Simple Spring Research Articles

Ordered deformation localization in cellular mechanical metamaterials

Localized deformations in materials and structures are usually due to instability and are sensitive to various stochastic imperfections introduced during either the manufacturing processes or in-service life. As a result, they always occur in an uncertain manner. In this study, a two dimensional bistable cellular mechanical metamaterial (CMM) is designed, showing highly ordered localized deformation under static loading. The metamaterial consists of periodically distributed elliptical holes of dual sizes. By varying the geometrical parameters of the holes, the CMM can be monostable or bistable. The responses of the CMM to uniaxial compression are systematically explored by finite element (FE) simulations. It is shown that the monostable CMM can have either positive or negative Poisson's ratio and undergo homogeneous deformation up to moderate uniaxial compression. However, the bistable CMM has negligible Poisson's ratio and, most interestingly, shows highly ordered localized deformation zones, similar to the multi-soliton feature in fluids and physics. Based upon the unit cell of the CMM, a simplified spring chain model is developed. In the continuum limit, the model reduces to the Klein–Gordon equation. Analytical trivial solution and kink–antikink solution of the spring chain model are obtained. They are found to faithfully capture the FE simulated homogeneous deformation of the monostable CMM and the ordered localized deformations of the bistable CMM. The findings can provide insight into the ordered localized deformation, phase transformation, and static topological soliton of mechanical metamaterials.

Next-generation diamond cell and applications to single-crystal neutron diffraction.

A diamond cell optimized for single-crystal neutron diffraction is described. It is adapted for work at several of the single-crystal diffractometers of the Spallation Neutron Source and the High Flux Isotope Reactor at the Oak Ridge National Laboratory (ORNL). A simple spring design improves portability across the facilities and affords load maintenance from offline pressurization and during temperature cycling. Compared to earlier prototypes, pressure stability of polycrystalline diamond (Versimax®) has been increased through double-conical designs and ease of use has been improved through changes to seat and piston setups. These anvils allow ∼30%-40% taller samples than possible with comparable single-crystal anvils. Hydrostaticity and the important absence of shear pressure gradients have been established with the use of glycerin as a pressure medium. Large single-crystal synthetic diamonds have also been used for the first time with such a clamp-diamond anvil cell for pressures close to 20 GPa. The cell is made from a copper beryllium alloy and sized to fit into ORNL's magnets for future ultra-low temperature and high-field studies. We show examples from the Spallation Neutron Source's SNAP and CORELLI beamlines and the High Flux Isotope Reactor's HB-3A and IMAGINE beamlines.

Direct approach for the fluctuation-dissipation theorem under nonequilibrium steady-state conditions

The test mass suspensions of cryogenic gravitational-wave detectors such as the KAGRA project are tasked with extracting the heat deposited on the optics. Thus these suspensions have a non-uniform temperature, requiring the calculation of thermal noise in non-equilibrium conditions. While it is not possible to describe the whole suspension system with one temperature, the local temperature anywhere in the system is still well defined. We therefore generalize the application of the fluctuation-dissipation theorem to mechanical systems, pioneered by Saulson and Levin, to non-equilibrium conditions in which a temperature can only be defined locally. The result is intuitive in the sense that the temperature-averaging relevant for the thermal noise in the observed degree of freedom is given by averaging the temperature field, weighted by the dissipation density associated with that particular degree of freedom. After proving this theorem we apply the result to examples of increasing complexity: a simple spring, the bending of a pendulum suspension fiber, as well as a model of the KAGRA cryogenic suspension. We conclude by outlining the application to non-equilibrium thermo-elastic noise.

영상처리 방법을 이용한 송전선의 진동계측

This paper is concerned with the vibration measurement of a transmission line by image processing technique. The measurement system consists of a CCD camera and zoom lens. An image data is transferred to the PC and post-processed using a Matlab program. In this study, a numerical algorithm was developed to process the acquired image data. After acquiring the image data for each frame, this data is binarized to trace the cable vibration. In doing so, the area occupied by the cable is expressed by 1 and the background is expressed by 0. By using the proposed image processing technique, the displacement of the cable can then be calculated. The natural frequencies and mode shapes of the cable can be also calculated by applying the FFT algorithm to the time-series data of the cable displacement. In this study, a simple spring cable was first used to verify the proposed technique. Experimental results on the simple spring cable show that the tracing of the cable displacements is possible and natural frequencies and mode shapes can also be computed. Based on this test, the vibration measurement of a full-scale transmission line was carried out by the proposed technique. The field test proves that the proposed image processing technique can be used to measure the vibration of the transmission line.

