Increasing Vibration Frequency Research Articles

Insights into vibration-induced softening effect: A thermodynamic approach

This work investigates the wear behavior of nickel-based alloy during ultrasonic vibration-assisted machining (UVAM) by combining molecular dynamics simulation and thermodynamic theory. The research reveals that the tangential force exhibits periodic variations during UVAM, with a period half of the vibration period. Tangential force and total resistance decrease due to the synergistic effect of vibration-induced softening and thermal softening. A deeper understanding of the total resistance variation during the UVAM process can be achieved by the dimensionless resistance coefficient, which is difficult for the traditional friction coefficient (CoF). The Bejan number elucidates the contributions of the thermal softening and vibration-induced softening effects in the wear process. The findings highlight that the vibration-induced softening effect dominates when adjusting the amplitude for the active control of friction. In contrast, when the frequency is modulated, the contributions of vibration-induced softening and thermal softening effects are nearly equivalent. Furthermore, the wear mode transitions with increasing vibration frequency, characterized by the Strouhal number (Srw). The vibration wear mode attains dominance when Srw > 1.88. This work provides essential theoretical guidance to gain insight into the wear behavior in UVAM to optimize the machining performance.

Study on the vibration characteristics of angular contact ball bearing cage under rolling-sliding compound motion

Abstract Cage fracture has become the main form of bearing failure, the study of factors affecting the operating condition of the cage has an important impact on the operating performance and life of bearings. This study takes the angular contact ball bearing H7006C as the object of study and extracts the bearing inner ring and cage speed to analyze the bearing slip rate law. Extract cage vibration data and analyze cage vibration frequency characteristics using the VMD method. The effects of load and speed induced bearing slippage on the vibration characteristics of cages are investigated by varying the induced bearing slippage factors. The effects of load and speed induced bearing slip on the vibration characteristics of cages are investigated separately by varying the induced bearing slip factors. The study found that, at a fixed rotational speed, the bearing slip rate decreases as the axial load increases from 0 to 350N, and then stabilizes beyond 350N. Under fixed load conditions, the bearing slip rate increases with the rotational speed ranging from 1000 to 9000rpm. At a constant speed, the axial load is varied within 50 to 100N, resulting in vibration frequency increases of 72Hz, 43.5Hz, and 24Hz at 1000 rpm, 5000 rpm, and 9000 rpm, respectively. The characteristic frequency of cage vibration rises with increasing load, contributing to smoother cage operation. Nonetheless, as the rotational speed increases, the influence of axial load-induced slippage on the vibration characteristics of the cage diminishes gradually. At a set load of 500N, the amplitudes of the cage vibration eigenfrequencies at 1000rpm, 3000rpm, and 7000rpm are 0.0317, 0.0288, and 0.0174, respectively, decreasing with rotational speed. This indicates that the cage does not operate smoothly. The findings of this study serve as a theoretical foundation for detecting and diagnosing bearing slip and vibration issues in rotating machinery.

The experimental research of which different types of impact signals affect the bifurcation chaos behavior of three-degree-of-freedom collision system

Abstract Collision is a faulty behavior in mechanical equipment, which greatly affects the safety of equipment. In this paper, aiming at the collision failures that are prone to occur in mechanical equipment, the nonlinear fault collision behavior of a class of three-degree-of-freedom collision systems is studied. A three-degree-of-freedom piecewise non-smooth collision experiment platform system has been established to facilitate further analysis of the bifurcations and chaos inherent to the bearings system. This analysis is conducted through the use of Poincaré mapping on the collision plane. The excitation signals employed, which include sinusoidal, triangular, and rectangular signals, result in the emergence of specific types and orders of bifurcation behaviours within the system, as evidenced by the establishment of a Poincaré mapping at the collision surface, and this is observed to occur as the vibration frequency increases. The characteristics of impact signals generated by force sensors and the influence of impact signal type on the system are investigated. The nonlinear impact behavior of three-degree-of-freedom collision systems provides a reliable foundation for the design, fault diagnosis, and theoretical guidance of large-scale high-speed rotating machinery, as well as technical support for safe and stable operation of high-speed rotating machinery, which is essential for failure analysis and vibration reduction in equipment.

