Squeeze Force Research Articles

Viscoplastic fluids in 2D plane squeeze flow: A matched asymptotics analysis

A matched asymptotic expansions approach is used to determine the flow behaviour of Casson and Herschel–Bulkley fluids between two parallel plates that are approaching each other with a constant velocity. The present study is based on the earlier work of Muravleva (2015), who has analyzed the squeeze flow of a Bingham fluid using the method of matched asymptotic expansions. A naive application of classical lubrication theory leads to a kinematic inconsistency in the predicted plug region - the well known “squeeze flow paradox” for a viscoplastic fluid. The objective of this work is to determine a consistent solution for the aforementioned constitutive equations. Based on the technique of matched asymptotic expansions, the solution is formulated in terms of separate expansions in the regions adjacent to the two plates where the shear stress is dominant, and a central pseudo-plug (plastic) region where the normal stresses become comparable to the shear stress; the two regions being separated by a pseudo-yield surface. In this manner, a complete asymptotic solution is developed for the squeeze flow of both Casson and Herschel–Bulkley fluid models. Using this solution, we derive expressions for the velocity, pressure and stress fields, and the squeeze force acting to retard the plates. The effect of the yield threshold on the pseudo-yield surface that separates the sheared and plastic zones, pressure distribution and squeeze force is investigated.

Effect of three types of piezoelectric cantilever on the topography quality in the vicinity of rough surface in a fluid ambient

• Advanced mathematical modeling for different types of piezoelectric micro cantilever. • Utilizing modified couple stress theory. • Advanced liquid modeling. • Predicting the piezoelectric non uniform micro cantilever vibration behavior in fluid. • Tapping and non-contact topography in liquid. The use of higher vibration modes and different geometries of the atomic force microscopy (AFM) piezoelectric micro cantilever (MC) is affected by the surface topography quality in a liquid medium. Therefore, utilizing an appropriate MC geometry and vibration mode is of a great importance. This paper analyzes the effect of different types of AFM MCs on the surface topography quality in the noncontact and tapping modes in a liquid medium. The modified couple stress theory (MCS) in a liquid based on the Timoshenko beam theory is used in order to enhance the accuracy of MC dynamic modeling. In addition, the differential quadrature (DQ) method has been used to discrete the equations. Identification of environmental forces helps to measure the accurate MC vibration amplitude. Investigating the effect of geometric and force parameters on the MC vibration behavior leads to understanding the system to design it properly in a liquid medium. Based on the advanced dynamic modeling, the best MC geometry for the specific surface roughness has been determined in the liquid for the surface topography. Also, due to oscillating the MC near the sample surface, the effect of interaction forces between the sample surface and the MC, including van der Waals, contact and squeeze forces is analyzed in a liquid medium in addition to the hydrodynamic forces. Furthermore, due to the reduction of the MC amplitude caused by the squeeze force; the MC is angled in proportion to the horizontal surface.

A robustness analysis of the bonding process of joints in wind turbine blades

In this paper, a numerical model is used to perform a robustness analysis of the bonding process of a joint between the two shells composing a wind turbine blade. The flow behaviour of the bonding adhesive is quantified on a rheometer and the Herschel-Bulkley material model is utilized to approximate the rheological data set. The material model parameters are implemented in the numerical model, which is validated by comparison with experimental results. The robustness analysis is focused on analysing the adhesive position and initial shape as well as the inclination angle's effect on the squeeze force and final adhesive geometry. The results illustrate that the numerical model can assist in increasing the strength of the joint, decreasing the risk of residual stress induced cracks, and minimizing cost/waste and mass of the blade.

Asymptotic Solutions of the Planar Squeeze Flow of a Herschel-Bulkley Fluid

In this study, we present the analysis of the squeeze flow of a Herschel-Bulkley fluid between parallel plates that are approaching each other with a constant squeeze motion. The classical lubrication analysis predicts the existence of a central unyielded zone bracketed between near-wall regions. This leads to the well-known squeeze flow paradox for viscoplastic fluids. Since the kinematic arguments show that there must be a finite velocity gradient even in the unyielded zone, thereby precluding the existence of such regions. This paradox may, however, be resolved within the framework of a matched asymptotic expansions approach where one postulates separate expansions within the yielded and apparently unyielded (plastic) zones. Based on the above technique, we circumvent the paradox, and develop complete asymptotic solutions for the squeeze flow of a Herschel-Bulkley fluid. We derive expressions for the velocity, pressure and squeeze force. The effects of the yield threshold on the pseudo-yield surface that separates the sheared and plastic zones, and squeeze force for different values of non-dimensional yield stress have been investigated.

