Effect of interface layer on the enhancement of thermal conductivity of SiC-Water nanofluids: Molecular dynamics simulation.

To investigate the impact of interfacial layer effects on the thermal conductivity of nanofluids and the microscopic mechanisms of enhanced thermal conductivity, this study employed non-equilibrium molecular dynamics to compute the thermal conductivity, number density, radial distribution function, and mean square displacement distribution of SiC nanofluids. The impact of nanoparticle volume fraction and particle size parameters on the thermal conductivity of nanofluids and the structure of interfacial adsorption layers was discussed. The simulation calculation results show that the coefficient of thermal conductivity of nanofluid is positively related to the volume fraction of nanoparticles, increasing from 0.6529 W/(m·K) to 0.8159 W/(m·K), and the enhancement of thermal conductivity by the volume fraction can be up to 33.97 %. The thermal conductivity is inversely correlated with the change in particle size, and the maximum improvement in thermal conductivity by particle size can reach up to 12.05 %. The simulated results of the thermal conductivity of nanofluid are almost consistent with the predicted results of the Yu&Choi model, and the error is controlled within 5 %. Simultaneously, the thickness of the interfacial adsorption layer decreases with an increase in particle size. This reduction arises due to larger particles having a smaller specific surface area, resulting in fewer particle surfaces covered by the interface layer. Moreover, the impact of particle size on the arrangement and affinity of molecules within the interface layer contributes to this decrease. Overall, interface layer effects exhibit a dual impact on the thermal conduction of nanofluids. The structured formation and high-density distribution of the adsorption layer contribute to enhanced heat transfer, while thermal resistance between nanoparticle surfaces and the fluid restricts heat transmission.

MC design and FIB preparation of a YSZ biochemical material microstructure.

Aiming at the difficulty of traditional machining of Y2O3-ZrO2 (YSZ) inert ceramic materials, a different method using focused ion beam to selectively create nanoscale microscale structures on the surface of materials was proposed. The sputtering yield, surface damage, and the energy loss of YSZ materials was investigated using the SRIM software using the Monte Carlo method. It is shown that the sputtering yield increases with ion energy in the range 0-30 keV, reaching a maximum of 9.4 atoms/ion at 30 keV. At an ion beam voltage of 30 keV, the most severe damage to the material is 8 mm on the surface. At the same time, the main forms of energy loss in the treatment are phonon energy loss and ionization energy loss, of which phonon energy loss due to the recoil atoms is the largest. In addition, we continue to perform focused ion beam processing experiments on YSZ materials, combining previous MC modeling to optimize different operating conditions such as ion beam, voltage and processing mode. The optimized processing parameters are 30 keV and 2.5 nA. It is shown that the quality of the deep grooves gradually improves with decreasing ion beam current at the same ion beam voltage. However, an excessively small ion beam current leads to an excessively large depth of the deep grooves and lengthy processing times.

Effect of Al Content on the Wear Evolution of Ti1-xAlxN-Coated Tools Milling Ti-6Al-4V Alloy.

Ti1-xAlxN coating is formed by replacing some Ti atoms in TiN with Al atoms, and their properties are closely related to Al content (0 < x < 1). Recently, Ti1-xAlxN-coated tools have been widely used in the machining of Ti-6Al-4V alloy. In this paper, the hard-to-machine material Ti-6Al-4V alloy is used as the study material. Ti1-xAlxN-coated tools are used for milling experiments. The evolution of the wear form and the wear mechanism of Ti1-xAlxN-coated tools are studied, and the influence of Al content (x = 0.52, 0.62) and cutting speed on tool wear are analyzed. The results show that the wear on the rake face changes from the initial adhesion and micro-chipping to coating delamination and chipping. Wear on the flank face varies from the initial adhesion and grooves to boundary wear, build-up layer, and ablation. The main wear mechanisms of Ti1-xAlxN-coated tools are dominated by adhesion, diffusion, and oxidation wear. Ti0.48Al0.52N coating protects the tool well and extends its service life.

Accurate Cutting-Force Measurement with Smart Tool Holder in Lathe.