Lateral kinematic properties of offshore pipe piles embedded in saturated soil considering soil plug effect

AbstractThis study establishes a theoretical framework for analyzing the lateral oscillation of marine pipe piles. The additional mass model is introduced herein to consider the inertial fluctuation effect of the soil plug. Analytical mathematical methods are used to determine the complex impedance variation of the pile over a range of frequency effects. An investigation is performed to determine how the presence of soil plugs changes the lateral complex stiffness and natural frequency of pipe piles. Additionally, comparisons of the applicability of the plane strain model and continuous medium model have been conducted to enable the easy use of the theoretical model. The main conclusions can be drawn as (1) if the fluctuation inertia effect of the soil plug is not taken into consideration, the dynamic active length and the dynamic stiffness of the pipe pile will be underestimated; (2) for the soft soil, the plane strain model may give rise to substantial calculation errors attributed to them regardless of the vertical continuity of the soil, nevertheless, the calculation error decreases rapidly with the increase of soil shear modulus and vibration frequency.

Impact of acoustic wave propagation characteristics on aerodynamic damping of rotor blades in a transonic axial compressor

The aeroelastic stability associated with the acoustic wave propagation characteristics of transonic rotor blades was numerically investigated in this study. The influence of the vibration frequency on the aerodynamic damping of the first bending mode was primarily considered at different speeds, including both work and stall points. We found that the state of acoustic wave propagation associated with aeroelastic instability is closely related to rotational speed. At low speeds near stall points, the risk of aeroelastic instability is confined to the upstream cut-off state. However, at high speeds near stall points, aeroelastic instability may occur in both the downstream cut-off state and the acoustic wave propagation state of the upstream cut-off frequency, further expanding the range of the acoustic wave propagation state in which aeroelastic instability can arise. The research findings show that for suction surfaces, aerodynamic work is affected not only by acoustic wave propagation characteristics, but also by shock waves, radial flow, and reflux in the flow field. However, for pressure surfaces, the acoustic wave propagation characteristics play a significant role. When aeroelastic instability occurs, negative damping predominantly arises from the pressure surface. To investigate why lower-order modes are more prone to aeroelastic instability, specific simulations were conducted for the first bending and twisting modes under different operating conditions in the downstream cut-on state. When the vibration frequency significantly exceeds the downstream cut-off frequency, the blade phase is minimally influenced by acoustic wave propagation characteristics, and the rotor is aeroelastically stable in these phases. Simultaneously, there is an approximately linear increase in the unsteady pressure amplitude with increasing vibration frequency, and the aerodynamic work is predominantly influenced by the unsteady pressure amplitude.

Model test on the effects of shield machine cutterhead vibration on tunnel face stability in sandy ground

Face stability is one of the essential problems in shield tunneling. When tunneling in cobble stratum or mixed face ground conditions, significant cutting-induced cutterhead vibration would occur and affect the face stability. To reveal the mechanism and effect of vibration on the tunnel face stability, a transparent tunnel model with a movable vibration exciter was designed and a series of model tests were performed under different vibration magnitudes Aa and frequencies f. Meanwhile, particle image velocimetry was used to reveal the displacement field and the failure pattern of the tunnel face. The test results indicate that the cutting-induced vibration produces a significant reduction effect on the tunnel face stability, as expressed by the increase of the face support pressure and the failure zone when the vibration magnitude and frequency increase. Compared with the static unloading conditions, the width of the failure wedge Lwt increased by about 5.75% and 35.66% for the loose and dense sand, respectively, under dynamic unloading conditions (Aa = 0.2 g, f = 10 Hz). The limit support pressure increased up to about 0.20γD at a vibration of 0.3 g and 50 Hz, much larger than those of static conditions, which were about 0.08γD–0.09γD. An observable self-stabilizing arch can be formed in dense sand under static unloading conditions, while under dynamic unloading conditions, the long-time stable soil arch would not occur. The contributions of this paper could provide an insightful understanding of the effects of cutterhead vibration on tunnel face stability.

