Quasi-static State Research Articles

A thermodynamic framework for nonequilibrium self-assembly and force morphology tradeoffs in branched actin networks.

Branched actin networks are involved in a variety of cellular processes, most notably the formation of lamellipodia in the leading edge of the cell. These systems adapt to varying loads through force dependent assembly rates that allow the network density and material properties to be modulated. Recent experimental work has described growth and force feedback mechanisms in these systems. Here, we consider the role played by energy dissipation in determining the kind of growth-force-morphology curves obtained in experiments. We construct a minimal model of the branched actin network self assembly process incorporating some of the established mechanisms. Our minimal analytically tractable model is able to reproduce experimental trends in density and growth rate. Further, we show how these trends depend crucially on entropy dissipation and change quantitatively if the entropy dissipation is parametrically set to values corresponding to a quasistatic state. Finally, we also identify the potential energy costs of adaptive behavior by branched actin networks, using insights from our minimal models. We suggest that the dissipative cost in the system beyond what is necessary to move the load may be necessary to maintain an adaptive steady state. Our results hence show how constraints from stochastic thermodynamics and non-equilibrium thermodynamics may bound or constrain the structures that result in such force generating processes.

Relaxation mechanisms of near – α titanium alloy during stress relaxation with synchronous aging

Stress relaxation with synchronous aging (SRSA) could not only reduce springback but as well improve the performance of titanium alloy components. To reveal the relaxation mechanisms during SRSA, solution treatments of Ti-6.5Al–2Zr–1Mo–1V alloy under different temperatures were carried out to obtain diverse initial microstructures. The evolutions of microstructure including phase transformation, dislocation movement and stress-induced twinning were meticulously characterized. The progress of activation energy was analyzed quantitatively by the Kohlrausch-Williams-Watts equation. Results show that SRSA under all different conditions exhibits a rapid stress decline initially followed by a quasi-static stage, due to a shift in the driving force from stress-driven to thermally activated driven. The activation energy changes from a quasi-static state to a rapid rise with relaxation time. After two-phase solution treatment, the primary α (αp) dominant mechanism is the dislocation movement, including dislocation tangles and then recovery. The relaxation mechanism of the supersaturated metastable β phase is phase transformation (precipitation and growth of secondary α (αs)) and stress-induced twinning, and the αs realizes stress release through the globularization in the later stage. The full martensite microstructure was obtained by solution treatment in a single-phase region, and the main relaxation mechanism involves stacking faults, stress-induced twinning and then globularization. The enhancement in strength following SRSA is primarily attributed to the formation of αs, dislocation strengthening, and stress-induced twinning.

‘IT FROM BIT’: How does information shape the structures in the Universe?

Based on a synthesis of three main ingredients: (i) the Shannon information in non-equilibrium systems, (ii) the semiclassical energy-time quantization rule and (iii) the quasi-static information-energy correspondence, a new general rule for the quantization of quasi-static information states supported by an environment away from equilibrium is introduced if the history of the environment is known as a function of time in terms of its thermodynamic potential for information T ( t ) Δ S ( t ) that is a free energy measuring the distance from equilibrium Δ S ( t ) , and T ( t ) is the mean temperature of the environment at time t . This all new quasi-static information-time quantization rule is applied to the expanding Universe using a phenomenological thermodynamic potential for information in the matter-dominated era in order to find the eigen-information of the persistent structures that are supported by the universe (or the local environments therein) at any given epoch, thus providing an information–theoretic foundation for formation of structures and rise of complexity with time that embodies the cosmic evolution as epitomized by the late Wheeler’s famous conjecture ‘it from bit’. This theoretical procedure must also open new avenues for further research into the quantum theory of information and complexity in non-equilibrium thermodynamics.

A new insight into the macroscopical cause of wheel rolling contact fatigue on Y25 wagons – axle box longitudinal guidance deviation

Wheel rolling contact fatigue (RCF) is a tricky issue for the railway industry. It is recently reported that the wheel RCF on Y25 bogies is more severe compared to other bogies with similar primary suspension structures. The axle box longitudinal guidance deviation (ALGD) could be a reason for the wheel RCF according to field observations. In this paper, a Y25 wagon dynamics model is firstly established and validated. The ALGD is modelled using non-linear force elements. The wheel damage function is used for RCF evaluation. Then, effects of ALGDs on force balances of wheelsets are preliminarily analysed in a quasi-static state. Four different scenarios for ALGDs are simulated and corresponding wear numbers are calculated. It proves that the wheelset lateral displacement, wheel‒rail contact forces, and RCF index will dramatically increase with the ALGD value. Potential wheel‒rail contact zones for the bogies with ALGDs are basically consisted with the recorded wheel RCF zones. Finally, maintenance suggestions are proposed according to the wheelbase deviation. The ALGD threshold should be 1.0 and 2.75 mm for the prevention on wheel RCF and wear, respectively. The results of this paper may provide a new insight into the macroscopical cause of wheel RCF on Y25 bogies.

