Pinning Forces Research Articles

Low-frequency electrodynamics in the mixed state of superconducting NbN and a-MoGe films using two-coil mutual inductance technique

We investigate the low-frequency electrodynamics in the vortex state of two type-II superconducting films, namely, a moderate-to-strongly pinned Niobium Nitride (NbN) and a very weakly pinned amorphous Molybdenum Germanium (a-MoGe) film. We employ a two-coil mutual inductance technique to extract the complex penetration depth, λ~ . The sample response is studied through the temperature variation of λ~ in the mixed state, where we employ a model developed by Coffey and Clem (the CC model) to extract different vortex lattice (VL) parameters, such as the restoring pinning force constant (Labusch parameter), VL drag coefficient and pinning potential barrier. We observe that a consistent description of the inductive and dissipative part of the response is only possible when we take the viscous drag on the vortices to be several orders of magnitude larger than the viscous drag estimated from the Bardeen–Stephen model.

A Hybrid Actuator Model for Efficient Guided Wave based Structural Health Monitoring Simulations

Abstract Simulation has been recognized as a promising option to reduce the time and costs associated with determining Probability of Detection (POD) curves to demonstrate the performance of Guided Wave based Structural Health Monitoring (GW-SHM) systems. Time domain transient spectral finite element schemes have been used for large GW-SHM simulation campaigns, but the most common piezoelectric transducer model used for actuation, the pin force model, has limitations in terms of its range of validity. This is because the excitation frequency for the pin force model has only been validated far below the first electromechanical resonance frequency of the piezoelectric transducer mainly due to not considering the normal stress and dynamics of the transducer. As a result, the value of simulation tools for performance demonstrations may be limited. To address this limitation, this paper introduces a Hybrid Actuator Model that integrates frequency-dependent complex interfacial stresses in both the shear and normal directions, computed using finite elements. These surface stresses are compatible with time domain transient spectral finite element schemes, enabling their seamless integration without compromising the required performance for conducting intensive simulation campaigns. The proposed hybrid actuator model undergoes validation through a combination of simulation and experimental studies. Additionally, a comprehensive parametric study is conducted to assess the model's validity across a wide range of excitation frequencies. The results demonstrate the accurate representation of the transduction signal above the piezoelectric transducer's first free electromechanical resonance frequency.

Modeling of Strain Actuation on Relatively Soft Curved Beams by Piezoelectric Ceramics for De-Icing Systems

In this work, the effects of some geometric and mechanical parameters that characterize curved and relatively soft structures integrated with piezoelectric actuators are investigated. The effect of parameters such as the curvature, location, and extension of the piezo device, as well as the thickness of the bonding and its strength, are considered in view of a potentially lighter model that replaces the piezoelectric device via its actions, namely pin forces, whose layout and values are strongly dependent on the curvature. When comparing the results obtained by a finite element model of the structure with the piezo device and of the structure alone under the action of pin forces, dedicated indicators were found, which could be useful to support lighter modeling approaches and to predict the authority of the piezoelectric device.

Extrapolation of Tractor Traction Resistance Load Spectrum and Compilation of Loading Spectrum Based on Optimal Threshold Selection Using a Genetic Algorithm