High Power Pulsed LED Driver for Vibration Measurements.

Vibration measurements pose specific experimental challenges to be faced. In particular, optical methods can be used to obtain full-field vibration information. In this scenario, stereo-camera systems can be developed to obtain 3D displacement measurements. As vibration frequency increases, the common approach is to reduce camera exposure time to avoid blurred images, which can lead to under-exposed images and data loss, as well as issues with the synchronization of the stereo pair. Both of these problems can be solved by using high-intensity light pulses, which can produce high-quality images and guarantee camera synchronization since data is saved by both cameras only during the short-time light pulse. To this extent, high-power Light-Emitting Diodes (LEDs) can be used, but even if the LED itself can have a fast response time, specific electronic drivers are needed to ensure the desired timing of the light pulse. In this paper, a circuit is specifically designed to achieve high-intensity short-time light pulses in the range of 1 µs. A prototype of the designed board was assembled and tested to check its capability to respect the specification. Three different measurement methods are proposed and validated to achieve short-time light pulse measurements: shunt voltage measurement, direct photodiode measurement with a low-cost sensor, and indirect pulse measurement through a low-frame-rate digital camera.

Effects of mechanical vibration on melting characteristics of latent thermal energy storage units using the dynamic mesh method

Phase change materials (PCM) based thermal energy storage technology is an efficient method to overcome the intermittency and instability of energy supply. The heat transfer performance of PCM can be enhanced by the mechanical vibration technique, but the potential mechanisms remain to be revealed. In this study, a dynamic mesh approach was proposed to numerically investigate the effect of mechanical vibrations on the heat transfer performance of PCM. The results indicate that the increase of the vibration frequency leads to the increase of the melting rate, with the vibration frequency increasing from 0 to 3π and 5π, the complete melting time of PCM under vertical vibration can be decreased by 2.21 % and 3.74 %, and complete melting time under horizontal vibration can be decreased by 34.35 %, and 44.39 %, which means that the horizontal vibration exhibits a superior heat transfer enhancement effect. However, it was also found that the energy utilization effect was decreased with the increase of vibration frequency through energy assessment. In addition, the vibration has both promoting and inhibiting effects on the phase transition process, which is related to the melting state and vibration phase. This work provides a novel approach to vibrational simulations and an important guide for practical applications of vibrational heat transfer enhancement.

Shear flow dynamics in vibrated granular materials: Analysis of viscosity transitions and non-Newtonian behaviors

In a continuous fluid, the presence of a velocity gradient perpendicular to the flow creates shear stress and shear rate between adjacent layers. The fluid's viscosity can be constant, depending only on temperature (Newtonian fluid), or vary with shear rate (non-Newtonian fluid). However, the viscosity characteristics of shear flows in discrete media, such as vibrated granular materials, remain insufficiently understood. This study experimentally investigated shear flows in vibrated granular media, exploring the relationship between shear stress, shear rate, and the impact of vibration conditions and particle number on granular viscosity. The findings indicate that the viscosity of sheared granular material transitions between dilatant and pseudoplastic non-Newtonian states with increasing vibration strength, shifts from pseudoplastic non-Newtonian fluid to Newtonian fluid with increasing vibration frequency, and remains consistently pseudoplastic non-Newtonian with increasing particle number. Two continuous non-Newtonian fluid models were utilized for comparison with our experimental results. Additionally, ascending curves of granular viscosity against granular temperature reveal gas-like flow characteristics in the sheared granular material, albeit with an abnormal descending viscosity–temperature relationship. These are attributed to volume expansion and oblique collisions in the vibrated granular medium. This study uncovers distinct viscosity properties in a discrete medium under shear flows, markedly different from those in continuous fluids, and highlights potential new applications for granular materials.

Development of a mathematical model for the prediction of drill quality in voice-activated ultrasonic vibration assisted drilling process.