Analysis and Design of a Bioinspired Vibration Sensor System in Noisy Environment

Absolute displacement signals of vibrating platforms/objects are often needed in vibration control, signal processing, and object tracking. Motivated by the practical requirement of engineering applications, this study presents the analysis and design of a novel bioinspired dynamics vibration sensor system for absolute vibration displacement measurement. The sensor system is constructed using simple beams and springs, which indicates a possible way in achieving nonlinear quasi-zero stiffness and consequently creating a broadband vibration-free point for absolute displacement measurement in vibrating platforms. The theoretic analysis of the influence of different structure parameters on the bioinspired sensor system is conducted for achieving an excellent isolation property, and thus realizing an outstanding measurement performance. Importantly, to avoid the drawback of measurement noises from the sensor data, the square root unscented Kalman filter technique for estimating the system of the bioinspired dynamic sensor is developed, which improves the accuracy of the resulting vibration measurement. A series of simulations demonstrate the effectiveness of this novel sensor system. Experiments are also conducted using an in-house prototyped sensor testbed, to validate the displacement measurement results and assess the filter algorithms.

Static behaviour and simplified design method of a Tensairity truss with a spindle-shaped airbeam

To provide solutions for large span structures, the use of a Tensairity truss with a 60-m span, which was studied numerically, is proposed. The influence of the internal pressure and cable tension length on the mechanical properties is investigated for several load cases. A simplified spring model based on the vertical stiffness formula of the inflated airbeam is presented, and a static design principle and a design method are proposed. The results show that the adoption of a steel truss can greatly increase the spanning capacity of a Tensairity structure, and the stiffness and load bearing capacity for the structure increase with the increase in air pressure. However, the structure is very sensitive to wind load, which can be improved by re-tensioning the lower cable. Comparisons between the simplified spring model and the original model show a good correlation for the displacement distribution and overall stiffness at a relatively high internal pressure for all load cases considered. The simplified design method will be an easy way for designers to evaluate the behaviour of Tensairity structures, and can be conveniently applied to practical engineering cases.

Kinematics of lower limbs during walking are emulated by springy walking model with a compliantly connected, off-centered curvy foot

The dynamics of the center of mass (CoM) during walking and running at various gait conditions are well described by the mechanics of a simple passive spring loaded inverted pendulum (SLIP). Due to its simplicity, however, the current form of the SLIP model is limited at providing any further information about multi-segmental lower limbs that generate oscillatory CoM behaviors and their corresponding ground reaction forces. Considering that the dynamics of the CoM are simply achieved by mass-spring mechanics, we wondered whether any of the multi-joint motions could be demonstrated by simple mechanics. In this study, we expand a SLIP model of human locomotion with an off-centered curvy foot connected to the leg by a springy segment that emulates the asymmetric kinematics and kinetics of the ankle joint. The passive dynamics of the proposed expansion of the SLIP model demonstrated the empirical data of ground reaction forces, center of mass trajectories, ankle joint kinematics and corresponding ankle joint torque at various gait speeds. From the mechanically simulated trajectories of the ankle joint and CoM, the motion of lower-limb segments, such as thigh and shank angles, could be estimated from inverse kinematics. The estimation of lower limb kinematics showed a qualitative match with empirical data of walking at various speeds. The representability of passive compliant mechanics for the kinetics of the CoM and ankle joint and lower limb joint kinematics implies that the coordination of multi-joint lower limbs during gait can be understood with a mechanical framework.

Study of cell irregularity effects on the compression of closed-cell foams

Closed-cell aluminum foam is widely used as energy absorbing material. The cell regularity profoundly affects the mechanical behavior of this material. To investigate the influence of irregularity on elastic and plastic behavior of closed-cell foams, the compression behavior of Voronoi foams was simulated using the finite element method. The results show that with the increasing randomness of the foam, the elastic modules decrease a little while the collapse-strength decrease considerably. A theoretical analysis is conducted with the simple springs model. The results match well with simulation which shows theoretical analysis is reasonable. The Voronoi models were also compressed under different loading velocities and with different relative densities in simulation. The results reveal that foams with low regularity are more suitable for application in protective structures.

A study of mode-I self-similar dynamic crack propagation using a lattice spring model

The spontaneous crack growth in an infinite domain is studied using the distinct lattice spring model (DLSM). The kinetic energy, strain energy, crack opening, and crack branching during the crack growth are investigated numerically using a simple spring model. The discrete simulation satisfactorily reproduces the experimental observations and the theoretical predictions of the fracture energy increase even without considering the crack tip damage zone and crack bifurcation. Moreover, from analysis of the intrinsic fracture energy release rate, it was concluded that the observed fracture energy increase should originate from the distribution of kinetic energy during self-similar crack growth.