Analysis of hysteresis effect on the vibration behavior of AFM intelligent MC in the vicinity of sample surface by considering the size effect in air and liquid

Nowadays, scientists consider AFM as a powerful Nanorobot for the measurement of inter-molecular forces as well as identification and topography of sample surfaces. In order to enhance the performance of this Nanorobot, the modified couple stress (MCS) theory in the air and the liquid environment has used to reduce the error resulting from the modeling of AFM microcantilever (MC) based on classic continuum mechanic theory. In this paper, using the Hamiltonian principle and based on the Euler Bernoulli beam theory, motion equations are extracted taking into account the capillary, van der Waals and contact forces between the tip and the sample, as well as the hydrodynamic and the squeeze force in the liquid environment. Modeling is carried out for two dagger and rectangular geometries considering the geometric discontinuities due to the presence of a piezoelectric layer enclosed between the two sides of the electrode and the change in the cross-section of the MC when connecting the probe to the MC. Galerkin method is employed for the discretization of equations. In order to analyze the effects of geometry and environment on the MC vibration behavior, the time and frequency response are obtained at distances away from the surface for both MC geometries in the air and liquid environment. Comparison results suggest that the natural frequency is reduced due to the added mass of the dagger MC. This reduction is more tangible in the liquid environment because of the added mass. Also, the effect of the hysteresis phenomenon caused by the ferromagnetic property of materials is analyzed in order to approximate the theoretical model to the real model using the PI, Bouce-van and Duhem models. Surface topography is illustrated considering the hysteresis effect on rectangular and dagger MC. According to the results, the amplitude is amplified by using the three models. This amplification is higher in the PI model.

Axisymmetric squeeze flow of a viscoplastic Bingham medium

We develop an asymptotic solution for the axisymmetric squeeze flow of a viscoplastic medium. The standard lubrication-style expansions of the problem predict a plug speed which varies slowly in the principal flow direction. This variation implies that the plug region cannot be truly unyielded. Our solution shows that this region is a pseudo-plug region in which the leading order equation predicts a plug, but really it is weakly yielded at a higher order. We follow the asymptotic technique suggested earlier by Balmforth and Craster (1999) and Frigaard and Ryan (2004). This method involves no relaxation of the exact Bingham model. The analytical expression for the squeeze force is in good agreement with previous numerical results. In the second part of the paper, the axisymmetric squeeze flow of a Bingham fluid with slip yield boundary condition at the wall is considered. We provide an asymptotic solution for this type of flow. Depending on the ratio of two dimensionless parameters partial slip (stick-slip) or full slip at the wall (slip) are possible.

Effects of squeeze force on static behavior of riveted lap joints

To study the effects of the squeeze force used in the rivet installing process on structural behavior of the riveted lap joints, three-stage finite element simulation and workshop experiment of single-row countersunk riveted lap joints were implemented. Force–displacement curves and explicit configuration after various processes were obtained from both methods. Additionally, stress/strain fields were obtained from finite element analysis, and strain values at specific positions were measured by micro strain gauge during the experiment. Based on the consistency of the results, stresses on the edge of dangerous holes, load transmission, and secondary bending of joints under tensile load were analyzed. The result shows that increasing squeeze force does not have a significant influence on joint stiffness but results in a slight decrease in joint strength. Greater squeeze force introduces greater residual stress around the hole, and the maximum principal stress around the hole becomes greater tensile stress instead of initial compressive stress introduced by riveting process, thus causes weaker static strength. It is also shown that under static load, breakage occurs in the outer sheet at the end hole due to the largest load transmission and secondary bending, whereas these two aspects not only depend on the rivet installation squeeze force but also depend on the size of the exterior tensile load.

