Increase In Applied Force Research Articles

Thiol Coordination Softens Liquid Metal Particles To Improve On-Demand Conductivity.

Achieving tunable rupturing of eutectic gallium indium (EGaIn) particles holds great significance in flexible electronic applications, particularly pressure sensors. We tune the mechanosensitivity of EGaIn particles by preparing them in toluene with thiol surfactants and demonstrate an improvement over typical preparations in ethanol. We observe, across multiple length scales, that thiol surfactants and the nonpolar solvent synergistically reduce the applied stress requirements for electromechanical actuation. At the nanoscale, dodecanethiol and propanethiol in toluene suppress gallium oxide growth, as characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. Quantitative AFM imaging produces force-indentation curves and height images, while conductive AFM measures current while probing individual EGaIn particles. As the applied force increases, thiolated particles demonstrate intensified softening, rupturing, and stress-induced electrical activation at forces 40% lower than those for bare particles in ethanol. To confirm that thiolation facilitates rupturing at the macroscale, a laser is used to ablate samples of EGaIn particles. Scanning electron microscopy and resistance measurements across macroscopic samples confirm that thiolated EGaIn particles coalesce to exhibit electrical activation at 0.1 W. Particles prepared in ethanol, however, require 3 times higher laser power to demonstrate a similar behavior. This unique collection of advanced techniques demonstrates that our particle synthesis conditions can facilitate on-demand functionality to benefit electronic applications.

Piezoionic SnSe Nanosheets‐Double Network Hydrogel for Self‐Powered Strain Sensing and Energy Harvesting

AbstractFlexible strain sensors have enormous potential in wearable devices, robots, and health monitoring equipment. However, the poor stretchability of strain sensors based on semiconductors and the low sensitivity of resistance change‐based hydrogel strain sensors hinders the comprehensive application. Herein, a flexible piezoionic SnSe‐hydrogel composite with an optimized structure and improved performance is designed. The piezoionic output rises nonlinearly as the applied force increases, with the piezoionic coefficient up to 1780 nV Pa−1 and −7.21 nA Pa−1. The composite can realize the continuous positioning in 1D space based on the piezoionic effect. It also demonstrates self‐powered characteristics, an ultrafast response speed of 6–8 ms, and a high gauge factor of 95.89. The sensor is exemplified to monitor fist clenching and finger bending, which has the potential to discriminate different joint movements. Meanwhile, the device can light up a light–emitting diode under pressure and bending. The as‐prepared piezoionic SnSe‐hydrogel device, having both high stretchability and sensitivity, may shed light on developing high‐performance flexible strain sensors and generators.

Precisely Controlled Two-Dimensional Rhombic Copolymer Micelles for Sensitive Flexible Tunneling Devices

Nanoscale two-dimensional (2D) organic materials have attracted significant interest on account of their unique properties, which result from their ultrathin and flat morphology. Supramolecular 2D ...

Interaction between a motorized walker and its user: effects of force level on within-stride speed and direction fluctuations

Motorized walkers are among assistive devices that are currently in development that aim to help older adults maintain their independence, which is of growing importance in today’s ageing world. However, motorized walkers attempt to combine two different modes of generating forward motion: the user’s bipedal gait and the motorized walker’s wheel-driven locomotion. In contrast to the uninterrupted propulsion and continuous motion of wheel-driven locomotion, bipedal gait is cyclical, whereas propulsion occurs mainly in the push-off phase and the velocity and position of its center of mass oscillate within each gait cycle. This study aimed to explore the consequence of combining these two incompatible modes by investigating the effects of different force magnitudes applied by the motorized walker on the within-stride fluctuations generated from interactions with its user. When a constant force is applied by a motorized walker, regardless of whether the force is assistive or resistive, the magnitudes of the within-stride speed and directional fluctuations during the steady-state use increase as the magnitude of the applied force increases. The increase in fluctuations may be attributed to the conflict between the cyclical nature of walking and the continuous force applied.

