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Abstract Creep is a time-dependent deformation of soil under constant effective stresses. For investigation on the creep of rock fill materials, 3 samples from 3 dams of Iran that are already under construction were selected. Normal effective stresses were applied on the specimens with a large-scale odometer apparatus that is specially designed for the research. Comparison of creep rate, amount of particle breakage and results of Los Angeles test shows a relationship between these three parameters. Consequently Los Angeles test that is a simple and accessible test, can give a prediction and estimation of behavior and properties of rock fill materials. Based on the test results, an approximate relationship could be found between creep, particle breakage and Los Angeles test results.

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Abstract Gotvand rock fill dam is being constrcted on Karun river located in Khoozestan province south of Iran. The dam is foung on Aghagari formation which is consisted of mudstone and sandstone layers. These layers are intermittent of weak to medium strength with uniaxial compressive strength 15 and 25 MPa respectibely. Some regional factors as continuous unloading caused by river flood washed off and horizontal tectonic loading have created a local anticline in the foundation of dam. According to previous analyses, results have shown that this folding will continue over the time. In this research effect of the dam weight on time d- dependant deformation of the dam foundation has been studied. Ration of horizontal to vertical stresses (K) was estimated to be 0.4 to 0.7 by in-situ tests, so dam site numerical models were executed (numerical analysis wity the FLAC3D code) with K equal to 0.4,0.55 and 0.7. First, the models were executed statically. Maximun settlement of foundation due to the dam weight was estimated a bout 37cm. Ihen for time dependent analysis, the behavior of rocks is assumed to obeay Maxwell creep viscousplastic rheological model and the models were executed for 100 years equal to the dam life time. The results of numerical analysis show that upward deformations of the foundation with K=0.55 and 0.7 is continuously, even in the central region of dam where the dam weight is maximum. But in the model with K=0.4, in the first 60 years after the construction, creep deformation are downward and after this time, directions of deformation were changed to upward.

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Abstract Prestressing techniques are generally used for the construction of large containment shells to overcome tension and to ensure tightness. Thus, the evaluation of the prestressing force variations considering the geometry and mechanical characteristics of tendons becomes an important matter. This paper considers the effects of time dependent deformations of materials on the circumferential prestress force in prestressed concrete cylindrical containments. Numerical studies are performed using creep and relaxation models presented in different codes of practice after checking the numerical model by experimental data reported elsewhere about a prestressed concrete beam. The effects of vertical prestressing and wall thickness are also studied. Obtained results show an amount of 15% to 22% of prestress loss in tendons, specially in those located around wall’s mid-height , on which relaxation of steel has a dominant effect. Furthermore, the minor effect of vertical prestresssing might be mentioned. Besides, the creep model of Iranian concrete code is studied and some suggestions are made for the modification of the coefficient used for the prestress losses due to relaxation effects.

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The aim of this study was production of fish protein isolate (FPI) and surimi from a low cost and underutilized fish species, carpio (Cyprinus carpio), and investigation of their gel textural properties. FPI was prepared by pH shifting at acidic (2.5 and 3.5) and basic (11 and 12) pHs. Surimi was prepared by 3 times water washing and at the third stage 0.2% NaCl was added to remove the water more efficiently. The results showed that production yield of FPI was significantly (P< 0.05) higher than surimi due to removal of soluble proteins during surimi production. Among the FPI, the FPI produced at acidic condition had higher production efficiency than the others. Protein recovery content of FPI was higher than surimi. FPI prepared at pH 11 showed harder textures compared with the others. Production of hard texture and easy preparation process of FPI compared with surimi were other findings of this study.    

