Dynamic Force Measurement Research Articles

The role of copolymer composition on the specific ion and thermo-response of ethylene glycol-based brushes

Thermoresponsive ethylene glycol based comb-polymer brushes were studied as a function of copolymer composition in aqueous electrolyte solutions. Homopolymer poly oligo(ethylene glycol) methyl ether methacrylate (POEGMA300) and statistical copolymer brushes with 60 mol% OEGMA300 and 40 mol% (di(ethyleneglycol) methyl ether methacrylate) (MEO2MA) underwent a monotonic swollen to collapsed transition with increasing temperature. Neutron reflectometry and ellipsometry measurements showed that the higher ethylene glycol content of the homopolymer brush led to a higher degree of swelling for a given temperature, with the transition occurring over a wider temperature range than the copolymer brush. Dynamic atomic force microscopy force measurements revealed minimal impact of probe velocity on normal interaction forces for the homopolymer brush. In contrast, a significant increase in both repulsion and adhesion was observed for the copolymer brush. Exposure to potassium thiocyanate solutions increased the degree of swelling at any given temperature while potassium acetate showed the opposite behaviour for both brush compositions. However, the homopolymer brushes displayed a greater increase in swelling due to thiocyanate and reduced collapse due to acetate.

Friction from Transduction Channels’ Gating Affects Spontaneous Hair-Bundle Oscillations

Hair cells of the inner ear can power spontaneous oscillations of their mechanosensory hair bundle, resulting in amplification of weak inputs near the characteristic frequency of oscillation. Recently, dynamic force measurements have revealed that delayed gating of the mechanosensitive ion channels responsible for mechanoelectrical transduction produces a friction force on the hair bundle. The significance of this intrinsic source of dissipation for the dynamical process underlying active hair-bundle motility has remained elusive. The aim of this work is to determine the role of friction in spontaneous hair-bundle oscillations. To this end, we characterized key oscillation properties over a large ensemble of individual hair cells and measured how viscosity of the endolymph that bathes the hair bundles affects these properties. We found that hair-bundle movements were too slow to be impeded by viscous drag only. Moreover, the oscillation frequency was only marginally affected by increasing endolymph viscosity by up to 30-fold. Stochastic simulations could capture the observed behaviors by adding a contribution to friction that was 3−8-fold larger than viscous drag. The extra friction could be attributed to delayed changes in tip-link tension as the result of the finite activation kinetics of the transduction channels. We exploited our analysis of hair-bundle dynamics to infer the channel activation time, which was ∼1 ms. This timescale was two orders-of-magnitude shorter than the oscillation period. However, because the channel activation time was significantly longer than the timescale of mechanical relaxation of the hair bundle, channel kinetics affected hair-bundle dynamics. Our results suggest that friction from channel gating affects the waveform of oscillation and that the channel activation time can tune the characteristic frequency of the hair cell. We conclude that the kinetics of transduction channels’ gating plays a fundamental role in the dynamic process that shapes spontaneous hair-bundle oscillations.

Сalibration method for a strain-gauge measurement system based on bidirectional rail loading

At present, all railways tend to increase the speed of passenger trains and axle loads in transportation of goods. These processes contribute to the improvement of rolling stocks and railway infrastructures. At the same time, there is a need to maintain a high level of safety in transportation. Therefore, experimental research and feasibility studies of the existing monitoring solutions are of the highest priority. Being experimental in nature, this study is aimed at increasing the reliability of the strain-gauge method in measurement of dynamic forces transferred from the wheel to the rail in real operating conditions. Rail strains were experimentally studied under bidirectional loading using a special-purpose impact device. Results of this research are presented in the paper. An experimental measuring section was created for recording loads. Strain gauges were installed on rails in several cross-sections. Rails were loaded with a special-purpose device, which was designed to adjust a loading force and shift a contact point. The structure of the loading device and its basic features are described in the paper.

Probing nano-scale viscoelastic response in air and in liquid with dynamic atomic force microscopy.

We perform a comparative study of dynamic force measurements using an Atomic Force Microscope (AFM) on the same soft polymer blend samples in both air and liquid environments. Our quantitative analysis starts with calibration of the same cantilever in both environments. Intermodulation AFM (ImAFM) is used to measure dynamic force quadratures on the same sample. We validate the accuracy of the reconstructed dynamic force quadratures by numerical simulation of a realistic model of the cantilever in liquid. In spite of the very low quality factor of this resonance, we find excellent agreement between experiment and simulation. A recently developed moving surface model explains the measured force quadrature curves on the soft polymer, in both air and liquid.

