Small Thickness Ratio Research Articles

Lubrication condition monitoring of journal bearings in diesel engine based on thermoelectricity

There is still a lack of effective lubrication condition monitoring methods in the field of diesel engines. The paper proposes a novel thermoelectric approach to divide the lubrication state of bearings. First, the generation mechanism of thermoelectric potential on bearings is clarified. Then, both experimental and simulation studies are done, and a strong correlation between lubrication and thermoelectric potential is shown. The film thickness and temperature are further confirmed as significant factors influencing thermoelectric potential. Generally, the thermoelectric potential increases with temperature. However, a small film thickness ratio (when the film thickness ratio is less than 4) will suppress the thermoelectric potential. Three typical lubrication states of bearings are distinguished through thermoelectric potential and supported by the Stribeck curve results. Moreover, the significant influence of lubrication on the bearing is confirmed through the analysis of surface morphology and composition.

Lamellar aspect-ratio and thickness-dependent strength-ductility synergy in pure nickel during in-situ micro-tensile loading

In order to overcome the trade-off between strength and ductility in traditional metallic materials, the gradient lamellar structure was fabricated through an ultrasound-aided deep rolling technique in pure Ni with high stacking fault energy after heat treatment. The gradient lamellar Ni was successively divided into three regions. In-situ micro-tensile tests were performed in different regions to reveal the corresponding microscopic mechanical behaviors. Microscopic characterization techniques were adopted to explore the effects of microstructural parameters and defects on mechanical properties. This work demonstrates that the micro-tensile sample with small lamellar thickness and large aspect ratio possesses excellent strength and ductility when the loading direction is parallel to the long side of lamellar grain boundaries. The finding is helpful to the design of metallic material microstructure with superior comprehensive properties. On one hand, the reason for high strength is that the strength increases with the decrease of lamellar thickness according to the Hall-Petch effect. Besides, initial dislocation density also participates in the strengthening mechanism. On the other hand, the deformation mechanisms include dislocation slip, grain rotation, and the effects of grain boundaries on dislocations, jointly contributing to good ductility.

Mechanical performance of multi-cell thin-walled tubes under static and dynamic axial loading

In this paper, the mechanical performance of multi-cell thin-walled tubes with small aspect ratio and diameter thickness ratio and the same weight was studied theoretically, numerically and experimentally. The lightweight devices impact test was designed to get a higher velocity than the drop-weight crashing test or impacting trolley test and the experimental tests were carried out under static and dynamic axial loading. The theoretical mean crushing force (MCF) was obtained according to the simplified super folding element (SSFE) theory, and structural coefficient of the homoeomorphic structure was obtained. Then the numerical models were conducted to investigate the strain hardening on the matrix material. The results showed that the dynamic amplification factor (DAF) for the multi-cell tube to predict the MCF precisely could be ignored at or below the impact velocity 50 m/s. In addition, the experimental results indicated the initial peak forces (IPF) of the tubes were sensitive to the total length of all flanges of the cross-section. The multi-cell partitioning could improve the energy absorption of the thin-walled structures and relieve the increment of the dynamic axial loads. The energy absorption efficiency of multi-cell structure with circular tube is higher than that of multi-cell structure with square tube. The numerical model indicated the dynamic axial impact could lead to the strain hardening of the matrix material. The significant strain hardening could lead to more increment of the force.

A Unified Asymptotic Theory of Supersonic, Transonic, and Hypersonic Far Fields

The problems of steady, inviscid, isentropic, irrotational supersonic plane flow passing a body with a small thickness ratio was solved by the linearized theory, which is a first approximation at and near the surface but fails at far fields from the body. Such a problem with far fields was solved by W.D. Hayes’ “pseudo-transonic” nonlinear theory in 1954. This far field small disturbance theory is reexamined in this study first by using asymptotic expansion theory. A systematic approach is adopted to obtain the nonlinear Burgers’ equation for supersonic far fields. We also use the similarity method to solve this boundary value problem (BVP) of the inviscid Burgers’ equation and obtain the nonlinear flow patterns, including the jump condition for the shock wave. Secondly, the transonic and hypersonic far field equations were obtained from the supersonic Burgers’ equation by stretching the coordinate in the y direction and considering an expansion of the freestream Mach number in terms of the transonic and hypersonic similarity parameters. The mathematical structures of the far fields of the supersonic, transonic, and hypersonic flows are unified to be the same. The similar far field flow patterns including the shock positions of a parabolic airfoil for the supersonic, transonic, and hypersonic flow regimes are exemplified and discussed.