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To prevent unpleasant incidents, preservation high-speed railway vehicle stability has vital importance. For this purpose, the Railway vehicle dynamic is modeled using a 38-DOF includes the longitudinal, lateral and vertical displacements, roll, pitch and yaw angles. A heuristic nonlinear creep model and the elastic rail are used for simulation of the wheel and rail contact. To solve coupled and nonlinear differential equations, Matlab software and Runge Kutta methods are used. In order to study stability, bifurcation analyses are performed. In bifurcation analysis, speed is considered as the bifurcation parameter. These analyses are carried out for different wheel conicity and radius of the curved track. It is revealed that critical hunting speed decreases by increasing the wheel conicity or decreasing the radius of the curved track. Keywords: railway vehicle dynamics, nonlinear creep model, critical hunting speed, numerical simulation, bifurcation analysis Keywords: railway vehicle dynamics, nonlinear creep model, critical hunting speed, numerical simulation, bifurcation analysis

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In the present work, creep buckling of linear viscoelastic plate was studied. Pseudo-transient or Dynamic Relaxation method with finite element discritization was used for solving the nonlinear governing equations of the plate. The displacements were based on first order shear deformation theory. Von Karman assumptions were considered for strains, including initial imperfection of the plate. Central deflections of the rectangular PMMA plate as well as end-shortenings were obtained during the loading of the plates with simply supported and clamped edges. The results compared well with commercial finite element code ANSYS.

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In this paper the creep behavior of a functionally graded (FG) rotating disc made of Aluminum 6061 and Silicon Carbide is investigated and the optimum volume fraction of FG disc and its profile has been obtained. For this purpose, the temperature gradiant along the disc radius is obtained by solving the govering heat transfer differential equation. All the thermal properties of the material are assumed to be the function of temperature and volume fraction. To obtain material properties, two models of Mori-Tanaka and Hashin-Schtrickman are used. To validate the results, they are compared with those given in the literature. Two solution methods: semi-analytical and closed form are employed and the results are compared. The optimum design is carried out with one, and multi-objective methods which are based on genetic algorithm. The objectives are increasing the factor of safety, reducing the weight of the disc and reducing the range between minimum and maximum safety factors. The design variables are percentage of volume fraction, the power of material distribution formula, and the thickness of the disc. The results show that two solution methods compare well. Also, it has been shown that high fraction of Silicon Carbide in the outer side the disc provide optimum results. Also, contradiction of the objectives is reviled, hence the results are presented as Pareto front.

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Permanent deformation or rutting in wheel paths is one of the most important failure modes in asphalt pavements that affect the pavement life . Permanent deformation in asphalt mixtures can be defined as the unrecoverable cumulative deformation that occurs mainly at high temperatures in the wheel paths as a result of repeated traffic loading . The deformation results in depressions on the pavement surface along the wheel tracks relative to other points on the surface . Permanent deformation in wheel paths is one of the fundamental defects that occur due to lack of bearing capacity in flexible pavement layers . This type of defect usually occurs in the roads in the tropical areas . Rutting occurs due to cumulative non - reversible Permanent deformations in the pavement layers under repeated traffic loading . In order to increase pavement life and consequently decrease maintenance related traffic delays , great demands are placed on permanent deformation resistance of asphalt mixtures . Hot Mix Asphalt is composed of aggregates and asphalt binder . Properties of these materials have important effects on the pavement structure performance. Although , asphalt binder is a little part of mixture ( in comparison with aggregates ) , but has major effects on the performance , durability and stability of the asphalt concrete mixture . Any change in asphalt properties will result significant changes in the asphalt concrete mixture performance . Since asphalt cement ( AC ) never fully satisfying lacks the physical and mechanical properties , researchers are constantly trying to improve the asphalt cement properties . Asphalt cement modification will result improved quality and increased life of the pavement . Nano - particles is one of the additives that are used to modify the properties of asphalt cement . Nano - clays are unique materials as additives to make significant improvements in the material properties of polymer Nano -composites. Nano-clay polymer materials typically strengthen the mechanical properties, modulus and stability of these cases. In this research, it is assumed that subgrade, sub-base and base layers of flexible pavement have sufficient resistance to rutting. Nanoclay is used to modification of bitumen properties for Hot Mix Asphalt mixtures better bearing capacity and resistance to rutting. So, limestone aggregate with 4 degration number, AC 60-70 and two types of montmorillonite Nanoclay: Cloisite 15A and Cloisite 30B are used in this study. Marshall and Dynamic creep tests in two stress levels ( 300 and 450 KPa ) at 50 ° C , as well as rutting test on the HMA samples with 0 , 2 , 4 and 6 percent of each Nanoclay were performed . Test results show that adding Nanoclay will result the better performance of HMA samples .