A fractional-order accumulative regularization filter for force reconstruction

Abstract The ill-posed inverse problem of the force reconstruction comes from the influence of noise to measured responses and results in an inaccurate or non-unique solution. To overcome this ill-posedness, in this paper, the transfer function of the reconstruction model is redefined by a Fractional order Accumulative Regularization Filter (FARF). First, the measured responses with noise are refined by a fractional-order accumulation filter based on a dynamic data refresh strategy. Second, a transfer function, generated by the filtering results of the measured responses, is manipulated by an iterative Tikhonov regularization with a serious of iterative Landweber filter factors. Third, the regularization parameter is optimized by the Generalized Cross-Validation (GCV) to improve the ill-posedness of the force reconstruction model. A Dynamic Force Measurement System (DFMS) for the force reconstruction is designed to illustrate the application advantages of our suggested FARF method. The experimental result shows that the FARF method with r = 0.1 and α = 20, has a PRE of 0.36% and an RE of 2.45%, is superior to other cases of the FARF method and the traditional regularization methods when it comes to the dynamic force reconstruction.

Dynamic correction of oscillatory forces during ultrasonic-assisted metal forming

Numerous investigations in the past decades reported that the forces required for forming processes can be reduced by superimposing high frequency oscillation. Even though many studies have been carried out identifying and assessing the complex cause of this reduction, cause-effect relationships are generally not yet established in detail. Since the measurement of dynamic forces plays a key role in clarifying the causes, a precise measurement of the forming forces oscillating with high frequency is necessary. Although dynamic force measurement is a well-known field of research, this study focuses on its utilisation for ultrasonic-assisted forming processes. Since dynamic effects distort original measurements in this frequency range, adjustment is required. Based on measurement instruments with high temporal resolution the present study introduces an approach for creating and employing a frequency dependent force correction in the high dynamic range. The experimental procedure for creating a transfer function up to a limiting frequency of 40 kHz is later analysed and verified by numerical modal and transient simulations. The results indicate that the highly location dependent dynamic force detection has major influence on peak forces. Observed deviations can be precisely corrected using the generated frequency dependent transfer function.

Dynamic Forces Induced by a Single Pedestrian: A Literature Review

With the use of lighter construction materials, more slender architectural designs, and open floor plans resulting in low damping, vibration serviceability has become a dominant design criterion for structural engineers worldwide. In principle, assessment of floor vibration serviceability requires a proper consideration of three key issues: excitation source, system, and receiver. Walking is usually the dominant human excitation for building floors. This paper provides a comprehensive review of a considerable number of references dealing with experimental measurement and mathematical modeling of dynamic forces induced by a single pedestrian. The historical development of walking force modeling—from single harmonic loads to extremely complex stochastic processes—is discussed. As a conclusion to this effort, it is suggested that less reliance should be made by the industry on the deterministic force models, since they have been shown to be overly conservative. Alternatively, due to the random nature of human walking, probabilistic force models seem to be more realistic, while more research is needed to achieve enough confidence to implement in design practice.

Shape Memory Alloy Wire for Force Sensing

Shape memory alloy (known dominantly as SMA actuator) which is well known for its actuation, is hereby proposed to be designed exclusively as a sensor. A principle of active force sensing using shape memory effect (SME) of SMA is evolved. SMA wire along with a passive bias (antagonistic) element performs sensing as an actuated sensor, by the variation in its electrical resistance for a contact force, in a linear elastic manner. The principle is validated on a measurement system, which resembles that of a standard load cell. The SMA-based sensor is able to provide an accurate static and dynamic force measurement. The variation in the electrical resistance of the SMA is a measure of the strain induced on the load cell for a contact force placed upon it. The objective of sensing is accomplished by overcoming the nonlinearity of the SMA with a passive biasing element. A prototype of the active force sensor is realized to evaluate its sensing ability for serving a motor. The measurement principle of the sensor and test on its static calibration are described; the experimental results demonstrate the validity and reliability of the sensor. The uniqueness of this contribution is that- a new dimension is added to SMA’s functionality by the design of a linear active sensor for force measurement, though it is an inherently non-linear element.

Direct mapping of chemical oxidation of individual graphene sheets through dynamic force measurements at the nanoscale.

