Direct Mechanical Contact Research Articles

Surface hardness imaging of a low-alloy steel using laser-induced breakdown spectroscopy

Conventional tactile hardness testing methods such as Brinell, Rockwell or Vickers rely on direct mechanical contact, which results in significant surface damage and prohibits their application to complex specimen geometries. Furthermore, the sample must have a certain thickness for tactile testing methods to be applied. In this work, we investigated the use of laser-induced breakdown spectroscopy as a fast non-quantitative alternative for visualizing surface hardness gradients. To eliminate the influence of different chemical compositions, we manually heat-treated low-alloy steel pieces cut from the same raw material and batch. By partially quenching a sample piece, we were able to obtain a hardness gradient along the longitudinal axis. We found a positive correlation between the ratio of ionic to atomic line intensities of iron (I Fe II 263.1 nm / I Fe I 358.1 nm) and the mechanical hardness of the sample surface. By scanning the surface and measuring the line intensity ratios, we were able to obtain a spatially resolved map directly correlating with the surface hardness distribution. Additionally, it was observed that the irradiation of laser pulses resulted in significant surface alterations, thereby invalidating subsequent measurements and scans at identical positions.

Non-Gaussian Displacements in Active Transport on a Carpet of Motile Cells.

We study the dynamics of micron-sized particles on a layer of motile cells. This cell carpet acts as an active bath that propels passive tracer particles via direct mechanical contact. The resulting nonequilibrium transport shows a crossover from superdiffusive to normal-diffusive dynamics. The particle displacement distribution is distinctly non-Gaussian even at macroscopic timescales exceeding the measurement time. We obtain the distribution of diffusion coefficients from the experimental data and introduce a model for the displacement distribution that matches the experimentally observed non-Gaussian statistics. We argue why similar transport properties are expected for many composite active matter systems.

Bistable Actuation Based on Antagonistic Buckling SMA Beams

Novel miniature-scale bistable actuators are developed, which consist of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to have opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snap-through motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography, and systems integration. The stationary force–displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact to a low-temperature heat source in the range of 130–190 °C. The bistable actuation is characterized by a large stroke up to 3.65 mm corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature. The bistable actuation at low-temperature differences provides a route for waste heat recovery.

Electrochemical properties of bismuth chalcogenide/MXene/CNT heterostructures for application in Na-ion batteries

The development of high-performance anodes for sodium-ion batteries (SIBs) has recently attracted great attention. Most of the proposed anode materials for SIB systems suffer from insufficient electrical and mechanical contact of the active material with the current collector causing low reversible capacity and short lifespan. To solve this issue, an innovative approach could be the direct synthesis of the active material around and on the top of an electrically conductive network. The nanostructuring with SWCNTs and MXenes increases the active surface area, improves expansion/contraction properties, and establishes a direct mechanical and electrical contact. In this work the performance of binder-free Bi2Se3/SWCNT and Bi2Se3/MXene/SWCNT anode materials, which were synthesized by the direct physical vapor deposition of Bi2Se3 nanostructures on SWCNT and MXene/SWCNT network systems, was investigated. The results showed that the Bi2Se3/SWCNT electrode with the mass ratio of (1:1) exhibits excellent rate performance and high discharge capacity in the short-term (0.1 A g−1) and long-term (5.0 A g−1) cycling by delivering 247 and 120 mAh g−1 respectively demonstrating its perspectives for the application as an anode in SIBs.