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In order to avoid unpleasant incidents, it is crucial to maintain the stability for a high-speed railway vehicle. In this research, a high-speed railway vehicle dynamics with 38 degrees of freedom was investigated, adding longitudinal movement equations. Another innovation of this investigation is to determine the critical velocity for the studied railway vehicle and using nonlinear elastic rail for the wheel and rail contact. In this study, the stable and hunting behavior of the system was investigated. To identify the chaotic motion of the system, frequency analysis has been performed. Also, by plotting the Poincaré map, dynamic behavior of the system is illustrated in a discrete state space, which could be a good criteria for the chaotic or periodic behavior of the system. Long-term behavior reveals that at Speeds lower than the critical speed, the system oscillates until it reaches the steady-state of the system. In steady motion, the oscillation continues until the critical speed When the system reaches the critical velocity, the motion on the limit cycle occurs for the first time and when the speed is higher than critical speed, the vibration amplitude increased smoothly. It was observed from the frequency response plot that the hunting frequency evaluated via the linear elastic rail is higher than that of derived using a nonlinear model.

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Creep behavior of butt-welded joints in pressurized steel pipes operating at high temperature is one of the major concerns in industry. The creep behavior of 1.25Cr0.5Mo weldment has been investigated in this paper. Three different layers: Base Metal (BM), Heat Affected Zone (HAZ) and Weld Metal (WM) have been considered and the creep behavior of each layer has been modeled using constitutive equations. Constitutive parameters have been determined using the results of uniaxial constant load creep tests. A numerical approach based on least square method has been used to calculate optimum values of the constitutive parameters. The results have been compared with those provided in the literature for different alloys and good agreement has been observed. Creep tests have been carried out at 30, 35, 40 and 50 MPa and temperature levels of 670, 700, 725, 750 and 800 °C. Specimens have been machined out from Base and Weld Metal. Since machining specimens with appropriate size from HAZ is impossible, a method is proposed to obtain constitutive parameters for this layer. This method is validated by comparing the constitutive parameters which have been calculated for WM with those obtained using creep tests. Micrographical and microhardness tests show that there are significant differences in the microstructure of the layers. Consequently, the creep behavior of layers is different. The results show that steady state creep strain rate for WM is higher than the rates for BM and HAZ; also at low stress levels, creep strain rate of HAZ is larger than BM.

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Thermal creep is often associated with the flowing of a rarefied gas via the effect of temperature difference in solid boundaries. Recently the feasibility of such flow in dense fluids becomes a challenge. This paper deals with simulating the thermal creep flow in liquids confined in nanotubes. The investigations are carried on by molecular dynamics simulation method. The goal of this work is providing a clean picture of the thermal creep phenomenon mechanism in liquids. Simulation results show the existence of such flow in liquids in nanotubes. The thermal creep effect is stronger in nanotubes with narrower cross sections. Molecular data provided by the simulations shows there is a fluid layering phenomenon near the solid wall. The fluid layering together with the wall temperature gradient develops a pressure gradient near the wall. This pressure gradient acts as a planar force and is assumed to be responsible for the thermal creep effect. This force causes the fluid to flow toward the hot side of the tube. The mechanism of thermal creep phenomena is justified by the use of molecular principles and molecular data which are obtained from the molecular dynamics simulations.

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Creep fracture mechanic parameter, C*, is an essential tool for creep crack growth rate estimation and so remnant life determination of components operating at high temperature. For determining this parameter experimental works, FE methods, and engineering approaches can be utilized. In this paper in order to facilitate FE methods in C* determination for a CT specimen, creep behavior models of Norton and Liu-Murakami were developed and related subroutines were created. Each of the aforementioned models has its own temperature dependent material coefficients which were determined and validated based on creep rupture tests on crack free uniaxial specimens of P91 steel and IN718 super alloy respectively in 650˚C and 620˚C temperature. In this study creep fracture mechanic parameter value of a CT specimen made of P91 steel were derived by application of Norton and Liu-Murakami creep behavior models and results were compared with results of the experimental tests and reference stress engineering approach results. The results indicate that Liu-Murakami creep behavior model most exactly estimates creep fracture mechanics parameter, but yet reference stress engineering approach is the most economical way to determine this parameter.