Design and evaluation of a four-DoF upper limb exoskeleton with gravity compensation

Gravity compensation (GC) mechanisms are commonly employed to either support limb gravity in passive exoskeletons or decrease motor power for safe human-robot interaction in active exoskeletons. This paper proposes a four-degree-of-freedom (DoF) upper limb exoskeleton with a theoretically perfect GC system, incorporating three DoFs in the shoulder and one DoF in the elbow. Paired with the anthropomorphic structure, the compact and adjustable GC system housed within the exoskeleton's linkages, reduces limitations on the limb's motion range and facilitates the integration of actuators for an active system. First, the GC system is designed through the analysis of potential energy equations, employing five cable-pulley-spring based units interconnected by parallel and differential mechanisms. Subsequently, the mechanical structure of the exoskeleton is developed, and the theoretically perfect GC in the quasi-static state is verified through numerical calculations. Then, the prototype is fabricated, and its actual performance is evaluated through experiments. The experimental results demonstrate the effectiveness of the exoskeleton with GC. Finally, a potential solution for the integration of actuators is demonstrated, and the limitation of the proposed system is also well discussed.

DLP printed 3D gyroid structure: Mechanical response at meso and macro scale

Rapid prototyping (RP) technology enables the fabrication of complex geometries, making lattice structures increasingly popular. Lattice structures, known as cellular materials, have garnered significant attention over the past two decades due to their ability to optimise mass distribution in components. These structures excel in mechanical properties, catering to energy absorption (bending-dominated structures) and structural performance (stretch-dominated structures). In this paper, we investigate the behaviour of stretch-dominated lattice structures using periodic surface models, specifically focusing on sheet-based Gyroid cells, to allow for a more efficient macroscale modelling. We study cells and scaffolds of different sizes, considering various triply periodic minimal surface thicknesses and relative densities ranging from approximately 0.2 to 0.65. We explore load applications in directions different from the unit cell's principal axes and analyse the strain rate effect on both bulk and cellular material. The lattice structures are manufactured using epoxy resin and digital light processing (DLP) technology. In the range of relative density investigated, both in quasi-static and dynamic conditions, a linear trend is observed for Young's modulus and compression yield strength. To extend the quasi-static results to the dynamic regime, we employ a more generalized normalization technique. This approach divides Young's modulus and compression yield strength by the behaviour of the base material at a specific strain rate, facilitating the correlation of mechanical properties across the two loading regimes. Based on experimental findings, we implemented and calibrated a bi-linear material model for describing, in macroscale, triply periodic minimal surface (TPMS) Gyroid structures. The model coefficients are parameterized with respect to relative density. In addition, the presented material law was compared with that proposed by Gibson-Ashby. Furthermore, we evaluated the anisotropy of both the base material and the unit cell. The first one is done by testing the 3D printed samples in directions different from the printing one, the latter by using the Zener factor. The anisotropy evaluation confirmed the isotropic behaviour of the unit cell within the range of relative density and test conditions investigated. Finally, we perform linear elastic 3D macroscopic and mesoscopic model simulations for combined shear-compression tests using the implemented bi-linear material model and the anisotropic stiffness matrix (obtained through the homogeneous formulation) for the macroscale, and the base material for the mesoscopic one. The results demonstrate the suitability of the proposed equivalent material model for studying the TPMS Gyroid structure in the elastic regime, both in quasi-static and dynamic states. This allows for an efficient FE modelling process of complex lattice structures.

Mechanical properties of homogeneous and functionally graded spinodal structures

This paper investigates the compressive mechanical behavior of spinodoid metamaterials in a quasi-static state through experimental and numerical analysis at the macroscopic level. This homogeneous structure exhibits weak strain hardening, resulting in a lower initial peak compression force and higher specific absorption energy compared to other mechanical metamaterials. The homogeneous model has multiple low-density regions uniformly distributed within the three-dimensional space due to the random nature of the Gaussian field. Thus, the transition from low-density to high-density regions is described as a gradual process, implying that the deformation of metamaterial shifts to region-by-region compaction. Besides, the functionally graded spinodoid structure shows strong strain hardening, whose deformation mainly tends to collapse layer by layer along a positive graded direction. The graded structures with low densities have a lower energy absorption capacity than the corresponding homogeneous structure, while higher-density structures show a reverse trend. This phenomenon originates from the superimposed effect of two kinds of strain hardening.

