Effect Of Thermal Field Research Articles

Free vibrations of axially loaded thin-walled shaft-disk rotors subjected to non-uniform temperature field

Research on vibrations of shaft-disk rotors in non-uniform thermal field is essential for the design of rotating machinery. In this paper, the dynamic model of axially loaded thin-walled shaft-disk rotors in axial non-uniform temperature field is developed, considering three-dimensional displacement fields of the shaft and disk. This model introduces the temperature-dependent properties of materials, and gyroscopic and centrifugal effects. Based on the Euler-Bernoulli beam theory and the Kirchhoff plate theory, Lagrange's equation is used to derive the differential equations of motion. By comparing with the results of the existing reference and finite element results, the accuracy of the present model is verified. The effects of the axial displacement of shaft, temperature-dependent material property, temperature difference, temperature distribution, disk position and axial preload on the free vibration of shaft-disk rotors are discussed. Results show that the present model can effectively predict free vibrations of shaft-disk rotors in axial non-uniform temperature field. The effect of thermal field on vibrations of shaft-disk rotors is affected by the rotational speed and disk location as well.

Evaluation of the Effect of Thermal Fields on the Strain Stress State of Parts in the Case of Pendulum Surface Plastic Deformation

Evaluation of the Effect of Thermal Fields on the Strain Stress State of Parts in the Case of Pendulum Surface Plastic Deformation

Inorganic photochromism material SrHfO3:Er3+ integrating multiple optical behaviors for multimodal anti-counterfeiting

Photochromic materials usually have different physical and chemical properties when they are in different states. Inorganic photochromic materials are widely used in the fields of information storage, optical switches and sensors due to their long lifetime, good thermal stability and fatigue resistance. However, the current inorganic photochromic materials, possessing a unitary optical property, cannot fulfill the requirement of multimodal high-level security anti-counterfeiting. In this work, we report the multiple optical behaviors integrated inorganic photochromic Er3+-doped strontium hafnate ceramics. It integrates multiple optical functions, including photochromism, downshifting photoluminescence, up-conversion luminescence, afterglow, and thermoluminescence. The fluorescence modulation contrast (FMC) maximum of SrHfO3: Er3+ can achieve as high as to 77.21% in the mode of photochromism-driven the quenching of downshifting photoluminescence. The FMC maximum can approach 70.24% in the mode of photochromism-driven the quenching of up-conversion luminescence. By alternating the light stimulation and thermal field effect, both photochromism and fluorescence modulation exhibit excellent stability and robust fatigue resistance. The mechanisms of the observed photochromism, downshifting and up-conversion luminescence, fluorescence modulation, afterglow, and thermoluminescence were studied systematically. The combination of the multiple optical behaviors functionalizes the as-obtained material for versatile applications. As a proof of concept, a flexible film was designed and prepared, demonstrating the practical application of SrHfO3: Er3+ material for multimodal high-level security anti-counterfeiting.

Thermal Field Effect in Resistive Random Access Memory With Sidewall Structures of Different Thermal Conductivity

The effect of different pulse rise time in resistive random access memory (RRAM) is presented in this study. The result shows that the length of pulse rise time will lead to variations in RRAM OFF-state resistance that occur due to which of two distinct effects governs the reaction, either the electric field or the thermal field. Different sidewall materials are adopted in RRAM devices to verify these phenomena, and a physical model supplemented with COMSOL simulation is proposed.

Effect of viscous-Pasternak foundation on laser-excited microbeams via modified thermoelastic MGT model

Due to the wide variety of applications in many fields of science and engineering, the subject of foundations is considered highly attractive to many investigators. Foundations are also essential in maintaining microstructural systems during oscillations. In the current paper, a modified model of a microbeam resting on a viscous Pasternak foundation under the influence of axial tension will be presented. The microbeam is described as an Euler-Bernoulli beam as it was heated by a very short laser pulse. Based on the Moore-Gibson-Thompson (MGT) model of non-Fourier-heat-conduction and thermal field effect, the equation governing the vibration of the thermoelastic microbeam was derived. An analytical solution is presented for the studied field variables based on the Laplace transform method, in addition to an approximate numerical technique for calculating inverse transformations. The effects of different effective factors on the deflection, temperature, and thermal stresses are demonstrated, including viscoelastic damping structures, damping coefficients, laser pulse heating, and stiffness of the viscoelastic substrate. Furthermore, the estimated outcomes are compared with those obtained in the previous literature to ensure that the derived formulas are acceptable. Additional numerical results are summarized in the tables and presented graphically in order to make comparisons and reveal the effect of all effective thermal parameters. Finally, the importance of the thermo-elastic MGT model over the previous corresponding models was explored.

