Effect Of Thermal Vibrations Research Articles

Evaluation of thermal performance and vibration effects on automotive headlights for selection of heat sink geometry

Evaluation of thermal performance and vibration effects on automotive headlights for selection of heat sink geometry

Toward better understanding of anharmonic structural, thermodynamic, and elastic properties of CaSiO3 perovskite under extreme conditions via statistical moment method

CaSiO3 perovskite is thought to be the third most abundant minerals in both the Earth’s transition zone and lower mantle but its structural, thermodynamic, and elastic properties have not been well characterized. In this work, for the first time, we apply the statistical moment method (SMM) to determine analytical expressions of thermoelastic quantities such as isothermal and adiabatic elastic moduli, Grüneisen parameter, Young’s and shear moduli, compression wave and shear velocities including the full anharmonic effects of thermal lattice vibrations of perovskite crystals with cubic structure. The theoretical results are applied for numerical calculations for cubic CaSiO3 perovskite, which is a strongly anharmonic system, at temperatures and pressures up to 4000 K and 180 GPa corresponding to the extreme conditions of the Earth’s lower mantle. Our results for temperature and pressure dependences of unit cell volume, thermal expansivity, isochoric and isobaric heat capacities, Grüneisen parameter, isothermal and adiabatic elastic moduli, Young’s and shear moduli, compression wave and shear velocities are important signs of anharmonic effects under high temperatures and pressures. The SMM results are compared with experiments and other calculations. The present study provides an effective theoretical approach for finding the structural, thermodynamic, and elastic properties of strongly anharmonic materials under extreme conditions.

Simulation and experimental study on laser cleaning of paint-rust mixed layer on a Q235 surface

In this paper, the theoretical model of laser cleaning of paint-rust mixed layer on the surface of a Q235 steel plate is established from the perspective of the laser ablation effect and the thermal vibration effect. The study simulates the temperature and stress field variations of the mixed layer under different laser power densities. The experiment recorded ablative fumes and vibrational spattering generated during the cleaning process and measured the micro-morphology and surface roughness of the cleaned specimens. The results show that the cleaning mechanism of the paint-rust mixed layer is dominated by the ablation effect at low laser power densities, while the combined effects of ablation and thermal vibration dominate at high laser power densities. However, excessive laser energy can damage the substrate. At a laser power density of 12.37×106W/cm2, the substrate surface is free from contamination residues and exhibits a bright, white, metallic gloss, which can be determined as the cleaning threshold for laser cleaning of paint-rust mixed layers. This study provides a valuable reference for the laser cleaning of mixed pollutants of paint and rust on metal surfaces.

Comparative study of infrared nanosecond laser surface paint removal for carbon fiber reinforced polymer and glass fiber reinforced polymer

Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) are widely used in aerospace applications due to their excellent properties. Green and efficient laser cleaning technology has a broad development prospect in the paint removal treatment of aerospace composites. However, the lack of theoretical analysis and guidance has prevented the industrial application of laser paint removal technology. An infrared nanosecond laser is used to clean the paint layer on the surface of CFRP and GFRP, and the best paint removal process parameters are explored. Surface micromorphology and 3D morphology of CFRP and GFRP after cleaning are observed to reveal the cleaning quality. The FTIR spectrum is used to verify the cleanliness of the paint layer. In addition, the contact angle and bonding force are tested, and the experimental results show that the surface wettability of both surfaces is enhanced after cleaning, and the paint adhesion of both surfaces is improved after repainting. Temperature monitoring, acoustic signal monitoring and high-speed photography monitoring are used to monitor the two cleaning processes respectively. The temperature, amplitude intensity, and plasma size of the two in the cleaning process are compared and analyzed. Based on the monitoring results, it is found that the cleaning mechanism of fiber-reinforced composites includes thermal ablation, vibration effect and plasma impact effect.