Метод расчета силовых и геометрических характеристик закидного равнокрылого невода в квазистатической постановке

The process of sampling a beach winged seine (BWS) is complex, it occurs with a change in geometric and power characteristics that are interrelated and depend on each other. Solving problems of this level of complexity is possible only with the help of discrete methods, using computers. However, in order to take operational actions of the fishing crew to adjust the rigging, the sampling rate of the cuts and when making structural changes to the grid part of the BWS, it is necessary to promptly solve the tasks of determining geometric and power characteristics. In this regard, it is possible with a small error (no more than 10%) to determine the effort in the process of sampling the cuts at the appropriate tone based on a quasi-static process. If each quasi-static state of the BWS is close to the equilibrium state and, since the sampling rate of the cuts is small, then it is customary to use the V–axiom of statics - the transfer of forces is possible only along the line of action of the force itself. If, on the other hand, we determine the relationship of the shape of the BWS with the acting forces, then, taking into account the equation of the sum of the moments of forces relative to the point of fixing the edges, it is possible to determine the geo-metric parameters of the entire BWS as a whole. This condition is necessary, but insufficient, and additional conditions are required in each specific case. These conditions are the temporary areas of the “melting” of the BWS. A method for calculating the geometric and power characteristics of the 451 × 4.5 m BWS is given, and an example of the calculation used for catching hydrobionts of the Northern Caspian is also given.

Toward large-scale fine resolution DEM landslide simulations: periodic granular box for efficient modeling of excavatable slope

Understanding landslide hazards and developing mitigation measures is critical to protecting lives and property. The Discrete Element Method (DEM) has demonstrated its ability to simulate landslides and estimate impact forces on mitigation structures. Such simulations often model slope surfaces as bedrock on which a fixed amount of earth mass is released and slides. Mass entrainment due to local failure of an excavatable slope surface is rarely modeled with sufficient resolution. Fine-resolution modeling of an excavatable slope for simulation is necessary and non-trivial to improve DEM simulations of large-scale landslides. In this study, we present a method based on Periodic Granular (PG) boxes for efficient modeling of excavatable slopes. A PG box is a packing of particles in a quasi-static state inside a virtual unit box, where the periodic boundary conditions are satisfied at the box surfaces. The procedures used to construct a PG box are presented. The quality of PG boxes is analyzed both at the particle contact scale and at the laboratory specimen scale by measuring contact orientation statistics and by performing numerical triaxial tests. As a demonstration, a centimeter resolution slope model constructed using the PG box-based method is presented using topographic data for the Aso Bridge landslide. In addition, landslide simulations to verify the excavation effect were performed on sub-meter resolution slope models. Our simulations show that landscape shape and particle size have a direct effect on the movement and deposition of earth masses. This highlights the need for detailed 3D terrain modeling and further study of particle size effects. By constructing the first excavatable DEM slope model with billions of centimeter-sized particles, this study can be considered a solid step toward fine-resolution DEM simulations of large-scale landslides, which can contribute to both scientific understanding and engineering countermeasures to mitigate the catastrophic consequences of large-scale landslides.

Dynamic enhancing effect of free water on the dynamic tensile properties of mortar

This study investigates free water effect on the dynamic tensile properties of mortar. Fully saturated and saturated-then-redried mortar specimens with two porosities, namely common and high-porosity, are prepared and tested under quasi-static and dynamic split-tension states covering strain rates between 1.49e−06s−1 and 5.29s−1. The split-tensile strength and elastic modulus at different strain rates are quantified. Comparing the dynamic increase factor (DIF) for mortar tensile strength, a maximum difference of 1.2 at strain rate 5 s−1 is found between saturated and dried high-porosity mortars revealing the influence of free water. The testing data is compared with other existing data which shows the mortar water effect is more similar to concrete than limestone and sandstone. The high-speed camera images during the dynamic tests are analysed which revealed a water retarding effect on the dynamic split-tension failure process, resulting in an initial crack delay of up to 0.4 ms due to free water. The wave speed for different mortar specimens at different strain rates is analysed, which shows that higher porosity is more sensitive to the water effect. Possible mechanisms leading to this water effect is discussed. Overall, the study provides a quantitative measure of the water enhancing effect on the dynamic tensile strength of mortar and offers insights into the practical use of water in the design and construction of mortar structures.