To obtain the load spectrum of the traction resistance of the three-point suspension device under tractor-plowing conditions, a load spectrum extrapolation method based on a genetic algorithm optimal threshold selection is proposed. This article first uses a pin force sensor to measure the plowing resistance of the tractor’s three-point suspension device under plowing conditions and preprocesses the collected load signal. Next, a genetic algorithm is introduced to select the threshold based on the Peak Over Threshold (POT) extremum extrapolation model. The Generalized Pareto Distribution (GPD) fits the extreme load distribution that exceeds the threshold range, generating new extreme points that follow the GPD distribution to replace the extreme points in the original data, achieving the extrapolation of the load spectrum. Finally, the loading spectrum that can be achieved on the test bench is obtained based on the miner fatigue theory and accelerated life theory. The results show that the upper threshold of the time-domain load data obtained by the genetic algorithm is 10.975 kN, and the grey correlation degree is 0.7249. The optimal lower threshold is 8.5455 kN, the grey correlation degree is 0.7722, and the fitting effect of the GPD distribution is good. The plowing operation was divided into five stages: plowing tool insertion, acceleration operation, constant speed operation, deceleration operation, and plowing tool extraction. A traction resistance loading spectrum that can be achieved on the test bench was developed. The load spectrum extrapolation method based on the genetic algorithm optimal threshold selection can improve the accuracy of threshold selection and achieve the extrapolation and reconstruction of the load spectrum. After processing the extrapolated load spectrum, it can be transformed into a load spectrum that can be recognized by the test bench.

A Finite Element Model for Predicting the Static Strength of a Composite Hybrid Joint with Reinforcement Pins.

This paper presents a finite element model for predicting the performance and failure behaviour of a hybrid joint assembling fibrous composites to a metal part with reinforcement micro pins for enhancing the damage tolerance performance. A unit-strip model using the cohesive elements at the bond interface is employed to simulate the onset and propagation of debonding cracks. Two different traction-separation laws for the interface cohesive elements are employed, representing the fracture toughness properties of the plain adhesive bond and a pin-reinforced interface, respectively. This approach can account for the large-scale crack-bridging effect of the pins. It avoids using concentrated pin forces in the numerical model, thus removing mesh-size dependency, and permitting more accurate and robust computational analysis. Lap joints reinforced with various pin arrays were tested under quasi-static load. Predicted load versus applied displacement relations are in good agreement with the test results, especially for the debonding onset and early stage of crack propagation.

Study of vortex dynamics in an a-MoGe thin film using low-frequency two-coil mutual inductance measurements

We extract the vortex lattice (VL) parameters using low-frequency two-coil mutual inductance measurements in a 20-nm-thick superconducting amorphous Molybdenum-Germanium (a-MoGe) thin film. We fit the temperature dependence of ac penetration depth in the mixed state using a model developed by Coffey and Clem and demonstrate a procedure for extracting VL parameters such as the restoring pinning force constant (Labusch parameter) VL drag coefficient, and pinning potential barrier. We show that the extracted parameters follow the magnetic field variation expected for a weakly pinned two-dimensional vortex lattice.

Fabrication of ultrafine-grained Ti-15Zr-xCu alloys through martensite decompositions under thermomechanical coupling conditions

• Ultrafine-grained microstructure was successfully achieved in Ti-15Zr- x Cu system by hot rolling. • Cu alloying increased dynamic recrystallization nucleation rate and formed Ti 2 Cu along grain boundaries, which inhibited grain growth. • The comprehensive mechanical properties of the ultrafine grained Ti-15Zr-5Cu alloy are better than that of the Roxolid Ti-Zr alloy currently used for dental implants. Grain refinement is a well-recognized method to simultaneously increase the strength and ductility of metallic materials. Fabrication of ultrafine-grained metals in bulk using a simple low-cost approach is a long-term goal for material scientists. In this work, based on the chemical composition of a biomedical Ti-15Zr alloy, a series of novel Ti-15Zr- x Cu ( x = 0, 3, 5, 7 wt.%) alloys were designed and fabricated. The alloys were quenched in the single β phase region to obtain a martensitic microstructure and deformed in the temperature range of 710–750 °C to obtain an ultrafine-grained microstructure through martensite decomposition under thermomechanical coupling conditions. Experimental results showed that Cu alloying could increase the dynamic recrystallization (DRX) nucleation rate due to its role in both refining martensitic lath width and increasing dislocation density. Cu alloying could also suppress grain growth due to the precipitated Ti 2 Cu particles exerting pinning forces on the grain boundaries. The optimal Cu content in the Ti-15Zr- x Cu alloy was determined to be 5 wt.%. After being subjected to a compression leading to a 70% height reduction at 730 °C and 1 s –1 , the grain size of the Ti-15Zr-5Cu alloy was only 180 ± 70 nm. The tensile strength of the as-prepared alloy reached 975 ± 10 MPa, which was 45% higher than that of the conventional Ti-15Zr alloy (673 ± 16 MPa). This increase in strength was achieved without any reduction in ductility. The comprehensive mechanical properties of the ultrafine-grained Ti-15Zr-5Cu alloy are better than that of the Roxolid Ti–Zr alloy currently used for dental implants.