Effect of Thermal Response and Vibration on the Multicracked Rotor Immersed in a Fluid Medium Using Finite Element Method

A rotor shaft under high rotating speeds and heavy loading may establish fatigue damage in terms of cracks due to the long duration of the operation. Analysis of the size and location of the crack in the rotor shaft becomes very difficult, especially while the rotor shaft revolves in a viscous fluid medium. This research is an attempt to measure the vibration signature of a multicracked cantilever rotor shaft with additional mass at the free end in a different fluid medium at a finite region. The dynamic response of a cracked cantilever rotor shaft, with additional mass at the free end, partly immersed in air and diverse viscous mediums are measured experimentally. The existence of open cracks in the rotor shaft in both transverse directions, along the crack and perpendicular to the crack, was considered. The experimental analysis is performed to examine the variation in vibration response with varying the size of the rotor shaft, crack depth, and fluid properties. The finite element analysis technique is employed by using ANSYS to authenticate the vibration response of the same multicracked cantilever rotor shaft in air and different viscous mediums.

Spin Coherence and Spin Relaxation in Hybrid Organic-Inorganic Lead and Mixed Lead-Tin Perovskites.

Metal halide perovskites make up a promising class of materials for semiconductor spintronics. Here we report a systematic investigation of coherent spin precession, spin dephasing and spin relaxation of electrons and holes in two hybrid organic-inorganic perovskites MA0.3FA0.7PbI3 and MA0.3FA0.7Pb0.5Sn0.5I3 using time-resolved Faraday rotation spectroscopy. With applied in-plane magnetic fields, we observe robust Larmor spin precession of electrons and holes that persists for hundreds of picoseconds. The spin dephasing and relaxation processes are likely to be sensitive to the defect levels. Temperature-dependent measurements give further insights into the spin relaxation channels. The extracted electron Landé g-factors (3.75 and 4.36) are the biggest among the reported values in inorganic or hybrid perovskites. Both the electron and hole g-factors shift dramatically with temperature, which we propose to originate from thermal lattice vibration effects on the band structure. These results lay the foundation for further design and use of lead- and tin-based perovskites for spintronic applications.

Temperature effects on thermodynamic and mechanical properties of the InP, InAs and InSb compounds

The thermodynamic and mechanical properties of the zinc-blende indium pnictides InP, InAs and InSb compounds have been investigated thanks to the statistical moment method in statistical mechanics. We have derived the analytical expressions of thermal induced atomic displacement, lattice constant, elastic moduli (Young’s modulus, bulk modulus and shear modulus) and elastic constants of the zinc-blende compounds. The difference of temperature effects on mechanical properties of InSb comparing to InP and InAs compounds has been pointed out. We show that InSb is less affected by temperature while InP changes its mechanical properties from hardness to softness quickly when the temperature increases. The advancement of this method is that it has included the anharmonic effects of thermal lattice vibrations by taking into account the higher-order atomic displacement terms.

Origin of irregular X-ray mirage fringes from a bent, thin crystal.

The dynamical theory of diffraction is used to analyse irregular X-ray mirage interference fringes observed in Si220 X-ray reflection topography from a weakly bent, thin crystal due to gravity. The origin of the irregular fringes is attributed to the interference between mirage diffracted beams and a reflected beam from the back surface, which is a new type of interference fringe. The irregular fringes are reproduced by calculating the reflected intensities numerically. The effects of absorption and thermal vibration are quite important for the reproduction. The result shows that the interference fringes depend on the strain as well as the thickness of the crystal, which indicates that the fringes should be useful for analysing weak strain in a crystal as an application.

Effects of temperature on the electrical properties of samaria-doped ceria predicted with the statistical moment method

Samaria-doped ceria (SDC) is an important candidate electrolyte for use in solid oxide fuel cells, but the effect of lattice thermal vibrations on its electrical properties are unclear. In this study, the statistical moment method was employed to predict the temperature dependences of vacancy–dopant association, migration and activation energies, and ionic conductivity in four theoretical regimes comprising static, harmonic, semi-classical anharmonic, and quantum anharmonic regimes. The lattice thermal vibrations weakened vacancy–dopant associations and significantly inhibited vacancy hopping, and these effects were more pronounced as the temperature increased. The strongest vacancy–dopant associations and less convenient movement of oxygen vacancies could occur in the crystal lattice including anharmonic vibrations. Considerable enhancement of the ionic conductivity and a shift in the optimal dopant concentration toward higher values were found in the harmonic regime. Increasing the temperature also led to similar changes in the ionic conductivity. The maximum ion conductivity was governed by trapping and blocking effects, but also by lattice thermal vibrations. The results indicated the trivial influence of quantum effects in the anharmonic vibrations on the electrical properties. These findings provide a deeper understanding of the underlying atomistic mechanisms that determine the effects of temperature and lattice thermal vibrations on the electrical properties, and they may be beneficial for optimizing the ionic conductivity of SDC electrolytes.