Viscoelastic stressed microbeam analysis based on Moore–Gibson–Thompson heat equation and laser excitation resting on Winkler foundation

In this work, a modified viscoelastic model of initially stressed microbeam on the base of the Winkler foundation under the effect of ultrafast laser heating and axial stress has been proposed. Viscosity effects are taken into account following the Kelvin–Voigt model. The governing equation for the thermoelastic vibration of the microbeam is obtained when the thermal field effect is defined by the non-Fourier Moore–Gibson–Thompson (MGT) heat equation. The microbeam is seen as an Euler–Bernoulli beam that is exposed to varying sinusoidal heat. An analytical solution to the problem has been presented on the basis of the Laplace transform in addition to applying a numerical method to find inverse transformations. A numerical illustration is organized in the discussion section which discusses the impact of different effective parameters both on the vibrational behavior of a microbeam system and on the field variables. The viscous damping coefficient, laser pulse duration, and axial load greatly affect the deflection and temperature responses. The results obtained are verified and compared with the literature.

Comparison of sequential and circular scanning thermal fields and their influence on microstructure of Alnico alloy produced by laser powder bed fusion

Residual stress create deformations and stress in additive structures that lead to geometry deviations of created elements of 3D models and defects as pores and cracks that occur in construction process. Our work rests upon theoretical and experimental approach to the study. The main objective is to compare thermal fields with the microstructure of samples and to establish relationship between laser powder bed fusion (LPBF) modes and the structure of the samples to be created. 3D finite element method (FEM) is used for macroscopic modeling to assess the effect of thermal fields on the microstructure of Alnico alloy. Comparison of the temperature fields with the microstructure of samples made by LPBF showed that the type of scanning (both bidirectional and circular) had a strong influence on the distribution of the thermal fields and, accordingly, on the microstructure of the samples made by LPBF.

Silkworm-inspired electrohydrodynamic jet 3D printing of composite scaffold with ordered cell scale fibers for bone tissue engineering

The combination of biomimetic and 3D printing has created novel opportunities for the manufacture of 3D engineered materials. A sub-microscale E-Jet 3D printing method, inspired by the dehydration and protein enrichment process of silkworm, was developed to fabricate composite bone tissue scaffold with the characteristics of controllability, fast and inexpensive. By applying the resultant effects of thermal field and flow field to low viscous composite ink, the concentration gradient biopolymer ink was obtained near the needle tip, mimicking the advanced dehydration of natural spinning apparatus. After electrical shearing force were applied on concentration gradient ink, a stable and fine jet formed. Various printing modes (droplet, continuous fiber) and structure resolutions were achieved by adjusting local solvent evaporation. Thin film, high resolution 2D structures, high aspect ratio well-bonding 3D structures were fabricated. The printed result showed that a 100 μm-sized needle could be employed directly to print patterning down to 800 nm. The printed composite scaffold with controllability of fiber size and space has been proved the feasibility as a medium for bone tissue regeneration. It can be estimated that the novel biomimetic E-Jet 3D printing technique is a new and promising way for bone tissue repairing.

Photothermally boosted water splitting electrocatalysis by broadband solar harvesting nickel phosphide within a quasi-MOF

The thermal field effect effectively boosts water splitting electrocatalysis by lowering activation energy barriers and accelerating sluggish kinetics.

Effect of external electric field on diffusivity and flash sintering of 8YSZ: A molecular dynamics study

The atomistic structural modification and ionic diffusivity in 8YSZ at elevated temperature with the presence of an external electric field (E-field) were investigated by molecular dynamics (MD) simulations. As an example, a sufficiently large system of atomic configuration for a bi-crystal ∑5(310)/[001] grain boundary (GB) model was studied. MD results show that the E-field promotes the formation of Frenkel pair defects. Notably, some Zr ions diffuse out of GB regions at E-field>∼500-1000V/cm, resulting in an “avalanche” of cation vacancies at GBs and reduction of GB space charge. Consequently, the diffusivities of cations and anions are enhanced in the 8YSZ system with the presence of E-field. The atomistic level understanding of E-field induced structural modifications and ionic diffusivities provide an in-depth insight to unravel the flash sintering mechanisms of ionic ceramics, especially the coupled thermal-field effect during the flash sintering process.

