Micro-rotary ratchets driven by migratory phytoplankton with phototactic stimulus

This study proposes micro-rotary ratchets driven by a migratory phytoplankton–Volvox, exhibiting a positive phototaxis. Two types of micro-discs, i.e., ratchet- and starfish-like ratchets are fabricated using conventional photolithography. The ratchet is floated in the center of a Petri dish filled with Volvox suspension under an optical microscope with halogen lamp illumination and is covered by a mask with a small hole so that the microorganisms are concentrated around the micro-ratchets by the phototaxis. Rotations of the ratchets with the same diameter of 0.567 mm were observed through a biological microscope; a rotation speed of 0.86 rpm for the micro-ratchet and 2.01 rpm for the starfish ratchet were obtained for a Volvox density of 1000–3000/mL under an illumination intensity of 0.18 W/cm². As the driving mechanism of the ratchet is based on the microorganisms adhesion to the ratchets surface rather than collision impacts, a gelatin coating on the ratchet was used to enhance the adhered number of Volvox. Although the drag force was increased owing to the larger ratchet diameter, a rotation speed of 0.16 rpm was observed. A particle tracking velocimetry measurement using polystyrene beads was performed to study the fluid flow around the micro-ratchet. A vortex generation by the micro-ratchets was confirmed; this effect may work as a micro-mechanical power booster for microorganisms. This drive system may open the possibility of a solar-power-driven and sustainable micro-mechanism using phytoplankton.     

Design and experimental evaluation of a precise and compact tubular ultrasonic motor driven by a single-phase source

A precise and compact tubular ultrasonic motor driven by a single-phase source is proposed and tested in this study. The motor is designed by modeling a motor stator in FEM software. The motor fabricated according to the design is tested experimentally and its working characteristics including speed and torque are measured and presented. The maximum speed and torque of the motor are 59 rpm and 0.28 mN m at 80 V_pp of applied voltage. The proposed motor possesses advantages such as a simple and compact structure with application in the fields of robotics, space, medical devices and high-resolution stages, among others. The proposed motor is a good candidate for applications where accurate control and high resolution at low speed is required.     

Effect of carbide volume fraction on erosive wear behaviour of hardfacing cast irons

The present work reports the effect of carbide volume fraction on erosive wear behaviour of hardfacing cast irons. Five different grades of weld hardfacing cast irons were selected for the present investigation. The solid particle erosion experiments were carried out with blast furnace sinter, silica sand and alumina particles under mild (53–75 μm, 25 m s⁻¹), moderately severe (125–150 μm/100–150 μm, 50 m s⁻¹) and under severe erosion conditions (300–425 μm, 90 m s⁻¹) at impingement angles of 30 and 90°. The variation in erosion rate with carbide volume fraction was observed to be strong function of the erodent particle hardness, impingement angle and the impact velocity. Under mild erosion conditions, erosion rate decreased with increasing carbide volume fraction (CVF), whereas erosion rate increased with CVF under moderately severe erosion condition with alumina particles. With silica sand particles under moderately severe erosion conditions the beneficial effect of large volume fraction of carbides could only be observed at 30°, whereas at normal impact erosion rate increased with increasing CVF. The erosion rate showed power law relationship with ratio of hardness of erodent particle to that of the target material (H_e/H_t) and expressed as E=c(H_e/H_t)^p.With increasing severity of erosion conditions erosion rate showed stronger dependence on H_e/H_t as compared to those under mild and moderately severe erosion conditions. The mechanism of materials removal from the carbides involved Hertzian fracture with softer sinter particles, whereas harder alumina particles could plastically indent and cause gross fracture of the carbides.     

The lubrication of poly(etheretherketone) by an aqueous solution of nattokinase

Poly(etheretherketone) (PEEK) is a high strength and high temperature engineering polymer. However, its tribological performance is not very good in its pure form unless fillers or fibers are added to form composites. As polymers are often used for applications where traditional oil based lubrication may become an issue, water-based lubrication is desirable. This paper explores the lubrication performance of a natural fibrinolytic enzyme, nattokinase, found in fermented soybean (natto) in the aqueous solution. Pins of PEEK were slid against a steel disk in a pin-on-disk tester with the aqueous lubrication. The counterface disk material was a tool steel (R_a=0.37 μm). Tests were conducted at a rotational speed of 100 rpm and a normal load of 80 N. For comparison, tests were also conducted in NaCl solution. Nattokinase aqueous solution provides a coefficient of friction of 0.2 between PEEK and steel as compared to 0.3–0.35 for dry condition. The specific wear rates of PEEK for dry, deionized water, NaCl solution and aqueous nattokinase solution conditions were 10.5×10^?6, 51.6×10^?6, 228×10^?6 and 8.8×10^?6 mm³/N m, respectively. The fibrinolytic nattokinase enzyme provides lubricity with alkalinity reducing corrosion and eventually reducing wear.     