Displacement Correlations in Disordered Athermal Networks

We derive exact results for correlations in the displacement fields \(\{ \delta \mathbf {r} \} \equiv \{ \delta r_{\mu = x,y} \}\) in near-crystalline athermal systems in two dimensions. We analyze the displacement correlations produced by different types of microscopic disorder, and show that disorder at the microscopic scale gives rise to long-range correlations with a dependence on the system size L given by \(\langle \delta r_{\mu } \delta r_{\nu } \rangle \sim c_{\mu \nu }(r/L,\theta )\). In addition, we show that polydispersity in the constituent particle sizes and random bond disorder give rise to a logarithmic system size scaling, with \(c_{\mu \nu }(\rho ,\theta ) \sim \text {const}_{\mu \nu } - \text {a}_{\mu \nu }(\theta )\log \rho + \text {b}_{\mu \nu }(\theta ) \rho ^{2} \) for \(\rho ~(=r/L) \rightarrow 0\). This scaling is different for the case of displacement correlations produced by random external forces at each vertex of the network, given by \(c^{f}_{\mu \nu }(\rho ,\theta ) \sim \text {const}^{f}_{\mu \nu } -( \text {a}^{f}_{\mu \nu }(\theta ) + \text {b}^{f}_{\mu \nu }(\theta ) \log \rho ) \rho ^2 \). Additionally, we find that correlations produced by polydispersity and the correlations produced by disorder in bond stiffness differ in their symmetry properties. Finally, we also predict the displacement correlations for a model of polydispersed soft disks subject to external pinning forces, that involve two different types of microscopic disorder. We verify our theoretical predictions using numerical simulations of polydispersed soft disks with random spring contacts in two dimensions.

Mode-I fracture control of unidirectional laminated composites using MFC actuators

This article presents an experimental and numerical investigation of Mode-I fracture control in aerospace grade unidirectional laminated composites (AS4/914) using the smart material approach. The P1 type macro fiber composites (MFC) actuators are selected for current research because of their higher free strain, high mechanical flexibility, and good blocking force. The opening mode (Mode-I) interlaminar fracture tests have been carried out on DCB specimens having surface bonded MFC actuator patches under the application of electric voltage within a range of 0–1500 V. These fracture control tests have been performed on pre-cracked (PC) and non pre-cracked (NPC) double cantilever beam specimens. The modified pin force model has been adopted for the evaluation of actuation forces in surface bonded MFC actuators. The XIGA-CZM based numerical formulation is utilized for numerical fracture modeling under electromechanical loading conditions. The MFC actuators have significant control over Mode-I fracture energy under the application of peak operating voltage. The numerical model using a modified pin force model in combination with XIGA-CZM based fracture model shows a good agreement with experimental observations.

Study of the Droplet Pinning Force in the Transition from Dry to Liquid-Infused Thin Polymer Films.

The change in the pinning force during the transition from dry to oil-impregnated thin polymer films is studied for droplets of water and hexadecane. A careful variation of the oil amount in the films is performed by means of supercritical impregnation. The film thickness dependence on the oil content is measured using ellipsometry and compared to gel swelling theory estimates. Depending on the oil content, two cases of pinning force behavior have been identified. For each case, the factors that determine the pinning force are discussed. The pinning force in the transition from dry to equilibrium swollen gel films is well approximated by the Joanny and de Gennes hysteresis model of dilute defects.