Influence of thermal vibration impact on the strength characteristics of composite materials used in dentistry

The article discusses the evaluation of the effectiveness of the influence of thermal vibration effects on the bending strength and surface hardness of composite filling materials.The study was conducted on the basis of the Department of Therapeutic Dentistry of the Kuban State Medical University, as well as at the Krasnodar Instrument Plant “Cascade”. The samples under study were made according to the group affiliation from three different composite materials: Estelite Sigma Quick, Filtek Bulk Fill Posterior Restorative and DentLight. The bending strength was evaluated on the “MIP-10” testing machine of the company “NPK TECHMASH”. Determination of the surface hardness according to Vickers was carried out on the device PMT-3 of the company “LOMO”.According to laboratory studies, a statistically significant increase in flexural strength and surface hardness according to Vickers was determined for all samples of composite materials subjected to thermal vibration before polymerization.The data obtained indicate an increase in the strength characteristics of composite filling materials as a result of thermal vibration exposure before their polymerization, which increases the service life of composite fillings and reduces the risks of secondary caries formation after filling.

Metal-Insulator phase transition in thin films of vanadium dioxide doped with indium

The electrical conductivity of thin polycrystalline films V(1-x)InxO2 has been studied in a wide temperature range covering the regions of existence of both the metallic and insulator phases. It is shown that with increasing indium concentration, the temperature of the metal-insulator phase transition decreases, and the width of the temperature region of phase coexistence monotonically increases. To explain the temperature dependence of the electrical conductivity of the insulator phase V(1-x)InxO2, a model of hopping conductivity is applied, taking into account the effect of thermal vibrations of atoms on the resonance integral. Calculated the values of the parameter ε depend on the degree of doping of VO2. Keywords: phase transition, vanadium oxides, thin films, polaron, electrical conductivity.

Effect of thermal cycling and vibration on cracking in Sn-3.0Ag-0.5Cu solder bump

In present study, the effects of thermal cycling and vibration on cracking in Sn-3.0Ag-0.5Cu (SAC305) solder bump (interconnection between flip chip and printed circuit board) were studied. The thermal cycling test was set in 2 conditions as “TC180C” and “TC140C” that differed in temperature cycle i.e. 15 °C to 180 °C and 15 °C to 140 °C, respectively. While, the vibration test was also set in 2 conditions as “VB20G”and “VB05G” that differed in vibration acceleration ranges i.e. 20G and 5G respectively. Crack initiation and propagation in SAC305 solder bump were investigated by interrupted tests using scanning electron microscope. Results of the thermal cycling tests indicated that cracks initially developed at the edge of solder bump and subsequently propagated along solder/intermetallic compounds layer interface for TC180C condition. While crack propagated to bulk solder for TC140C. And crack initiation cycle differed between test conditions that were 40 cycles and 60 cycles for TC180C and TC140C, respectively. Crack initiation and propagation were accelerated by temperature range. The lower number of crack initiation cycle for TC180C condition, which was operated under a large temperature range, would be induced by higher thermal strain that could accelerate crack initiation in SAC305 solder bump. Results of the vibration tests showed that crack initiation and propagation were found only under VB20G condition, the number of crack initiation cycle was 12 cycles at X vibration axis. While any crack was not found for VB05G condition. The crack initiation and propagation in the SAC305 solder bump under VB20G condition would be induced by higher mechanical vibration acceleration. Whereas, damage accumulation in the SAC305 solder bump would not be induced by lower mechanical vibration acceleration under VB05G condition.