Developing Thermal Regulating and Electromagnetic Shielding Nacre-Inspired Graphene-Conjugated Conducting Polymer Film via Apparent Wiedemann-Franz Law.

In this work, we observed size-dependent behavior of filler on both the thermal and electrical conductivities of nacre-like graphene-conjugated conducting polymer films and demonstrated the display of apparent Wiedemann-Franz law and tunability of Lorenz constant in such films. The maximum thermal and electrical conductivities of as-fabricated films can reach over 73 W·m-1·K-1 and 1200 S·cm-1, respectively. Furthermore, the maximum value of electromagnetic interference shielding reaches 54 dB with SSE/t over 16000 dB·cm2·g-1. These films can not only show high-quality electromagnetic interference shielding performance with small thickness and low filler ratio but also achieve simultaneous thermal management during electromagnetic shielding. The findings in this work offer new insight into designing flexible graphene-conjugated polymers with customizable thermal and electrical properties in the broad fields of thermal management systems, electromagnetic defense systems, and flexible electronic systems.

Dynamic enhancement mechanism of energy absorption of multi-cell thin-walled tube

In order to study dynamic response of multi-cell thin-wall tubes with small aspect ratio and diameter thickness ratio under high velocity impacts of lightweight devices, the mass block impact tests were performed on three types of thin-walled tubes including circular tube (CirT), multi-cell tube (MT) and polyurethane foam (PUR) filled multi-cell tube (FMT). The dynamic enhancement mechanism of collapse force of MTs was discussed based on numerical simulation and deformation pattern analysis of MTs and FMTs. The results indicated that the dynamic enhancement coefficient of mean crushing force (MCF) was 1.0–1.17 and 1.12–1.3 for MTs and FMTs, respectively. The dynamic enhancement of EA was 24–29.2% for CirTs, 0–14.7% for MTs and 9.42–21.16% for FMTs, compared to the quasi-static compression. The multi-cellularization tended to degenerate the sensitivity of collapse force of MTs to the loading rate, while the foam filling increased the rate sensitivity. With the impact velocity increasing from 30 to 70 m/s, the folding half-wavelength of MTs and FMTs decreased about 2–5 mm. Also, the effective stress level of the MTs increased with the impact velocity and the material strain hardening mechanism. The folding pattern of MTs could be improved by foam filling and enhancing the impact velocity.

Accurate determination of the stiffness properties for an elastic interface under peeling conditions between homogeneous materials

In this paper, several models for analysing peeling tests are considered, including numerical models based on FEM, semi-analytical approaches, and beam models including an elastic interface. Results show that none of the beam models including an elastic interface represents correctly the mixity at the crack tip for small thickness ratios. To avoid this inconsistency, the problem is studied in the framework of Fracture Mechanics, concluding that the stiffness in both directions must fulfil a material-dependent relationship (besides, the tangential stiffness is independent of the shear modulus). The new proposed interface stiffnesses depict accurately both the mixed-mode conditions at the crack tip and the load versus displacement evolution for the full range of thickness ratios.

Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength.

Preventing nugget shifting in joining of dissimilar steels via resistance element welding: a numerical simulation

Joining the advanced high-strength steels and conventional steels is a critical issue for the manufacturing of lightweight vehicles. Resistance element welding (REW) is an emerging joining method for dissimilar metals and alloys by applying an auxiliary rivet-like resistance element in resistance spot welding (RSW). In this study, an electrical-thermal-mechanical coupled REW model for high-strength dual-phase (DP) steel and Q235 steel was developed by considering contact resistances as functions of temperature and surface contacting area. The results show that the welding element in REW serves to concentrate the current flow and thus Joule heat generation at the faying interface between the element and workpiece. For welding DP600 and Q235 workpieces with a small thickness ratio (≤0.4) or a high electrical resistivity ratio (≥3), REW could effectively mitigate nugget shifting between workpieces and reducing the thermal excursion to the electrode compared to RSW. Adding well-designed insulation layers in REW could further concentrate the current within the welding element, and enables a large-sized nugget at a lower current. This study is significant because it provides a better understanding of the nugget development under the electrical-thermal-mechanical interaction at interfacial contacts in REW and contributes to its further advance.