A highly stable and fully tunable open microcavity platform at cryogenic temperatures

Open-access microcavities are a powerful tool to enhance light–matter interactions for solid-state quantum and nanosystems and are key to advance applications in quantum technologies. For this purpose, the cavities should simultaneously meet two conflicting requirements—full tunability to cope with spatial and spectral inhomogeneities of a material and highest stability under operation in a cryogenic environment to maintain resonance conditions. To tackle this challenge, we have developed a fully tunable, open-access, fiber-based Fabry–Pérot microcavity platform that can be operated under increased noise levels in a closed-cycle cryostat. It comprises custom-designed monolithic micro- and nanopositioning elements with up to mm-scale travel range that achieve a passive cavity length stability at low temperature of only 15 pm rms in a closed-cycle cryostat and 5 pm in a more quiet flow cryostat. This can be further improved by active stabilization, and even higher stability is obtained under direct mechanical contact between the cavity mirrors, yielding 0.8 pm rms during the quiet phase of the closed-cycle cryocooler. The platform provides the operation of cryogenic cavities with high finesse and small mode volume for strong enhancement of light–matter interactions, opening up novel possibilities for experiments with a great variety of quantum and nanomaterials.

High temperature difference in a new flexible thermoelectric bismuth telluride microgenerator

We present new microTEGs based on doped Bi 2 Te 3 thin films deposited on polyimide membrane able to operate under a temperature difference as high as 280 K. We developed two microTEGs with different designs to obtain the lowest internal resistance possible. The thermoelectrical properties coupled to the low contact resistance lead to an open circuit voltage of 64 mV and a maximum output power of 36 µW under a temperature difference of 206 K. Such high temperature difference cannot be obtain in bulk commercial TEG systems; it is maintained without heat sink but only using a copper ring supporting a thin polyimide membrane. These thermoelectric devices deposited on suspended polyimide membranes open new ways for waste heat applications, in particular by direct mechanical and thermal contact with hot sources. • We present new microTEGs based on doped Bi 2 Te 3 thin films deposited on polyimide membrane. • An open circuit voltage of 64 mV and a maximum output power of 36 µW under a temperature difference of 206 K is obtained. • The temperature difference up to 206 K is obtained without heat sink but only using a copper ring.

Non-contact stress-strain characterization of aluminum alloy by laser-induced thermal-wave radar (LTR) imaging

Evaluation of the stress/strain state in alloys is usually performed by direct mechanical measurements, contact ultrasound or ionizing-radiation nondestructive testing (NDT). Safe and totally non-contact methods have considerable advantages and are worthy of further development. In this work, a novel active infrared NDT framework with a linear-frequency-modulated laser-induced thermal-wave radar (LFM-LTR) imaging modality was proposed to quantitatively analyze thermo-mechanical properties as a function of the changing external loading. Chirp-modulated laser emission generates a depth-resolved diffusion-wave field which is analyzed with a modified anisotropic LTR theory. Features of stress-induced thermal anisotropy within uniaxial loaded materials were parametrized and extracted from simulated LTR signals which form the basis for solving the inverse problem of determining tensorized thermo-mechanical properties. An LTR experimental setup was built and used to validate the foregoing theoretical model and numerical analysis. Experimental thermo-mechanical property variation throughout the tensile test was eventually determined in terms of the nominal conductivity tensor without using any contacting sensors. The proposed active infrared testing scheme is promising to facilitate remote and indirect sensing of residual stresses in materials.

Hydrostatic pressure in granular environment

The problem is that to date there is no general theory of the granular state of matter in a closed form. However, there are some well-developed models that use, for example, the representation of a continuous environment. Typical bulk material is a large conglomeration of micro-mechanical particles of different sizes and shapes that interact with each other and the walls contain containers by mainly repulsive forces in direct mechanical contact (by nature it is forces of electromagnetic origin – dry and viscous friction forces, as well as traction).In the proposed work to study the pressure in a multiparticle micro-mechanical system, a model of a lattice gas in a gravitational field is considered. Analysis of the determination of free energy and entropy allowed us to establish the corresponding equilibrium density profile, which is described by a Fermi-type function. The Fermi profile in the form of a density field was used to find the vertical hydrostatic pressure for which the analytical expression was obtained. Hydrostatic pressure was different from the known relations derived from the theory of condensed matter. The obtained results are confirmed by experimental observations, which indicate a complex, anisotropic significantly different from the known from the theory of condensed matter distribution of even vertical pressure in large conglomerations of discrete micro-mechanical particles. Which really repeats the Fermi distribution. The obtained results stimulate the revision of typical ratios of hydrostatics of continuous media, such as Pascal's laws. Torricelli, Archimedes and Bernoulli in the case of discrete micro-mechanical (granular) systems. The conclusions of the work can be significant in the design and evaluation of operating parameters of storage, release and transportation of bulk cargo, which consist of discrete micro-mechanical conglomerations with different degrees of compaction and compaction.