Compression of A Midfoot Osteotomy Using A Circular External Fixator: What is the Ideal Pin Configuration?

Category:Midfoot/Forefoot; Diabetes; TraumaIntroduction/Purpose:Foot and ankle deformity correction through midfoot osteotomy can be implemented in a wide variety of clinical situations. Use of a circular ring fixator for osteotomy fixation is particularly useful for patients with poor soft tissue envelopes and/or active infection as can occur in diabetes and Charcot arthropathy. The foot pins in a ring fixator can be configured to apply compression at the osteotomy site. However, the optimal pin configuration and force has yet to be determined. The purpose of this study was to quantify compressive forces achieved across midfoot osteotomies with various wire configurations in a circular ring fixator construct.Methods:Nine through-knee amputation cadavers were stabilized with a standard circular external fixation carbon frame. A midfoot osteotomy through the transverse tarsal joint was performed using an oscillating saw. A 4mm bone wedge was removed from the osteotomy site for placement of a Tekscan pressure sensor. A two-ring frame was applied in the standard fashion and three parallel 1.8mm smooth wires were placed parallel to each other through the foot distal to the osteotomy: wire #1 proximally through the cuneiforms, wire #2 through the base of the metatarsals, wire #3 through the metatarsal shafts. After baseline pressure readings, wires were sequentially attached (wire #1 alone, wire #1-2, wire #1-3) to the ring fixator and tensioned to 90kg. Pressure readings were recorded at the osteotomy site for each sequential wire tensioning both at the hole location where the wire naturally crossed, 'neutral', and again at one hole 'proximal' (e.g., toward the osteotomy).Results:Average compressive load at neutral hole positioning for wire #1 was 382 N. The addition of wire #2 increased the compressive load to 439 N on average. The addition of wire #3 decreased compressive force to 372 N. Similar trends were seen in proximal hole positioning where average compressive force increased following tensioning of wire #2 from 580 N to 600 N but compressive force decreased on wire #3 addition to 425 N. Therefore, tensioning forefoot thin wires in the proximal hole position increases compressive forces by 50% compared to neutral position, and adding a second wire increased compressive force by up to 15% compared to a single forefoot wire.Conclusion:In a circular frame midfoot fusion model, the greatest compressive force was achieved with two wires tensioned in the proximal hole position. The addition of a third wire led to force decrease likely due to off-axis forces that may distract the osteotomy site given the difficulty of passing all wires perfectly parallel in all planes. Ideal positioning and tensioning of forefoot pins may optimize construct stability and compression and improve healing of the midfoot osteotomy.

Active matter shepherding and clustering in inhomogeneous environments.

We consider a mixture of active and passive run-and-tumble disks in an inhomogeneous environment where only half of the sample contains quenched disorder or pinning. The disks are initialized in a fully mixed state of uniform density. We identify several distinct dynamical phases as a function of motor force and pinning density. At high pinning densities and high motor forces, there is a two-step process initiated by a rapid accumulation of both active and passive disks in the pinned region, which produces a large density gradient in the system. This is followed by a slower species phase separation process where the inactive disks are shepherded by the active disks into the pin-free region, forming a nonclustered fluid and producing a more uniform density with species phase separation. For higher pinning densities and low motor forces, the dynamics becomes very slow and the system maintains a strong density gradient. For weaker pinning and large motor forces, a floating clustered state appears, and the time-averaged density of the system is uniform. We illustrate the appearance of these phases in a dynamic phase diagram.