Cutting force in lathe work is closely related to tool wear and affects the turning quality. Direct measurement of the cutting force by measuring the strain of the tool holder is challenging because the tool holder design aims to be highly rigid in order to undertake large cutting forces. Accordingly, the most popular dynamometer designs modify the standard tool holder by decreasing the structural rigidity of the holder, which reduces the machining precision and is not widely accepted. In order to solve the issue of the low stiffness of the dynamometer reducing the machining precision, in this paper, the ultra-low strain on the tool holder was successfully detected by the highly sensitive semiconductor strain gauges (SCSG) adjacent to the blade cutting insert. However, the cutting process would generate much heat, which increases the force measuring area temperature of the tool holder by about 30 °C. As a result, the readout drifted significantly with the temperature changes due to the high temperature coefficient of SCSG. To solve this problem, the temperature on the tool holder was monitored and a BP neural network was proposed to compensate for temperature drift errors. Our methods improved the sensitivity (1.14 × 10-2 mV/N) and the average relative error of the BP neural network prediction (≤1.48%) while maintaining the original stiffness of the tool holder. The smart tool holder developed possesses high natural frequency (≥6 kHz), it is very suitable for dynamic cutting-force measurement. The cutting experiment data in the lathe work show comparable performance with the traditional dynamometers and the resolution of the smart tool holder is 2 N (0.25% of total range).

Experimental Research and Numerical Simulation of Laser Welding of 303Cu/440C-Nb Stainless-Steel Thin-Walled Natural-Gas Injector for Vehicles.

This paper presents the results of research on laser lap welding technology of heterogeneous materials and a laser post-heat treatment method to enhance welding performance. The purpose of this study is to reveal the welding principle of austenitic/martensitic dissimilar stainless-steel materials (3030Cu/440C-Nb) and to further obtain welded joints with good mechanical and sealing properties. A natural-gas injector valve is taken as the study case where its valve pipe (303Cu) and valve seat (440C-Nb) are welded. Experiments and numerical simulations were conducted where the welded joints' temperature and stress fields, microstructure, element distribution, and microhardness were studied. The results showed that the residual equivalent stresses and uneven fusion zone tend to concentrate at the joint of two materials within the welded joint. The hardness of the 303Cu side (181.8 HV) is less than the 440C-Nb side (266 HV) in the center of the welded joint. The laser post-heat treatment can reduce the residual equivalent stress in the welded joint and improve the mechanical and sealing properties. The results of the press-off force test and the helium leakage test showed that the press-off force increased from 9640 N to 10,046 N and the helium leakage rate decreased from 3.34 × 10-4 to 3.96 × 10-6.

Gut-on-a-chip for exploring the transport mechanism of Hg(II).

Animal models and static cultures of intestinal epithelial cells are commonly used platforms for exploring mercury ion (Hg(II)) transport. However, they cannot reliably simulate the human intestinal microenvironment and monitor cellular physiology in situ; thus, the mechanism of Hg(II) transport in the human intestine is still unclear. Here, a gut-on-a-chip integrated with transepithelial electrical resistance (TEER) sensors and electrochemical sensors is proposed for dynamically simulating the formation of the physical intestinal barrier and monitoring the transport and absorption of Hg(II) in situ. The cellular microenvironment was recreated by applying fluid shear stress (0.02 dyne/cm2) and cyclic mechanical strain (1%, 0.15 Hz). Hg(II) absorption and physical damage to cells were simultaneously monitored by electrochemical and TEER sensors when intestinal epithelial cells were exposed to different concentrations of Hg(II) mixed in culture medium. Hg(II) absorption increased by 23.59% when tensile strain increased from 1% to 5%, and the corresponding expression of Piezo1 and DMT1 on the cell surface was upregulated.

Addition of Nano CaF2@SiO2 and SiC Whiskers in Ceramic Tools for Wear Reduction and Improved Machinability.

The addition of CaF2@SiO2 and SiC whiskers to ceramic tools can improve their flexural strength and fracture toughness, reduce surface damage, and improve their cutting performance. The cutting experiments showed that under the same cutting conditions, the surface roughness of the workpiece processed with the Al2O3/TiC/SiC/CaF2@SiO2 (ATSC10) tool was significantly lower than that of the workpiece processed with the Al2O3/TiC/ SiC (ATS) tool. Additionally, the main cutting force and cutting temperature when cutting with the ATSC10 tool were lower by 30 and 31.7%, respectively. These results were attributed to the precipitation of CaF2 from the nanocoated particles during cutting and the formation of a uniform and continuous lubricating film on the surface of the tool. The wear on the front surface of the ATS tool was mainly adhesive, and that on the back tool surface was mainly abrasive. For ATSC10, the main forms of wear on the tool front surface were adhesive and abrasive, whereas the main form of wear on the tool back surface was abrasive with slight adhesive wear. The addition of nano-coated particles and whiskers improved the mechanical properties of the cutting tool while maintaining good cutting performance.