High-Density Nanowells Formation in Ultrafast Laser-Irradiated Thin Film Metallic Glass

HighlightsUltrafast laser-induced nano-topography modifications: generation of highly concentrated 20 nm diameter nanowells on the surface with expected applications for storage of chemical and biological active species and for blocking crack propagation.Ultrafast laser-induced structural modifications: turning of a metallic glass to a composite material of monoclinic zirconia crystallites embedded inside amorphous metallic glass.A flexible one-step laser irradiation process without direct mechanical contact for thin film metallic glasses surface functionalization.

Magnetic Contactless Crank-rocker Machine

Objective: In this paper, a proposed technique of motion transmission is introduced, which is based on the crank-rocker principle of motion. The energy transmission action is performed through magnetic force, in which no direct connection is made between the energy source input and the energy load output. Also, to illustrate the concept of motion and to approve the continuity of energy transmission using this proposed technique, a simple model of this mechanism has been built and run, showing the basic sequence of operation. Methodology/analysis: In this mechanical transmission mechanism, one side is rotating and the other side is vibrating, in which any side is energy input (which is usually the vibrating rocker), and the other side is energy output (which is the rotating crank). That seems similar to the classical crank-rocker machine in the four-bar mechanism, but without direct mechanical contact between the input and output energy stream. The concept of motion and mathematical analysis with structuring conditions is provided in this paper, where the dynamic analysis of the system is left for future work. A pilot physical prototype is manufactured and experimentally tested, validating the proposed design. Findings: The structural parameters of this proposed contactless crank-rocker machine have been modelled and simulated using the MATLAB program. It shows that these parameters could be selected and optimized to guarantee the minimum conditions for continued energy transmission. Based on these parameters, a simple model has been built and operated, which illustrates the concept of motion and validates the finding of MATLAB simulation. Novelty/improvement:Contactless crank-rocker motion is a very promising technique. It is possible to apply it in many applications, like the energy harvesting area, and it could be employed certainly in specific designs, such as MEMS, where no other motion transmission types can be used. Doi: 10.28991/ESJ-2022-06-02-07 Full Text: PDF

Design of a tunable electromagnetic vibration absorber for transient vibration suppression under impulse

Vibration absorbers usually aim to control the steady-state vibration of harmonic excitation based on the traditional fixed point theory, but few efforts focus on suppressing the transient vibration caused by impulse excitation. In this paper, the excitation is regarded as impulse in modeling, and it can be used for impulse excitation. Thus, the transient vibration absorber is designed to control the transient vibration, and the stiffness of the absorber is a key factor to control the response of the primary system. This paper presents a tunable electromagnetic transient vibration absorber to avoid direct mechanical contact for the absorber. The analytical results of the transient response indicate that the vibration can be attenuated by adjusting the stiffness of the absorber. In order to establish the model of the electromagnetic stiffness, the absorber is divided into three equivalent virtual springs. The circular current loop is equivalent to the rectangular current loop to show the spatial distribution of the magnetic flux density in the air gap. The experimental tests demonstrate that the transient vibration of the primary system can be attenuated by 13% when the current of the coil is 6 A.

Noncontacting optostriction driven anisotropic and inhomogeneous strain in two-dimensional materials

The authors propose a novel optostriction effect to induce intrinsic tensile/compressive strains in two-dimensional materials without suffering Euler's instability. The technique can avoid direct and invasive mechanical contacts, and can be further tuned to create in-plane optoflexoelectricity without any symmetry constraint.