Models for FSW forces using a square pin profile tool

In this paper, mechanical models for FSW are developed for a square pin profile tool. The models express the oscillation of the forces over time and their mean values. The welding, transverse, radial, and tangential forces are modeled as a function of the rotational and welding speeds and the instantaneous angle of rotation. The models include the concept of a specific force, based on the mechanics of orthogonal cutting, to describe the relation between the forces and the area of the deformed material. Additionally, experimental measurements for the forces and torque are performed for different parameters to calibrate and validate the models. Due to the square profile of the tool pin, the welding, transverse, radial, and tangential experimental forces exhibit periodic variations along the tool advancing path. The maximum radial force occurs at 45° of the welding direction, and the mean welding and transverse forces present similar magnitudes in all experiments. The results show good agreement between the models and the experimental data with a correlation coefficient greater than 0.97. With increasing rotational speed, the torque decreases linearly, and the axial force is almost constant.

Long-range correlations in pinned athermal networks

We derive exact results for displacement fields that develop as a response to external pinning forces in two-dimensional athermal networks. For a triangular lattice arrangement of particles interacting through soft potentials, we develop a Green's function formalism which we use to derive exact results for displacement fields produced by localized external forces. We show that in the continuum limit the displacement fields decay as 1/r at large distances r away from a force dipole. Finally, we extend our formulation to study correlations in the displacement fields produced by the external pinning forces. We show that uncorrelated pinned forces at each vertex give rise to long-range correlations in displacements in athermal systems, with a nontrivial system size dependence. We verify our predictions with numerical simulations of athermal networks in two dimensions.

Performance of a flexoelectric actuator for lamb wave excitation

A flexoelectric actuator represents a new approach for exciting Lamb waves in plate structures and, thus, can be potentially used for active structural health monitoring systems and microsensors. This paper analytically investigated the performance of a flexoelectric actuator for Lamb wave excitation. The constitutive equation for a thin plate flexoelectric structure was derived using the thermodynamics theory. A significant size effect could be demonstrated by the constitutive equation, which suggests a greatly enhanced curvature excitation performance at a small dimension. The interaction between the ideally bonded flexoelectric actuator with the plate could be simplified into two pairs of pin force and pin moment under the assumption of a weak coupling condition. The strain and the displacement responses to the pin-force and pin-moment pairs were obtained using the integral transform techniques and residue calculus. The pin-moment component mainly yielded an antisymmetric Lamb wave mode, while the pin force was reminiscent of its piezoelectric counterpart. The tuning of either a symmetric or an antisymmetric mode could be achieved by choosing an appropriate excitation frequency. The response under a five-cycle Hanning-window toneburst excitation signal was compared with the finite element analysis results and good agreement between them was found.

Determination of pin forces in longitudinal reinforcement and stiffness at torsion reinforced concrete elements with normal cracks

Determination of pin forces in longitudinal reinforcement and stiffness at torsion reinforced concrete elements with normal cracks

Effects of Grain Boundary Faceting, Grain Boundary Anisotropy and Interface Natures on the Maximum Pinning Force of a Differently Shaped and Oriented Particle

Zener pinning between a curved Cu grain boundary (GB) and a differently shaped and oriented Ag particle has been simulated via molecular dynamics. The computed magnitudes of the maximum pinning force agreed with theoretical predictions only when the force was small. As the force increased, discrepancy became obvious. Through carefully inspecting structures of the Cu-Ag interfaces, detailed interaction processes and variation of the Cu GB during the interaction, the discrepancy is found to mainly result from GB faceting, which can reduce the maximum pinning force and facilitate boundary passage. GB anisotropy and/or interface natures are also found to slightly contribute to the discrepancy. These findings suggest that the assumption of an isotropic GB with constant energy utilized in previous theoretical works for deriving the maximum pinning force is inappropriate and a correct maximum pinning force could not be predicted without knowing the effects of GB evolution together with detailed properties of both GBs and interfaces.

The Ring-Pull Assay for Mechanical Properties of Fibrous Soft Tissues - An Analysis of the Uniaxial Approximation and a Correction for Nonlinear Thick-Walled Tissues.

