenetrating polymer network (IPN) structure and nanocomposite hydrogels. Through this approach, the influence of nanofiller in the single network and IPN hydrogel properties was also studied in detail. For this purpose, a novel full interpenetrating polymer network (IPN) hydrogel nanocomposite based on 2-acrylamido-2-methylpropane sulfonic acid (AMPS)/acrylic acid (AA)–sodium acrylate (AANa) was synthesized in two steps through a facile solution polymerization with incorporation of modified bentonite (MBE) as...
Improvement in mechanical performance of anionic hydrogels using full-interpenetrating polymer network reinforced with graphene oxide nanosheets, Article Advances in Polymer Technology ; Volume 35, Issue 4 , 2016 , Pages 386-395 ; 07306679 (ISSN) ; Bagheri, R ; Kabiri, K ; Ossipov, D. A ; Jokar, E ; Asadian, E ; Sharif University of Technology
John Wiley and Sons Inc
Weak mechanical possession is one of the limiting factors in application of hydrogels. To modify this inherent disadvantage, different approaches have been studied including synthesizing interpenetrating polymer network (IPN) and nanocomposite hydrogels. So, this study has focused on preparation of a novel full-IPN structure based on anionic monomers of 2-acrylamido-2-methylpropane sulfonic acid/acrylic acid–sodium acrylate via facile solution polymerization technique in an aqueous media with incorporation of graphene oxide (GO) nanosheets. Mechanical performance of materials in the “as-prepared condition” and “swollen state” was characterized via tensile, compression, and rheology tests,...
Article Journal of Materials in Civil Engineering ; Volume 29, Issue 5 , 2017 ; 08991561 (ISSN) ; Karimi, M. M ; Tabatabaee, N ; Sharif University of Technology
American Society of Civil Engineers (ASCE) 2017
The present experimental study investigated the behavior of hot-mix asphalt (HMA) under repetitive creep and recovery loading. Cylindrical samples of HMA were subjected to trapezoidal and haversine loading followed by unloading. Different amounts of unloading (stress reduction) and relaxation periods (rest periods in complete unloading) were tested. The measured vertical deformation was decomposed into viscoelastic and viscoplastic components. It was observed for cyclic loading that an increase in unloading and/or relaxation period increased the recovery of viscoelastic strain, which in turn increased the accumulated viscoplastic strain in subsequent loading cycles. It appears that...
Article 5th RSI International Conference on Robotics and Mechatronics, IcRoM 2017, 25 October 2017 through 27 October 2017 ; 2018 , Pages 69-75 ; 9781538657034 (ISBN) ; Behzadipour, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2018
Gait training is a critical rehabilitation procedure for patients suffering from walking problems. It, however, puts the therapist in high orthopedic risk since he should prevent the patient from possible falling. Body weight support system is a new technology helping such patients and the involved therapist by unloading a percent of the patient's weight. A new over-ground body weight support is introduced in this article. The system is composed of two main modules namely unloading and traction. The unloading module is capable of suspending an individual's weight up to 1000N dynamically. The whole system is attached to an overhead rail, moving over the head of the patient by the traction...
Micro-structural aspects of fatigue crack propagation in atomistic-scale via the molecular dynamics analysis, Article Engineering Fracture Mechanics ; Volume 226 , 2020 ; Khoei, A. R ; Sharif University of Technology
Elsevier Ltd 2020
In this paper, the fatigue crack propagation is modeled using the Molecular Dynamics (MD) analysis based on the Embedded Atom Method (EAM). The crack growth simulation is performed for the single-crystal and poly-crystalline specimens subjected to cyclic loading/unloading conditions, and the crack growth rate is investigated at the atomistic level. The MD simulations are carried out under different model parameters, including the load pattern, maximum applied strain, temperature, loading frequency, and percentage of defects by employing more than 4000 molecular dynamics analyses to study the sensitivity of crack propagation process to the simulation parameters. The threshold values of...
Article Nondestructive Characterization and Monitoring of Advanced Materials, Aerospace, Civil Infrastructure, and Transportation XV 2021, 22 March 2021 through 26 March 2021 ; Volume 11592 , 2021 ; 0277786X (ISSN); 9781510640139 (ISBN) ; Khaloo, A ; Sharif University of Technology
Surface crack patterns can easily show the behavior of concrete elements and structures. However, visual damage inspection performed by experts is a subjective approach and is prone to inaccuracies. The quantification makes this process objective and more reliable. In that regards, the maximum crack width is used as a practical measurement. It has been shown that the crack width is not a good indicator of damage due to its inherent uncertainties; In fact, it might bounce back after unloading. As such, a dimensionless parameter so-called Fractal Dimension has been introduced as a robust index that can quantify the complexity of crack distribution efficiently. The present study aims to...
An analytical framework for the solution of autofrettaged tubes under constant axial strain condition, Article Journal of Pressure Vessel Technology, Transactions of the ASME ; Volume 131, Issue 6 , 2009 ; 00949930 (ISSN) ; Farrahi, G. H ; Movahhedy, M. R ; Sharif University of Technology
Autofrettage is a technique for introducing beneficial residual stresses into cylinders. Both analytical and numerical methods are used for the analysis of the autofrettage process. Analytical methods have been presented only for special cases of autofrettage. In this work, an analytical framework for the solution of autofrettaged tubes with constant axial strain conditions is developed. Material behavior is assumed to be incompressible, and two different quadratic polynomials are used for strain hardening in loading and unloading. Clearly, elastic perfectly plastic and linear hardening materials are the special cases of this general model. This quadratic material model is convenient for the...
Article Journal of Mechanics in Medicine and Biology ; Volume 12, Issue 1 , 2012 ; 02195194 (ISSN) ; Farahmand, F ; Shirazi Adl, A ; Arjmand, N ; Malekipour, F ; Parnianpour, M ; Sharif University of Technology
In spite of earlier experimental and modeling studies, the relative role of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study employs simple analytical and finite element (FE) models of the spine and its surrounding structures to investigate the contribution of IAP to spinal loading and stability. The analytical model includes the abdominal cavity surrounded by muscles, lumbar spine, rib cage and pelvic ring. The intra-abdominal cavity and its surrounding muscles are represented by a thin deformable cylindrical membrane. Muscle activation levels are simulated by changing the Young's modulus of the membrane in the direction of muscle fibers, yielding...