Dynamic modeling of oblique non-uniform piezoelectric MC in liquid with various percentages of glycerin in the presence of rough surface

One of the most useful applications of an AFM is imaging of biological particles in a liquid medium. The increase of the topography accuracy in a liquid medium requires accurate dynamic modeling of a Microcantilever (MC). This article investigates the accurate dynamic modeling of the non-uniform AFM piezoelectric MC with rectangular geometry in the amplitude mode in liquid medium for rough surfaces. To increase the accuracy of the modeling, the Modified couple stress (MCS) theory in the liquid medium according to the Timoshenko beam model has been used. Moreover, the differential quadrature (DQ) method has been used for solving equations, because in comparison with the other methods it has a high speed in solving equations and is accurate in the number of fewer elements. In addition, the accurate force modeling has been established by considering the shear forces caused by liquid on the sides of the piezoelectric MC by solving the Navier-Stokes equations, and by considering the hydrodynamic force, squeeze force and applied forces between the sample surface and the MC tip. The results illustrate that utilizing higher vibration modes affect the quality of rough surface topography with the step roughness in the liquid medium and increase the quality of surfaces topography in the tapping mode, especially in the second MC vibration mode. Moreover, it should be noted that the sensitivity of the MC vibration amplitude to the piezoelectric MC angle is higher in comparison with other investigated parameters.

The application of dynamic replacement method in deviation rectification of support pile

The dynamic replacement method is appled widely to the soft soil treatment, but is seldom used in retificating pile deviation. By the ways of dynamic replacement method gravel block can form underground, the gravel block can be treated as reaction-froce base, the magnitude of squeeze force needed for retificating pile deviation is related to the scale of gravel block. Take a sheet pile retaining wall for instance, the treatment scheme and paramters calculating method for deviation rectification of support pile was put forward. The project case demonstrate that this method is effective when the layout of gravel column is reasonable to a certain degree, it is a good reference to similar projects.

An investigation on the mitigation of end-stop impacts in a magnetorheological damper operated by the mixed mode

This paper presents mitigation behaviour of magnetorheological (MR) damper operated with a mixed working modes. A combination of the shear and squeeze modes is employed in the structure of MR damper to obtain the field-dependent normal yield stress as well as strengthen the squeeze effect. The experimental evaluation shows that when the piston is squeezing the bottom gap from the stroke of 25 to 26 mm, the sudden increase of squeeze force is observed confirming the existence of the mitigation effect. It is also observed that the magnitude of mitigation force is positively correlated with the magnitude of current given to the electromagnet. The measured peak mitigation forces are ranged from 722 N to 1032 N when the electromagnet currents are varied from 0.2 A to 0.8 A, respectively. The variable mitigation effect indicates that the concept can be further discussed as a potential impact protection feature in an MR damper.

Effect of load transfer by friction on the fatigue behaviour of riveted lap joints

An experimental investigation of load transmission throughout a riveted lap joint is presented with a focus on the role of friction. The main objective was to generate results to be utilized in a semi-empirical model for predicting the fatigue life of riveted joints, which is being developed by the authors. The test variables accounted for in the experiments were the rivet squeeze force and the faying surface condition. Triple-row riveted lap joint coupons of aluminium alloy 2024-T3 Alclad sheets intended to be a simple representation of longitudinal connections in the aircraft fuselage skin structure were assembled with two different rivet squeeze forces. For either force half of the joints had a thin Teflon interfoil in the overlap area in order to minimize friction between the sheets. Friction measurements reveal that, contrary to the friction coefficient between the Alclad mating surfaces, the friction coefficient between the Teflon and Alclad contact surfaces is considerably lower and does not increase with the cycle number.A convenient method of the determination of load transmission throughout a lap joint is proposed utilizing measurements by strain gauges mounted on only outer surfaces of the overlapping sheets supplemented by the secondary bending analysis according to a simple theoretical model. The results obtained indicate that the effect of the squeeze force and the faying surface condition on axial forces in the overlapping sheets is quantitatively insignificant. It is noted that an analytical procedure commonly used to compute axial forces in the sheets of joints with mechanical fasteners considerably underestimates load transfer by the critical, outer rivet rows.Comparative fatigue tests on the riveted coupons with the Teflon interlayer and without such a layer reveal superior fatigue lives of the former. These results demonstrate, contrary to the prevailing opinion, an overall detrimental influence of frictional load transfer at applied stress values representative of those experienced in service by lap splices of the aircraft fuselage.Post-failure examinations of the riveted joints provide evidence that the crack initiation locations and crack paths depend on the test variables and the stress level. For the uncoated joints, the effect of the squeeze force and applied load on the area of fretted regions around the rivet holes was noted, whilst the total roughness heights did not exhibit such a dependency.It is shown that the present and reported in other works experimental results on the effect of coatings on the fatigue performance of riveted joints cannot be explained based on FE stress analyses available in the literature due to simplifications involved in modelling the faying surface condition. A major conclusion of the present work is that because of the extremely complex determinants of frictional load transfer, its effect on the fatigue behaviour of riveted joints can only be predicted using a semi-empirical approach.