The ring-pull test, where a ring of tissue is hooked via two pins and stretched, is a popular biomechanical test, especially for small arteries. Although convenient and reliable, the ring test produces inhomogeneous strain, making determination of material parameters non-trivial. To determine correction factors between ring-pull-estimated and true tissue properties. A finite-element model of ring pulling was constructed for a sample with nonlinear, anisotropic mechanical behavior typical of arteries. The pin force and sample cross-section were used to compute an apparent modulus at small and large strain, which were compared to the specified properties. The resulting corrections were validated with experiments on porcine and ovine arteries. The correction was further applied to experiments on mouse aortic rings to determine material and failure properties. Calculating strain based on centerline stretch rather than inner-wall or outer-wall stretch afforded better estimation of tissue properties. Additional correction factors were developed based on ring wall thickness H, centerline ring radius R c , and pin radius a. The corrected estimates for tissue properties were in good agreement with uniaxial stretch experiments. The computed corrections improved estimation of tissue material properties for both the small-strain (toe) modulus and the large-strain (lockout) modulus. When measuring tensile strength, one should minimize H/a to ensure that peak stress occurs at the sample midplane rather than near the pin. In this scenario, tensile strength can be estimated accurately by using inner-wall stretch at the midplane and the corrected properties.

Energy analysis and experimental evaluation of momentum exchange impact damper with pre-straining spring mechanism

ABSTRACT The aim of this research is to evaluate the performance of impact-induced vibration control using momentum exchange impact damper with pre-straining spring mechanism (PSMEID) based on the energy analysis and verifying the effectiveness of the proposed method experimentally using a simple three-body collision model. It is shown from the simulation study that the fraction of energy absorbed by the primary mass was small if the excitation frequency differs from the primary mass natural frequency. In the case of excitation frequency is lower than the primary mass natural frequency, most of the impact energy is transferred to the damper mass. For excitation frequencies higher than the primary mass natural frequency, a large amount of impact energy is reflected after the collision. The energy absorption ratio is small if the damper mass ratio(Md /Mp ) approaches 0.2 and the ratio between pin force (fpin )and the reference friction force (ffref ) closest to 1. The optimum condition of the pre-straining spring stiffness increases when the impact damper mass ratio is increased. The experiment was conducted to validate the simulation results. The experimental data has shown that the minimum acceleration response is obtained using the pre-straining spring deflection ratio (xps /xpsref = 0.18).

Effects of 6 MeV proton irradiation on the vortex ensemble in BaFe2(As0.67P0.33)2 revealed through magnetization measurements and real-space vortex imaging

The change in vortex ensemble in BaFe$_{2}$(As$_{0.67}$P$_{0.33}$)$_2$, an isovalently doped iron-based superconductor (IBS), is studied through global magnetization measurements and single vortex imaging before and after 6 MeV proton irradiation. The field dependence of the critical current density ($J_\mathrm{c}$) is analyzed through the strong pinning model, with which the pristine sample is consistent. After the irradiation, the $J_\mathrm{c}$ aberrates from the strong pinning field dependence of $B^{-5/8}$, and evolves to a weaker $B^{-1/3}$ dependence with an anomalous two-step behavior creating a cusp like feature. The cusp coincides with the field of the local minima in the normalized relaxation rate ($S$), manifested by increased pinning due to increased intervortex interactions followed by fast vortex dynamics caused by flux activation at higher fields. Furthermore, single vortex imaging reveals that while long-range triangular correlation of the Abrikosov vortex lattice is observed in pristine samples, irradiated samples exhibit a highly disordered glassy vortex state which is more densely packed with increased pinning force. These artificial defects incorporated via proton irradiation have the same pinning effect as Co doping which not only shifts the pinning force to a higher degree but also broadens its distribution, in contrast to P doping which only broadens the pinning distribution without inducing a shift. All in all, through this investigation, we provide a systematic understanding of the pinning behavior in BaFe$_{2}$(As$_{0.67}$P$_{0.33}$)$_2$ through carefully controlling the defects in the system.