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Creep failure is one of the most common mechanisms which determine the life of mechanical components operating at high temperature. Gas turbine blades are among the components which operate at high temperature under mechanical loads. In new designs, cooling flow passes through the inner channels of the blade to decrease blade temperature. One of the main parameters of the cooling system is the coolant’s heat transfer coefficient. In this paper, the effect of wall roughness of the cooling channels and coolant’s specific humidity on the cooling heat transfer coefficient has been investigated. The blade body and cooling channels are regarded as a heat exchanger with a thermal barrier coating and convective- film cooling. For this purpose, the physical properties of the coolant have been considered as a function of temperature and humidity. Then, the influence of the channel’s roughness on the heat transfer coefficient has been investigated and an analytical method has been used to obtain the temperature distribution. The results show that in the rough channels, coolant receives more heat from the blade body and consequently decreases its temperature especially in the critical section. Also, it has been shown that with increasing humidity; the coolant temperature reduces along the blade span comparing with the case of using dry air and consequently, the blade metal temperature reduces with about 2.5 percent. It has been shown that by increasing coolant’s humidity and roughness of the channels in a reasonable range, blade’s creep lifetime can be increased by up to 3.18 times.

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In this work, an analytical micromechanical model based on unit-cell approach is used to study the effect of interphase on the non-linear viscoelastic response of multiphase polymer composites. The representative volume element of composite consists of three phases including unidirectional fibers, polymer matrix and fiber/matrix interphase. Perfect bonding conditions are applied between the constituents of composites. The Schapery viscoelastic constitutive equation is used to model the nonlinear viscoelastic matrix. Prediction of the presented micromechanical model for the creep response of polymer material and two-phase composites shows good agreement with available experimental data. Furthermore, the predicted overall elastic behavior of three-phase composites demonstrates close agreement with other numerical results available. The effects of material and thickness of interphase on the creep-recovery strain curves of three-phase composites are studied in details. Results show that the interphase thickness and material properties have significant effect on the creep-recovery strain responses of the three-phase composites under transverse loading. According to micromechanical modeling results, it is found that the interphase negligibly affects the nano-linear viscoelastic behavior of three-phase composites under axial loading. Effects of the different stress levels and the variation of fiber volume fraction on the creep-recovery strain curves of three-phase composites are also investigated.

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A micro-mechanical model based on the representative volume element (RVE) is presented to study the time-dependent and creep behavior of fibrous composite material. To this aim a finite element model is presented for analysis of creep behavior of material in multi-axial creep are presented. The generalized plane strain condition is employed to model the behavior of the RVE in axial and transverse normal loading. The governing equations of the problem in the RVE are discretized using the presented finite element method and the stiffness and force matrixes are presented. Appropriate boundary conditions are implied to the RVE in order to consider the transverse and axial loading conditions including creep behavior. The Euler explicit method is employed to solve the discretized equations in the time domain. The distribution of micro-stresses and the effect of creep in re-distribution of the stresses are studied. The steady state creep behavior of composite in macro-mechanical scale is investigated by analysis of the micromechanical behavior of the RVE. The macro-mechanical creep behavior of metal matrix composite in axial and transverse loading are predicted from the presented micromechanical model.

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The Assessment of strain accumulation due to nonlinear events like creep, plasticity or ratcheting phenomenon has gained importance, since it causes an increase in creep and fatigue damage of materials. Some factors like the magnitude of loading, constitutive equations or the elastic regions around the nonlinear events have effect on the rate of strain accumulation. The elastic follow-up can explain the mechanism of strain accumulation. This phenomenon may occur when a mechanical structure with elastic manner is connected to non-linear events and they are subjected to a displacement load. In these cases, the high rigidity portion of elastic region of mechanical structure may enhance the force to the regions with low rigidity. So in the local non-linear portion, the strain is accumulated. This phenomenon is proposed as an important instruction in mechanical assessment codes. In this study, the effects of Elastic Follow-up phenomenon on strain accumulation due to elastic-plastic and local creep are investigated. So the Elastic Follow-up parameter is defined by the methods which are described in high temperature assessment procedures (R5). The results revealed that the strain accumulation depends on the elastic region in structures which is described by the Elastic Follow-up phenomenon.