Graphene oxide is one of the most studied nanomaterials owing to its huge application potential in many fields, including biomedicine, sensing, drug delivery, optical and optoelectronic technologies. However, a detailed description of the chemical composition and the extent of oxidation in graphene oxide remains a key challenge affecting its applicability and further development of new applications. Here, we report direct monitoring of the chemical oxidation of an individual graphene flake during ultraviolet/ozone treatment through in situ atomic force microscopy based on dynamic force mapping. The results showed that graphene oxidation expanded from the graphene edges to the entire graphene surface. The interaction force mapping results correlated well with X-ray photoelectron spectroscopy data quantifying the degree of chemical oxidation. Density functional theory calculations confirmed the specific interaction forces measured between a silicon tip and graphene oxide. The developed methodology can be used as a simple protocol for evaluating the chemical functionalization of other two-dimensional materials with covalently attached functional groups.

Experimental and Numerical Investigation of Burr Formation in Intermittent Turning of AISI 4140

Burr formation is a problematic aspect in the machining of ductile metals. Understanding the formation mechanism and being able to model the plastic workpiece behavior during tool exits is key to burr minimization. A 3D finite element model is used to simulate burr formation during the exit phase of intermittent turning of AISI 4140, using a nose radiused insert. The model is validated by experimental results of dynamic force measurement and analysis of the burrs produced. The exit burr height obtained via simulation closely corresponds to the experimentally obtained values.

Development of three-dimensional dynamic grinding force measurement platform

In order to accurately measure and control high-frequency grinding force in the process of grinding, a novel measurement method of three-dimensional grinding force with mutual perpendicular and independent elastic elements is proposed in this paper. To detect the high frequency grinding force, a resistance strain-type three-dimensional grinding force measurement platform was designed and developed. The key performance indicators of the measurement platform were investigated via finite element simulation. In addition, the detection performance of the measurement platform was researched and verified through natural frequency measurement experiments, static calibration experiments, and grinding experiments. The results show that the proposed method can effectively alleviate the inherent contradiction between natural frequency and sensitivity in the traditional dynamometer; the measurement platform as-established fully meets the performance requirements of three-dimensional dynamic grinding force detection. To this effect, the results discussed here provide technical support for achieving accurate detection of high frequency grinding force, monitoring grinding processes, optimizing grinding parameters, and improving grinding quality.

Active flow control on a NACA 23012 airfoil model by means of magnetohydrodynamic plasma actuator

The paper is devoted to the study of high speed flow control around the airfoil by means of the Lorentz force. The latter is formed by creating the pulsed arc filament, moving in the magnetic field along the upper airfoil surface. The research was performed for the NACA23012 airfoil model at flow velocities up to 60 m/s (134 mph). The dynamic measurement of the aerodynamic forces on the airfoil was made. Changes up to 5% in an average value of lift and pitching moment were obtained at pulse repetition frequency up to 13 Hz and average discharge power less than 200 W. The amplitude of lift force oscillation was obtained as high as 10%, with the integration time of the balance 30 ms. The dynamic flow visualization of an airfoil model after a single discharge ignition was performed. It is shown that interaction of the main flow with the arc-induced disturbance leads to the dramatic changes in the flow structure. It was shown that the upstream movement of the arc channel (I = 40-700 A) leads to the local flow separation and simultaneously to the formation of a high pressure region above the model surface. Current paper presents investigation of previous work.

Experimental Analysis of Dynamic Oil Film Pressure of Tilting-Pad Journal Bearings

With the increase in capacity demand, the development of rotating machinery is toward larger scale, higher speed, and intellectualization. In order to achieve a safer and more reliable operation, a better vibration performance of the rotor-bearing system is expected. Tilting-pad journal bearings have many advantages such as improved dynamic performance and drastic reduction in instability; therefore, they are widely used in rotating machinery. The nonlinearity of the dynamic oil film force is one of the fundamental parameters for an oil film bearing supported rotor system. A mounts of scholars and technicians have conducted theoretical research in this field. This paper focuses on the experimental research of the nonlinearity of dynamic oil film force. Oil film force was measured in various experiments, where relevance and sensitivity to vibration responses were evaluated under different operation speeds and excitation frequencies. The research was mainly divided into three steps. Firstly, experimental measurements data of oil film pressure under different speeds and static loads were verified by theoretical numerical calculation. Secondly, the feature information of displacement and pressure under different dynamic loads and excitation frequency was obtained from experiments. In addition, the frequency compositions of displacement and pressure were compared. Finally, a newly developed time–frequency analysis tool, named the synchrosqueezing wavelet transform, was employed to characterize the displacement and pressure features. Through the comparison between the time–frequency compositions of these two features,there are more signal characteristics presented in the time–frequency spectrums of dynamic oil film force. Characteristics like amplitude of both excitation frequency and half-frequency whirl frequency are more obvious in those spectrums. It can be concluded that the measurement of dynamic oil film force is an effective method to monitor the real-time status of the rotor-bearing system vibration.