A method of reducing windage power loss of a high-Speed motor using a viscous vacuum pump

A new structure for reducing the windage power loss of a high-speed rotor using a spiral grooved viscous vacuum pump combined with an aerodynamic step thrust bearing is proposed. The proposed structure can pump out the air from within the sealed space of the motor housing by using the pumping effect of the spiral grooves and thereby reduce the windage power loss of the rotor. In addition, a small gap was automatically formed between the rotor and the viscous vacuum pump by using the force balance between the aerodynamic step thrust bearing and the elastic material supporting the flat plate of the vacuum pump. It was numerically shown that the proposed structure could reduce the pressure in the sealed space of the motor housing to 0.02 MPa at 30,000 rpm at a gap of 10 μm. In addition, the calculated results at 10,000 rpm were compared with the experimental results and showed good agreement and the proposed structure was very useful in reducing the windage power loss of a high-speed motor.     

Optimisation of parameters affecting surface roughness of Co28Cr6Mo medical material during CNC lathe machining by using the Taguchi and RSM methods

This study involves modelling of experimental data of surface roughness of Co28Cr6Mo medical alloy machined on a CNC lathe based on cutting parameters (spindle rotational speed, feed rate, depth of cut and tool tip radius). In order to determine critical states of the cutting parameters variance analysis (ANOVA) was applied while optimisation of the parameters affecting the surface roughness was achieved with the Response Surface Methodology (RSM) that is based on the Taguchi orthogonal test design. The validity of the developed models necessary for estimation of the surface roughness values (Ra, Rz), was approximately 92%. It was found that for Ra 38% of the most effective parameters is on the tool tip radius, followed by 33% on the feed rate whereas for Rz tool tip radius occupied 43% with the feed being at 33% rate. To achieve the minimum surface roughness, the optimum values obtained for spindle rpm, feed rate, depth of cut and tool tip radius were respectively, 318 rpm, 0.1 mm/rev, 0.7 mm and 0.8 mm.     

1-N-alkyl -3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel–aluminium contacts

The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X⁻ [X = PF₆; n = 6 (L-P106). X = BF₄; n = 2 (L102), 6 (L106), 8 (L108). X = CF₃SO₃; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 °C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al₂O₃ and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 °C, tribocorrosion processes are not observed and a friction reduction (69–75% for 1 wt.% L102) and a change from severe (10⁻³ mm³ m⁻¹) to mild wear (10⁻⁴ to 10⁻⁶ mm³ m⁻¹) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 °C.     

Performance evaluation of a cheap,open source,digital environmental monitor based on the Raspberry Pi

We report on the design, construction and evaluation of a low-cost digital environmental monitoring system based on a popular micro-computer board and mass market digital sensors. The system is based around the use of open source software and readily available digital sensors, providing key parameters required for environmentally-controlled calibration laboratories: air temperature, pressure and humidity. Each system logs data at set intervals with front-panel display, web page graphical display and email alerting when exceeding set tolerances. The sensors have been calibrated at the National Physical Laboratory using standards traceable to the SI. Long term stability of the system is estimated and in addition to monitoring of laboratory environments for regulatory purposes, the systems can also be used to provide on-demand values for local refractive index with an expanded (k = 2) uncertainty of 1.1 × 10⁻⁷ as required for many optical-based measuring systems.     

Feasibility assessment of magnetic resonance-thermometry on pancreas undergoing laser ablation: Sensitivity analysis of three sequences