Study on thermo-mechanical coupling characteristics of angle contact ball bearing with fix-position preload

PurposeUnder fix-position preload, the high rotation speed of the angular contact ball bearing exacerbates the frictional heat generation, which causes the increase of the bearing temperature and the thermal expansion. The high rotation speed also leads to the centrifugal expansion of the bearing. Under the thermal and centrifugal effect, the structural parameters of the bearing change, affecting the mechanical properties of the bearing. The mechanical properties of the bearing determine its heat generation mechanism and thermal boundary conditions. The purpose of this paper is to study the effect of centrifugal and thermal effects on the thermo-mechanical characteristics of an angular contact ball bearing with fix-position preload.Design/methodology/approachBecause of operating conditions, elastic deformation occurs between the ball and the raceway. Assuming that the surfaces of the ball and channel are absolutely smooth and the material is isotropic, quasi-static theory and thermal network method are used to establish the thermo-mechanical coupling model of the bearing, which is solved by Newton–Raphson iterative method.FindingsThe higher the rotation speed, the greater the influence of centrifugal and thermal effects on the bearing dynamic parameters, temperature rise and actual axial force. The calculation results show that the effects of thermal field on bearing dynamic parameters are more significant than the centrifugal effect. The temperature rise and actual axial force of the bearing are measured. Comparing the calculation and the experimental results, it is found that the temperature rise and the actual axial force of the bearing are closer to reality considering thermal and centrifugal effects.Originality/valueIn the past studies, the thermo-mechanical coupling characteristics research and experimental verification of angular contact ball bearing with fix-position preload are not concerned. Research findings of this paper provide theoretical guidance for spindle design.

Thermo-mechanical-dynamic coupling analysis on cold compressor rotor

Cold compressor rotor works in complex thermal filed, which endures huge temperature differences from room temperature to low-temperature. To study the effect of thermal field on deformation and dynamics of cold compressor rotor, a thermo-mechanical-dynamic coupling analysis is carried out by finite element software ANSYS. Firstly, a thermal analysis on the entire compressor is carried out by CFX and the temperature distribution is obtained. Secondly, a static structural analysis considering thermal loads and contact effect is performed. The thermal stress and deformation are obtained. Finally, a pre-stress modal analysis in working thermal field is carried out. The results show that: The axial distance between blade tip and thrust disc reduces by 117.41 μm. The first two natural frequencies of the cold compressor rotor have a slight improvement by less than 2.16% and higher order natural frequency is more sensitive to thermal effect.

Моделирование воздействия теплового поля пожара на заряды взрывчатых веществ в условиях лабораторного эксперимента

Моделирование воздействия теплового поля пожара на заряды взрывчатых веществ в условиях лабораторного эксперимента

Investigations on the laser color marking of TC4

In this work, we studied a technology of laser-induced coloration of TC4 by surface oxidation, the aim is to explore the effect of thermal field on the marking color which is applied to control the color in single operating variable. The controllable coloration of TC4 surface at laser heating in the air was conducted; the surface morphology and microstructure of the specimens were examined by optical microscopy (OM) and scanning electron microscopy (SEM), the reflectance spectra of the oxide film were measured by optics spectrometer, and the color images are fabricated finally.

On the electro-thermo-mechanical vibration characteristics of elastically restrained functionally graded nanobeams using differential transformation method

In this investigation, free vibration of piezoelectric functionally graded nanobeams in the presence of thermal field effects for various elastic boundary conditions is studied. Formulations are established in the framework of nonlocal elasticity theory of Eringen accompanied by Euler–Bernoulli beam theory. Further, the material characteristics are supposed to change through the thickness based on the power law. Discretization of the equations of motion and the relative boundary conditions are carried out by utilizing the differential transformation method. The presented model is validated through obtaining numerical results for conventional boundary conditions in comparison with the corresponding benchmark results. Finally, numerical results are given in details to demonstrate the impact of material gradient, nonlocal effect, piezoelectric voltage, along with temperature changes on vibration characteristic of piezoelectric functionally graded nanobeams, with various elastic boundary conditions.