A Simple Mechanical Model for Synthetic Catch Bonds

Summary Catch bonds are protein-ligand bonds that become more difficult to break as the applied force increases, a counterintuitive phenomenon that has not yet been reproduced in synthetic systems. Here, we have demonstrated that a simple mechanical design based on a tweezer-like mechanism can exhibit catch bond characteristics under thermal excitations. The tweezer has a force-sensitive switch that controls the transition of the system to a high-ligand-affinity state with additional ligand-tweezer interactions. Applying kinetic theory to a two-mass-two-spring idealized model of the tweezer, we show that by tuning the shape of the switch and the ligand-tweezer interaction energy landscapes, we can achieve greater lifetimes at larger force levels. We validate our theory with molecular dynamics simulations and produce a characteristic lifetime curve reminiscent of catch bonds. Our analysis reveals minimal design guidelines for reproducing the catch bond phenomenon in synthetic systems such as molecular switches/foldamers, DNA linkers, and nanoparticle networks.

Comparative analysis of three methods of risk assessment for repetitive movements of the upper limbs: OCRA index, ACGIH(TLV), and strain index

PurposeLiterature proposes different methods for risk assessment due to repeated movements of upper limbs. The results are sometimes different even if methods are applied in the same work conditions. This study, based only on hand/wrist work involving ulnar deviation, compares three methods among those most used for distal upper extremity (DUE) work-related musculoskeletal disorders (WMSDs): OCRA Index (O.I.), Strain Index (S.I.) and ACGIH(TLV). Design/methodology/approachThe work analyzes the algorithms of the methods in terms of number of parameters considered in the formulas, range of variability for each one, and their interaction in determining the final results. Starting to calculate maximum frequency that each method allows in no-risk conditions (varying force and duty cycle), specific scenarios were also created varying one parameter at a time among those determining risk (i.e. force, posture, recovery time …) for a better comprehension of the different algorithms proposed and the provided final results. FindingsThe results are generally different: in the 21 scenarios analyzed, all the methods indicate the same level of risk in only 6 cases when using the formula for the calculation of the hand activity level (HAL) in ACGIH(TLV), and in only 3 cases when using the table. Force bears a higher relative weight for ACGIH(TLV) compared to the others methods: the number of exertions per second allowed in the no-risk zone decreases markedly as the applied force increases. The S.I. was noted to generally be the most precautionary among those examined regarding the frequencies of movements allowed in the no-risk range. The use of categorical multiplier instead of linear, made the results mainly different in the intermediate risk conditions. Originality/valueThe differences in results are due not only to the different number of parameters considered by methods but also to the different risk limit values inside each algorithm. A greater amount of epidemiological data would be desirable in order to better define the conditions to be considered harmful for a worker performing repeated movements of the upper limbs.

Evaluation of Die Strength by Using Finite Element Method With Experiment Validation

3-D chip stacking packaging is becoming increasingly popular in the electronics packaging industry because the demand of current market has focused on cheaper products with higher performance characteristics and smaller form factors. Silicon wafers must be ground using wafer-thinning processes to achieve smaller packaging sizes. However, cracks may form in the silicon chips during stacking or while the device is in use. In this paper, the ball-breaker test is used to determine the maximum allowable force on a (1 0 0) silicon die. Finite element (FE) analysis using the commercial software ANSYS/LS-DYNA3-D is introduced to calculate the strength of the silicon die and compared with the experimental findings shows that the results are consistent with Hertzian contact theory. The effects of silicon die thickness and foundation material on the silicon die strength are also discussed in this paper. As the applied force increases, a crack appears on the edge of the contact area and propagates within the die. A decrease in die thickness results in the formation of radial cracks on the bottom surface as well as significant bending effects on the test die. The initial failure may originate from the radial crack and propagate toward the top surface of the die leading to die breakage. The strengths determined in this experiment decrease as the test die becomes thinner. Furthermore, if the insignificant bending behavior is observed, simulation results show that the maximum allowable force on a silicon die increases when a softer foundation material is used. However, a thin test die placed on a soft material is considerably easy to break because the tensile stress on the bottom surface of the die caused by the rapid increase in bending behavior significantly affects die breakage.