Flexible Piezoelectric Tactile Sensor Array for Dynamic Three-Axis Force Measurement.

A new flexible piezoelectric tactile sensor array based on polyvinylidene fluoride (PVDF) film is proposed for measuring three-axis dynamic contact force distribution. The array consists of six tactile units arranged as a 3 × 2 matrix with spacing 8 mm between neighbor units. In each unit, a PVDF film is sandwiched between four square-shaped upper electrodes and one square-shaped lower electrode, forming four piezoelectric capacitors. A truncated pyramid bump is located above the four piezoelectric capacitors to improve force transmission. A three-axis contact force transmitted from the top of the bump will lead to the four piezoelectric capacitors underneath undergoing different charge changes, from which the normal and shear components of the force can be calculated. A series of dynamic tests have been carried out by exerting sinusoidal forces with amplitudes ranging from 0 to 0.5 N in the x-axis, 0 to 0.5 N in the y-axis, and 0 to 1.5 N in the z-axis, separately. The tactile units show good sensitivities with 14.93, 14.92, and 6.62 pC/N in the x-, y-, and z-axes, respectively. They can work with good linearity, relatively low coupling effect, high repeatability, and acceptable frequency response in the range of 5–400 Hz to both normal and shear load. In addition, dynamic three-axis force measurement has been conducted for all of the tactile units. The average errors between the applied and calculated forces are 10.68% ± 6.84%. Furthermore, the sensor array can be easily integrated onto a curved surface, such as robotic and prosthetic hands, due to its excellent flexibility.

A Miniaturized Hemoretractometer for Blood Clot Retraction Testing.

Blood coagulation is a critical hemostatic process that must be properly regulated to maintain a delicate balance between bleeding and clotting. Disorders of blood coagulation can expose patients to the risk of either bleeding disorders or thrombotic diseases. Coagulation diagnostics using whole blood is very promising for assessing the complexity of the coagulation system and for global measurements of hemostasis. Despite the clinic values that existing whole blood coagulation tests have demonstrated, these systems have significant limitations that diminish their potential for point-of-care applications. Here, recent advancements in device miniaturization using functional soft materials are leveraged to develop a miniaturized clot retraction force assay device termed mHemoRetractoMeter (mHRM). The mHRM is capable of precise measurements of dynamic clot retraction forces in real time using minute amounts of whole blood. To further demonstrate the clinical utility of the mHRM, systematic studies are conducted using the mHRM to examine the effects of assay temperature, treatments of clotting agents, and pro- and anti-coagulant drugs on clot retraction force developments of whole blood samples. The mHRM's low fabrication cost, small size, and consumption of only minute amounts of blood samples make the technology promising as a point-of-care tool for future coagulation monitoring.

Development of an experimental set-up for dynamic force measurements during impact and perforation, coupling to numerical simulations

Quasi-static tension and dynamic compression experiments on S235JR mild steel were performed using a screw-driven machine and a split Hopkinson pressure bar (SHPB) device. A wide range of strain rates from 10−4 to 2500 s−1 has been covered during experiments. The Johnson–Cook constitutive relation was adopted to describe the material visco-plastic behaviour. Ballistic impact experiments on S235JR plates with conical-nose shaped projectile were carried out using pneumatic gas gun having different impact velocities varying from 49 to 181 m/s. A new experimental set-up allowing resistance force measurement during impact and perforation was developed. Different impact velocities and thicknesses were evaluated during ballistic experiments. All the projectiles are 12.8 mm in diameter and 28g in weight. The ballistic impact device is equipped with laser sensors for velocities measurements and piezoelectric sensors for dynamic force measurement. Based on numerical and experimental investigations, the ballistic properties and failure modes of the material have been studied. The finite element code ABAQUS/Explicit was used to simulate the perforation process but also to have a better understanding of the measurement. A good agreement between experiments and numerical results has been observed in terms of ballistic curves, failure patterns, resistance force as well as the energy balance.