Transonic flows of single-phase supercritical fluids over thin airfoils

Abstract

Regional Associations of Cortical Thickness With Gait Variability: The Tasmanian Study of Cognition and Gait

Gait variability is a marker of cognitive decline. However, there is limited understanding of the cortical regions associated with gait variability. We examined associations between regional cortical thickness and gait variability in a population-based sample of older people without dementia. Participants (n=350, mean age 71.9±7.1) were randomly selected from the electoral roll. Variability in step time, step length, step width and double support time (DST) were calculated as the standard deviation of each measure, obtained from the GAITRite walkway. MRI scans were processed through FreeSurfer to obtain cortical thickness of 68 regions. Bayesian regression was used to determine regional associations of mean cortical thickness and thickness ratio (regional thickness/overall mean thickness) with gait variability. Smaller overall cortical thickness was only associated with greater step width and step time variability. Smaller mean thickness in widespread regions important for sensory, cognitive and motor functions were associated with greater step width and step time variability. In contrast, smaller thickness in a few frontal and temporal regions were associated with DST variability and the right cuneus was associated with step length variability. Smaller thickness ratio in frontal and temporal regions important for motor planning, execution and sensory function and, greater thickness ratio in the anterior cingulate was associated with greater variability in all measures. Examining individual cortical regions is important in understanding the relationship between gray matter and gait variability. Cortical thickness ratio highlights that smaller regional thickness relative to global thickness may be important for the consistency of gait.

Synthesis of thin alpha alumina platelets with a large aspect ratio

Since α-Al2O3 platelets with small thickness and large aspect ratio are needed in various applications, it is of great importance to control their morphology. In the present work, we successfully fabricated α-Al2O3 platelets with small average thickness below 100 nm and large average aspect ratio above 100 by molten-salt method, using Al2(SO4)3 as the raw material, eutectic mixtures of Na2SO4 and K2SO4 as the molten salt as well as TiO2 and SiO2 as the co-dopants. The effects of calcination temperature, seeds amount and seeds morphology on the final morphology of α-Al2O3 platelets were investigated. The growth mechanism of the α-Al2O3 platelets in molten salt was also discussed. A new growth mechanism of α-Al2O3 platelets in molten salt has been proposed, which is different from previous mechanism but can explain the two different phenomena caused by seeds with different sizes and quantity.

Onset of thermal convection in a superposed fluid-porous layer subjected to high-frequency longitudinal vibration in weightlessness

The onset of thermal vibrational convection in a fluid layer overlaying a fluid-saturated porous layer is studied in zero gravity. A thermal gradient is imposed transverse to the layers. The two-layer system performs high-frequency small-amplitude oscillations perpendicular to the thermal gradient. We solve a linear stability problem with respect to the fluid quasi-equilibrium state. The basic closed-looped oscillatory flow with zero average velocity characterizes the quasi-equilibrium state. The average roll convection is generated if the Rayleigh number exceeds its threshold value. The bimodal marginal stability curves are revealed at different ratios of the fluid layer thickness to that of the porous layer. They are somewhat similar to the curves first obtained by Chen and Chen for the onset of thermal convection in a superposed fluid-porous layer in a gravity field. We find that short-wave convection replaces the long-wave one with an increase in the ratio of layer thicknesses. The transition is accompanied by a jump-wise increase in the wave number of the most dangerous convective rolls. However, the critical wave number of the vibrational convection rolls can change by several orders of magnitude in contrast to that of the gravitational convection rolls. So, one can have super short-wave convection in zero gravity. A value of the instability threshold varies non-monotonically. The convection onset delays rather weakly at small thickness ratios. On the contrary, sufficiently high thickness ratios make the convection onset speed up strongly.

Regional Associations of Cortical Thickness With Gait Variability-The Tasmanian Study of Cognition and Gait.