Laser ablation (LA) is a minimally invasive technique for the treatment of tumors as an alternative to surgical resection. The light absorbed by tissue is converted into heat, and causes irreversible cell damage when temperatures higher than 60 °C are reached. The knowledge in real time of temperature may be particularly beneficial for adjusting laser settings applied during treatment and to be notified in real time about its end-point. As a consequence, several techniques for temperature monitoring within the tissue have been investigated along the last decades. In the field of LA, particularly attractive are non-invasive methods. Among these techniques, thermometry based on the analysis of Magnetic Resonance Imaging (MR-thermometry) has gaining large acceptance in this field. MR-thermometry allows estimating the temperature variation thanks to the thermal dependence of several MRI parameters, among others the most promising are T₁ relaxation time, and proton resonance frequency shift.The aim of this study is to assess the sensitivity of MRI thermometry using three T₁-weighted sequences (i.e., Inversion Recovery Turbo-FLASH, IRTF, Saturation Recovery Turbo-FLASH, SRTF, and FLASH) using an 1.5-T MR scanner on healthy swine pancreases undergoing LA. The reference temperature was measured by MRI-compatible fiber optic sensors (fiber Bragg grating sensors). The sensitivity of the proposed techniques was estimated and compared. The thermal sensitivity of the three sequences was −1.47 ± 0.08 °C⁻¹, −0.95 ± 0.05 °C⁻¹, and −0.56 ± 0.04 °C⁻¹ for IRTF, SRTF and FLASH, respectively. Results show that the proposed technique may be adequate for temperature monitoring during LA.     

Cavitation erosion of Fe–Mn–Si–Cr shape memory alloys

Cavitation erosion tests of three Fe–Mn–Si–Cr shape memory alloys were carried out at speed 34 and 45 m/s using a rotating disc rig, and their cavitation damage has been investigated by comparison with a referring 13Cr–5Ni–Mo stainless steel used for hydraulic turbine vanes. The research results proved that the cavitation erosion of the Fe–Mn–Si–Cr shape memory alloys is a failure of low cycle fatigue and fracture propagates along grain boundaries. After 48 h cavitation erosion the cumulative mass losses of the studied alloys at speed 45 m/s are more than theirs at speed 34 m/s; however, the effect of velocity on cavitation damage of the Fe–Mn–Si–Cr alloys is much lower than that of 13Cr–5Ni–Mo stainless steel. The cumulative mass loss of the 13Cr–5Ni–Mo stainless steel are 26.3 mg at speed 45 m/s and 3.2 mg at speed 34 m/s, and the mass losses of the Fe–Mn–Si–Cr alloys are within the range of 3.6–7.3 mg at speed 45 m/s and 2.0–4.1 mg at speed 34 m/s. The surface elasticity of the Fe–Mn–Si–Cr shape memory alloys is better than that of the 13Cr–5Ni–Mo stainless steel, and the effect of surface elasticity on cavitation damage increases with velocity. The excellent surface elasticity of the cavitation-induced hexagonal closed-packed (h.c.p.) martensite plays a key role in contribution of phase transformation to the cavitation erosion resistance of the Fe–Mn–Si–Cr shape memory alloys. The cavitation damage of the studied alloys at speed 45 m/s mainly depends on their surface elasticity, and the variation of 48 h cumulative mass loss (Δm) as a function of the elastic depth (h_e) can be expressed as Δm=2.695+[1371.94/(4(h_e−46.83)²+12.751)] with a correlation factor of 0.99345.     

Assessment of thermal effects on the levitation speed of bump foil bearings made of low cost spring steel

The demand for higher speeds and torque capacity from micro turbines, heat pumps and turbochargers has necessitated the development of high temperature resistant foil bearings. This paper focuses on investigating the effects of successive thermal cycles on the levitation speed of bump foil bearings made up of low cost spring steel. Bump foil bearings were designed for high stiffness of 1.64 MN/m². Rotor dynamic analysis indicated highest frequency of 4790.5 Hz corresponding to second flexure mode of rotor bearing system up to which it remained stable. The bump foil bearing fabrication procedure was established and rotor was tested under suitably designed bearing rig. The orbital analysis indicated that levitation speed decreased with increase in temperature. During second and third thermal cycle, at lower rotor speeds drastic variations in amplitude of vibrations and uneven waveforms were indicative of unbalance condition of rotor. With further increase in rotor speeds, the rotor - bump foil bearing system attained the balanced state indicative of safe design.     

On-site calibration system for trace humidity sensors

A portable device for calibration of trace humidity sensors and an adopted calibration procedure have been developed. The calibration device is based on humidity generation by permeating water through polymeric membrane tubes. Water vapour transmission rates for various polymers were experimentally determined in order to select the most suitable polymeric material. The developed trace humidity generator consists of a gas-flow polymeric hose immersed in a water reservoir thermostated by a sensor-controlled heater. Mole fractions of water vapour between 1 μmol mol⁻¹ and 350 μmol mol⁻¹ (equivalent to frost-point temperatures from −76 °C to −31 °C) were generated by varying either the operating temperature or gas flow. The operating temperature can be varied from 20 °C to 60 °C and kept stable within 0.1 K. Uncertainty analysis indicated that the trace humidity generator produces gas flows of constant humidity amounts with a relative expanded uncertainty less than 3.4% (k = 2) of the generated value.     

