Action Of Temperature Gradient Research Articles

Study on pore behavior of laser welding process between steel and CFRP based on numerical simulation

In order to understand the pore behavior during laser welding of metal and polymer, the laser welding of steel and carbon fiber reinforced plastics (CFRP) was studied. A three-dimensional transient model of multi-physical field couple with heat, flow and force was constructed to simulate the temperature distribution, fluid flow, stress change and solidification under the thermal decomposition of CFRP based on the experiments. The formation, function and evolution mechanism of pores in welded joints were discussed, and the relationship between heat input and pore morphology at the interface was clarified. The results show that the model error is lower than 9 %, and the model is reliable. In laser welding process, bubbles generate, expand and fuse in the center of CFRP molten pool, which changes the local flow velocity and direction, but most of the fluid still flows to the molten pool edge under the action of temperature gradient, and forms pores of stable size with the cooling process. When the heat input is high, the large pores are formed at the interface due to the violent thermal decomposition of CFRP and big stress difference. When the heat input is low, there is still a large stress gradient in the center of the interface, and it is difficult for the insufficiently melted polymer to provide sufficient resistance to deformation, resulting in obvious pore phenomenon in the center of the interface.

Refined Analysis of Spatial Three-Curved Steel Box Girder Bridge and Temperature Stress Prediction Based on WOA-BPNN

Bridges often improve the visual appeal of urban landscapes by incorporating curve elements to create iconic forms. However, it is noteworthy that curved bridges have unique mechanical properties under loads compared to straight bridges. This study analyzes a spatial three-curved steel box girder bridge based on an actual engineering case with a complex configuration. Initially, the finite element software Midas/Civil 2021 is utilized to establish a beam element model and a plate element model to examine the structural responses under dead loads in detail. Then, two different temperature gradient distribution models are employed for the temperature effect analysis. The backpropagation neural network (BPNN) optimized by the WOA algorithm is trained as a surrogate model for finite element models based on the results of temperature stress simulation. The results reveal that the bending–torsion coupling effect in the second span of the spatial three-curved steel box girder bridge is pronounced, with the maximum torque reaching 40% of the bending moment. The uneven distribution of cross-section stress is particularly significant at the vertices, where the shear lag coefficient exceeds 3. Under the action of temperature gradients, the bridge displays a warped stress state; the stress results obtained from the exponential model exhibit a 21% increase compared to BS-5400. Optimization of the weights by the WOA algorithm results in a significant improvement in prediction accuracy, and the convergence speed is improved by 30%. The coefficient of determination (R2) for predicting temperature stress can reach as high as 0.99.

Mapping the relationship between the temperature gradient of CRTS Ⅲ slab track on bridge and rail deformation in high-speed railways

Temperature gradient is an important factor affecting the periodic rail deformation of CRTS Ⅲ and the running stability of high-speed trains. The Comprehensive Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) method is employed for the analysis of test data in site from CRTS III slab tracks on high-speed railway bridges. The correctness of the coupling model has been validated through data on-site. To analyze the mapping relationship between the temperature gradient of the CRTS Ⅲ slab track on the bridge and rail deformation in high-speed railways, a rail-slab track-bridge thermal coupling model was established, and the rail deformation distribution characteristics of the slab track on the bridge under the complex temperature gradient load were calculated. Furthermore, a prediction model of rail deformation under the action of the complex temperature gradient was proposed. The study results showed that the intrinsic mode function (IMF) decomposed by the CEEMDAN method reflects the sensitive wavelength of track irregularity and quantitatively describes the corresponding relationship between amplitude and seasonal temperature. In the measured data, the maximum amplitude of rail deformation caused by temperature differences in different seasons was 1.99 mm, reflecting the significant impact of temperature gradient on the additional track irregularities on the bridge. Under the action of the temperature gradient, the rail deformation of CRTS Ⅲ slab track on the bridge is the superposition of periodic sinusoidal fluctuation of the track and parabolic fluctuation of the simply supported beam. This study could provide a new method for predicting rail deformation and controlling track smoothness, so as to improve the stability and operation efficiency of trains.

Tensile Fatigue Properties of Ordinary Plain Concrete and Reinforced Concrete under Flexural Loading.