Crack Sensing of Cardiomyocyte Contractility with High Sensitivity and Stability.

Measuring myocardial contractility is of great value in exploring cardiac pathogenesis and quantifying drug efficacy. Among the biosensing platforms developed for detecting the weak contractility of a single layer of cardiomyocytes (CMs), thin brittle metal membrane sensors with microcracks are highly sensitive. However, their poor stability limits the application in long-term measurement. Here, we report a high stability crack sensor fabricated by deposition of a 105 nm thick Ag/Cr with microcracks onto a carbon nanotubes-polydimethylsiloxane (CNT-PDMS) layer. This brittle-tough bilayer crack sensor achieved high sensitivity (gauge factor: 108 241.7), a wide working range (0.01-44%), and high stability (stable period >2 000 000 cycles under the strain caused by a monolayer of CMs). During 14-day continuously monitoring CMs culturing and drug treatment testings, the device demonstrated high sensitivity and stability to record the dynamic change caused by contractility of the CMs.

Green Manufacturing of Flexible Sensors with a Giant Gauge Factor: Bridging Effect of CNT and Electric Field Enhancement at the Percolation Threshold.

Toxic organic solvents are commonly used to disperse nanomaterials in the manufacturing of flexible conductive composites (e.g., graphene-PDMS). The dry-blended method avoids toxic organic solvent usage but leads to poor performance. Here, we proposed an innovative manufacturing method by adapting the traditional dry-blended method, including two key steps: minor CNT bridging and high-frequency electric field enhancement at the percolation threshold of graphene-PDMS. Significant improvement was achieved in the electrical conductivity (1528 times), the giant gauge factor (>8767.54), and the piezoresistive strain range (30 times) over the traditional dry-blended method. Further applications in measurements of culturing rat neonatal cardiomyocytes and mouse hearts proved that the proposed method has great potential for the manufacturing of nontoxic flexible sensors.

Modelling and Prediction of Cutting Temperature in the Machining of H13 Hard Steel of Transient Heat Conduction.

Cutting heat conduction undergoes three stages that include intensity transient-state, transient-state, and steady-states. Especially during machining with coated cutting tools, in the conduction process, cutting heat needs to pass through a few micron thick coatings and then flow into the tool body. This heat conduction presents typical non-Fourier heat conduction characteristics. This paper focuses on the cutting temperature in transient heat conduction with a coated tool. A new analytical model to characterize the thermal shock based on the non-Fourier heat conduction was proposed. The distribution of cutting temperature in mono-layer coated tools during the machining was then illustrated. The cutting temperature distribution predicted by the Fourier heat conduction model was employed to compare with that by non-Fourier heat conduction in order to reveal the non-Fourier heat conduction effect in transient heat conduction. The results show that the transient heat conduction analytical model is more suitable for the intensity transient-state and transient-state in the process of cutting heat conduction.

Electrochemical biosensors for measurement of colorectal cancer biomarkers.

Colorectal cancer (CRC) is associated with one of the highest rates of mortality among cancers worldwide. The early detection and management of CRC is imperative. Biomarkers play an important role in CRC screening tests, CRC treatment, and prognosis and clinical management; thus rapid and sensitive detection of biomarkers is helpful for early detection of CRC. In recent years, electrochemical biosensors for detecting CRC biomarkers have been widely investigated. In this review, different electrochemical detection methods for CRC biomarkers including immunosensors, aptasensors, and genosensors are summarized. Further, representative examples are provided that demonstrate the advantages of electrochemical sensors modified by various nanomaterials. Finally, the limitations and prospects of biomarkers and electrochemical sensors in detection are also discussed. Graphical abstract.

Advances in reconstructing intestinal functionalities in vitro: From two/three dimensional-cell culture platforms to human intestine-on-a-chip.