Postures of the Head, Upper, and Lower Neck in Forward Head Posture: Static and Quasi-static Analyses

Background: Abnormal head and neck postures play a significant role in developing cervical spine dysfunction. Forward head posture (FHP) is one of the most common findings in individuals who experience head and neck disorders. Objectives: This study used a photographic method to analyze the head, upper neck, and lower neck postures in forward head posture in both static and quasi-static states. Since timely diagnosis and appropriate treatment are important in preventing further complications of this kinematic chain disorder, the postural variables of the head and neck were evaluated by focusing on their separate parts in both static and quasi-static states. Methods: This observational-analytical case-control study included 175 individuals with no history of neck pain in the past 6 months, 138 with FHP, and 37 with non-FHP. The postural angles, including the upper cervical, lower cervical, craniovertebral, head posture, and head tilt angles, were measured through photography in both the static state (with the head and neck in a neutral position) and the quasi-static state (while moving the head and neck in the sagittal plane) in a sitting position. The measurements were taken in two groups (FHP and non-FHP). Results: In a static state, the upper cervical angle was higher in the FHP group than in the non-FHP group. The lower cervical measurements were higher in the non-FHP group than in the FHP group. In the quasi-static state, significant differences existed in the changes of the upper cervical, lower cervical, craniovertebral, head postural, and head tilt angles between the two groups (P-value < 0.05). Conclusions: During full flexion to full extension of the neck, subjects with FHP exhibited reduced mobility in the cervical spine, particularly in the lower cervical region. Additionally, the position of the head relative to the neck remained unchanged in this group.

Dynamic properties and fragmentation fractal characteristics of water-saturated reef limestone concrete under impact loading

Reef limestone was used as a coarse–fine aggregate to prepare concrete with a strength class of C30. The mechanism of influences of water-saturated state on dynamic compressive strength, energy dissipation, and macroscopic and microscopic failure modes of reef limestone concrete was studied, and the relationships between fractal dimension and loading rate, fragmentation characteristics, and energy dissipation were discussed. The results indicated that the dynamic compressive strength of reef limestone concrete presents power function growth with increasing loading rate, the free water reduces the degree of cementation among particles and weakens the quasi-static state and dynamic mechanical properties of reef limestone concrete. Meanwhile, under the same loading rate, water-saturated reef limestone concrete demonstrates a stronger energy absorption effect and a greater energy dissipation density, and the energy dissipation density is linearly correlated with the dynamic compressive strength. In addition, the irregular shape and porous structure of reef limestone aggregate particles effectively enhances the friction strengths between the aggregates and cement slurry, causing most of the dynamic cracks in reef limestone concrete to occur in the cement-sand slurry and aggregates themselves. Finally, the results also show that the fractal dimension of the fragments of reef limestone concrete increases linearly with increases in the loading rate and fragmentation energy dissipation density. At approximately the same loading rate, the fractal dimension of dry specimens was larger, and when the fractal dimensions in the two states were similar, the energy consumed per unit mass water-saturated specimen exceeds that of dry specimens.

Three-heat-reservoir thermal Brownian heat transformer and its performance limits

Waste heat recovery has great value in energy saving and decreasing environmental pollution. A three-heat-reservoir (THR) heat transformer can raise waste heat to a higher temperature for recovering and reusing easily. At present, the research on THR heat transformer is mainly focusing on macro field. This paper extends the THR heat transformer cycle to micro field, and models a THR thermal Brownian heat transformer. The model is a combined cycle of a thermal Brownian heat pump driven by a thermal Brownian engine. According to non-equilibrium thermodynamics, the analytical expressions for heating load and coefficient of performance (COP) are derived. The coupling relation of the combined cycle is obtained by solving the heat balance equation, and the operating mechanism of the new cycle is explained. The external load, barrier height, potential asymmetry and temperature ratio effects on system performances are studied, and the maximum heating load and corresponding COP are given. The optimal operating range and performance limits are obtained. Results show that the THR thermal Brownian heat transformer can raise the “heat” to a higher temperature. The heating load can reach peak value by modulating the design parameters carefully. The system operates in a quasi-static state and the heating load is zero when COP increases to its upper bound, and the system is reversible at this time. The new model proposed in this paper can guide the design of actual device, and the performance limit can guide the performance optimization of the actual device.