Dynamic viscous behavior of magneto-rheological fluid in coupled mode operation

A new method of measuring the coupled mode viscosity behavior of magneto-rheological (MR) fluid using the resonance concept is proposed. The coupled mode viscosity measurement device is designed as a resonant system using a cantilever beam probing with the rotating shaft mechanism. The ‘C’ shaped iron core of an electromagnetic coil, mounted in a resonating cantilever beam is used as a probing tip. The MR fluid between the probing tip and the rotating shaft mechanism experiences both squeeze and shear force. The vibration induced by the resonating cantilever beam creates only squeeze force on the MR fluid when the shaft is stationary. When the cantilever beam is vibrating at resonance and the shaft is rotating, the MR fluid experiences coupled (shear and squeeze) force. The cantilever beam is vibrated at its resonant frequency using the piezoelectric actuation technique and the resonance is maintained using simple closed loop resonator electronics. The input current to the probing coil is varied to produce a variable magnetic field which causes the viscosity change of the MR fluid. The viscosity change of the MR fluid produces a coupled force, which induces an additional stiffness on the resonating cantilever beam and alters its initial resonant frequency. The shift in resonant frequency due to the change in viscosity of the MR fluid is measured with the help of a resonator electronics circuit and its viscosity is related to the field dependent coupled mode yield stress of the MR fluid. The proposed measurement device is analytically derived and experimentally evaluated.

Payoff Information Biases a Fast Guess Process in Perceptual Decision Making under Deadline Pressure: Evidence from Behavior, Evoked Potentials, and Quantitative Model Comparison.

Humans and other animals often face situations in which they must make choices based on uncertain sensory information together with information about expected outcomes (gains or losses) about each choice. We investigated how differences in payoffs between available alternatives affect neural activity, overt choice, and the timing of choice responses. In our experiment, in which participants were under strong time pressure, neural and behavioral findings together with model fitting suggested that our human participants often made a fast guess toward the higher reward rather than integrating stimulus and payoff information. Our findings, taken with findings from other studies, support the idea that payoff and prior probability manipulations produce flexible adaptations to task structure and do not reflect a fixed policy.

Bouncing on thin air: how squeeze forces in the air film during non-wetting droplet bouncing lead to momentum transfer and dissipation

Millimetre-sized droplets are able to bounce multiple times on flat solid substrates irrespective of their wettability, provided that a micrometre-thick air layer is sustained below the droplet, limiting $\mathit{We}$ to ${\lesssim}4$. We study the energy conversion during a bounce series by analysing the droplet motion and its shape (decomposed into eigenmodes). Internal modes are excited during the bounce, yet the viscous dissipation associated with the in-flight oscillations accounts for less than 20 % of the total energy loss. This suggests a significant contribution from the bouncing process itself, despite the continuous presence of a lubricating air film below the droplet. To study the role of this air film we visualize it using reflection interference microscopy. We quantify its thickness (typically a few micrometres) with sub-millisecond time resolution and ${\sim}30~\text{nm}$ height resolution. Our measurements reveal strong asymmetry in the air film shape between the spreading and receding phases of the bouncing process. This asymmetry is crucial for effective momentum reversal of the droplet: lubrication theory shows that the dissipative force is repulsive throughout each bounce, even near lift-off, which leads to a high restitution coefficient. After multiple bounces the droplet eventually hovers on the air film, while continuously experiencing a lift force to sustain its weight. Only after a long time does the droplet finally wet the substrate. The observed bounce mechanism can be described with a single oscillation mode model that successfully captures the asymmetry of the air film evolution.

Effect of interference fit size on local stress in single lap bolted joints

The interference fit is an effective process technique to improve the fatigue life of aircraft structures. In this article, the experiments including the interference fit bolt installation and tensile loading in bolted joint were carried out. A three-dimensional finite element model was established to simulate the experimental process, and the finite element model was validated by comparing the simulated data with the experimental data of the squeeze forces and the strains. By finite element simulation and analysis, it can be concluded that the location of maximum value of the maximum principal stress on the upper plate faying surface is going far away from the hole edge with the increase in interference fit size. Furthermore, by analyzing the hoop stress variations along a prescribed path, the maximum value of the hoop tensile stress is smallest at the interference fit size of 1.5%.

