Twist Test Research Articles

Design of Machine-Washable and Wearable Supercapacitors Using Composite Laminates

Flexible and wearable supercapacitors, as a rechargeable energy storage device, are promising power sources for next-generation wearable electronics and electronic textiles in many consumer, medical, and military applications, as they offer safety, mechanical flexibility, stability, and durability that are lacking in current batteries. However, flexible supercapacitor prototypes reported so far have not demonstrated sufficient mechanical properties that could withstand critical situations, such as folding, twisting, and machine washing, which are commonly happening for real-world applications. Here we present the design of flexible supercapacitors that are foldable, twistable, and machine-washable due to exceptional mechanical properties of the materials. The devices are constructed using thin composite laminates as electrodes and ion-conducting separators. Each layer of the laminates is composed of randomly distributed activated carbon fibers or glass fibers in polymer electrolyte matrix. Calculations and simulations show that such laminates with proper fiber length and volume fraction of fibers can provide both high strength and high flexibility that enable them to survive critical mechanical deformations, while traditional particle-based electrodes cannot. The electrochemical and mechanical tests demonstrate that the activation of the carbon fiber surface does not affect much of the mechanical properties of the laminates, but greatly improves the surface area of electrodes, which leads to two orders increase in their electrical double-layer capacitance. The prototypes made of electrode/separator/electrode laminates show adjustable areal capacitances of over 10 mF/cm2. The electrochemical performance has remained unchanged after repeated folding and twisting tests. Moreover, we sewed the devices onto fabrics and washed them together with daily garments in a washing machine, after which we observed no mechanical damage or capacitance degradation. In conclusion, we believe that the excellent electrochemical performance, flexibility and mechanical durability make the composite laminates-based flexible supercapacitors promising to be integrated with daily garments to power various wearable electronics. The design rules and results are also applicable to developing other flexible functional devices that require extraordinary mechanical properties without sacrificing another function.

In-Situ Observation of Adhesion Behavior During Ultrasonic Al Ribbon Bonding

In-situ observation was performed on a transparent silica substrate during ultrasonic Al ribbon bonding, using a high-speed video camera with differing frame rates, 104 fps and 103 fps, to clarify the adhesion behavior. The bonding process was observed as follows. Initially, friction slip occurred, producing multiple island streaks in the direction parallel to the ultrasonic vibration. The island streaks were formed as a scratch, due to surface waviness of the Al ribbon. Momentarily, a belt-shaped bond zone was formed at the center, normally due to the ultrasonic vibration. The island streaks could be clearly observed at 104 fps. However, the central belt zone was unclear and appeared translucent at 104 fps; although it was clear when observed at 103 fps. The island streaks were unclear at 103 fps. The positional relation of the island streaks and the central belt zone was confirmed from in-situ observation results of a twist and peel test of Al ribbon bonded to silica substrate. The central belt zone was between the island streaks and the silica substrate.

Influence of Kinetic Parameters on Vehicle Twist Test of Exported Train

Influence of Kinetic Parameters on Vehicle Twist Test of Exported Train

Multilevel PWM: A Tool to Explore Insulation PD Characteristics

The benefits of employing multilevel pulsewidth-modulated (PWM) waveforms for diagnostic purposes compared to sinusoidal- and square-shaped voltages are presented in this paper. Examples on how the high voltage circuits are designed to enable these studies, as well as results, are discussed. To demonstrate the approach, it is investigated what influence the choice of PWM levels has on the partial discharge (PD) characteristics for two similar wire specimens insulated by different materials. Here, to resemble a motor winding, two different twisted pair test objects insulated by either pure polyamide-imid (PAI) material or with added conductive Cr2O3 material were exposed to voltages with ultrashort rise times. The test objects were fed from either two-, three-, five-, or seven-level inverter waveforms of similar shape as in actual applications. To compare the performances, measurements of the PD characteristics were conducted. Specifically, the total number of PDs, as well as their average maximum amplitude per cycle, was obtained together with the phase-resolved PD pattern for each case. The experimental results presented in this paper show that the total peak and summed PD magnitude (exposure) drop considerably more for the Cr2O3 insulation compared to PAI when applying a five-level or higher level inverter. This reduction is more significant for the insulation with added Cr2O3 material and the usage of higher inverter levels reveals this. As more information can be obtained using higher inverter levels, the evaluation of new material constitutions is preferably done utilizing at least a three-level inverter or higher.