Standard two/three dimensional (2D/3D)-cell culture platforms have facilitated the understanding of the communications between various cell types and their microenvironments. However, they are still limited in recapitulating the complex functionalities in vivo, such as tissue formation, tissue-tissue interface, and mechanical/biochemical microenvironments of tissues and organs. Intestine-on-a-chip platforms offer a new way to mimic intestinal behaviors and functionalities by constructing in vitro intestinal models in microfluidic devices. This review summarizes the advances and limitations of the state-of-the-art 2D/3D-cell culture platforms, animal models, intestine chips, and the combined multi-organ chips related with intestines. Their applications to studying intestinal functions, drug testing, and disease modeling are introduced. Different intestinal cell sources are compared in terms of gene expression abilities and the recapitulated intestinal morphologies. Among these cells, cells isolated form human intestinal tissues and derived from pluripotent stem cells appear to be more suitable for in vitro reconstruction of intestinal organs. Key challenges of current intestine-on-a-chip platforms and future directions are also discussed.

Effect of the Characteristic Size and Content of Graphene on the Crack Propagation Path of Alumina/Graphene Composite Ceramics.

In this paper, the Voronoimosaic model and the cohesive element method were used to simulate crack propagation in the microstructure of alumina/graphene composite ceramic tool materials. The effects of graphene characteristic size and volume content on the crack propagation behavior of microstructure model of alumina/graphene composite ceramics under different interfacial bonding strength were studied. When the phase interface is weak, the average energy release rate is the highest as the short diameter of graphene is 10-50 nm and the long diameter is 1600-2000 nm. When the phase interface is strong, the average energy release rate is the highest as the short diameter of graphene is 50-100 nm and the long diameter is 800-1200 nm. When the volume content of graphene is 0.50 vol.%, the average energy release rate reaches the maximum. When the velocity load is 0.005 m s-1, the simulation result is convergent. It is proven that the simulation results are in good agreement with the experimental phenomena.

A CNT-PDMS wearable device for simultaneous measurement of wrist pulse pressure and cardiac electrical activity.

Simultaneous measurement of multi-physiological signals can provide effective diagnosis and therapeutic assessment of diseases. This paper reports a carbon nanotube (CNT) - Polydimethylsiloxane (PDMS) - based wearable device with piezo-resistive and voltage-sensing capabilities for simultaneously capturing wrist pulse pressure and cardiac electrical signal. The layout design of sensing elements in the device was guided by analyzing strain distribution and electric field distribution for minimizing the interference between wrist pulse and cardiac electric activity during measurement. Each device was preconditioned under the strain of 20% until the resistance change of the device reached equilibrium. After preconditioning, the relationship between the resistance change and the pressure was calibrated, which determined the device sensitivity to be 0.01 Pa-1 and the linear pressure range of the device to be 0.4 kPa to 14.0 kPa. Mechanisms of CNT-PDMS for sensing strain signal and electrical pulse signal were explored by scanning electron microscopy (SEM) imaging and equivalent circuit modeling. The device was applied to monitor the wrist pulse and ECG signals of volunteers during the recovering process after physical exercises.

Influence of CaF2@Al2O3 on Cutting Performance and Wear Mechanism of Al2O3/Ti(C,N)/CaF2@Al2O3 Self-Lubricating Ceramic Tools in Turning.

This study aimed at improving the cutting performance of a ceramic tool to which were added solid lubricant particles. We prepared the self-lubricating ceramic tool by adding CaF2@Al2O3 instead of CaF2, and the self-lubricating ceramic tool with Al2O3 as matrix phase, Ti(C,N) as reinforcement phase. The properties of the ceramic tool with different contents of CaF2@Al2O3 and CaF2 were studied by turning 40Cr. Compared with the ceramic tool with 10 vol.% CaF2, the main cutting force and the cutting temperature of the ceramic tool with 10 vol.% CaF2@Al2O3 decreased by 67.25% and 38.14% respectively. The wear resistance and machining surface quality of the ceramic tool with CaF2@Al2O3 were better than the ceramic tool to which were directly added CaF2. The optimal content of CaF2@Al2O3 particles was determined to be 10 vol.%. The addition of CaF2@Al2O3 particles effectively reduces the adverse effect of direct addition of CaF2 particles on the ceramic tool, and plays a role in improving the cutting performance of the ceramic tool.

Synthesis and Mechanical Characterization of a Ti(C,N)/Mo-Co-Ni/CaF2@Al2O3 Self-Lubricating Cermet.