Wide-angle diamond cell for neutron scattering

ABSTRACTA new diamond cell with extreme apertures is described. It is tailored for a large variety of neutron scattering techniques such as inelastic neutron scattering and single-crystal diffraction both at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Simple springs enable forces of over 10 metric tons to be clamped in for low-temperature measurements. At present, low-cost polycrystalline diamond (Versimax®) pressure anvils are used. We predict a routine pressure regime up to 20 GPa with sample volumes of ∼0.5 mm3. Future use of large CVD single-crystal diamond anvils will significantly expand this pressure range. We show examples for measurements at the SNAP, VISION and CORELLI beamlines of the SNS.

Control system for the haptic paddle used in mobile robotics

A haptic interface is a kinaesthetic link between a human and some real or virtual environment. In this article, we discuss whether the haptic technology (virtually touching objects and feeling forces) could be effectively implemented in the industrial applications. As an example, we will examine the virtual wall which is a fundamental component of almost all virtual objects. Typically, it is based on a simple spring and damper model with constraints that allow the user to make contact with an object. Various factors lead to an unstable behaviour in a controlled system such as the virtual wall. Main causes of disturbances are the sensor (e.g. the signal resolution) and the actuator (e.g. the dynamics of the system which are not covered by the controller design). Some of these disturbance mechanisms can be excluded by mechanical design, and others are more difficult to eliminate – following two are discussed in the article: First one is the zero-order hold effect caused by sampling and the second one is the shifted synchronization of the wall threshold crossings with the sampling times. Both have unwanted effects on the sampled data within the virtual wall system.

Fluctuating Elasticity Mode in Transient Molecular Networks.

Transient molecular networks, a class of adaptive soft materials with remarkable application potential, display complex, and intriguing dynamic behavior. By performing dynamic light scattering on a wide angular range, we study the relaxation dynamics of a reversible network formed by DNA tetravalent nanoparticles, finding a slow relaxation mode that is wave vector independent at large q and crosses over to a standard q^{-2} viscoelastic relaxation at low q. Exploiting the controlled properties of our DNA network, we attribute this mode to fluctuations in local elasticity induced by connectivity rearrangement. We propose a simple beads and springs model that captures the basic features of this q^{0} behavior.

Heat transfer losses in reciprocating compressors with valve actuation for energy storage applications

Understanding the exergy losses stemming from heat transfer in compressors and expanders is important for many energy storage applications such as compressed air and pumped thermal storage. In order to obtain a better understanding of these losses, CFD simulations were performed for simple gas springs, for a gas spring with an internal grid to mimic valve flow, and for a reciprocating compressor with functioning inlet and outlet valves. The wall heat exchanges for these three cases were examined and compared. The model adopted has previously been validated for a simple gas spring using experimental data from literature. For the gas spring with an internal grid it was found that increased mixing leads to higher heat-transfer-induced hysteresis losses and (at high piston speeds) to a significant pressure loss. These two types of loss can be distinguished by undertaking adiabatic-wall calculations. For a compressor (i.e., with valve flows) heat transfer over the cycle depends very much on valve timing. For example, at 1500rpm, when the delivery valve is opened at 7bar the heat transfer coefficient for the initial stages of compression is similar to that for a simple gas spring, whereas for the same speed at 6bar it is more than doubled.

Parametric Study of Single Bolted Composite Bolted Joint Subjected to Static Tensile Loading

The use of composites is increasing in the engineering applications in order to reduce the weight, building energy efficient systems, designing a suitable material according to the requirements of the application. But at the same time, building a structure is possible only by bonding or bolting or combination of them. There are limitations for the bonding methods and problems with the bolting such as stress concentration near the neighborhood of the bolt hole, tensile or shear failure, delamination etc. Hence the design of a composite bolted structure needs a special attention. This paper focuses on the performance of the composite bolted joint under static tensile loading and the effect of variation in the parameters such as the bolt pitch, plate width, thickness, bolt tightening torque, composite material, coefficient of friction between the bolt and plate etc. A simple spring mass model is used to study the single bolted composite bolted joint.The influencing parameters are identified through the developed model and compared with the results from the literature. The best geometric parameters for the applied load are identified for the composite bolted joints.

Measurement of mass by optical forced oscillation of absorbing particles trapped in air

We demonstrate the measurement of mass of the absorbing micro-particle trapped in air by optical forced oscillation. When the trapping light intensity is modulated sinusoidally, the particle in the trap undergoes forced oscillation and the amplitude of the oscillation depends directly on the modulated frequency. Based on a simple spring model, we fit the amplitudes versus the modulated frequencies and obtain the stiffness of the optical trap and the mass of the trapped particle. The fitting results show that, for a certain particle, the stiffness varies linearly with the trapping light intensity while the mass is consistent. The density of the micro-particle is then estimated and could be used to classify different kinds of absorbing particles, like C and CuO.