Gait variability is a marker of cognitive decline. However, there is limited understanding of the cortical regions associated with gait variability. We examined associations between regional cortical thickness and gait variability in a population-based sample of older people without dementia. Participants (n = 350, mean age 71.9 ± 7.1) were randomly selected from the electoral roll. Variability in step time, step length, step width, and double support time (DST) were calculated as the standard deviation of each measure, obtained from the GAITRite walkway. Magnetic resonance imaging (MRI) scans were processed through FreeSurfer to obtain cortical thickness of 68 regions. Bayesian regression was used to determine regional associations of mean cortical thickness and thickness ratio (regional thickness/overall mean thickness) with gait variability. Smaller global cortical thickness was only associated with greater step width and step time variability. Smaller mean thickness in widespread regions important for sensory, cognitive, and motor functions were associated with greater step width and step time variability. In contrast, smaller thickness in a few frontal and temporal regions were associated with DST variability and the right cuneus was associated with step length variability. Smaller thickness ratio in frontal and temporal regions important for motor planning, execution, and sensory function and greater thickness ratio in the anterior cingulate was associated with greater variability in all measures. Examining individual cortical regions is important in understanding the relationship between gray matter and gait variability. Cortical thickness ratio highlights that smaller regional thickness relative to global thickness may be important for the consistency of gait.

Influence of structural parameters on wavy-tilt-dam hydrodynamic mechanical seal performance in reactor coolant pump

This work analyzes the operation conditions of the wavy-tilt-dam (WTD) mechanical seal under different structural parameters using the DNS method. The pressure difference within the liquid film is considered due to the complicated constructor of the WTD mechanical seal. The effects of the main structural parameters on the mechanical seal are studied, including the film thickness, taper, dam-width ratio, and waviness amplitude. Numerical results show that the increase of base film thickness will increase the leakage rate and decrease the opening force. The larger taper will lead to a higher leakage rate and opening force. As the taper increases, the stiffness increases first and then decreases. As the dam-width ratio increases, the leakage rate, the opening force, and the stiffness will increase correspondingly. The waviness amplitude has a small effect on these three performance parameters. Besides, the comparisons between the Reynolds approximation and the DNS technique show that the Reynolds approximation can be applied to analyze the leakage rate under different thicknesses, small tapers, and large dam-width ratios. The opening force under small thickness, different tapers, and different dam-width ratios can also be considered using the Reynolds approximation. To ensure the safe and stable operation of RCP, the optimal structural parameters can be set as taper β = 600 μrad, dam-width ratio ϖ = 0.2, waviness amplitude α = 0.8, and wavenumber k = 9.

A 30-nm thick integrated hafnium zirconium oxide nano-electro-mechanical membrane resonator

This paper reports a 30 nm-thick integrated nano-electro-mechanical resonator based on atomically engineered ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2) film. A 10 nm-thick Hf0.5Zr0.5O2 layer is atomically engineered through capping with 10 nm-thick titanium nitride (TiN) layer and rapid thermal annealing to promote the orthorhombic crystal phase with strong ferroelectric properties. The resulting metal-ferroelectric-metal (MFM) membrane is then patterned to create an integrated nano-electro-mechanical resonator with an overall thickness of 30 nm and a planar-to-vertical aspect ratio exceeding 104:1. Benefiting from large electrostrictive effects in ferroelectric Hf0.5Zr0.5O2, the 30 nm-thick nanomechanical resonator is excited into flexural resonance at 195 kHz with a very large vibration amplitude of ∼100 nm. The transmission response of the nano-electro-mechanical resonator is extracted, using a two-port apodization of the TiN electrodes, showing quality factors (Q) of 15 and 3300 at atmospheric and 10−7 Torr ambient pressures, respectively. Finally, the structural robustness of the MFM nano-membrane is explored through the application of a ∼24 μm deflection, using a point-force by a micro-probe, highlighting the extended elasticity despite the small thickness and ultra-high aspect ratio. The atomic-level thickness, fully integrated operation, high Q, and structural robustness of the Hf0.5Zr0.5O2-based nano-membrane resonator promise its potential for the realization of highly integrated transducers for chip-scale classical and quantum information processing and sensing applications.

Wind tunnel investigation of autorotation of plate: The effects of geometry, Reynolds number and rotation direction

This paper presents a wind tunnel investigation of the autorotation of plates. The effects of geometry, the Reynolds number, and rotation direction on the aerodynamics of the plate, including the rotation rate, lift and drag coefficient, are analyzed. The autorotation rate of plate with smaller aspect ratio is more sensitive to the thickness ratio, whereas when the aspect ratio is larger than 1.5, its effect on the sensitivity of the autorotation rate to the thickness ratio can be ignored. The lift coefficient of plate with larger aspect ratio and smaller thickness ratio is larger when aspect ratio is smaller than 2. Otherwise, the lift coefficient increases first and then decreases with an increase in the thickness ratio. Meanwhile, the lift coefficient of plate decreases as Reynolds number increases, and the relationship between the lift coefficient and the Reynolds number is close to a straight line in logarithmic coordinate. Moreover, the clockwise rotation direction leading to upward lift was found to have a higher absolute value of the lift coefficient than the counterclockwise direction leading to downward lift, especially at low rotation rates. However, the drag coefficient, which fluctuates around a constant of 1.3, is independent of such factors.