Temperature and Force Dependence of Nanoscale Electron Transport via the Cu Protein Azurin

Solid-state electron transport (ETp) via a monolayer of immobilized azurin (Az) was examined by conducting probe atomic force microscopy (CP-AFM), as a function of both temperature (248-373K) and applied tip force (6-15 nN). At low forces, ETp via holo-Az (with Cu(2+)) is temperature-independent, but thermally activated via the Cu-depleted form of Az, apo-Az. While this observation agrees with those of macroscopic-scale measurements, we find that for holo-Az the mechanism of ETp at high temperatures changes upon an increase in the force applied by the tip to the proteins; namely, above 310 K and forces >6 nN ETp becomes thermally activated. This is in contrast to apo-Az, where increasing applied force causes only small monotonic increases in currents due to decreased electrode separation. The distinct ETp temperature dependence of holo- and apo-Az is assigned to a difference in structural response to pressure between the two protein forms. An important implication of these CP-AFM results (of measurements over a significant temperature range) is that for reliable ETp measurements on flexible macromolecules, such as proteins, the pressure applied during the measurements should be controlled or at least monitored.

Axial buckling of multi-walled carbon nanotubes and nanopeapods

In this paper, we investigate both pre- and post-buckling behaviors of multi-walled carbon nanotubes and multi-walled carbon nanopeapods by incorporating into the applied forces of a prescribed beam equation both van der Waals interactions between the adjacent walls of the nanotubes and the interactions between the fullerenes and the inner wall of the nanotube. Two beam theories are employed. First, we utilize Donnell’s equilibrium equation to derive an axial stability condition for the multi-walled carbon nanotubes and multi-walled carbon nanopeapods. We then determine analytically the critical forces for single-walled and double-walled nanotubes and nanopeapods. Given the outer nanotube of a fixed radius, we observe that the critical force and strain derived from the axial buckling stability criterion decrease as a result of the molecular interactions between the adjacent layers of the nanotubes and the molecular interactions between the embedded fullerenes and the inner carbon nanotube, which is in agreement with existing literature. Next, we utilize an Euler–Bernoulli beam equation incorporating the curvature effect to obtain the post-buckled axial bending displacement for the multi-walled nanotubes and nanopeapods. We find that the interactions between molecules generate an inward force, which tends to resist any applied forces. While the inward force induced by the fullerenes to the inner wall of the nanotube vanishes as we increase the applied force, the inward force induced by the layers increases as the applied force increases. The main contribution of this paper is the incorporation of both van der Waals interactions and the curvature effect into prescribed beam theories to accurately measure the critical forces and the buckled displacements of multi-walled nanotubes and nanopeapods subject to a small external force. Our analysis is relevant to future nano devices, such as biological sensors and measuring devices for small forces arising from electrical charges or Casimir forces.

Dynamic behaviour of laterally loaded model piles in clay

Dynamic experiments in lateral mode were carried out on model aluminium single piles in a simulated elastic half-space filled with clay soil to determine dynamic constants of the soil–pile system and to study the bending behaviour of piles. Model piles with various lengths were subjected to steady-state harmonic vibrations with different magnitudes of force of 7–30 N applied over a wide range of frequencies from 2 Hz to 50 Hz. The load transferred to the pile, pile head displacement and strain gauge readings at different locations on the pile were measured. It is observed consistently that the magnitude of the applied force and the pile length significantly affect the natural frequency of the soil–pile system. It is found that rigid piles behave linearly even at the higher magnitudes of applied force, but that flexible piles behave non-linearly as the magnitude of the applied force increases, which leads to a substantial reduction of the lateral stiffness of the soil–pile system. Damping of the soil–pile system is found to increase with an increase in pile length and magnitude of the applied force, owing to the occurrence of radiation and hysteretic damping. Based on experiments carried out on model piles embedded in clay at low confining pressure, it is found that the maximum dynamic bending moment of long flexible piles is about four times higher than that of short rigid piles. The maximum bending moment under dynamic loads occurs at deeper depth than the corresponding depth for static loads, which indicates an increase of the active length of piles under dynamic load.