Many bridge structural components are subjected to repetitive vehicle load and temperature gradient action. The resulting cyclic tensile stresses within the structures could cause premature fatigue failure of concrete, dramatically impairing structural components' durability and sustainability. Although substantial knowledge of fatigue properties on low-strength pavement concrete and high-strength structural concrete has been obtained, research on the most widely used normal-grade ordinary concrete in bridge engineering is still ongoing. Therefore, a four-point bending fatigue test of 97 C50 concrete specimens under a constant amplitude sinusoidal wave was conducted in the laboratory, the flexural fatigue behavior of plain and reinforced concrete specimens was studied, and the cyclic deformation evolution of concrete under fatigue loading was obtained. The empirical fatigue S-N equations of concrete with a failure probability p of 0.1~0.5 were derived through statistical analysis of the test results. The fatigue life of the tested specimens exhibited a two-parameter Weibull distribution. In addition to the maximum stress level Smax, the stress ratio R is also a key factor affecting the flexural fatigue life of concrete N. The semi-logarithmic and logarithmic equations were almost identical at the tested stress levels, the latter predicting longer fatigue life for Smax < 0.70. The restraining effect from steel reinforcement slightly lengthened the concrete's fatigue cracking initiation life. The insight into concrete flexural fatigue properties from this study not only contributes to a better understanding of structural concrete, but also provides a basis for the practical evaluation of concrete or composite bridge decks.

THE SIMULATION OF EMERGENCY ACTION ON CONSTRUCTION MATERIALS BY HIGH CURRENT RELATIVISTIC ELECTRON BEAMS

Development of many innovative areas in energy, mechanical engineering, aircraft building and other industries is limited by the strength of materials under the action of temperature gradients. In this regard, the problem appears to find and justify technical means to model a complex of operating conditions. High-current relativistic electron beams reasonably belong to such instruments and means. As a result of their impact, pulsed electric and magnetic fields occur in the irradiated targets, temperature gradients are created, and shock waves are generated. The paper investigates the patterns of change in the internal structure of the blades of gas turbine engines and engineering materials, subjected to the action of an electron beam

Interfacial microstructure evolution for coordinated deformation of Mg/Al composite plates by asymmetrical rolling with differential temperature rolls

In this work, Mg/Al composite plates with different thickness ratios were prepared by the asymmetrical rolling process with differential temperature rolls and isothermal symmetrical rolling. Microstructural evolution and mechanical properties of matrix and composite materials with different thicknesses were analyzed. Influence of thickness ratios on the coordinated deformability of heterogeneous metals and interface toughness under the action of temperature gradient and shear force was investigated. Results show that the relative deformation rates of matrix and composite materials converge gradually under the influence of work hardening of Mg/Al layer. The Mg layer is mainly DRXed grains and texture intensity gradually weakens with increasing thickness ratio. The Al layer is mostly dominated by subgrains and deformed grains, which have a strong correlation with thickness ratio. Strength and plasticity of composites first increase and then decrease with increasing thickness ratio. Fracture of composite plate occurs in intermetallic compounds (IMCs). Thickness of IMCs has a strong positive correlation with thickness ratio. When the thickness ratio of AZ31B/Al6061 for 5, the relative thickness of IMCs is the largest and the relative bonding strength is the smallest. When the thickness ratio of AZ31B/Al6061 for 3, there is no element aggregation in IMCs, and the comprehensive mechanical properties of composite plate are comparatively better.

On the Evolution of Temperature and Combined Stress in a Work Roll under Cyclic Thermo-Mechanical Loadings during Hot Strip Rolling and Idling.

An accurate prediction of temperature and stress evolution in work rolls is crucial to assess the service life of the work roll. In this paper, a finite element method (FEM) model with a deformable work roll and a meshed, rigid body considering complex thermal boundary conditions over the roll surface is proposed to assess the temperature and the thermal stress in work rolls during hot rolling and subsequent idling. After that, work rolls affected by the combined action of temperature gradient and rolling pressure are investigated by taking account of the hot strip. The accuracy of the proposed model is verified through comparison with the calculation results obtained from the mathematical model. The results show that thermal stress is dominant in the bite region of work rolls during hot rolling. Afterwards, the heat treatment residual stresses which are related to thermal fatigue are simulated and introduced into the work roll as the initial stress to evaluate the redistribution under the thermal cyclic loads during the hot rolling process. Results show that the residual stress significantly changed near the roll surface.

Effect of the Temperature Gradient on the X-ray Diffraction Spectrum of a Quartz Crystal

The spectra of X-ray diffraction from the reflecting atomic plane (1 0 1 1) of a quartz single crystal are studied in Laue geometry under the action of temperature gradient on a BDER-KI-11K spectrometer with a resolution of 300 eV on the Am241 line of 17.74 keV. The temperature gradient leads to an increase in the intensity of the diffracted beam depending on the heating temperature. It is shown that the intensity of X-ray diffraction in Laue geometry may increase at a temperature gradient of 250°C/cm by two orders of magnitude in comparison with the uniform temperature state of the crystal. The rocking curve of the reflected beam is obtained at a fixed observation angle of 6° and a specified temperature gradient. It is demonstrated that the intensity of the reflected beam increases with increasing temperature gradient (to a certain value), while the spectral width of the reflection line remains constant and is governed by the energy resolution of the spectrometer. A further growth in the temperature gradient leads to an increase in the spectral width of the reflection line with decreasing intensity of the reflected beam.