Tribocorrosion behaviour of tin bronze CuSn12 under a sliding motion in NaCl containing environment: Contact to inert vs. reactive counterbody

Tribocorrosion behaviour of tin bronze was examined in NaCl environments using two counterbodies: inert alumina and reactive bearing steel. The results with inert counterbody disclosed growing alloy losses with increasing potential, due to wear-influenced corrosion. Degradation progressed through the development, modification and removal of corrosion products, exposing fresh surface for the environment. With reactive counterbody, galvanic coupling between the two metals played an important role in the behaviour of the tribopair. At the lowest potential, where counterbody corrosion progressed slowly, the metals were in a direct mechanical contact, introducing wear in the ploughing mode in tin bronze. At anodic potentials, counterbody provided cathodic protection to tin bronze, with most material losses occurring in the counterbody by corrosion and wear-influenced corrosion.

ТРАНСПОРТНЫЕ УСТРОЙСТВА ДЛЯ НЕЖЕСТКИХ ЦИЛИНДРИЧЕСКИХ ОБЪЕКТОВ ПРОИЗВОДСТВА С ГАЗО-МАГНИТНЫМИ НАПРАВЛЯЮЩИМИ ПАЛЕТ

The article presents typical layouts of technological equipment for processing non-rigid cylindrical parts using the levitation effect at the stage of their transportation and loading without direct mechanical contact with the mounting and guiding elements. The dependences of the carrying capacity of aerostatic supports on the size of the working gap and air pressure, varying in a wide range, are obtained experimentally. The design and principle of operation of transport devices using the effect of levitation of pallets with objects of processing are described.

Passive Alignment Method for the Bonding of Flat Surfaces Using a Squeeze Flow

A method to passively align bonded components without direct mechanical contact has been developed. This method uses the pressure field generated by the squeeze flow between the parts during the bonding process to increase the parallelism of planar components. A computational fluid dynamic (CFD) model has been developed to study the squeeze flow phenomenon and to determine generated efforts. Based on these calculations, an assembly stage standing on a flexure pinned linkage has been developed. This assembly stage had two purposes. The first was to show the possibility of passive mechanical alignment using a squeeze flow. The second was to measure efforts to confirm the CFD model. These measurements have led to a refined CFD model taking into account the non-Newtonian behavior of the fluid at high shear rates. This technique was initially developed for the assembly of a fiber-optic-to-silicon-chip-interface. Other potential applications could be wafer bonding, bonding of multiple wafer stacks, or 3D integrated circuits.

Discrete-element model of electrophoretic deposition in systems with small Debye length: effective charge, lubrication force, characteristic scales, and early-stage transport

Electrophoresis was recently proposed as a new method for controlling properties and structure of the interface between cement and steel elements in petroleum and construction industries (Lavrov A et al., 2018). Cement slurries typically contain a wide range of particle sizes (micron to hundred micron), and the particles have small Debye lengths (nanometer). The relative magnitude of different forces acting on particles in such systems was examined. A formulation based on the DLVO theory was used to calculate van der Waals forces and electric repulsion forces between particles. It was shown that the following forces need to be included in a discrete-element model of electrophoretic deposition in this case: viscous drag force, force due to the external electric field, gravity + buoyancy force, lubrication force, van der Waals force, and direct mechanical contact force. The recommended cut-off gaps for van der Waals and lubrication forces are equal to the radius of the larger particle participating in the interaction. An example DEM simulation has revealed that deposition starts with deposing finer particles. Shortly after, larger particles are deposited on the finer substrate. This is due to the larger speed-up time of larger particles. The difference in the speed-up time leads to some size segregation at the early stage of deposition, even though the particle mobility is independent of the particle size. The model enables some insight into the processes that take place during the earlier stages of electrophoretic deposition that are difficult to capture and analyze in laboratory experiments.

