Calculation of Mass Concrete Temperature and Creep Stress under the Influence of Local Air Heat Transfer

Temperature-induced cracking during the construction of mass concrete is a significant concern.Numerical simulations of concrete temperature have primarily assumed that the concrete is placed in an open environment.The problem of heat transfer between the air and concrete has been simplified to the concrete’s heat dissipation boundary.However,in the case of tubular concrete structures,where air inlet and outlet are relatively limited,the internal air temperature does not dissipate promptly to the external environment as it rises.To accurately simulate the temperature and creep stress in tubular concrete structures with enclosed air spaces during construction,we establish an air–concrete coupled heat transfer model according to the principles of conjugate heat transfer,and the accuracy of the model is verified through experiments.Furthermore,we conduct a case study to analyze the impact of airflow within the ship lock corridor on concrete temperature and creep stress.The results demonstrate that enhancing airflow within the corridor can significantly reduce the maximum concrete temperature.Compared with cases in which airflow within the corridor is neglected,the maximum concrete temperature and maximum tensile stress can be reduced by 12.5℃ and 0.7 MPa,respectively,under a wind speed of 4 m/s.The results of the traditional calculation method are relatively close to those obtained at a wind speed of 1 m/s.However,the temperature reduction process in the traditional method is faster,and the method yields greater tensile stress values for the corridor location.

Characteristics of transfer zones under the influence of preexisting faults and regional stress transformation:Wenchang A subsag,Zhujiang River Mouth Basin,northern South China Sea

A transfer zone in rift basins preserves important information on regional tectonic evolution and plays significant roles in hydrocarbon accumulation.Based on the systematic analysis of 3D seismic data and hydrocarbon accumulation conditions,the geometry,kinematics,and reservoir control of a large synthetic overlapping transfer zone in the south of the Wenchang A subsag in the Zhujiang(Pearl)River Mouth basin were investigated.Results indicate that the development and evolution of the transfer zone was controlled by the interaction between pre-existing faults and regional stress transformation.The intense rifting of the main faults of the transfer zone controlled the development of source rocks and faultcontrolled slope break paleogeomorphology.The strike-slip overprint since the Oligocene is conducive to the formation of a large-scale fault-anticline trap,and the secondary faults in the transfer zone contribute to the hydrocarbon transportation.The conjugate intersection area of the NE-and NW-trending faults offers more opportunity for hydrocarbon migration and accumulation.

Full-scale pullout tests of rock anchors in a limestone quarry focusing on bond failure at the anchor-grout and grout-rock interfaces

Rock anchors are a common safety measure for stabilising large-scale infrastructure,such as bridge towers,retaining walls,rock slopes and windmills.There are four principal failure modes for rock anchors:(a)tensile failure of the steel anchor,(b)anchor-grout interface failure,(c)grout-rock interface failure,and(d)rock mass uplift.Field tests were performed in a limestone quarry.These tests were designed to test failure modes B and C through pullout.In the tests of failure mode B,the shear stress on the anchor-grout interface is the largest at the top of the grout column and attenuates towards the distal end for small loads.The shear stress becomes uniformly distributed when the applied load is approximately 50%of the ultimate pullout load.The anchors designed to test failure mode C were installed with an endplate and had a higher toughness than the straight bar anchors.The shear stress on the grout-rock interface is the largest at the endplate and attenuates upward before slip starts along the interface.When the ultimate pullout load is reached,and the grout column starts to slip,the shear stress is approximately constant.The bond shear strength on the anchor-grout interface was approximately 20%of the uniaxial compressive strength of the grout,and the bond strength of the grout-rock interface was around 5%for that of the grout.The grout-rock interface is likely determined by whichever is weaker,the grout or the rock.

Thermo-structural analysis on evaluating effects of friction and transient heat transfer on performance of gears in high-precision assemblies

The high precision assemblies with considerable radial interference should be accompanied by heating and cooling processes.However,the mechanical properties of metals are greatly affected by thermal operations.So,for evaluating the stress distribution and distortion of teeth profiles in a gear/shaft assembly,a transient thermal analysis is necessary for finding the change in mechanical properties.The friction on the contact surface is another important parameter in interaction of the gear with the shaft.Evaluating the gear stress and deformation fields for several modes of heat transfer and friction coefficients showed that the maximum radial or tangential stresses on contact surface of the joint may have more than 8%increase by increasing friction coefficient;while the intensity of heat transfer at cooling stage has lower effect on stress distribution.

Forced Axial and Torsional Vibrations of a Shaft Line Using the Transfer Matrix Method Related to Solution Coefficients

This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the propeller and intermediate shafts, under the influence of propeller-induced static and variable hydrodynamic excitations are also studied. The transfer matrix method related to the constant coefficients of differential equation solutions is used. The advantage of the latter as compared with a well-known method of transfer matrix associated with state vector is the possibility of reducing the number of multiplied matrices when adjacent shaft segments have the same material properties and diameters. The results show that there is no risk of buckling and confirm that the strength of the shaft line depends on the value of the static tangential stresses which is the most important component of the stress tensor.