Partial discharge characteristics at ultra-short voltage risetimes

This paper describes continuation of author's works on the impact of PWM waveforms characterized by ultra-short rise times on PD characteristics in high voltage insulation systems. The implications of this kind of voltage exposure is becoming increasingly important as with rapid development of silicon carbide (SiC) and gallium nitride (GaN) based power electronic components the rise times used in machine control circuits keep getting shorter and the carrier frequencies higher. There is an imminent need to further develop diagnostic methods for PD detection at such extreme conditions. A PD measurement circuit based on capacitive decoupling and suitable for ultra-short rise times is presented here. Functionality of the circuit is demonstrated for a twisted pair test object insulated by enamel containing chromium oxide (Cr2O3) filler for rise times between 15 and 800 ns. The impact of voltage steepness on the PD extinction voltages (PDEV) and on other measurable parameters is reported. Specifically, the total number of PDs and their amplitude per modulated cycle are shown. The PD magnitude keeps increasing with the gradually decreased rise time, while the PDEV decreases. However, when compensating for voltage overshoot, less difference is noted. It is also demonstrated that the used PD detector allow for measurements at carrier frequencies well exceeding 1 kHz and rise times well below 100 ns as well as how the PD characteristics changes due to voltage overshoots inflicted by reflections.

Microstructural, Mechanical and Corrosion Investigations of Ship Steel-Aluminum Bimetal Composites Produced by Explosive Welding

In this study, explosive welding was used in the cladding of aluminum plates to ship steel plates at different explosive ratios. Ship steel-aluminum bimetal composite plates were manufactured and the influence of the explosive ratio on the cladded bonding interface was examined. Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) studies were employed for the characterization of the bonding interface of the manufactured ship steel-aluminum bimetal composites. Tensile-shear, notch impact toughness, bending and twisting tests, and microhardness studies were implemented to determine the mechanical features of the bimetal composite materials. In addition, neutral salt spray (NSS) tests were performed in order to examine the corrosion behavior of the bimetal composites.

Ultra-flexible and robust transparent electrodes by embedding silver nanowires into polyimide matrix

Silver nanowires (AgNWs) percolated films have been extensively considered as promising candidates for alternative transparent electrodes. However, due to their high surface roughness, poor adhesion and thermal stability, their practical use in transparent conducting film application is still heavily limited. In this paper, we report ultra-flexible transparent electrodes by imbedding AgNWs into polyimide (PI) thin films to achieve smooth surface, pronounced thermal stability, and high adhesion. Besides the excellent electrical conductivity of about 7-13Ω/□ in sheet resistance, the obtained AgNWs/PI films have excellent transparency and mechanical resilience due to the intrinsic physical and chemical properties of PI organic polymer. By embedding AgNWs into PI, the surface roughness of AgNWs percolated films can be reduced from 39.5 nm to 6 nm (RMS values), and the adhesion of AgNWs to PI is greatly enhanced if compared to the case of only AgNWs onto glass or plastic substrates. Additionally, the AgNWs/PI films show extraordinary stability in terms of electrical conductivity after the arbitrary twisting and thermal heating test, respectively, which are demonstrated by the electrical-thermal measurements via thermal IR imaging.

Specimen's plane misaligned installation solution based on charge fluctuation inside SEM

Precise specimen's installation is a sticking point to ensure the characterization accuracy of the in-situ material property test. Although it is common knowledge that specimen's plane misaligned installation (PMI) would cause extra force loading during mechanical testing, there are few effective solutions available to deal with it at the current stage, especially during the in-situ scanning electron microscopy (SEM) test. Taking into consideration the charge fluctuation phenomenon under SEM, this paper proposes a highlight area variation (HAV) method for specimen deformation judgment, i.e., the specimen deformation is defined when the highlight area changes greater than 20% of the initial value of the specimen surface. Three types of specimens with different resistivities, i.e., human hair (electrical resistivity ∼3 × 1012 Ω cm), optical fiber (electrical resistivity ∼1017 Ω cm), and magnetic wire (electrical resistivity ∼2 × 10−5 Ω cm), are chosen to verify the effectiveness of the HAV method. Furthermore, combined with the developed robot-aided alignment system, the specimen's PMI problem can also be solved. In the demonstration, the human hair specimen is installed across two specimen stages and its in-situ twisting (in 360°) test is implemented. The results clearly indicate that the HAV method and the robot-aided alignment system are practical and reliable, and the specimen can be aligned on the same plane and installed precisely with accuracy up to 3 μm. This method will benefit the in-situ SEM material mechanical property test and has a significant impact in fundamental material research.