Stripping polyacrylate paint with a pulsed laser: process development and mechanism analysis

Laser stripping paint was studied with a pulsed laser in our work, which focuses on the effect of the process parameters, and on the understanding of the mechanism of this type of technology. Regarding the characterization of the stripping surface, surface morphology and surface roughness had been determined by a three-dimensional profilometer. The orthogonal optimization experiment had been carried out to optimize the process parameters. Combining experiments with simulation calculation, the laser stripping paint mechanisms were thoroughly investigated. Stripping paint with a pulsed laser is dominated by the thermal combustion effect, thermal stress and thermal vibration effect, laser plasma shock effect.

Red afterglow and luminescence arising from defects in CaS:Eu2+, Tm3+

CaS:Eu2+, Tm3+ is a phosphor known to emit a long afterglow of red emission (650 nm) when excited by blue light (450 nm). It shows a long afterglow time of 700 s for Eu = 0.05% and Tm = 2%. The mechanism of this afterglow is investigated using time-resolved fluorescence (TR-F) spectroscopy from the nanosecond to millisecond region. At room temperature, it is not possible to investigate shallow levels because of the effects of thermal vibrations. The mechanism of the emission characteristics at room temperature would be affected by these levels that can be observed only at low temperatures. Therefore, the samples are cooled to 15 K for the TR-F measurements. The host material CaS emits blue light (420 nm) arising from sulfur defects, and the typical decay time is measured to be 6 ms. This blue emission becomes stronger when Tm3+ is doped. Furthermore, the doped Eu ions emit a broad red spectrum at 650 nm originating from the Eu2+-specific 4f65d1–4f7 transition. When the excitation is ceased, the red emission decays with a fast time constant of 0.6 μs. This value is a typical decay time for Eu2+. This red emission has multiple decay time constants, and a component with a decay time of 6 ms appears. This 6 ms decay time is the same as that of the blue emission from the sulfur defects, which have an important role on the red afterglow.

Stable and reversible phase change performance of TiO2 coated VO2 nano-columns: Experiments and theoretical analysis

We have fabricated VO2 nano-columns (NCs) on the aluminized quartz glass substrates using glancing angle deposition (GLAD) technique inside the electron beam (e-beam) evaporator chamber. An e-beam deposited TiO2 thin cap-layer has been introduced on the top of the VO2 NCs to protect VO2 phase which is usually unstable and turns to stable higher oxidation state, i.e., V2O5. The X-ray diffraction (XRD) analysis of TiO2 thin film (TF) coated VO2 NCs shows the presence of VO2 phases along with the other oxidation states. The Fourier-Transform-Infrared-Spectroscopy (FTIR) confirms the presence of Ti–O–V, V–O vibrations bands in VO2 NCs/TiO2 TF samples. The VO2 NCs/TiO2 TF sample possesses a sharp drop (~103 order) in resistance at the transition temperature (Tc) ~66 °C. This sample also shows a stable semiconducting to metallic phase (vice versa as well) transition temperature (PTT) hysteresis even after one month which ensures the stable performance in terms of phase transition characteristic. Small-radius polaron model (SRPM) is used to calculate the sheet resistance of the VO2 NCs, where we consider the effect of thermal lattice vibrations on the overlap integral of the crystal atoms. The temperature dependency of constants A and ε have been observed uniquely. The Fermi-Dirac (F-D), Migdal distribution (MD) model have been taken into account for the first time to calculate the conduction band carrier density of VO2 NCs and ratio of the resistance in the semiconducting (RS), metallic phase (RM) is also calculated. The calculated electron concentration (nc) is 3.1 × 1019 cm-3 at the point of PTT (66 °C).

Exchange coupling constants at finite temperature

An approach to account for the effect of thermal lattice vibrations when calculating exchange coupling parameters is presented on the basis of the Korringa-Kohn-Rostoker Green function method making use of the alloy analogy model. Using several representative systems, it is shown that depending on the material the effect of thermal lattice vibrations can have a significant impact on the isotropic exchange as well as the Dzyaloshinskii-Moriya interactions (DMI). This should lead in turn to an additional contribution to the temperature dependence of the magnetic properties of solids, which cannot be neglected in the general case. As an example, we discuss such an influence on the critical temperature of various magnetic phase transitions. In particular, in the case of skyrmion hosting materials, a strong impact of lattice vibrations on the DMI is an additional source for the temperature dependent skyrmion size and stability, which should be taken into consideration. The present approach gives also access to features of magnetic properties that are associated with static atomic displacements as, for example, in random high-entropy alloys.