Variable thickness rolling of plates thick in the middle and thin on the sides

Abstract Rolled profile strips (RPS) are poorly understood. In our previous work, only the type of rolled profile strips that are thick in both sides and thin in the middle (TM-type RPS) with a small thickness ratio of 1:1.3 were obtained by integrating the bending-spreading rolling (BSR) and the flattening rolling (FR). According to the process characteristics, the new process can be called variable thickness rolling (VTR). In this paper, experiments were performed to obtain RPSs that are thick in the middle and thin in both sides (TS-type RPS) with a thickness ratio of 1:1.8. The comparison between the influences of U-shaped and S-shaped roll design on the rolling results is carried out and the influences of different roll design parameters on thickness distribution, thickness uniformity, and the shape of the workpiece are discussed. The comparisons of stress and strain state of BSR process among different types of RPSs are conducted, and the forming characteristics of them are analyzed. Tension and the position of the target thinned areas have great influences on the results. The experimental results prove that the VTR technology can be well applied to TM-type as well as TS-type RPS. Through this work, varied RPSs with a thickness ratio from 1:1.3 to 1:1.8 can be produced, which contributes significantly to tailored blanks and lightweight development. In addition, a 3D RPS sample has also been made.

Comparing rib cortical thickness measurements from computed tomography (CT) and Micro-CT

BackgroundThe objective of this study was to compare cortical thickness of rib specimens scanned with clinical computed tomography (clinical-CT) at 0.5 and 1.0 mm slice thickness versus micro-CT at 0.05 mm slice thickness. Cortical thickness variation and accuracy was explored by anatomical region (anterior vs. lateral) and cross-sectional quadrants (superior, interior, inferior, and exterior). MethodsA validated cortical thickness algorithm was applied to clinical-CT and micro-CT scans of 17 rib specimens from six male post mortem human subjects aged 42–81 years. Each rib specimen was segmented and the thickness measurements were partitioned into cross-sectional quadrants in the anterior and lateral regions of the rib. Within each rib quadrant, the following were calculated: average thickness ± standard deviation, mean thickness difference between clinical-CT and micro-CT, and a thickness ratio between clinical-CT and micro-CT. Correlations from linear regression and paired-t tests were determined for paired clinical-CT and micro-CT results. ResultsOn average, the 0.5 mm clinical-CT underestimated the micro-CT thickness by 0.005 mm, while the 1.0 mm clinical-CT overestimated the micro-CT thickness by 0.149 mm. Thickness derived from 0.5 mm clinical-CT showed greater significant linear correlations (p < 0.05) with micro-CT thickness compared to 1.0 mm clinical-CT. ConclusionsThe small mean differences and thickness ratios near 1 show validation for the cortical thickness algorithm when applied to rib clinical-CT scans. Using clinical-CT scans as way to accurately measure rib cortical thickness offers a non-invasive way to analyze millions of CT scans collected each year from males and females of all ages.

Thermal Analysis of a Functionally Graded Coating/Substrate System Using the Approximated Transfer Approach

As a heterogeneous material, functionally graded material (FGM) behaves as continuously changed material properties in certain directions from one composition to another, and hence it has received much more attention for biomedical applications and thermal protections to achieve innovative functions that conventional homogeneous material cannot accomplish. However, due to the particularly small thickness ratio of coating to substrate in practice, the conventional mesh discretization of the coating region is inefficient. To simplify the meshing procedure and increase the efficiency of analysis, the approximated transfer algorithm based on the concept of finite difference is developed for transferring boundary conditions applied on the coating surface to the interface of coating and substrate. As a result, only the substrate with transferred convection boundary conditions needs to be solved numerically, i.e., by the fundamental-solution based hybrid finite element method (HFS-FEM) with high accuracy and feasible polygonal element construction, in which only integrals along the element boundary are evaluated because of the application of fundamental solutions of the problem as kernel functions of interior approximated fields. Finally, numerical experiments including the single-layered, multi-layered and functionally graded coatings are carried out to verify the accuracy and applicability of the present method.