Electronic, Optical, and Mechanical Properties of Diamond Nanowires Encapsulated in Carbon Nanotubes: A First-Principles View

In recent years, carbon-based complex nanostructures have been explored due to many of their unique properties and related applications. Here we employ theoretical simulation based on density functional theory to investigate electronic, optical, and mechanical properties of a new type of the carbon-based complex nanostructure, i.e., experimentally fabricated one-dimensional complex material of hydrogenated diamond nanowires encapsulated in carbon nanotubes (CNW@CNT). The complex structure CNW@CNT is found to possess metallicity for the outer CNT and wide band gap nature for the inner CNW simultaneously. Under uniaxial strain a specific insulator-to-metal transition occurs for the inner CNW in the complex structure, with threshold value much smaller than that for the individual insulator. This effect is interpreted as that the strain induces relative shifting of bands of CNW and CNT and even charge transfer between them, making the valence band of CNW become not fully occupied. The inner CNW in the complex structure has optical absorption only in the ultraviolet waveband. The further examinations on the conductive bands reveal existences of nearly free-electron states which entirely dominate the conductive bands of the inner CNW and suggest that the electron–hole separation will happen in the CNW@CNT upon the ultraviolet illumination. The simulation results also reveal higher Young’s modulus of the CNW@CNT and the individual CNW even larger than those of CNT and graphene. We propose a simple parallel spring model to establish the relationship between the Young’s modulus of the complex structure and the one of its component which should be helpful to future predictions for other complex structures. The potential applications of this new type of carbon-based complex structure as a multifunctional integrated nanomaterial in future nanoelectronics, nano-optoelectronics, and nanoelectromechanics are discussed.

Canine extrusion with a vertical tube supported cantilever spring

Maxillary canine is the most frequently impacted tooth in the dental arch and twice common in females than in males. Treatment of impacted maxillary canine can be difficult and time consuming, depending on its position. Improper direction and magnitude of applied force can lead to increased chances of adjacent tooth resorption. This article describes about a simple cantilever spring that can be fabricated at chair side for extrusion of a bucally impacted canine.

Analysis of mechanical properties in bending processes and optimal design of simple tape spring

AbstractTape spring is straight, thin-walled, elastic strip with curved cross-section, which can replace traditional hinges by allowing for folding elastically and unfolded releasing stored energy with fewer component parts. This work is devoted to the properties of the folding and deployment of simple tape spring by numerical simulation and experiment method. Firstly, the folding process of tape spring is experimentally investigated using a specially designed test rig and verified by using nonlinear finite element ABAQUS/Standard solver. Then the moment-rotation relationships for symmetric bending are studied, the effects of subtended angle of section, total tape spring length, thickness and cross section radius on the performance of tape spring are investigated. Furthermore, the optimal model of tape spring structure design is established based on the response surface methodology (RSM) and parameter’s effective analysis, which aims at maximum strain energy during the tape-spring hinge deployment and subjects to allowable stress of tape spring. And the interior point algorithm is used to solve the optimal model. The optimal results are of great importance to the design of novel deployable structures with high stability, reliability and lightweight.

Multicomponent adsorption in mesoporous flexible materials with flat-histogram Monte Carlo methods.

We demonstrate an extensible flat-histogram Monte Carlo simulation methodology for studying the adsorption of multicomponent fluids in flexible porous solids. This methodology allows us to easily obtain the complete free energy landscape for the confined fluid-solid system in equilibrium with a bulk fluid of any arbitrary composition. We use this approach to study the adsorption of a prototypical coarse-grained binary fluid in "Hookean" solids, where the free energy of the solid may be described as a simple spring. However, our approach is fully extensible to solids with arbitrarily complex free energy profiles. We demonstrate that by tuning the fluid-solid interaction ranges, the inhomogeneous fluid structure inside the pore can give rise to enhanced selective capture of a larger species through cooperative adsorption with a smaller one. The maximum enhancement in selectivity is observed at low to intermediate pressures and is especially pronounced when the larger species is very dilute in the bulk. This suggest a mechanism by which the selective capture of a minor component from a bulk fluid may be enhanced.

Geometric-based tyre vertical force estimation and stiffness parameterisation for automotive and unmanned vehicle applications

ABSTRACTAdvanced empirical, and physical-based tyre models have proven to be accurate for simulating tyre dynamics; however, these tyre models typically require expensive and intensive tyre parameterisation. Recent research into wheeled unmanned ground vehicles requiring vertical force analysis has shown good results using a simple linear spring model for the tyre which demonstrate the continued use for simple tyre models; however, parameterisation of the tyre still remains a challenge when load test equipment is not available. This paper presents a cost-effective tyre vertical stiffness parameterisation procedure using only measured tyre geometry and air pressure for applications where high-fidelity tyre models are unnecessary. Vertical forces calculated through an air volume optimisation approach are used to estimate tyre vertical stiffness. Nine tyres from the literature are compared to evaluate the performance of the vertical force estimation and stiffness parameterisation algorithms. Experimental results on a pair of ATV tyres are also presented.