Theory for High‐Angular‐Resolution Photoelectron Holograms Considering the Inelastic Mean Free Path and the Formation Mechanism of Quasi‐Kikuchi Band

In recent years, highly accurate measurements of photoelectron holograms have become possible through the development of electron energy analyzers with an energy range of 300–1000 eV. Effects of the inelastic mean free path (IMFP) and thermal vibration became apparent in the hologram pattern. For example, the quasi‐Kikuchi band is clearly observed, which cannot be explained by conventional multiple scattering theories. Herein, the theory of photoelectron holograms is summarized, considering the inelastic scattering (IES) and thermal vibration effects. Furthermore, the simulated hologram is compared with a diamond hologram measured at a kinetic energy of 563.4 eV. It is also shown that the formation mechanism of the quasi‐Kikuchi band differs from that of the normal Kikuchi band.

Interaction of dopants and functional groups adsorbed on the carbon fullerenes: Computational study

Abstract We apply density functional theory to study the effective interaction between dopant atoms (B, N, Si, P) and functional groups (H, F, Cl, OH) on the surface of carbon fullerenes. Both dopant atoms and functional groups strongly interact through the carbon cage even in diametrically opposite positions. Interaction energies distribute in a wide range from 0.1 to 2 eV and non-monotonically depend on fullerene size and distance between dopants or functional groups. Such interaction cannot be described as a simple Coulomb repulsion or sum of dopants binding energies and cage strain energy. We identify some general trends in relative positions of dopants or functional groups in low-energy isomers. Para position of two functional groups is the most feasible for C60 and larger cages. For lower fullerenes, ortho or other spaced positions may be more preferable. The interaction of foreign atoms embedded into the carbon cages is more complicated. The best relative positions intricately depend on the cage size and chemical nature of dopants. As a rule, ortho and para locations are feasible for C60 and larger cages. However, some exceptions are observed. The effect of thermal vibrations on the considered interactions in doped or functionalized fullerenes is negligible in the temperature range from 300 to 1000 K.

Laser cleaning performance and mechanism in stripping of Polyacrylate resin paint

Laser cleaning is a high-efficient, newly emerging and environmentally friendly technology. Removing paint from aircraft skin is an important application of this technology. This paper describes how a high repetition frequency fiber laser of 1064 nm was used to remove the 50-μm-thick polyacrylic resin primer paint layer on an aircraft skin (LY12 aluminum alloy plate). Experiments were conducted to study the cleaning performance by varying process parameters such as scanning speed, pulse frequency, scanning line interval and laser power. This paper found that the quality and efficiency could be improved by selecting the appropriate combination of scanning speed and pulse frequency. The amount of paint stripped by the single pulsed laser increased with an increase in laser power. By analyzing the cleaned surface and the particles collected from the process, we propose three different kinds of possible stripping mechanisms: combustion reaction, thermal stress vibration effect and plasma shock effect.

Suppression of conductance fluctuation of disordered carbon nanotubes caused by thermal atomic vibration

We have numerically succeeded in evaluating the conductance fluctuations of nitrogen-doped single-walled carbon nanotubes (N-SWCNTs), as a typical example of disordered quasi-one-dimensional materials, including the effect of thermal atomic vibration from the viewpoint of conductance histograms. We show that conductance histograms even of N-SWCNTs with over 100 nm length are described by a log-normal distribution function at tens of kelvins, which suggests that the N-SWCNTs shows localization at low temperature. On the other hand, conductance of the N-SWCNT are no longer described by a log-normal distribution function at hundreds of kelvins. Instead, the histograms are described by a Gaussian distribution function, which indicates that the N-SWCNTs definitely deviate from localization regime. In addition, we confirm that the conductance fluctuations of the N-SWCNTs are also suppressed as the temperature increases because of delocalization due to quantum decoherence caused by thermal atomic vibration.