Thermophysical Properties in Assembling Process at Macro and Micro Level

The electronic modules are complex ensemble of electronic components having terminals (PIN) connected by solder joints on dedicated metallic surfaces (PAD) parts of conductive interconnection structure realized on rigid or flexible dielectric substrate having different core materials. The reliability of the electronic modules could be considered as expression of solder joints functionality (SJF) relating to working conditions and unique defined by their electrical, mechanical and thermal properties. These properties are in close connection with the solder joints microstructures, result of the soldering Process temperature gradient action over the trinomial solder alloy Paste, Pin and Pad. Consequently the solder joints quality can be correctly evaluated taking into consideration not only the severally intrinsic parameters of the trinomial elements Pin-Pad-Paste characterized by specific thermophysical properties (ThP), but also interrelate the complex reaction at the interface between them and interdependence with the soldering Process parameters.In the paper, will be analyzed the influencing factors of manufacturing processes, the most important assembling defects at macro and micro level, their causes relating to specific ThP and processes at interfaces Pin-solder joints-Pad, it will be identify the Key Process Input Variables (KPIV) and propose a structural model for assembling processes, 4P Soldering Model, as an useful tool in engineering of electronic product in order to assure the assumed goal for assembling stage.

VOF simulation of marangoni flow of gas bubbles in 2D-axisymmetric column

Abstract The migration of gas bubbles immersed in a liquid under the action of temperature gradient and surface tension (Marangoni flow) in zero gravity environment is numerically investigated for different Ma, Re, and Pr (Marangoni, Reynolds, and Prandtl numbers). The full Navier–Stokes equations as well as the energy equation for temperature gradient are solved by a volume of fluid (VOF) method/Finite Volume method, and the surface tension force is modeled by a continuum surface force (CSF) model. The behavior of bubble migrating toward the hotter side by the action of surface tension using the flow relations between two bubbles (leading and trailing bubble), and the trajectories and the velocities of the different bubbles diameters, in microgravity environment have been investigated numerically. It has been verified that the calculated results are in good agreement with available experimental and numerical results. It is also concluded that the VOF is able to simulate two-phase flow under zero gravity conditions.

Fractional crystallization on cooled walls: Separation efficiency with a growing crystal layer, its diffusion washing, and partial melting

The redistribution of components in the crystal layer-melt system at the main stages of fractional crystallization on cooled walls is studied. Mathematical solutions that can be used for calculating the fraction of trapped melt and the value of effective distribution (partition) coefficient in the crystallization of systems of different types are obtained. The kinetics of diffusion of impurities and migration of liquid inclusions under the action of temperature gradients at the growth and diffusion-washing stages of a two-phase crystal layer is studied. Simple relations for calculating the holdup of a melt and the maximal degree to which the main component can be purified in the partial melting (sweating) of crystal layers are derived. The theoretical results are compared with the experimental data obtained in the fractional crystallization of organic mixtures and freezing of aqueous solutions. Comparative analysis of the efficiency of the studied stages of fractional crystallization is accomplished and some practical recommendations are formulated.

Mass transfer in frozen porous bodies

The theory of moisture transport in frozen porous bodies under the action of temperature gradient along unfreezing communications represented by water in thin pores and in interlayers between the pore surface and the ice was elaborated. It was shown that most of the flow in the pores filled with water is directed toward a cold side and can be calculated using the disjoining pressure isotherms of unfreezing interlayers. To obtain isotherms, we used the data of previous measurements of the thickness of unfreezing interlayers in micron-sized quartz capillaries as a function of pressure and temperature. The viscosity of unfreezing interlayers in quartz capillaries was estimated based on the measurements of the displacement velocity of ice columns in the quartz capillaries. Calculated flow rates of unfreezing moisture were consistent with the experimental data for the model porous bodies and frozen grounds.

Direct observation of processes in a solidifying dispersion

The evolution of a dispersion under the action of temperature gradients and solidification was followed optically in a transparent molten salt (CsCl) with inclusions of Pb-droplets and gas bubbles. This system is believed to model a solidifying metallic alloy. Rejection of Pb-particles by the solidification front was observed, while large gas bubbles were incorporated. Thermocapillary convection at the gas bubbles considerably distorted the temperature field and even caused local remelting. Marangoni migration of bubbles was not observed, contrary to expectations.