In different industries, drilling quality play an important role in the success of operations by producing millions of quality drilled parts. The production of high-quality parts at the lowest possible cost to the manufacturer is the primary goal of contemporary process and assembly industries. To assess the quality index of drilling holes; circularity index and surface roughness are important metrics. In order to produce better drilled parts at lower prices, this study work attempts to determine the key process variables using voice acting modules to investigate the induced vibrations effects that have the greatest impact on surface roughness and circularity index in a vertical CNC drilling machine. In order to forecast the surface roughness and circularity index of drilled holes within a given operational range, a mathematical model has been proposed by adopting a coupled algorithm using design expert and statistical approach. As an experimental design technique, Response Surface Methodology with small central composite design is used to enable the evaluation of various process parameters related with machining and vibration parameters and their effects on surface roughness and circularity index. The created model is improved using statistical tools to ensure the best match to the experimental data. It has been observed with the increase of RPM and vibration frequency the surface roughness increases up to a certain limit and then decrease whereas with the increase feed the surface roughness increases. But in terms of circularity index with the increase of the process parameters the plotted graph trends under perturbation analysis shows the similar pattern CI decreases up to a certain limit and then increases.

RESEARCH ON THE RESPONSE MECHANISM OF CLAMPING POINT POSITION TO THE VIBRATION PROPAGATION CHARACTERISTICS OF WOODEN MATERIALS

Vibratory harvesting is to dislodge fruits by applying excitation force to fruit trees, so the vibration response characteristics of fruit trees are of great significance for vibratory forest and fruit harvesting machinery to realize efficient harvesting. The effects of different clamping points and vibration frequencies on vibration responsiveness and energy transfer in Broussonetia papyrifera branches are investigated in this study. The results show that the effects of different clamping point positions and vibration frequencies on the branch vibration response are mutual. The ideal distance between the clamping point position and the base of the main branch should be between 48% and 73% of the branch length, and the distance between the clamping point position and the base of the main branch increased with the increase of vibration frequency. This is because, when the clamping point is close to the base of the main branch, a higher excitation frequency increases the energy consumption at the base of the main branch, and the amount of ineffective vibration energy transferred to the base of the main branch also increases. Therefore, when the location of the clamping point is close to the base of the main branch, the suppression of high-frequency vibration at the base of the main branch is stronger than the suppression of low-frequency vibration. When the clamping point is located in the center of the branch, the overall response of the branch to vibration is better.

Machinability of submillimeter holes in ceramic matrix composites by high-frequency ultrasonic vibration-assisted drilling

Ceramic matrix composites (CMCs) are highly promising for the hot components of the high thrust-to-weight ratio aeroengines because of their excellent high-temperature resistance and lightweight. Submillimeter cooling holes are necessary cooling structures for the extremely high working temperature of a CMCs hot component. However, CMCs are hard, brittle, and poorly conductive. Current machining is trapped in severe tool wear, poor hole quality, and low efficiency in machining such small size holes. This paper proposes high-frequency ultrasonic vibration-assisted drilling (UAD) to machine submillimeter holes of CMCs. It reveals that increasing vibration frequency during machining can enlarge the cutting edge's effective rake angle and reduce drilling forces. Correspondingly, the tool life and hole quality are improved. The machinability of high-frequency UAD is rationalized by both theoretical analysis and experiments. Results show that compared with low-frequency UAD and Conventional drilling (CD), the drilling force in high-frequency UAD is reduced by 47 % and 81 %, the tool life is more than three times, and the hole quality is improved by 12 % and 35 %, respectively. Therefore, the study paved the way for the machining of submillimeter cooling holes in CMCs, which is important to the industrial application of CMCs.