Fabrication of Gold Nanowires Using Contact Mode Atomic Force Microscope

Gold nanowires were fabricated using a contact mode atomic force microscope (AFM), the tip of which scans a thin gold layer predeposited on a mica substrate. The nanowires are spaced with an interval in the range of 130–590 nm. Their widths and heights are distributed in the range of 70–110 nm and 4–7 nm, respectively. By adjusting the strength of the force applied by the AFM tip, the spacing, width and height of the nanowires can be controlled and made to increase as the applied force increases. Scanning an extensional area enabled us to fabricate long nanowires.

Transition from continuous to discontinuous material failure in a simple model of an adhesive layer

A fine-scale, quasistatic model was used to study the removal of a disordered adhesive layer by a uniform force applied perpendicular to the layer. The model includes randomly chosen bonding forces of adhesion between imaginary ``gridblocks'' within the layer and a substrate, as well as cooperative forces of cohesion between adjacent gridblocks. For small cooperative forces, the amount of failure varies continuously with the applied force F. From infinitesimal failure at a minimum threshold value of the force, the fraction of the layer removed, ${f}_{m}(F),$ increases to encompass the total layer, as the applied force increases. This layer-removal function sharpens as the cooperative forces are increased; i.e., the slope of the layer-removal function, $\ensuremath{\Delta}{f}_{m}/\ensuremath{\Delta}F,$ increases, so that the amount of failure is more and more sensitive to changes in the applied force. Indeed, this slope diverges with an exponent $\ensuremath{\gamma}\ensuremath{\approx}0.85$ when the cooperative forces are approximately 2.1 as large as the adhesive forces. At small values of the cooperative forces, the layer-removal initiates at many locations and spreads to nearby blocks. The perimeter enclosing the area removed is fractal with a dimension ${D}_{p}\ensuremath{\approx}1.3.$ Increasing the cooperative forces causes the failure to initiate at fewer locations in the array, but to spread farther because of the larger cooperative forces. At the critical value of 2.1 for the ratio of cohesive to adhesive forces, the number density of these initiation sites goes to zero, and the ``correlation'' length (average range of the spread of failure) diverges with exponent $\ensuremath{\nu}\ensuremath{\approx}0.5.$ The characteristic time required for failure also diverges at the same critical value of cohesive/adhesive ratio with an exponent, $\ensuremath{\Delta}\ensuremath{\approx}0.9.$ Therefore, increasing the cooperative forces of cohesion effects a transition from the continuous response reminiscent of systems with depinning transitions to the discontinuous response characteristic of standard material fracture. Indeed, the divergent correlation length signals a transition to the long-range elastic forces that have enabled mean-field (fiber-bundle) models to be used in the study of standard material fracture.

Adhesion moment model for estimating particle detachment from a surface

In this paper particle detachment from a surface by a hydrodynamic moment is analyzed. The detachment occurs when this moment exceeds the moment exerted on the particle by surface forces. An expression for the moment of surface forces is derived from the existing adhesion models. This moment is a product of the force acting on the particle and the variable contact radius, which decreases when the applied force increases. Accordingly, a condition for particle detachment from a smooth surface is obtained. In addition, particle detachment from a rough surface is considered. We show that a single asperity contact is similar to the contact of a particle with a smooth surface, but the detaching moment is reduced, because of the lower adhesion force and smaller contact radius. We also consider a particle in contact with two and three asperities, and obtain a condition for particle detachment from a rough surface. It is also shown that the hydrodynamic moment can cause particle detachment, while the hydrodynamic lift force is smaller than the adhesion force by several orders of magnitude. On the other hand, the lift force exceeds the weight of the particle. Hence, the detached particle is eventually removed from the surface by this force.