Investigation of Coulomb stress changes in south Tibet(central Himalayas) due to the 25th April 2015 M_W 7.8 Nepal earthquake using a Coulomb stress transfer model

After Mw 7.8 Nepal earthquake occurred, the rearrangement of stresses in the crust commonly leads to subsequent damaging earthquakes. We present the calculations of the coseismic stress changes that resulted from the 25th April event using models of regional faults designed according to south Tibet-Nepal structure, and show that some indicative significant stress increases. We calculate static stress changes caused by the displacement of a fault on which dislocations happen and an earthquake occurs. A Mw 7.3 earthquake broke on 12 May at a distance of - 130 km SEE of the Mw 7.8 earthquake, whose focus roughly located on high Coulomb stress change （CSC） site. Aftershocks （first 15 days after the mainshock） are associated with stress increase zone caused by the main rupture. We set receiver faults with specified strikes, dips, and rakes, on which the stresses imparted by the source fault are resolved. Four group normal faults to the north of the Nepal earthquake seismogenic fault were set as receiver faults and variant results followed. We provide a discussion on Coulomb stress transfer for the seismogenic fault, which is useful to identify potential future rupture zones.

Stress Transfer and the Impact of the India-Eurasia Collision and the Western Pacific Subduction on the Geodynamics of the Asian Continent

The interaction between the India-Eurasia collision and the Western Pacific subduction and their contribution to recent geodynamics of the Asian continent are discussed. We perform a comparative analysis of the data available from world literature and new data on the slow strain and earthquake migration from the India-Eurasia collision and the Western Pacific subduction zones. Based on the concepts of wave dynamics of the deformation processes, a localization scheme is constructed illustrating the migration of slow strain fronts in central and eastern Asia, and the wave geodynamic impact of collision and subduction on the Asian continent is shown.

Some Further Considerations about the Theory of Elastic Stress Transfer from Partially Embedded Axially Loaded Fiber to Matrix

In this paper the elastic stress transfer from the fiber to the matrix is analysed for fiber-reinforced composites when the fiber is loaded axially.The dependence of the elastic stress transfer on the as- pect ratio of the fiber,the volume fraction of the fiber,the fiber-to-matrix elastic modulus ratio and the Poisson's ratio of the fiber and the matrix has been shown in detail.

The Effects of Interfaces on Stress Transfer in Short Fiber Reinforced Metal Matrix Composites

In this paper, the effects of interface properties on the stress transfer between matrix and fiber in short fiber reinforced metal matrix composites (SFRMMCs) is studied with the method of the elasto plastic finite element. The interface properties include Young’s modulus, thickness and elasto plastic performances. In the calculation an interfacial layer with given thickness is introduced into the single fiber model. It is shown that, for a soft interface, the variation in interfacial properties influences the stress transfer greatly.

Thermophysical Properties and Supercritical Heat Transfer Characteristics of R515A

The heat transfer of supercritical fluids is a vastly growing field, specifically to find suitable alternative to replace conventional R134a, which can be beneficial for climate change. A considerable suggestion is R515A which possesses considerably lower global warming potential. The present simulations are designed to study supercritical fluid R515A under cooling conditions in horizontal position. The effect of pressure, mass flux, heat flux and tube diameter were considered for horizontal tube in the vicinity of pseudo critical temperature. Numerical investigations on heat transfer characteristics of supercritical fluid R515A were performed using widely used shear-stress transport (SST) model. Moreover, heat transfer correlations were developed and suggested to accurately predict Nusselt number within 10% accuracy. The simulation results showed about 3.98% average absolute deviation.

On stress-forecasting strategy of earthquakes from stress buildup,stress shadow and stress transfer(SSS) based on numerical approach

Global Positioning System （GPS） and Interferometric Synthetic Aperture Radar （InSAR）, used for monitoring crust deformation, are found to be very promising in earthquake prediction subject to stress-forecasting. However, it is recognized that unless we can give reasonable explanations of these curious precursory phenomena that continue to be serendipitously observed from time to time, such high technology of GPS or InSAR is difficult to be efficiently used. Therefore, a proper model revealing the relation between earthquake evolution and stress variation, such as the phenomena of stress buildup, stress shadow and stress transfer （SSS）, is crucial to the GPS or InSAR based earthquake prediction. Here we address this question through a numerical approach of earthquake development using an intuitive physical model with a map-like configuration of discontinuous fault system. The simulation provides a physical basis for the principle of stress-forecasting of earthquakes based on SSS and for the application of GPS or InSAR in earthquake prediction. The observed SSS associated phenomena with images of stress distribution during the failure process can be continuously simulated. It is shown that the SSS are better indicators of earthquake precursors than that of seismic foreshocks, suggesting a predictability of earthquakes based on stress-forecasting strategy.