Effects of train vibration load on the structure and hydraulic properties of soils

Investigating the impact of train-induced vibration loads on soil hydraulic properties, this study conducted experiments using a self-designed indoor soil seepage platform that incorporates vibration loads. The experiments were complemented with scanning electron microscopy to analyze the influence of train-induced vibration loads on soil hydraulic conductivity and its evolutionary characteristics under different vibration frequencies. The experimental results indicated that as the vibration frequency increases from no vibration (0 Hz) to 20 Hz, the time required for the soil volumetric moisture content to reach its peak and stabilize decreases rapidly. However, after the vibration frequency exceeds 20 Hz, the rate at which the time required for the volumetric moisture content to reach its peak and stabilize decreases slows down. Furthermore, the soil pore water pressure increases with the increase in vibration frequency. At a vibration frequency of 80 Hz, the peak value of pore water pressure increases by 105% compared to the non-vibration state, suggesting that higher vibration frequencies promote the development and acceleration of soil pore moisture migration. Additionally, as the vibration frequency increases, the soil hydraulic conductivity initially experiences a rapid increase, with a growth rate ranging from 40.1 to 47.4%. However, after the frequency exceeds 20 Hz, this growth rate significantly decreases, settling to only 18.6% to 7.8%. When the soil was subjected to a vibration load, the scanning electron microscopy test revealed alterations in its pore structure. Micropores and small pores transformed into macropores and mesopores. Additionally, the microstructural parameters indicated that vibration load decreased the complexity of soil pores, thereby speeding up the hydraulic conduction process. This, in turn, affected the hydraulic properties of the soil and established a relationship between pore structure complexity and soil hydraulic properties.

Studying particle transport characteristics in centrifugal pumps under external vibration using CFD-DEM simulation

Centrifugal pumps play a crucial role in deep-sea mining systems. In the marine environment, external vibrations induced by ocean currents and waves can impact the particle transport characteristics of centrifugal pumps in mining systems. CFD-DEM coupling simulations were conducted to simulate operating conditions with external vibration frequencies of 5, 10, and 15 Hz. The study reveals that in the suction chamber, with increasing vibration frequency, the dynamic number of particles decreased, and the percentage of particles with greater velocities than the fluid velocity increased. In the impeller channel, with increasing vibration frequency, the number of collisions among particles and pressure surface of the impeller decreased, and the average energy loss per collision increased. Therefore, external vibrations provide additional kinetic energy for particles, reduce the deposition effects of particles, and improve the pass-ability of particles. This paper can provide theory and engineering support for operation of deep-sea mining centrifugal pumps.

Characteristics of Acid Leaching and Vibration Coupling Desorption of Gas-Saturated Coking Coal.

Permeability is a key factor affecting efficient gas drainage from coal seams, and acidification and vibration shock are effective means to increase permeability in original low-permeability coal seams. To study the gas desorption characteristics of coking coal under the coupling effect of mining disturbance and acidification permeability enhancement, taking the coal seam of Shoushan No. 1 coal as the research object, a self-built adsorption-desorption vibration test platform was used. Acid leaching vibration coupling desorption experiments at vibration frequencies of 0, 30, 60, and 100 Hz were conducted on selected particle coals with particle sizes of 0.18-0.25 and 1-3 mm. The experimental results show that the gas desorption amount of particle coal with the same particle size first increases and then decreases with the increase of vibration frequency, among which the desorption effect is the best under 60 Hz vibration condition. Under the condition of fixed vibration frequency, the desorption amount, initial desorption velocity, and velocity attenuation coefficient of particle coal increase as the particle size decreases. Under the same particle size and vibration frequency conditions, the acid leaching and vibration of coal samples have a synergistic effect on gas desorption, which is manifested in the promotion of gas desorption on the outer surface of the coal sample and the surface of open macropores. The research can provide theoretical reference for coal seam acidification and permeability enhancement under the influence of mining disturbance.

Effect of ultrasonic vibration-assisted laser cladding frequency on the microstructure and properties of Fe-0.5C-15Cr alloy cladding layers