In this paper, an Al2O3 coated CaF2 (CaF2@Al2O3) nanocomposite powder is used as the additive phase of a Ti(C,N)-based self-lubricating cermet material. A novel self-lubricating ceramic material with a multilayer core-shell microstructure was prepared using a vacuum hot-pressing sintering process. The results show that the surface of the CaF2 powder is coated with Al2O3, and when introduced into a Ti(C,N)-Mo-Co-Ni material system, it can utilize the high-temperature liquid phase diffusion mechanism of the metal Mo-Co-Ni phase in the sintering process. The CaF2@Al2O3@Mo-Co-Ni multilayer core-shell microstructure is formed in the material. Compared with the direct addition of CaF2 and Al2O3, the hardness and fracture toughness of the material are increased by 24.31% and 22.56%, reaching 23.93 GPa and 9.94 MPa·m1/2, respectively. The formation of the multilayer core-shell microstructure is the main reason for the improvement of the mechanical properties of the material.

Synthesis of CaF2 Nanoparticles Coated by SiO2 for Improved Al2O3/TiC Self-Lubricating Ceramic Composites.

In order to reduce the influence of CaF2 addition on the mechanical properties of self-lubricating ceramic tools, we applied a silicon dioxide (SiO2) coating on calcium fluoride (CaF2) nanoparticles through hydrolysis and condensation reactions using the tetraethoxysilane (TEOS) method. The powder was dried by the azeotropic method, so that it acquired a better dispersibility. The resulting composite powders were characterized using XRD (X-ray diffraction) and TEM (transmission electron microscopy), showing that the surface of CaF2 was coated with a layer of uniform and compact SiO2. SiO2 shells with different thicknesses could be obtained by changing the amount of TEOS added, and the thickness of the SiO2 shells could be controlled between 1.5 and 15 nm. At the same time, a ceramic material containing CaF2 nanoparticles and CaF2@SiO2-coated nanoparticles was prepared. It had the best mechanical properties when CaF2@SiO2-coated nanoparticles were added; its flexural strength, fracture toughness, and hardness were 562 ± 28 MPa, 5.51 ± 0.26 MPa·m1/2, and 15.26 ± 0.16 GPa, respectively. Compared with the ceramic tool containing CaF2 nanoparticles, these mechanical properties were increased by 17.57%, 12.67%, and 4.88%, respectively. The addition of CaF2@SiO2-coated nanoparticles greatly improved the antifriction and wear resistance of the ceramic material, and the antifriction and wear resistance were balanced.

Preparation of Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 Ceramic Tools and Cutting Performance in Turning.

Aiming at the contradiction between the lubricating performance and mechanical performance of self-lubricating ceramic tools. CaF2@Al(OH)3 particles were prepared by the heterogeneous nucleation method. An Al2O3/Ti(C,N) ceramic tool with CaF2@Al2(OH)3 particles and ZrO2 whiskers was prepared by hot press sintering (frittage). The cutting performances and wear mechanisms of this ceramic tool were investigated. Compared with the Al2O3/Ti(C,N) ceramic tool, the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool had lower cutting temperatures and surface roughness. When the cutting speed was increased from 100m/min to 300m/min, a lot of CaF2 was smeared onto the surface of the ceramic tool, and the flank wear of the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool was reduced. The main wear mechanisms of the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool were adhesive wear and micro-chipping. The formation of solid lubricating film and the improvement of fracture toughness by adding ZrO2 whiskers and CaF2@Al(OH)3 were important factors for the Al2O3/Ti(C,N)/ZrO2/CaF2@Al(OH)3 ceramic tool to have better cutting performances.

Lubrication Performance of Graphene as Lubricant Additive in 4-n-pentyl-4'-cyanobiphyl Liquid Crystal (5CB) for Steel/Steel Contacts.

The lubrication performance of graphene used as additive in 4-n-pentyl-4'-cyanobiphyl liquid crystal (5CB) for steel/steel contacts was studied on a ball-on-plate tribotester. The friction test results show that when the graphene content in the 5CB was 0.15 wt.%, and the lubricant and friction pairs were heated to 44⁻46 °C before friction tests, the lubrication performance of the 5CB was most improved. Compared with pure 5CB, 5CB+0.15 wt.% graphene suspension reduced the friction coefficient and wear scar diameter by up to 70.6% and 41.3%, respectively. The lubrication mechanisms have been tentatively proposed according to the test results. We speculate that the excellent lubrication performance of graphene/5CB suspensions may be attributed to the low shear resistance adsorption layer formed by graphene and 5CB molecules on the sliding surfaces. As the protective layer, it not only prevents direct contact between the rough sliding surfaces but also is easy to slide.