Simultaneous measurement of dynamic force and spatial thin film thickness between deformable and solid surfaces by integrated thin liquid film force apparatus.

Interactions involving deformable surfaces reveal a number of distinguishing physicochemical characteristics that do not exist in interactions between rigid solid surfaces. A unique fully custom-designed instrument, referred to as integrated thin liquid film force apparatus (ITLFFA), was developed to study the interactions between one deformable and one solid surface in liquid. Incorporating a bimorph force sensor with interferometry, this device allows for the simultaneous measurement of the time-dependent interaction force and the corresponding spatiotemporal film thickness of the intervening liquid film. The ITLFFA possesses the specific feature of conducting measurement under a wide range of hydrodynamic conditions, with a displacement velocity of deformable surfaces ranging from 2 μm s-1 to 50 mm s-1. Equipped with a high speed camera, the results of a bubble interacting with hydrophilic and partially hydrophobic surfaces in aqueous solutions indicated that ITLFFA can provide information on interaction forces and thin liquid film drainage dynamics not only in a stable film but also in films of the quick rupture process. The weak interaction force was extracted from a measured film profile. Because of its well-characterized experimental conditions, ITLFFA permits the accurate and quantitative comparison/validation between measured and calculated interaction forces and temporal film profiles.

Metrological approach to the force exerted by the axle of a road vehicle in motion carrying liquid

Weigh-in-motion (WIM) systems are used for identifying the dynamic force exerted on the ground by axles of a vehicle. These systems are important for monitoring the gross vehicle weight and the vehicle axle load. Overweighted trucks on the roads increase pavement damage and traffic accidents. Knowing the accuracy of WIM systems is necessary. In the case of liquid transport the ‘sloshing effect’ affects this accuracy. This paper aims to analyze the dynamic measurement of the axle forces in vehicles carrying liquid during WIM up to 6 km h−1. Laboratory experiments using one vehicle with six axles and liquid loads on different levels in weighing instruments are presented. A non-linear computational multi-mass-springs model was developed and laboratory experiments were carried out to show the acceleration influences on axle forces of vehicles with six axles and with and without baffles to vary the ‘sloshing effect’.

Verification of a multiple-machine program for material testing from quasi-static to high strain-rate

Nowadays characterization of the strain-rate dependence of materials becomes indispensable in crashworthiness design of structures (i.e. car-bodies, ships) with CAE approach. To gather sufficient test data for accurate characterization, various machines are usually selected to work together on material testing covering quasi-static, intermediate and high strain-rates, which is referred to as a multiple-machine program in the present paper. Relatively rigorous verification of the multiple-machine program, including two test schemes, was designed and executed to ensure the comparability of test data from various machines. First, an acknowledged rate-insensitive aluminum alloy material was tested with a universal material test machine, an intermediate strain-rate test machine and a drop tower, respectively. Second, a rate-dependent high-strength steel material was tested with the same multiple-machine program, focusing on two strain-rate overlaps. Rate sensitivities of the tested materials were demonstrated by the test results in the two test schemes, and consistencies of the test data in the strain-rate overlaps were satisfactory, strongly verifying reliability of the multiple-machine program. Crucial measurement approaches were also decided prior to the verification, including the DIC method for deformation measurement and the dynamic force measurement to attenuate the ringing effect.

Modular apparatus for electrostatic actuation of common atomic force microscope cantilevers.

Piezoelectric actuation of atomic force microscope (AFM) cantilevers often suffers from spurious mechanical resonances in the loop between the signal driving the cantilever and the actual tip motion. These spurious resonances can reduce the accuracy of AFM measurements and in some cases completely obscure the cantilever response. To address these limitations, we developed a specialized AFM cantilever holder for electrostatic actuation of AFM cantilevers. The holder contains electrical contacts for the AFM cantilever chip, as well as an electrode (or electrodes) that may be precisely positioned with respect to the back of the cantilever. By controlling the voltages on the AFM cantilever and the actuation electrode(s), an electrostatic force is applied directly to the cantilever, providing a near-ideal transfer function from drive signal to tip motion. We demonstrate both static and dynamic actuations, achieved through the application of direct current and alternating current voltage schemes, respectively. As an example application, we explore contact resonance atomic force microscopy, which is a technique for measuring the mechanical properties of surfaces on the sub-micron length scale. Using multiple electrodes, we also show that the torsional resonances of the AFM cantilever may be excited electrostatically, opening the door for advanced dynamic lateral force measurements with improved accuracy and precision.