Showing 13 results for Stress
S. M. Haeri, N. Sadati and R. Mahin-Rousta,
Volume 20, Issue 2 (4-2001)
Abstract
In this research, behaviour of clayey soils under triaxial loading is studied using Neural Network. The models have been prepared to predict the stress-strain behaviour of remolded clays under undrained condition. The advantage of the model developed is that simple parameters such as physical characteristics of soils like water content, fine content, Atterberg limits and so on, are used to model the stress-strain behaviour of clays under triaxial loading, without performing exact and time-consuming tests on samples.
Results from the network show that neural network is a good tool for prediction of stress-strain behaviour of clayey soils using simple physical characteristics of such soils
M.r. Bannazadeh, A. A. Bidokhti, M. Kherandish and H. F. Hosseini,
Volume 21, Issue 1 (7-2002)
Abstract
Observations of the Caspian Sea during August-September 1995 are used to develop a three-dimensional numerical model to be used in calculating temperature and current. The model has variable grid resolution and horizontal smoothing that filters out small scale vertical motion. Data from the meteorological buoy network on the Caspian Sea are combined with routine observations at first-order synoptic station around the lake to obtain hourly values of wind stress and pressure fields. The hydrodynamic model of the Caspian Sea has 6 vertical levels and a uniform horizontal grid size of 50 km. The model is driven with surface fluxes of heat and momentum derived from observed meteorological data. The model was able to reproduce all the basic features of the thermal structure in the Caspian Sea and larger-scale circulation patterns tended to be anticyclone, with anticyclone circulation within each sub-basin. The results matched observation data.
Keywords: Circulation, Temperature, Numerical model, Vorticity, wind stress
H. Moslemi Naeini, M. Maerefat and M. Soltanpour,
Volume 22, Issue 1 (7-2003)
Abstract
In hot forming process, the workpiece undergoes plastic deformation at high temperature and the microstructure of the workpiece changes according to the plastic deformation. These changes affect the mechanical properties of workpiece. In order to optimize this process, both the plastic deformation of workpiece and its microstructural changes should be taken into consideration. Since material behaviors at elevated temperatures are usually rate-sensitive, the analysis of the hot forming processes requires a thermo-viscoplastic model. In this paper, by coupling the flow stress prediction model developed with finite element analysis of thermo-viscoplastic of the hot upsetting process, temperature, strain rate, flow stress distributions and geometry of the workpiece at each time step can be calculated. At each time step, the strain rate and temperature at each element are obtained. From these values and the history of deformation, the changes in microstructure and flow stress can be determined.
Keywords: Hot forming, Process, Finite element analysis, Flow stress, Microstructure, Hot upsetting process
Hassan Haddadpour,
Volume 25, Issue 1 (7-2006)
Abstract
A method is presented for the stress analysis of flight vehicles under different flight conditions including gust and control surface deflection (or maneuver) using the governing equations of rigid-body motions and elastic deformations. The Lagrangian approach is used to derive the governing equations of motions. For this purpose, the basic equations of motions are derived in terms of potential energy, kinetic energy and generalized forces, which are, in turn, computed in terms of rigid-body motion variables, elastic mode shapes and distribution for aerodynamic forces. By replacing them into the relations obtained, the governing equations for aeroelastic behavior of the vehicle are derived. The system of aeroelastic equations of
motions is solved in time domain using numerical methods. The stress distribution is determined using the relation between modal variables and strain at each point. Finally, the prepared code is verified through comparison of the results obtained from the proposed method for the stability of a rocket and the same results reported by other studies. Also additional information such as maximum stress in the body is presented for various flight conditions.
H. R. Sheibani and H. Bayyat,
Volume 26, Issue 1 (7-2007)
Abstract
A physical model of gabion overflow dams was studied to determine the velocity profile and Reynolds shear stress. Physical tests were done under two different conditions of dam crest, overflow dams with impermeable and with permeable crests. Instantaneous velocity components over dam crest were measured by an ADV (Acoustic Doppler Velocimeter) instrument. This instrument is capable of measuring instantaneous velocity components with frequencies up to 25 Hz. Average velocity components and bed shear stress were extracted from ADV measurements. The results of this research show the effect of crest permeability on velocity and Reynolds shear stress. The magnitude of Reynolds shear stresses, horizontal velocity components, and absolute value of vertical velocity components under the permeable scenario are bigger than those of the impermeable scenario. Velocity distribution over the dam crest is different from the universal logarithmic profile.
A. Ghorbanpour, S. Golabi, and M. Sotoudeh,
Volume 26, Issue 2 (1-2008)
Abstract
M. Dehestani, Ali R. Khaloo, and P. Rahmatabadi,
Volume 26, Issue 2 (1-2008)
Abstract
M. Salimi, M. Jamshidian, A. Beheshti, and A. Sadeghi Dolatabadi,
Volume 26, Issue 2 (1-2008)
Abstract
The mechanical behavior of cold rolled sheets is significantly related to residual stresses that arise from bending and unbending processes. Measurement of residual stresses is mostly limited to surface measurement techniques. Experimental determination of stress variation through thickness is difficult and time-consuming. This paper presents a closed form solution for residual stresses, in which the bending-unbending process is modeled as an elastic-plastic plane strain problem. An anisotropic material is assumed. To validate the analytical solution, finite element simulation is also demonstrated. This study is applicable to analysis of coiling-uncoiling, leveling and straightening processes.
