Spring Constant Research Articles

Optimization of Spring Constant of a Pneumatic Artificial Muscle-Spring Driven Antagonistic Structure

Pneumatic artificial muscles (PAMs) have been widely applied to robotic systems, especially assistive devices, which could benefit from PAMs’ intrinsic viscoelasticity. However, nonlinearity and hysteresis make it challenging to achieve high-accuracy control. Using pre-tensioned springs to replace one side PAMs in an antagonistic structure is one efficient way to improve control accuracy. However, in the previous study, the selection method for spring, especially the range of spring constant has not been sufficiently investigated. This study designed a method to find the optimal spring constant based on gradient descent algorithm; and verified it with prototype and simulation experiments. Results showed that the group with optimal spring constant leads to a faster response time, smaller overshoot, and lower steady-state error, which indicated that the proposed method could find optimal spring constant. Moreover, the sensitivity of PAMs dynamic model parameters to the optimal spring stiffness was investigated. This study provides insights to practical use of soft actuators.

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Synergistic enhancement of spin–phonon interaction in a hybrid system

An investigation to significantly enhance coupling to nitrogen−vacancy (NV) centers at a single-quanta level is of great interest to further explore its applications in quantum information processing (QIP). This study explores a joint scheme to further enhance NV–phonon coherent coupling with two methods working together in hybrid optomechanical systems. Both methods are mechanics-induced mode field coupling (MFC) that lead, respectively, to the modification of the spatial distribution of the optical field and the mechanical parametric amplification (MPA) realized by modulating the mechanical spring constant in time. With the joint assistance of MFC and MPA, the coherent coupling between the NV spin and one supermode of the mechanical resonators (MRs) can be further significantly enhanced with the rate ∝ n ¯ cav e r . Several potential applications are also discussed in this work. With the ultimate goal to enhance the coupling to NV spin at a single-quanta level, this attempt may provide a promising spin–phonon platform to implement more active control.

Edge weights in a protein elastic network reorganize collective motions and render long-range sensitivity responses.

The effects of inter-residue interactions on protein collective motions are analyzed by comparing two elastic network models (ENM)-structural contact ENM (SC-ENM) and molecular dynamics (MD)-ENM-with the edge weights computed from an all-atom MD trajectory by structure-mechanics statistical learning. A theoretical framework is devised to decompose the eigenvalues of ENM Hessian into contributions from individual springs and to compute the sensitivities of positional fluctuations and covariances to spring constant variation. Our linear perturbation approach quantifies the response mechanisms as softness modulation and orientation shift. All contacts of Cα positions in SC-ENM have an identical spring constant by fitting the profile of root-of-mean-squared-fluctuation calculated from an all-atom MD simulation, and the same trajectory data are also used to compute the specific spring constant of each contact as an MD-ENM edge weight. We illustrate that the soft-mode reorganization can be understood in terms of gaining weights along the structural contacts of low elastic strengths and loosing magnitude along those of high rigidities. With the diverse mechanical strengths encoded in protein dynamics, MD-ENM is found to have more pronounced long-range couplings and sensitivity responses with orientation shift identified as a key player in driving the specific residues to have high sensitivities. Furthermore, the responses of perturbing the springs of different residues are found to have asymmetry in the action-reaction relationship. In understanding the mutation effects on protein functional properties, such as long-range communications, our results point in the directions of collective motions as a major effector.

Additive Manufacturing of Compliant Mechanisms for Deployable Aerospace Structures

In the past 10 years, complex deployable structures have become common on CubeSats and large-scale spacecraft. As new missions are pursued, there is an increased need for more mass and volume efficient deployments. Over the same period, metal additive manufacturing (AM) has enabled new forms of spaceflight hardware. However, AM of compliant mechanisms has not been fully leveraged for deployable aerospace structures. The Surface Water Ocean Topography and NASA-ISRO Synthetic Aperture Radar mission missions launching in 2022 both utilize large deployable masts. Each mast deployment is driven by numerous spring and damper mechanisms. Because of volume constraints, the spring mechanisms designed utilize high aspect ratio rectangular cross section torsion springs that represent the state of the art of manufacturing. This extreme spring design resulted in manufacturing difficulties and hardware failures during ground mechanism testing. Upon re-examining the mechanism design, AM enables torque performance, mass, and complexity improvements. AM allows for torsion spring cross sections not otherwise possible with traditional spring manufacturing methods. Prototype springs of various cross sections were printed in maraging steel and tested. Results confirmed design analysis, and doubling of the spring constant was achieved when compared to the traditional springs. The use of AM also allows springs to be built monolithically with surrounding structure. Design, manufacturing, and test findings will be discussed along with future implications for deployable aerospace structures.