Muscle-Driven Joint-Torque Estimation Based on Voltage-Torque Mapping of Electrical Impedance Sensing

This paper offers an impedance sensing method taking advantage of the conductivity changes due to muscle contraction to estimate muscle-driven joint torques through a convolutional neural network (CNN) where the input images are derived from a finite set of boundary voltage measurements. Guided by a physical model combining the forearm biomechanics and the muscle electric field along with the CNN criteria considering the receptive fields, the effects of two image formats (for quasi-static and dynamic states) on the CNN performance are experimentally studied on eight human subjects’ forearms using a prototype impedance sensing system. By comparing the CNN-estimated torques with that measured on a haptic device, the findings verify that the impedance-based method can estimate the joint torques driven by both the deep and superficial muscles within 9% errors of the three degrees-of-freedom wrist torque and 10% error of the gripping torque, and that it is feasible to share data among a similar group to reduce data collection and time when training a CNN for uses on a new subject.

Modeling and Dynamic Impact Analysis of Prismatic Lithium-Ion Battery

Battery modules of new energy vehicles are frequently exposed to dynamic impacts during traffic accidents. However, current research on the mechanical safety of prismatic lithium-ion batteries (PLIBs) primarily focuses on quasi-static states, and the failure mechanism of batteries under dynamic impact remains incompletely understood. Therefore, to investigate the failure mechanism and critical failure displacement of PLIB under dynamic impacts, this study establishes a computational model of PLIB considering anisotropy based on experimental data and extends the simulation to the case of high-velocity battery collision. On this basis, the deformation feature, mechanical response, and failure mechanism of PLIB under different impact velocities are analyzed. The results show that the deformation feature of PLIB under dynamic impact differs from that under quasi-static loading. As the loading velocity increases, the inertial effect gradually becomes apparent, causing the deformation of PLIB to localize and the failure displacement to decrease. Three critical failure displacements were identified within the velocity range of 0–20 m/s. This study can serve as a reference for battery safety design.

Role of graded microstructure and electrolyte distribution in electrochemical capacitance of compressible three-dimensional carbon nanotubes-polymer foam based supercapacitor

Three-dimensional microstructure of carbon materials has a prime importance in supercapacitor for energy storage. Carbon nanotubes (CNT) provide microstructurally porous structure via entangled nodes that dynamically changes with the uniaxial compression. A unique graded CNT-polymer based three-dimensional compressible cellular foam is used as an electrode material for the solid-state supercapacitor. A direct correlation was established between the applied strain and resulting electrochemical capacitance when the foam electrode was soaked and unsoaked in the electrolyte. In a novel finding, unsoaked electrodes revealed in an extraordinary enhancement of ∼1216% in gravimetric capacitance measured at a uniaxial strain of 80% and to no surprise, the electrochemical capacitance of electrolyte-soaked electrodes remained nearly invariant from its uncompressed state. The response of electrochemical capacitance under compression is also observed varying with the mode of compression i.e. quasi-static versus pre-compressed state to a targeted strain. The role of graded microstructure during uniaxial compression was verified by using as-grown CNT mat for the electrodes of a supercapacitor. The results demonstrated a dominating contribution of dynamic variation in the density of nodes in the compressed CNT mat. The impact of macroscopic variation on the response of electrochemical capacitance of a compressed cellular CNT-polymer foam was further understood using the separators of varying pore sizes. Our results pave the way to engineer the three-dimensional compressible cellular structures for extraordinarily large energy storage capacity.

Bipedal driven inertial type piezoelectric motor working under quasi-static and resonant states

An inertia piezoelectric motor based on bipedal driven, which can work in not only quasi-static but also resonant states, is proposed, designed, fabricated and studied considering the high resolution of quasi-static piezoelectric motor and the high speed of resonant piezoelectric motor. The two stators of the piezoelectric motor are drived by two sinusoidal electrical signals with 1:2 frequency ratio to generate sinusoidal vibration on the corresponding driving foot. A continuous step motion without frequency limitation is realised under the action of inertia and friction forces after synthesising the sinusoidal vibration of different frequencies into mechanical sawtooth vibration. The natural resonant frequencies of the piezoelectric motor are adjusted to a specific proportion to combine the vibrations in the resonant state through finite element analysis. In the structure of two stators, each stator has a corresponding inertia block, and the corresponding resonant frequency can be altered by adjusting the mass of the inertial block without affecting the other resonant frequency, thus markedly simplifying the design difficulty of the piezoelectric motor which can work in quasi-static and resonant states. The motion characteristics of the prototype are tested by building the prototype and experimental platform. Experimental results show that the maximum speed of the prototype is 29.3 mm s−1 and the maximum load is 2 N in the resonant state, the minimum displacement resolution of prototype motor is 0.26 μm in the quasi-static state. The motion characteristics of the prototype are consistent with the theoretical analysis, which provides an effective idea to improve the comprehensive performance of the piezoelectric motor.