Partial discharge characteristics within motor insulatioi exposed to multi-level PWM waveforms

The frequent use of variable speed drives fed by pulse width modulated (PWM) inverters allow for a more efficient utilization of electric energy. The drawback is however that the stress imposed on motor winding insulation increases and partial discharges (PDs) may appear under such conditions, being considered the major contributor to the reduction of the insulation life time. This paper presents what influence the choice of PWM level and rise time has on the PD characteristics for two different motor insulations as well as introducing suitable high voltage generation test-set ups for these kinds of measurements. The two different test objects were twisted pair and a pig tail motor insulation test objects, the latter aimed for higher voltage levels. These test objects were fed from either two-, three-, four- or five level inverters of similar type, as often used in actual applications. Additionally a six level inverter was used for verification purposes. The twisted pair test objects were insulated by a polyamide-imide enamel, whereas the motor pig tail insulation objects were mica-epoxy based. To compare the performances, measurements of the PD characteristics are reported and observations concentrate on the importance of the voltage rise time, on the size of the voltage step in relation to the extinction voltages (PDEV). Specifically, the total number of PDs and their amplitude per cycle is obtained. The experimental results show that the total summed PD magnitude (exposure) drops considerably when applying the three- or higher level inverters. However the maximum PD magnitude is less dependent, which indicates that a change to a high level inverter alone may still not be sufficient condition for increasing motor insulation system life. In conclusion a combination of the PDEV level, rise time and PWM level must all together be considered in this complex design process.

Breakage of Automotive Spring Washer During Twist Test: A Metallurgical Analysis

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. The washer used in automotive engine component is of split or spring lock washer. A ring split at one point and bent into helical shape. The benefit of spring lock washers lies in the trapezoidal shape of the washer. When compressed to loads near proof strength of the bolt, it will twist and flatten. This reduces the spring rate of the bolted joint which allows it to maintain more force under the same vibration levels. This prevents from loosening. The steel washer is one of the critical safety components for automobile engine, and its failure may cause severe safety issue. Before subjecting to manufacturing, the washer undergoes different process lines (wire rod → drawing → annealing → pickling → flattening → spring washer → single spring washer). After manufacturing of washer, toughness test is done to find out the metallurgical soundness and surface quality of the washer. In this toughness test the washer in a vice with the split ends free and straight above the vice jaws, a 90° segment of the free end is gripped with a wrench and bent. Washers should withstand twist test through a 90° angle without signs of fracture. The present paper highlights premature failure of automotive washer which failed during twist test. From the analysis, it has been observed that the distribution of spheroidized carbide is more uniform in good samples than that of rejected samples. Hardness profile variation was observed between good and bad spring samples. Overall investigation does not indicate any problem related to supplied wire rod material quality as no wire breakage problem observed. Inhomogeneous annealed structure in flat wire seems to result into variation in washer performance during twist test.

Twisting fatigue in multilayer films of Ag-alloy with indium tin oxide on polyethylene terephthalate for flexible electronics devices

Twisting monotonic and fatigue experiments were conducted on multi-layered films of Ag-alloy based indium tin oxide (ITO) deposited on polyethylene terephthalate (PET). In the twisting tests, crack development and electrical resistance were monitored in situ. Cracks initiated at an angle of 39°±1.7° and propagated towards the direction of the sample length. Two sets of experiments were performed; the first set of experiments was conducted to study the effect of twisting angle and temperature on the film's electromechanical performance. The other set of experiments was conducted to study the effect of temperature in the absence of cyclic twisting deformation. The change in electrical resistance increased with number of twisting cycles and twisting angle. In addition, the highest change in electrical resistance was observed for samples subjected to cyclic fatigue at 100°C, which is attributed to crack growth and oxidation of the Ag-alloy layer. The cracks were observed to initiate not only from coating defects but also from edge defects. Development of cracks is accelerated due to the combined effects of the external repeated stress and temperature. Therefore, it is suggested that controlling temperature when using ITO/Ag-alloy/ITO thin film under mechanical stress is important for electrical device performance; temperatures in both fabrication and use should not exceed 50°C.

A Feasibility Study on CNT- and Graphene-aided Structural Health Monitoring of Wind Turbine Blades

This paper presents a study on incorporation of hybridized MWCNTS and rGO in fiber-reinforced plastics for structural health monitoring in real time. Carbon nanoparticle that has certain MWCNT to rGO ratio was dispersed in a solvent were uniformly spray-coated on the surfaces of glass fiber fabrics, which were then layed-up and impregnated with an unsaturated polyester resin using vacuum-assisted resin transfer molding(VARTM) to form composite samples. Prior to VARTM process, electrodes were embedded on the sprayed coated glass fiber ply for electrical resistance change monitoring. The composite sample was subjected to cantilever bending and twist test, during which the changes in resistances between various electrode pairs were measured and recorded. Experimental results showed the dependence of resistance change on the deformation. In particular, this research covers hybridized MWCNTS and rGO electrical network on wind turbine blade. Cantilever bending and twist test were demonstrated by simulation program and this paper gives proposal about future application on huge composite part with MWCNT and rGO.