Force sensors based on distortion in delay lines

The principle of operation of force sensors based on distortion in delay lines type of sensor is the distortion of an acoustic signal, in a pulse-excited magnetostrictive delay line due to a force applied at any point between the point where the pulse is generated and the receiving coil. A conductor orthogonal to the delay line is used for pulsed current transmission and its distance is fixed with respect to the delay line. The input and the output of the system are the applied force on the delay line support and the amplitude of the detected output V/sub o/, respectively. Under fixed amplitude of the pulsed current, V/sub o/ has a maximum value under zero input and decreases as the applied force increases. Experimental results show that the response of the sensor is a monotonic, exponential function of the applied force. A method is also proposed, according to which an integrated sensor array could be made based on this principle.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of geometrical arrangement and interdrop forces on coalescence time

AbstractAccording to the Reynolds' equation the time taken for a thin film to reach a critical thickness at which rupture occurs is a function of the film area and applied force. It follows that the coalescence time of a liquid drop is greatly affected by its geometrical configuration. If the drop is unconstrained the coalescence time increases when a vertical force is applied to the drop, but if the drop is constrained by the presence of surrounding drops its coalescence time decreases as the applied force increases. This explains why the rate of coalescence at the disengaging interface of a close‐packed dispersion increases with the dispersion height. The coalescence time for a planar film is usually less than for the spherical film formed between a drop and its homophase which explains why near‐horizontal surfaces inserted into close‐packed dispersion increase the rate of coalescence. The coalescence time of a drop in a close‐packed dispersion decreases as it approaches the disengaging interface. This means that the volume rate of coalescence at the interface may equal the disperse phase throughout without the necessity for interdrop coalescence. When the applied pressure is much greater than the van der Waals pressure, as in a close‐packed dispersion, the critical film thickness is itself a function of the film area and applied force, but this has little effect on the above conclusions. When the applied pressure is much less than the van der Waals pressure, as in a loose‐packed dispersion, the critical film thickness is only a function of the film area and the affect of the applied force on the coalescence time is then increased.

Effect of interdrop forces on the coalescence of drops in close-packed dispersions

The effect of a vertical force on the shape of a drop constrained by the presence of other drops in a horizontal array is considered. From the areas of the draining films above and below the drop and the forces acting on them, the coalescence time may be calculated relative to that of the draining film beneath a single drop subjected only to the weight of the drop. Calculations show that the coalescence time of a constrained drop decreases as the applied force increases, whereas that of an unconstrained drop increases. This suggests a relationship between the height of a close-packed droplet dispersion and the coalescence time of a drop at the disengaging interface.

A model for coalescence in a two-dimensional close-packed dispersion

The effect of a vertical force on the shape of a two-dimensional drop constrained by the presence of other drops in a horizontal row is considered. From the areas of the draining films above, below and to the side of the drop and the forces acting on them, the coalescence time may be calculated in relation to that of the draining film beneath a single drop subjected only to the weight of the drop. Calculations show that the coalescence time of a constrained drop decreases as the applied force increases, whereas that of an unconstrained drop increases. This suggests a relation between the height of a close-packed droplet dispersion and the coalescence time of a drop at the disengaging interface.

Interpretation of the Upper Plastic Limit of Clays

THE upper plastic limit, or liquid limit, of clays is regarded as that water content at which sufficient free water is present to allow clay particles to slip past one another under a certain applied force. It can also be interpreted as the distance between particles or between structural units of particles at which forces of interaction between the clay particles become sufficiently weak to allow easy movement of particles or units relative to each other. This interpretation allows an easier explanation of the influence on the liquid limit of such factors as exchangeable ion, salt concentration and pH. of the clay paste. For this interpretation it is convenient to define an ‘interaction volume’ for a unit mass of clay particles as that volume within which individual particles or units of particles interfere with the movement of adjacent particles or units. The interaction volume will decrease as the applied force increases.