Improved wear resistance in alumina-PTFE nanocomposites with irregular shaped nanoparticles

Past studies with PTFE nanocomposites showed up to 600× improvements in wear resistance over unfilled PTFE with the addition of Al₂O₃ nanoparticles. Irregular shaped nanoparticles are used in this study to increase the mechanical entanglement of PTFE fibrils with the filler. The tribological properties of 1, 2, 5 and 10 wt.% filled samples are evaluated under a normal pressure and sliding speed of 6.3 MPa and 50.8 mm/s, respectively. The wear resistance was found to improve 3000× over unfilled PTFE with the addition of 1 wt.% nanoparticles. The 5 wt.% sample had the lowest steady state wear rate of K = 1.3 × 10⁻⁷ mm³/N m and the lowest steady friction coefficient with μ = 0.21.     

Externally pressurized gas journal bearing with slot restrictors arranged in the axial direction

In this study, a novel rectangular slot restriction-type externally pressurized gas journal bearing was developed for use in high-speed rotating machinery, such as medical devices and industrial machines. The proposed bearing has several rectangular slot restrictors arranged in the inner surface of the bearing. To measure the bearing characteristics, a model was developed for the numerical calculation of the pressure distribution in the bearing clearance and the static characteristics of the bearing. The proposed bearing, which consists of two parts, was designed and can be manufactured using appropriate techniques. In this study, a prototype bearing with eight slots in its surface was manufactured as a test piece for fundamental tests. The diameter and length of the test bearing are 30 and 40 mm, respectively. The roundness of the bearing was measured using a three-dimensional coordinate measuring machine, and the results were used in the analysis. The pressure distribution and static characteristics obtained experimentally were found to be in good agreement with the calculated values. In the rotational tests, the rotor speed exceeded 380 Hz (22,800 rpm), and whirl vibration did not occur. During testing, the maximum rotor vibration amplitude was 0.002 mm, corresponding to an eccentricity ratio of 0.3.     

Effect of process parameters on the macrostructure and defect formation in friction stir lap welding of AA5456 aluminum alloy

Friction stir welding could be considered as a suitable technique for joining of aluminum alloys due to the emerging of different problems in fusion welding of these alloys, especially in lap joint designs. For this purpose, it is necessary to optimize the process parameters while in this study, the combined effects of tool rotation and welding travel speed on the macrostructure and defect formation of friction stir lap welding of AA5456 was investigated. The rotating tool was plunged from the 5 mm-thick AA5456-H321 (top sheet) surface into the 2.5 mm-thick AA5456-O (bottom sheet) and lap joints were fabricated by rotational speeds of 300, 600, 800 and 1000 rpm and welding speeds of 15, 30, 60 and 100 mm min⁻¹. The effect of tool rotation and welding speed on the macrostructure, material flow and defect formation, i.e. hooking, kissing-bond and cavity, were studied by optical microscopy and scanning electron microscope. The results declared that hooking height decreased as the welding speed increased while kissing-bond was formed at higher welding speeds. Moreover, hooking region was extended as the tool rotational speed increased. However, at a high rotational speed, cavity was even created.     

Effect of tool pin design on the microstructural evolutions and tribological characteristics of friction stir processed structural steel

In this research, friction stir processing (FSP) technique is applied for the surface modification of ST14 structural steel. Tungsten carbide tools with cylindrical, conical, square and triangular pin designs are used for surface modification at rotational speed of 400 rpm, normal force of 5 KN and traverse speed of 100 mm min⁻¹. Mechanical and tribological properties of the processed surfaces including microhardness and wear characteristics are studied in detail. Furthermore, microstructural evolutions and worn surfaces are investigated by optical and scanning electron microscopes. Based on the achievements, all designed pins were successfully applicable for low carbon steel to produce defect-free processed material. By the microstructural changes within the stirred zone, the processed specimen is obtained higher mechanical properties. This is due to the formation of fine grains as the consequence of imposing intensive plastic deformation during FSP; however, this issue is highlighted by using square pin design. In this case, minimum grain size of 5 μm and maximum hardness of 320 VHN, as well as, maximum wear resistance are all examined for the specimen modified by square pin.     