Nanorobotic System iTRo for Controllable 1D Micro/nano Material Twisting Test

In-situ micro/nano characterization is an indispensable methodology for material research. However, the precise in-situ SEM twisting of 1D material with large range is still challenge for current techniques, mainly due to the testing device’s large size and the misalignment between specimen and the rotation axis. Herein, we propose an in-situ twist test robot (iTRo) to address the above challenges and realize the precise in-situ SEM twisting test for the first time. Firstly, we developed the iTRo and designed a series of control strategies, including assembly error initialization, triple-image alignment (TIA) method for rotation axis alignment, deformation-based contact detection (DCD) method for sample assembly, and switch control for robots cooperation. After that, we chose three typical 1D material, i.e., magnetic microwire Fe74B13Si11C2, glass fiber, and human hair, for twisting test and characterized their properties. The results showed that our approach is able to align the sample to the twisting axis accurately, and it can provide large twisting range, heavy load and high controllability. This work fills the blank of current in-situ mechanical characterization methodologies, which is expected to give significant impact in the fundamental nanomaterial research and practical micro/nano characterization.

Investigation of the Microstructural, Mechanical and Corrosion Properties of Grade A Ship Steel-Duplex Stainless Steel Composites Produced via Explosive Welding

Grade A ship-building steel-AISI 2304 duplex stainless steel composite plates were manufactured via explosive welding. The AISI 2304 plates were used to clad the Grade A plates. Optical microscopy studies were conducted on the joining interface for characterization of the manufactured composite plates. Notch impact, tensile-shear, microhardness, bending and twisting tests were carried out to determine the mechanical properties of the composites. In addition, the surfaces of fractured samples were examined by scanning electron microscopy (SEM), and neutral salt spray (NSS) and potentiodynamic polarization tests were performed to examine corrosion behavior. Near the explosion zone, the interface was completely flat, but became wavy as the distance from the explosion zone increased. The notch impact tests indicated that the impact strength of the composites decreased with increasing distance from the explosion zone. The SEM studies detected brittle behavior below the impact transition temperature and ductile behavior above this temperature. Microhardness tests revealed that the hardness values increased with increasing distance from the explosion zone and mechanical tests showed that no visible cracking or separation had occurred on the joining interface. The NSS and potentiodynamic polarization tests determined that the AISI 2304 exhibited higher corrosion resistance than the Grade A steel.

Breakage of Automotive Spring Washer during Twist Test: A Metallurgical Analysis

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. The washer used in automotive engine component is of split or spring lock washer. A ring split at one point and bent into helical shape. The benefit of spring lock washers lies in the trapezoidal shape of the washer. When compressed to loads near proof strength of the bolt, it will twist and flattern. This reduces the spring rate of the bolted joint which allows it to maintain more force under the same vibration levels. This prevents from loosening. The steel washer is one of the critical safety component for automobile engine and its failure may cause severe safety issue. Before subjecting to manufacturing the washer undergoes different process lines (Wire Rod → Drawing → Annealing → Pickling → Flattening → Spring Washer → Single Spring Washer). After manufacturing of washer toughness test is done to find out the metallurgical soundness and surface quality of the washer. In this toughness test the washer in a vice with the split ends free and straight above the vice jaws, a 90° segment of the free end is gripped with a wrench and bent. Washers should withstand twist test through a 90° angle without signs of fracture. The present paper highlights premature failure of automotive washer which failed during twist test. From the analysis, it has been observed that the distribution of spheroidized carbide is more uniform in good samples than that of rejected samples. Hardness profile variation was observed between good and bad spring samples. Overall investigation does not indicate any problem related to supplied wire rod material quality as no wire breakage problem observed. Inhomogeneous annealed structure in flat wire seems to result into variation in washer performance during twist test.