T. Shahrabi Farahani, V. Baigi and S. A. Lajevardi,
Volume 27, Issue 1 (7-2008)
Abstract
Prediction of SCC risk of austenitic stainless steels in aqueous chloride solution and estimation of the time to failure as a result of SCC form important and complicated topics for study. Despite the many studies reported in the literature, a formulation or a reliable method for the prediction of time to failure as a result of SCC is yet to be developed. This paper is an
effort to investigate the capability of artificial neural network in estimatiing the time to failure for SCC of 304 stainless steel in aqueous chloride solution and to provide a sensitivity analysis thereof. The input parameters considered are temperature, chloride ion concentration, and applied stress. The time to failure is defined as the output parameter and the key criterion to evaluate the effective parameters. The statistical performance of the neural network is expressed as the average of three learning and testing results. The SCC database is divided into two sections designated as the learning set and the testing set. The output results show that artificial neural network can predict the time to failure for about 74% of the variance of SCC experimental data. Furthermore, the sensitivity analysis also exhibits the effects of input parameters on SCC of 304 stainless steel in aqueous chloride solutions.
S.a. Tabatabaei,
Volume 27, Issue 1 (7-2008)
Abstract
A review of pavement thickness designs shows that two kinds of failure criteria are used in most cases. They are: 1) The tension strain under the asphalt layer that causes cracking and 2) the vertical compression strain on the sub-grade that causes deflection. In this study, various factors affecting thickness design are first defined and more than 216 pavement conditions are introduced. Structures are analyzed using the Flex pass program and their strains and stresses are investigated severally by choosing the failure criteria one at a time.
Mr S. A. Razavi, Mr S. F. Ashrafizadeh,
Volume 36, Issue 2 (9-2017)
Abstract
Age hardening processes cause a wide range of changes in 17-4 PH stainless steel properties. Aging at 480ºC for 1 hour (A480-1) and aging at 620ºC for 4 hours (A620-4) are two most applicable heat treatment processes for this alloy. Not only the studies on fatigue behavior of this alloy in these two heat treatment conditions are few, but also the methods of fatigue test were mostly axial. In this study, after microstructure studies, hardness and tension tests, fatigue behavior at A480-1 and A620-4 conditions were evaluated by using a rotational bending fatigue test machine. Tension results showed that yield strength and ultimate tensile strength of A480-1 specimens were 40 percent more than A620-4 specimens. However, elongation of A620-4 specimens was 30 percent more than A480-1 specimens. Fatigue results revealed the endurance limit of aged specimens is 50 MPa more than overaged specimens. Overall results showed that A480-1 condition specimens are more resistant to fatigue than A620-4 condition specimens.
A. Borouni, A. Kermanpur,
Volume 39, Issue 3 (12-2020)
Abstract
In this study, the effect of Ta/W ratio on the microstructure and stress rupture properties of Ni-based single crystal (SX) superalloy PWA1483 was investigated. For this purpose, single crystal (SX) superalloys with different Ta/W ratios (0.75, 1.0, 1.32 and 1.5 in wt.%) were fabricated. The alloys were directionally solidified by Bridgman method under the same solidification condition at withdrawal velocity of 3 mm/min and thermal gradient of about 7 K/mm followed by standard age hardening heat treatment. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM). The stress rupture properties were investigated at 982 °C and 248 MPa. The results showed that increasing the Ta/W ratio decreases the size and volume fraction of micro-pores together with the size of γ' precipitates. Hence, the stress rupture life increased. The superalloy with Ta/W ratio of 1.5 showed the minimum size of micro-porosity (18.2 μm) and the maximum stress rupture life (~34 h). The superalloy with Ta/W ratio of 1 showed the most uniform microstructure and creep behavior. It seems that the presence of topologically closed packed (TCP) η-phases is the main reason for stress rupture life decrease in SX superalloy as micro-pores initiated from TCP phases or the TCP/matrix interfaces.
S. Arjmand, G. H. Akbari, G. R. Khayati,
Volume 39, Issue 4 (2-2021)
Abstract
The purpose of the present work is to investigate the influence of the number of weld-passes on microstructure, hardness and residual stresses of composite coatings composed of Ti-Al-Si intermetallic compounds. In this regard, surface coating of pure Ti was carried out using one and two passes of tungsten inert gas (TIG) welding with an Al filler alloy (grade 4043). Phase and structural evaluations of the coatings were investigated by X-ray diffraction, optical and scanning electron microscopies. microhardness and residual stress values of the coatings were measured using ASTM E384-HV device and the Sin2ψ method, respectively. The results showed that as the number of welding passes increased or the dilution ratio decreased, the volume fraction of Ti5Si3-Al3Ti intermetallic phases within the fusion zone increased and the volume fraction of martensite phase in the heat affected zone decreased. As a result, the average hardness value of the coating increased to be about 130 % compared to that of the pure Ti substrate. The tensile residual stresses at the center line of fusion zone were 165 ± 30 and 210 ± 35 MPa for the coatings prepared in one and two welding passes, respectively.