Ultrasonic vibration assisted grinding of hard and brittle linear micro-structured surfaces

In this paper, a novel ultrasonic vibration assisted grinding (UVAG) technique was presented for machining hard and brittle linear micro-structured surfaces. The kinematics of the UVAG for micro-structures was first analyzed by considering both the vibration trace and the topological features on the machined surface. Then, the influences of the ultrasonic vibration parameters and the tilt angle on the ground quality of micro-structured surfaces were investigated. The experimental results indicate that the introduction of ultrasonic vibration is able to improve the surface quality (The roughness SR_a was reduced to 78 nm from 136 nm), especially in guaranteeing the edge sharpness of micro-structures. By increasing the tilt angle, the surface roughness can be further reduced to 56 nm for a 59% improvement in total. By using the preferred UVAG parameters realized by orthogonal experiments, a micro cylinder array with surface roughness of less than 50 nm and edge radius of less than 1 μm was fabricated. The primary and secondary sequence of the grinding parameters obtained by the orthogonal experiments are as follows: feed rate, tilt angle of workpiece, depth of grinding, vibration frequency and amplitude. The spindle speed in the range of 1000 rpm–3000 rpm does not significantly affect the machined micro-structured surface roughness. Finally, more micro-structures including a micro V-groove array and a micro pyramid array were machined on binderless WC as well as SiC ceramic by means of the UVAG technique. The edge radius on the V-grooves and pyramids are both less than 1 μm, indicating the feasibility of UVAG in machining hard and brittle micro-structured surfaces for an improved surface quality.     

Friction and wear durability studies on the 3D negative fingerprint and honeycomb textured SU-8 surfaces

The effects of two different textures (a 3D negative fingerprint texture and a honeycomb texture) on the tribological performance of SU-8 polymer surface have been investigated with a ball-on-disc tribometer. Friction and wear behaviors of the textured surfaces are conducted against a 4 mm diameter silicon nitride (Si₃N₄) ball counterface. The coefficient of friction for the negative fingerprint textured surface (μ=∼0.08) is much lower than that of the untextured surface (∼0.2) and the honeycomb textured surface (∼0.41) under a normal load of 100 mN and a rotational speed of 2 rpm. The coefficients of friction of the textured surfaces decrease with increasing normal loads between 100 mN and 300 mN. Above the normal load of 300 mN, the coefficient of friction of the negative fingerprint textured surface increases due to the occurrence of plastic deformation. The honeycomb textured surface has shown the highest coefficient of friction. The wear durability tests are also conducted at a normal load of 100 mN and a rotational speed of 500 rpm on the untextured/textured surfaces on SU-8 in the presence of an overcoat of a nano-lubricant, perfluoropolyether(PFPE). Six samples i.e. the untextured surface (Si/SU-8 and Si/SU-8/PFPE), the 3D negative fingerprint textured surface (Si/SU-8/FP and Si/SU-8/FP/PFPE) and the honeycomb textured surface (Si/SU-8/HC and Si/SU-8/HC/PFPE), each with and without PFPE nano-lubricant, have been investigated for their tribological behaviours. The negative fingerprint pattern on SU-8 with PFPE coating has shown the highest wear life of 60,000 cycles under a normal load of 100 mN. The reasons for excellent tribological performance of 3D fingerprinted SU-8 surface are analyzed using the Hertzian contact area calculation.     

Mechanical and unlubricated tribological properties of titanium-containing diamond-like carbon coatings

Titanium-containing diamond-like carbon (Ti-DLC) coatings were deposited on steel with a close-field unbalanced magnetron sputtering in a mixed argon/acetylene atmosphere. The morphology and structure of Ti-DLC coatings were investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Nanoindentation, nanoscratch and unlubricated wear tests were carried out to evaluate the hardness, adhesive and tribological properties of Ti-DLC coatings. Electron microscopic observations demonstrated the presence of titanium-rich nanoscale regions surrounded by amorphous carbon structures in Ti-DLC coating. The Ti-DLC coatings exhibit friction coefficients of 0.12–0.25 and wear rates of 1.82 × 10^?9 to 4.29 × 10^?8 mm³/Nm, depending on the counterfaces, sliding speed and temperature. The Ti-DLC/alumina tribo-pair shows a lower friction coefficient than the Ti-DLC/steel tribo-pair under the identical wear conditions. Increasing the test temperature from room temperature to 200 °C reduces the coefficient of friction and, however, clearly increases the wear rate of Ti-DLC coatings. Different wear mechanisms, such as surface polishing, delamination and tribo-chemical reactions, were found in the tribo-contact areas, depending on different wear conditions.