Flow and thermal field effects on cycle-to-cycle variation of combustion: scale-resolving simulation in a spark ignited simplified engine configuration

Premixed, spark ignited combustion of lean methane at fuel to air equivalence ratio of 0.58 is numerically investigated in a piston-cylinder assembly. The simplified numerical configuration is tailored to emulate the intake, compression and spark ignition processes in engines. Large-eddy simulation is employed in the core flow along with a zonal hybrid wall treatment in near-wall regions. The G-equation level-set method is used to simulate flame propagation with a detailed chemistry based laminar flame speed correlation developed herein. The main numerical findings of this paper are as follows: (1) Despite the geometrical simplicity, the present set-up is shown to exhibit relatively large cycle-to-cycle variation for the three investigated cycles. (2) The local thermodynamics and fluid dynamic conditions around the spark close to the ignition location initiate the first discrepancies between the cycles. (3) These early variations are then amplified due to the subsequent differences in the early growth of flame area. (4) The cycle-to-cycle variation in the present set-up is shown to be largely a consequence of the local flow fluctuations close to the spark position and timing, while the results indicated a less dominating role of thermal stratification on cycle-to-cycle variation. (5) The asymmetric combustion behavior was explained to be a combined effect of burning rate and convection velocity, while convection velocity proved to be the major contributor. (6) Finally, a numerical test in the present model setup indicated large spark kernels being less prone to cycle-to-cycle variations than small kernels.

On wave propagation in a random conducting magneto-non-simple thermo-viscoelastic medium

• The waves in a random magneto-non-simple thermo-visco-elastic medium is studied. • The couple dispersion equation for longitudinal and transverse waves is analyzed. • The effect of thermal field to attenuate longitudinal waves is discussed. • Effect of magnetic conductivity is studied both theoretically and numerically. • Effect of visco-elasticity is discussed both analytically and numerically. The paper examines the problem of wave propagation in a random conducting magneto- non-simple thermo-viscoelastic medium. The medium has been assumed to be weakly conducting and weakly thermal. The thermomechanical coupling parameter and the conductivity are random functions, proportional to ε, with non-zero mean values, ε measuring the smallness of the scale of random fluctuation of inhomogeneities of the medium. The smooth perturbation technique enunciated by Keller (1964) has been employed to analyze the appropriate dispersion equation in non-simple thermoelastic medium. The longitudinal and transverse waves were discussed by using a particular form of thermomechanical coupling parameter representing the corresponding auto-correlation function. The effect of magnetic conductivity has been investigated. The phenomena of attenuation of waves and change of phase speed were discussed numerically in details.

Thermal-field effects on interface dynamics and microstructure selection during alloy directional solidification

We carry out three-dimensional phase-field simulations to model unique experimental observations of cellular and dendritic solidification structures formed under diffusive growth conditions in the DSI (Directional Solidification Insert) of the DECLIC (DEvice for the study of Critical LIquids and Crystallization) aboard the International Space Station. We had previously shown experimentally that complex thermal conditions affect the stationary position of the solid-liquid interface, as well as its dynamics of relaxation towards this stationary position over a finite time after the onset of sample pulling. Here, we discuss the effects of thermal diffusion within the adiabatic zone of the directional solidification setup and of latent heat release at the solid-liquid interface by means of quantitative phase-field simulations. Simulations and experiments characterize the entire evolution of the primary spacing of cellular/dendritic array structures from the onset of morphological instability to the establishment of the final steady-state spacing, including the transient coarsening regime associated with a sharp increase of spacing. Accounting for these thermal effects leads to a major improvement in the agreement between simulations and microgravity measurements for both the time of occurrence of morphological instability after the start of the experiment and the subsequent spacing evolution, which are not accurately predicted using the standard frozen temperature approximation.

Effect of Thermal Fields on the Structure of Corrosion-Resistant Steels Under Different Modes of Laser Treatment

The influence of temperature fields on the structure and properties of corrosion-resistant chromium steels under different modes of laser treatment is investigated. A model of heat transfer under laser impact on target is used to plot thermal fields and cycles and cooling rates. It is shown that the model used for computing thermal fields gives tentative geometric sizes of the fusion zones under laser treatment and selective laser fusion. The cooling rate is shown to have decisive influence on the structure of corrosion-resistant steels after laser treatment with surface fusion in devices for pulsed, continuous, and selective laser melting.

Hardening Roll Surface by Plasma Nitriding with Subsequent Hardfacing

The wear of the surface layer of rolls after ion nitriding in glow discharge, followed by a coating of TiN -TiAlN plasma arc are studied and simulated. stress-strain state of the material rolls under asymmetric rolling with ultra-high shear deformations is simulated. The effect of thermal fields, formed upon contact of the tool and a deformable sheet, the structure of aluminum alloys, are considered.