Optical Phase Measurements of Disorder Strength Link Microstructure to Cell Stiffness

There have been sustained efforts on the part of cell biologists to understand the mechanisms by which cells respond to mechanical stimuli. To this end, many rheological tools have been developed to characterize cellular stiffness. However, measurement of cellular viscoelastic properties has been limited in scope by the nature of most microrheological methods, which require direct mechanical contact, applied at the single-cell level. In this article, we describe, to our knowledge, a new analysis approach for quantitative phase imaging that relates refractive index variance to disorder strength, a parameter that is linked to cell stiffness. Significantly, both disorder strength and cell stiffness are measured with the same phase imaging system, presenting a unique alternative for label-free, noncontact, single-shot imaging of cellular rheologic properties. To demonstrate the potential applicability of the technique, we measure phase disorder strength and shear stiffness across five cellular populations with varying mechanical properties and demonstrate an inverse relationship between these two parameters. The existence of this relationship suggests that predictions of cell mechanical properties can be obtained from examining the disorder strength of cell structure using this, to our knowledge, novel, noncontact technique.

Examining the structural contribution to the electrical character of single wall carbon nanotube forest by a height dependent study

We report an electrical investigation of single-wall carbon nanotube (SWCNT) forests where we have succeeded in elucidating the electrical contributions of the forest surface (cap) and vertically aligned (body) structures of the assembly. We applied an electrical characterization method to SWCNT forests patterned into a Hall bar-like configuration to reliably evaluate the lateral (i.e. in-plane) resistance for a series of SWCNT forests spanning three orders of magnitude, 0.3–700 μm, in height while avoiding direct mechanical contact to the measurement region. A simple model based on treating the forests as two parallel resistors was used to explain the observed behavior of the lateral resistivity and forest height. Through this approach we showed that the forests could be described electrically by two structural features, the cap and body. In addition, our analysis found that the resistivity of the body was about 22–720 times higher than that of the cap.

Determination of Aspect Ratio Limitations, Accuracy and Repeatability of a Laser Line Scanning CMM Probe

Coordinate measurement machine (CMM) probing techniques can involve direct mechanical contact (e.g., tactile probing) or diverse non-contact principles (e.g., laser line scan probing). For some applications, contact methods are not capable of measuring fast enough to ensure 100% quality controlled parts. A laser line scanning probe uses a laser triangulation-based method to acquire 3D measurement points on a workpiece relative to a sensor. Mounting the sensor in a 3D coordinate frame, e.g., in a CMM provides enough information to fully examine the workpiece. These techniques are most commonly exploited in medical industry and industries involving plate materials. A high data density and measurement speed are significant advantages when measuring free-form surfaces by laser line scanning, making the process much more time-efficient. However, high-precision geometrical features (such as cylinders, spheres, etc.) must be measured for locating and aligning the free-form shapes. The accuracy of the equipment therefore has to be assessed. Probe Maximum Permissible Error (MPEP) values below 10μm have been reported for cutting-edge laser line scanners. This paper compares the major influences on measurements on cylindrical features. First, the aspect-ratio limitations are considered by comparing two inherently different techniques. The stable inspection of reference features is important, while trying to maximize the spatial extent of the measured features. Second, the measurement method is analyzed in two ways: by using a limited sample of the features to increase stability and eliminate interference from neighboring features; by varying the number of scan tracks, which greatly affects the measurement time.

Magnetic excitation and identification of flexural modes of a circular plate

A spatially localized, oscillating, magnetic field was used to induce resonant vibrations in an aluminum circular plate without direct mechanical contact. Experiments were done with the plate in air, at a free surface, and fully submerged in water. This allowed the effect of fluid loading on the plate's spectrum to be examined for both the fully loaded and half loaded case. Since the magnetic field is spatially localized, identification of the mode shapes is possible by scanning the source along the target and measuring the varying response of the plate. Additional experiments were done with an open-ended fluid filled copper circular cylinder in which both resonant frequencies and mode shapes were identified. Both targets responded at twice the oscillation frequency of the applied field [B. T. Hefner and P. L. Marston, J. Acoust. Soc. Am. 106, 3340–3347 (1999)]. The response corresponds to the oscillation frequency of the Maxwell stress associated with combined applied field and induced eddy-current field. Excitation of both plate and cylinder was found to be measurable with a steady state and a tone burst source. [Work supported by ONR.]