Eulerian multifluid simulations of proppant transport with different sizes

Proppant transport is critical in hydraulic fractures and enhanced geothermal systems. Proppant transport is essentially a dense granular flow in narrow slots, and the Euler–Euler methods are commonly used to study the principle of proppant transport at the field scale. However, the simulated results cannot reproduce the laboratory observations well because some closure equations are not suitable for describing the quasi-static state of proppants after settlement, and only monodisperse granular flow is considered in simulations, which neglects the interaction between large and small particles. To improve the applicability of the numerical simulation of proppant transport in hydraulic fracturing treatment, binary-size proppant transport numerical simulations using the Eulerian multifluid method (EMM) are performed in this study. First, the motion characteristics of the suspended and settled proppants were analyzed using the kinetic theory of granular flow (KTGF) and the frictional theory of viscous particles. Thereafter, the solid–liquid momentum exchange considering the wall retardation effect and the solid–solid momentum exchange considering the endurable contact among the particles are discussed. Finally, the numerical results are qualitatively and quantitatively verified using proppant transport experiments and particle image velocimetry tests. The combination of traditional KTGF models and frictional models exhibits better performance than the modified KTGF models when considering the inertia flow regime in the proppant transport simulation, and the contribution of viscous-particle cohesion to friction must be considered. Notably, the simulated results are close to the experimental results for the development process of sand banks and the velocity distribution of particles. This verified method is efficient in computing and it will provide new insights into the pumping procedure design for hydraulic fracturing.

Using a poroelastodynamic model to investigate the dynamic behaviour of articular cartilage

Background and objectiveThere is still a few studies about the poroelastic model that performed dynamic behaviour, especially for the case of the poroelastic cartilage model. Therefore, this study is aimed to use the poroelastodynamic model to simulate the dynamic behaviour of cartilage. MethodsThe governing equations of the poroelastodynamic model is firstly established. The validation of the model is initialised by modifying the equations into the static poroelastic model. The modified equations are then discretised using the finite element method. Mandel's problem is used to validate the discretised equations. The numerical solution calculated using FreeFEM++ is validated with the analytical solution for the quasi-static state and compared with the results generated using COMSOL Multiphysics software. Finally, the quasi-static solution is compared with the dynamic solution to discuss the difference in pore pressure and displacement variations of the poroelastic cartilage model. ResultsThe dynamic solution showed transient behaviour at the beginning of the excitation. When the compressive force acts on the cartilage, there are obvious fluctuations during the initial stage and then the dynamic numerical solution gradually approaches the quasi-static value over a period of time. The deduced results of the analytical solution were approximately the same as the numerical simulation results. ConclusionThis study was able to use the poroelastodynamics equation to simulate the dynamic behaviour of the poroelastic cartilage model. The comparison between the result coming from poroelastodynamics equation with that of the validated numerical solution was satisfactorily compared. The approximate similarity between the results of quasi-static and dynamic solutions underscored the importance of performing the dynamic solution for a more realistic simulation. This dynamic solution can be further used for the analysis of vibration or stress waves in future research.

Capillary forces and capillary bridges between a three-finger microgripper and a plate

ABSTRACT The presence of surface tension in liquids, which induces a strong capillary force between wetting particles in micro/nano scale, has aroused extensive attention. In present study, a fundamental investigation on capillary forces and rupture behaviors of capillary bridges between a three-finger microgripper and a plate is conducted in quasi-static state. Theoretical analysis is performed for solutions of the capillary force. The capillary bridges between a three-finger microgripper and a plate are established based on the principle of energy minimization. An analytical approach for computing the capillary force for the three-finger/plate geometry is proposed by means of variables obtained from the simulation models. The comparison of the single-finger capillary bridge and three-finger capillary bridge is investigated based on the developed models. The effects of separation distance, capillary bridge volume, radial distance and contact angle on the capillary force of three-finger capillary bridges are analyzed in detail. The results demonstrate that the variation of capillary force with separation distance and volume changing is not monotonic, which is caused by the edge effect of the three-finger microgripper. Capillary force measurements were experimentally characterized to demonstrate the reliability of the simulation models and the capillary force solution method based on an established experimental platform.