Influence of initial fit tolerance and squeeze force on the residual stress in a riveted lap joint

Residual stress in a riveted lap joint is tightly related to the fatigue performance of the structure. This paper is devoted to a comprehensive study of the residual stress distribution in a plate that resulted from the riveting process, concerning the influence of initial fit tolerance and the squeeze force. Following a finite element (FE) simulation, an analytical model of the riveting process was built based on the deformation theory of elasticity and plasticity. The result shows that nonuniform expansion along the axis of the hole was observed which resulted in a nonuniform distribution of through-thickness stress. Huge compressive stress in the tangential direction was observed surrounding the hole, which explains the long life effect due to interference fit. Both increasing the squeeze force and initial fit tolerance would lead to increased residual stresses in the plate. Compared to a bigger squeeze force, the initial interference fit is more likely to produce a high residual stress level. In the case of initial interference fit, the residual stress variation will be less sensitive to the change of the squeeze force than that for clearance fit. With increasing squeeze force, the riveted lap joint may appear in different crack morphology and location under the fatigue load. Except for the fretting, secondary bending, and compressive residual stress, the boundary of the hardening zone at which the tangential stress turns into maximum tensile stress accounts for such phenomenon.

FEM analysis of the vibrational motion of oblique piezoelectric microcantilever in the vicinity of a sample surface in liquid

This article examines an oblique Microcantilever (MC) with an extended piezoelectric layer in liquid. The study of hydrodynamic force in MC which has been floated in viscous fluid is considered as paramount importance. To model the Vibrational motion, the Hamilton's principle has been used. For this purpose, the Vibrational motion equation has been modeled by considering the continuous beam based on the Euler–Bernoulli beam theory in liquid. Furthermore, using the Galerkin method and the Newmark algorithm, the differential equations of the MC has been solved. In this modeling, the inter-atomic forces between the MC tip and the sample surface have been considered in addition to the hydrodynamic and squeeze forces. The simulation results illustrate a reduction in the sensitivity of the vibrational motion under the effect of the squeeze force during the angularization of the MC. Moreover, the results illustrate that by reducing the MC distance from the sample surface, the Vibration amplitude decreases due to the increase in the fluid squeeze force. At the end, it has been shown that the time delay in sample surface topography in liquid substantially decreases in comparison with the air.

Squeeze plane flow of viscoplastic Bingham material

We develop an asymptotic solution for the plane squeeze flow of a viscoplastic medium. The standard lubrication-style expansions of the problem predict plug speed which varies slowly in the principal flow direction. This variation implies that the plug region cannot be truly unyielded. Our solution shows that this region is a pseudo-plug region in which the leading order equation predicts a plug, but really it is weakly yielded at higher order. We follow the asymptotic technique suggested earlier by Balmforth and Craster (1999) and Frigaard and Ryan (2004). We also provide comparison between analytical solution and numerical computations using the augmented Lagrangian method. The results of computations show presence of unyielded regions near the two stagnation points of flow close to centers of plates (that was found earlier by many researchers) and new additional unyielded regions at the outer edge of the material (both for short and long plates). The obtained analytical expression for the squeeze force is in a good agreement with the numerical results and previous results of Mitsoulis and Matsoukas (2003).

Application of ultrasound technique to evaluate contact condition on the faying surface of riveted joints

Contact area and pressure distributions on the faying surfaces of riveted joints are critical to fretting fatigue crack. However, these contact conditions are hard to evaluate by experimental methods. This study proposed an application of ultrasound technique to quantify contact area and pressure distribution on the faying surface of riveted joints. This ultrasound method consists of the ultrasonic reflection map measurement of the faying surface, and a parallel calibration procedure to establish the relationship between ultrasonic reflection and contact pressure. In this way, the contact area and pressure distributions of riveted joints installed with different riveting forces were investigated. The results show that the contact pressure increases rapidly with the squeeze force, while the contact area spreads slightly at the same time. The mean pressure profiles of the ultrasonic results were compared with the results of a finite element model for the riveted joints. The comparison shows that the mean pressure profiles are consistent with the numerical results.

Investigation of Load Transmission Throughout a Riveted Lap Joint

Results of comparative load transfer measurements and fatigue tests on riveted lap joints from Alclad sheets of a configuration representative of the aircraft fuselage are presented. Two different rivet squeeze force values were accounted for and in either case riveted specimens with the interfaying Teflon foil between the sheets to minimize friction, in addition to standard riveted joints without such a layer, were considered. The goal of the investigation was to recognize implications of friction between the mating sheets for the fatigue behaviour of riveted lap joints in order to derive riveting process dependent coefficients to be included in a fatigue life prediction model for this type of connections.