Use of infrared thermal imaging to diagnose health of Ammopiptanthus mongolicus in northwestern China

Population of the rare and endangered species Ammopiptanthus mongolicus （Maxim.） Cheng f. declined rapidly in China＇s add region and Central Asia. There is an urgent need to protect this species, which is particularly important in maintaining biodiversity throughout the arid region of northwestern China. By analyzing the infrared thermal images based on plant-transpiration transfer coef- ficient （hat） and photosynthetic parameters, we made quantitative and accurate diagnoses of the plant growth and health status of A. mongolicus. Using an LI-COR6400 photosynthesis system, we measured the net photosynthetic rate （Pn）, stomatal conductance （Gs）, and transpiration rate （Tr）. Infrared thermal images obtained in the field were processed by ENVI4.8 software to calculate surface tem- peratures of the plant subjects. We found that the plant transpiration transfer coefficient of A. mongolicus was inthe order of old plants 〉young plants 〉intermediate-aged plants. Declining health levels of young, intermediate, and old plants were divided into three categories： 〈0.4, 0.4-0.7, and 〉0.7. The coefficient showed a significant negative correlation with Tr, Gs, and Pn, indicating that they can simultaneously reflect the state of plant growth. By estab- lishing hat and photosynthetic parameters in regression model Y = a-blnx, we can accurately diagnose plant growth and decline of plant health conditions.

ANALYSIS OF THERMAL-ELASTIC STRESS OF WHEEL-RAIL IN ROLLING-SLIDING CONTACT

A coupling thermo-mechanical model of wheel/rail in rolling-sliding contact is put forward using finite element method. The normal contact pressure is idealized as the Hertzian distribution, and the tangential force presented by Carter is used. In order to obtain thermal-elastic stress, the ther-mal-elastic plane stress problem is transformed to an elastic plane stress problem with equivalent fictitious thermal body force and fictitious boundary distributed force. The temperature rise and ther-mal-elastic stress of wheel and rail in rolling-sliding are analyzed. The non-steady state heat transfer between the contact surfaces of wheel and rail, heat-convection and radiation between the wheel/rail and the ambient are taken into consideration. The influences of the wheel rolling speed and wear rate on friction temperature and thermal-elastic stress are investigated. The results show the following： ① For rolling-sliding case, the thermal stress in the thin layer near the contact patch due to the friction temperature rise is severe. The higher rolling speed leads to the lower friction temperature rise and thermal stress in the wheel; ② For sliding case, the friction temperature and thermal stress of the wheel rise quickly in the initial sliding stage, and then get into a steady state gradually. The expansion of the contact patch, due to material wear, can affect the friction temperature rise and the thermal stress during wear process. The higher wear rate generates lower stress. The results can help under-stand the influence of friction temperature and thermal-elastic stress on wheel and rail damage.

Utilizing a novel fiber optic technology to capture the axial responses of fully grouted rock bolts

Rock bolts are one of the primary support systems utilized in underground excavations within the civil and mining engineering industries. Rock bolts support the weakened rock mass adjacent to the opening of an excavation by fastening to the more stable, undisturbed formations further from the excavation. The overall response of such a support element has been determined under varying loading conditions in the laboratory and in situ experiments in the past four decades; however, due to the limitations with conventional monitoring methods of capturing strain, there still exists a gap in knowledge associated with an understanding of the geomechanical responses of rock bolts at the microscale. In this paper, we try to address this current gap in scientific knowledge by utilizing a newly developed distributed optical strain sensing(DOS) technology that provides an exceptional spatial resolution of 0.65 mm to capture the strain along the rock bolt. This DOS technology utilizes Rayleigh optical frequency domain reflectometry(ROFDR) which provides unprecedented insight into various mechanisms associated with axially loaded rebar specimens of different embedment lengths, grouting materials, borehole annulus conditions, and borehole diameters. The embedment length of the specimens was found to be the factor that significantly affected the loading of the rebar. The critical embedment length for the fully grouted rock bolts(FGRBs) was systematically determined to be430 mm. The results herein highlight the effects of the variation of these individual parameters on the geomechanical responses FGRBs.

Stagnation-point flow of couple stress fluid with melting heat transfer

Melting heat transfer in the boundary layer flow of a couple stress fluid over a stretching surface is investigated. The developed differential equations are solved for homotopic solutions. It is observed that the velocity and the boundary layer thickness are decreasing functions of the couple stress fluid parameter. However, the temperature and surface heat transfer increase when the values of the couple stress fluid parameter increase. The velocity and temperature fields increase with an increase in the melting process of the stretching sheet.