In this paper, Fe-0.5C-15Cr wear and corrosion resistant alloy coating was prepared on 3Cr13 stainless steel surface by ultrasonic vibration assisted laser cladding technology. The effects of ultrasonic vibration frequency on the microstructure, microhardness and corrosion resistance of the coating were studied. The results show that the length of the dendrites of the cladding layer decreased significantly after ultrasonic vibration is applied, the grains size is refined significantly, and the morphology of the grain boundary carbides changed from fishbone-like to short rods, when the vibration frequency is 20.2 kHz, the grain refinement is the most significant, and the orientation of the dendrites is obviously weakened. The hardness of the applied ultrasonic vibration specimens increased by 10–20 HV0.2 relative to the non-ultrasonic specimens, with the increase of vibration frequency, the hardness of the cladding layer firstly increased and then slightly decreased, and the peak appeared at 20.2 kHz. The coefficient of friction of the specimens when the ultrasonic frequency of 20.2 kHz is applied is lower than that of the specimens with non-ultrasonic frequency by 12.8 %, and the abrasive wear rate is reduced by 14.3 %. After ultrasonic vibration, the pitting potential of the cladding layer increases, the dimensional passivation current density decreased, the width of the passivation zone becomes wider, and the intergranular corrosion reactivation rate decreased, When the ultrasonic frequency is 20.2 kHz and 20.4 kHz, the pitting corrosion resistance and intergranular corrosion resistance of the cladding layer are significantly improved. This is because the cavitation effect, resonance effect and acoustic flow effect of ultrasonic vibration promote the non-uniform nucleation, refine the dendrites and intergranular carbides, and promote the redistribution of the corrosion-resistant element Cr in the in-grain martensite and grain boundary carbides, increasing the content of Cr in the matrix, and thus improving the wear resistance and corrosion resistance of the cladding layer.

Study of nanoindentation behavior of NiCrCoAl medium entropy alloys under indentation process using molecular dynamics

Abstract The mechanical properties and deformation behavior of CoCrNiAl medium entropy alloy (MEA) subjected to indentation by an indenter tooltip on the substrate are explored using molecular dynamics (MD) simulation. The study investigates the effects of alloy compositions, temperature variations, and ultra vibration (UV) on parameters, such as total force, shear strain, shear stress, hardness, reduced modulus, substrate temperature, phase transformation, dislocation length, and elastic recovery. The findings indicate that higher alloy compositions result in increased total force, hardness, and reduced modulus, with Ni-rich compositions demonstrating superior mechanical strength. Conversely, increasing alloy compositions lead to reduced von Mises stress (VMS), phase transformation, dislocation distribution, and dislocation length due to the larger atomic size of Ni compared to other primary elements. At elevated substrate temperatures, atoms exhibit larger vibration amplitudes and interatomic separations, leading to weaker atomic bonding and decreased contact force, rendering the substrate softer at higher temperatures. Additionally, higher initial substrate temperatures enhance atom kinetic energy and thermal vibrations, leading to reduced material hardness and increased VMS levels. Increasing vibration frequency enlarges the indentation area on the substrate’s surface, concentrating shear strain and VMS with vibration frequency. Higher vibration amplitude and frequency amplify force, shear strain, VMS, substrate temperature, and dislocation distribution. Conversely, lower vibration amplitude and frequency result in a smaller average elastic recovery ratio. Moreover, increased amplitude and frequency values yield an amorphous-dominated indentation region and increased proportions of hexagonal close-packed and body-centered cubic structures. Furthermore, this study also takes into account the evaluation of a material’s ability to recover elastically during the indentation process, which is a fundamental material property.

Mixing mechanism of power-law non-Newtonian fluids in resonant acoustic mixing

Resonant acoustic mixing (RAM) is a widely applied technology that utilizes low-frequency vertical harmonic vibration for fluid transfer and mixing. However, the current research on the mixing mechanism of RAM technology primarily focuses on the initial mixing stages, neglecting the subsequent turbulent transition. This lack of understanding hinders the further improvement of RAM technology. This paper aims to investigate the mixing mechanism of power-law non-Newtonian fluids (NNF) in RAM using the phase field model and the spectral analysis. The study focuses on understanding the facilitating effect of turbulent transition in mixing and explores the influence of the power-law index and the excitation parameter on the mixing characteristics. The results indicate that the flow field experiences Faraday instability due to the intense perturbation during transient mixing. This leads to the fluid mixing through the development of large-scale vortex to small-scale vortex. During this process, the frequency components of the flow field are distributed around the working frequency, demonstrating transient and broad frequency characteristics. The steady state then dissipates energy through the viscous dissipation of small-scale vortices and ultimately relies on the single-frequency components such as submultiples and multiples excited by the nonlinear effect to complete the mixing. The mixing effects of NNF and Newtonian fluids (NF) are essentially the same, but they consume energy in different ways. The mixing uniformity and mixing efficiency of NNF increase with increasing vibration acceleration and decrease with increasing vibration frequency. These findings provide new insights into the RAM mechanism of power-law NNF.