The Strain Gradient Elasticity Theory in Orthogonal Curvilinear Coordinates and its Applications

AbstractThe strain gradient elasticity theory including only three independent material length scale parameters has been proposed by Zhou et al. to explain the size effect phenomena in micro scales. In this paper, the general formulations of strain gradient elasticity theory in orthogonal curvilinear coordinates are derived, and then are specified for the cylindrical and spherical coordinates for the convenience of applications in cases where orthogonal curvilinear coordinates are suitable. Two basic problems, one is the twist of a cylindrical bar and the other is the radial deformation of a solid sphere, are analyzed under the cylindrical and spherical coordinates, respectively. The results reveal that only the material length scale parameter l2 enters the torsion problem, while completely disappears in the problem of radial deformation of a sphere. The size effect of radial deformation of a solid sphere is controlled by the material length scale parameters l1 and l2. In addition, for the incompressible solid sphere especially, only the material length scale parameter l1 enters this radial deformation problem by neglecting the strain gradient terms associated with hydrostatic strains. Predictably, the present paper offers an alternative avenue for measuring the three independent material length scale parameters from bar twisting and sphere expansion tests.

Design Optimization of Round Strands Made by Twisted Stacks of HTS Tapes

A twisted stack of high-temperature superconducting (HTS) tapes soldered into copper profiles was used as a strand in the fabrication of the 60-kA/12-T HTS cable prototype at the Center for Research in Plasma Physics (CRPP). Considering the strand in general as a modular element for the high-current cables, design parameters of the strand need to be optimized in order to best fulfill requirements of appropriate application field. During the development program of the HTS fusion cable at CRPP, influence of the design parameters on the strand's performance was obtained as input data for the optimization process. In this paper, we summarize the results of the twisting, bending, and transverse pressure tests on strands of various tapes and profile's geometries. Finite-element model for the transverse pressure test was developed, validated with the test results, and used for the design proposals. Effect of the stack aspect ratio, tape properties, and anisotropy, as well as selection of HTS material for the strand, will be discussed.

形状記憶合金に生ずる相変態と塑性変形を表す構成方程式モデル

A constitutive model of shape memory alloys (SMAs) including phase transformation and plastic deformation is proposed. This model is based on the one-dimensional phase transformation model in which the austenite and the martensite phases transform one-dimensionally. A form of the yield function is assumed to the same as the driving energy minus the required transformation energy for the phase transformation. To show the validity of this model, a cyclic twisting test of an SMA shaft is simulated numerically. The result shows that the proposed model can reproduce the stress-strain-temperature relationship during the phase transformation and the plastic deformation qualitatively.

헬리콥터용 무베어링 로터 시스템의 강성 및 고유 진동수 측정

The stiffness and natural frequencies for blades, flexbeam, and torque tube of bearingless rotor system are measured to determine the material input properties such as mass distributions and stiffness distribution for the rotor dynamics and load analysis. The flap stiffness, lag stiffness, and torsional stiffness are calculated by measuring section strain or twist angle, gages position, and applied loads through bending and twist tests. The modal tests are undertaken to find out the natural frequencies for flap, lag, torsion modes in non-rotating conditions. The stiffness values and mass properties are tuned and updated to match prediction frequencies to the measured frequencies. The rotorcraft comprehensive code(CAMRAD II) is used to analyze the natural frequencies of the specimens. The analysis results with the updated material properties agree well with the measured frequencies. The updated properties will be used to analyze the rotor stability, dynamic characteristics and loads for the rotor rotation test in a whirl tower.

Numerical investigation of leaky modes in helical structural waveguides embedded into a solid medium

Helical multi-wire cables are widely used in bridges (suspended or prestressed) and anchored retaining wall constructions. Such structures can be damaged or degraded due to corrosion and fatigue. Non destructive evaluation techniques are required to reveal defects inside cable structures. Among these numerous techniques, elastic guided waves are of potential interest owing to their ability to propagate over long distances. However in civil engineering, cables are often buried or grouted in large solid media that can be considered as unbounded. Waves can strongly attenuate along the guide axis due to the energy leakage into the surrounding medium, which reduces the propagating distance. This energy leakage can be enhanced in helical structures, which further complicates their inspection. Searching modes with low attenuation becomes necessary. The goal of this work is to propose a numerical approach to compute modes in embedded helical structures, combining the so-called semi analytical finite element method and a radial perfectly matched layer technique. Two types of radial perfectly matched layer, centered and off-centered, are considered. Both are implemented in a twisting coordinate system which preserves translational invariance. The centered configuration is validated thanks to the twisted cylinder test case. The effect of twist on the eigenspectrum is briefly discussed. Then, an embedded helical wire of circular cross-section is considered. The off-centered configuration is shown to give the same results as the centered one. The effect of twist on modal attenuation is investigated. Finally, computations are performed for a seven-wire strand embedded into concrete, widely used in civil engineering cables.