Simulation on flow, heat transfer and stress characteristics of large-diameter thick-walled gas cylinders in quenching process under different water spray volumes

Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders and reduce production costs.To find the optimal water spray parameters,a fluid-solid coupling model with three-phase flow was established in consideration of water-vapor conversion.The inner and outer walls of gas cylinder with the dimensions of d914 mm×38 mm×12000 mm were quenched using multi-nozzle water spray system.The internal pressure,average heat transfer coefficient(have)and stress of the gas cylinder under different water spray volumes during quenching process were studied.Finally,the mathematical model was experimentally verified.The results show that both the internal pressure and have increase along with the increase of spray volume.The internal pressure increases slowly first and then rapidly,but have increases rapidly first and then slowly.To satisfy hardenability of gas cylinders,the minimum spray volume should not be less than 40 m^3/(h·m).The results of stress indicate that water spray quenching will not cause deformation of bottle body in the range of water volume from 40 to 290 m^3/(h·m).

Effect of friction stir processing on mechanical properties and heat transfer of TIG welded joint of AA6061 and AA7075

Tungsten inert gas(TIG) welding is the most commonly used joining process for aluminum alloy for AA6061 and AA7075 which are highly demanded in the aerospace engineering and the automobile sector, but there are some defects occur during TIG welding like micro-crack, coarse grain structure, and porosity. To improve these defects, the TIG welded joint is processed using friction stir processing(FSP).This paper presents the effect of friction stir processing on TIG welding with filler ER4043 and ER 5356 for dissimilar aluminum alloy AA6061 and AA7075. The mechanical characterization, finite element formulation and mathematical equations of heat transfer of TIG + FSP welded joints are investigated using ANSYS Fluent software by adjusting process parameters of FSP. The results show that the maximum compressive residual stress 73 MPa was obtained at the fusion zone(FZ) of the TIG weldment with filler ER4043, whereas minimum compressive residual stress 37 MPa was obtained at stir zone(SZ) of the TIG+ FSP with filler 5356. The maximum heat flux 5.33 × 106 W/m2 and temperature 515C have observed at tool rotation 1600 rpm with a feed rate of 63 mm/min. These results give a satisfactory measure of confidence in the fidelity of the simulation。

STUDIES ON STRESS TRANSFERENCE MECHANISM OF STEEL FIBRE REINFORCED CONCRETE

The stress transfer mechanism of steel fibre reinforced concrete is studied. The solutions for the stress and displacement were regarded as the superposition of ' the elementary solutions' and ' the improved solutions'. The elementary solutions were found by using two-dimensional elastic theory and the improved solutions were found by using the Love displacement function method. The calculated results indicate that the solutions possess good convergence. By comparing the three-dimensional solutions with the shear-lag solutions, evident difference may be found.

Heat transfer intensification in hydromagnetic and radiative 3D unsteady flow regimes: A comparative theoretical investigation for aluminum and γ-aluminum oxides nanoparticles

This article investigates the colloidal study for water and ethylene glycol based nanofluids.The effects of Lorentz forces and thermal radiation are considered.The process of non-dimensionalities of governing equations is carried out successfully by means of similarity variables.Then,the resultant nonlinear nature of flow model is treated numerically via Runge-Kutta scheme.The characteristics of various pertinent flow parameters on the velocity,temperature,streamlines and isotherms are discussed graphically.It is inspected that the Lorentz forces favors the rotational velocity and rotational parameter opposes it.Intensification in the nanofluids temperature is observed for volumetric fraction and thermal radiation parameter and dominating trend is noted for γ-aluminum nanofluid.Furthermore,for higher rotational parameter,reverse flow is investigated.To provoke the validity of the present work,comparison between current and literature results is presented which shows an excellent agreement.It is examined that rotation favors the velocity of the fluid and more radiative fluid enhances the fluid temperature.Moreover,it is inspected that upturns in volumetric fraction improves the thermal and electrical conductivities.

Three-dimensional finite element analysis of process-induced residual stress in resin transfer molding process

A three-dimensional finite element analysis of process-induced residual stress in resin transfer molding (RTM) process is presented. The finite element method (FEM) was employed to solve the coupled equations involved in the transient heat transfer and the cure kinetics of the resin, and the distributions of internal temperature and cure degree of the composite at any instant time were obtained. The self-consistent field micro-mechanics model was used to predict the cure-dependent mechanical properties of the composites. Thermal expansion and cure shrinkage were included in the analysis. The thermo-elastic mechanical governing equations were solved using the incremental stress-strain relationship based FEM and the residual stress development was predicted. The present results were validated by the comparisons with the pertinent literature. The numerical example of a half cylinder was presented. The results show that it is necessary to carry out the three-dimensional analysis due to the complex distributions of temperatures, cure degrees and process-induced stress for thick parts, which can be predicted at any point within composite structures in the present analysis.