Molecular dynamics simulation of mechanical strengthening properties of SiC substrate covered with multilayer graphene

A large number of practices have shown that under the coupling influence of complex working conditions and frequent reciprocating contact, the surfaces of semiconductor devices in micro/nano electromechanical systems often produce adhesive wear, which is the essential reason resulting in short durability service life and declining contact mechanical properties for microelectronics semiconductor devices. However, graphene can significantly improve the interface properties of mechanical components and electronic components due to its excellent mechanical properties, such as high carrier concentration, good thermal conductivity, and low shear. Thus, the study of mechanical strengthening properties and plastic deformation of SiC material with covered multi-layer graphene in MEMS devices will play a significant role in improving the durability service life of MEMS device, and understanding its strengthening and toughening mechanism. Therefore, this paper studies and discusses the effects of stacking type and extreme service temperature with low and high levels on the contact mechanical properties (maximum load, hardness, Young modulus, contact stiffness), micro-structure evolution, contact mass, fold morphology, and total length of dislocation. The atomic-scale mechanism of enhanced mechanical properties of SiC material with multi-layer graphene is explained. The research shows that the damage to carbon-carbon bond at the maximum indentation depth will lead graphene to lose the excellent in-plane elastic deformation capability when the graphene stacking type is AB stacking, so that the maximum load-bearing capacity of the substrate covered by three layers of graphene will drop linearly. In addition, the mechanical property of SiC material coated with three graphene layers is twice that of pure SiC substrate, and the strengthening mechanism is mainly due to the increase of wrinkle caused by the increase of multilayer graphene loading, which causes the quality of contact between the SiC substrate and the virtual indenter to decrease, thus increasing the interface contact stiffness. The increase of the active temperature will trigger off the increase of the atomic vibration frequency, which will cause the number of interface contact atoms to increase greatly, and the interface contact stiffness will weaken, and finally lead the interface contact quality to improve, This is because the mechanical properties of SiC substrate coated with multilayer graphene will decrease approximately linearly with the extreme service from low temperature to high temperature. In addition, the stress concentration in the subsurface layer of SiC substrate can induce the evolution of its micro-structure, and the increase of the number of graphene layers on the substrate can effectively reduce the stress concentration distribution in the subsurface layer of the substrate.

Theoretical perspective for hydrostatic pressure responsive mechanism of room temperature phosphorescence molecules

Stimulus-responsive organic room temperature phosphorescence (RTP) materials are a class of materials that show emission property changes when subjected to diverse environmental stimuli. The change of molecular stacking modes and intermolecular interactions can result in mechanical stimulus-induced emission switching behaviour. The underlying mechanism of mechanoresponsive luminescent material is still unclear. Herein, based on density functional theory and time-dependent density functional theory calculations, the photophysical properties with response to hydrostatic pressure of RTP molecules in crystal are theoretically studied. Excited state dynamic processes are investigated by using quantum mechanics and molecular mechanics method coupled with thermal vibration correlation function method. Results show that the increase of pressure can blue-shift the RTP emissions which is mainly caused by the change of molecular conformation and the increase of bending vibration frequency. Under 2 Gpa, large spin–orbit coupling effect is determined, remarkable radiative and non-radiative decay processes are achieved. At 0.6 Gpa, a small non-radiative decay rate from T 1 to S 0 is obtained, high efficiency and long lifetime (more than 10 times the other pressures) are realised. Through further analysing the staking modes, reorganisation energies and SOC constants, relationships between molecular structures and RTP properties are determined, hydrostatic pressure responsive mechanism is revealed.