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With the development of micro-mechanical systems, human became interested in concentrating on the small-scale impact on the flow and heat transfer in micro-channels. A micro-channel is required for a gas sensor to guide the gas flow. Reducing the size of channel has lead the scientist to concentrate on micro-sensor. Metal oxide gas micro-sensors are used to detect gases such as O3, SO2, CO2, NO, NH3, CH4 and etc. Metal oxide gas micro-sensors are small in size, low cost in fabrication and consume little power. The purpose of the current study is to numerically investigate the micro-channel wall thickness and diameter on gas inlet temperature under the influence of thermal creeping. The governing nonlinear differential equations, mass, momentum, energy, and species, are coupled and solved by a commercial code. The channel is assumed to be two dimensional. Since the Knudsen number is between 0.01 and 0.1, the slip boundary condition, Maxwell equation, is utilized. The result shows that as wall thickness increases the gas inlet temperature increases and temperature difference between gas inlet and outlet decreases. On the other hand as channel diameter decreases the gas inlet temperature increases.

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High temperature creep in nickel-based superalloys is investigated by discrete dislocation plasticity (DDP). A two-dimensional unite cell model representing micro-structure of superalloy and comprising γ^' particles in γ matrix phase is considered under uniaxial constant stress loading. While plastic deformation of γ phase occurs by a combination of dislocation glide and dislocation climb coupled to the diffusion of vacancies, elastic γ^' particles undergo deformation due to the stress-driven interfacial diffusion at the γ/γ^' interfaces in addition to bulk elastic deformation. It is noted that diffusion of vacancies is explicitly considered where local concentration of vacancies determines climb of dislocations. This model predicts the onset of tertiary creep in superalloys as extensively observed in experiments for commercially important nickel-based superalloys at moderate stress and temperature levels. Possible associated mechanisms are accordingly discussed. Moreover, effects of parameters such as volume fraction of γ^' particles are studied and discussed. Superalloys with three values for volume fraction of γ^' particles are investigated and obtained results indicate that the volume fraction of γ^' particles plays an important role in the creep behaviour of superalloys. Results of this study can be used in a continuum constitutive rule to investigate structural components under operational conditions.

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The response surface methodology was used to produce cherry jam containing stevia sweetener with desirable physicochemical, sensory and rheological properties. These experiments were planned using a central composite design (CCD) with three independent variables including sugar, pectin and stevia. The production process of samples was done in five levels of sucrose (50-10%), pectin (0.5-1%) and stevia (0.6-0.2%) in a constant amount of 300 g of fruit. To evaluate the jam, the physicochemical, sensory and rheological properties of the jam were determined and optimized. Concentrations of sucrose, pectin and stevia had a significant effect on the color, sensory and rheological properties of the jam. The results showed that none of the linear and interaction effects of the studied factors on the pH of cherry jam were significant. The values ​​of L * (brightness) and b * (yellowness) increased with increasing concentrations of sucrose and stevia, also increasing pectin increased a * (redness) of the jam. The evaluation results of sensory tests showed that the sugar variable plays an important role in improving the sensory parameters of the jam. Examination of the tests resulting from the creep test showed that the sugar factor plays an important role in the value of the parameters G0 and η0. The results show that the viscosity shown by Dashpot Maxwell (η0) can be a good indicator of the effect of sucrose concentration in the jam. Also, G1 and η1 parameters can not be clear indicators for understanding the structural changes in the jam with changes in the concentration of sugar, pectin and stevia. In general, the results of the study showed that using pectin and stevia sweetener can reduce the amount of sucrose in the jam and produce a low-calorie product with optimal quality and desirability index of 0.69 on a commercial scale.