Image-based parameter inference for epithelial mechanics.

Measuring mechanical parameters in tissues, such as the elastic modulus of cell-cell junctions, is essential to decipher the mechanical control of morphogenesis. However, their in vivo measurement is technically challenging. Here, we formulated an image-based statistical approach to estimate the mechanical parameters of epithelial cells. Candidate mechanical models are constructed based on force-cell shape correlations obtained from image data. Substitution of the model functions into force-balance equations at the cell vertex leads to an equation with respect to the parameters of the model, by which one can estimate the parameter values using a least-squares method. A test using synthetic data confirmed the accuracy of parameter estimation and model selection. By applying this method to Drosophila epithelial tissues, we found that the magnitude and orientation of feedback between the junction tension and shrinkage, which are determined by the spring constant of the junction, were correlated with the elevation of tension and myosin-II on shrinking junctions during cell rearrangement. Further, this method clarified how alterations in tissue polarity and stretching affect the anisotropy in tension parameters. Thus, our method provides a novel approach to uncovering the mechanisms governing epithelial morphogenesis.

Topological phase transitions of non-Abelian charged nodal lines in spring-mass systems

Although a large class of topological materials have uniformly been identified using symmetry properties of wave functions, the past two years have seen the rise of multi-gap topologies beyond this paradigm. Given recent reports of unexplored features of such phases, platforms that are readily implementable to realize them are therefore desirable. Here, we demonstrate that multi-gap topological phase transitions of non-Abelian charged nodal lines arise in classical phonon waves. By adopting a simple spring-mass system, we construct nodal lines of a three-band system. The braiding process of the nodal lines is readily performed by adjusting the spring constants. The generation and annihilation of the nodal lines are then analyzed using Euler class. Finally, we retrieve topological transitions from trivial nodal lines to a nodal link. Our work provides a simple platform that can offer diverse insights to not only theoretical but also experimental studies on multi-gap topology.

Analytical approach for evaluation of impact damage in nonlinear quasi-isotropic plates of arbitrary boundary conditions

An analytical study was performed to study the effects of various conditions on low-velocity impact damage in quasi-isotropic nonlinear composite laminates and provide a quick tool for evaluating the significance of low-velocity impact damage. Damaged laminates are modeled as quasi-isotropic nonlinear axisymmetric plates with multiple, equal-diameter, equally spaced, and circular delaminations. Its boundary is supported by distributed linear springs with arbitrary spring constants for rotational and in-plane movements to consider the effect of the arbitrary boundary constraints. Closed-form expressions of nonlinear simultaneous equations are derived for the responses of the damaged plates to a transverse concentrated load based on the Rayleigh–Ritz method. The resulting energy release rate is given in a closed-form in terms of the applied load and the generalized coordinates. The nonlinear response considering damage growth is solved to quantitatively show the effects of various design factors such as boundary conditions, dimensions of the plate, number of multiple delaminations, and interlaminar fracture toughness. The present solutions agree well with finite element solutions.

3D-printed actuator-based beam-steering approach for improved physical layer security in visible light communication.

In this study, we present the design, manufacture, and implementation of a 3D-printed lens scanner-based beam steering for use in visible light communication (VLC) applications. The 5cm×5cm scanner is designed for low-cost 3D printing with fused deposition modeling using polylactic acid. Scanning is facilitated through electromagnetic actuation of the lens frame, carrying a conventional 25 mm lens, from two nearly orthogonal directions. The serpentine spring that connects the lens frame to the external frame is tailored to offer similar spring constants in the directions of actuation and has minimal (<1.5mm) sag due to the mass of the lens. The manufactured actuator was integrated on a miniaturized VLC test bed (70cm×40cm×40cm). Using the test bed, we characterized the applied voltage versus beam displacement behavior of the actuator in the lateral plane and demonstrated beam steering on a moving target with face-recognition feedback. The proposed scheme was targeted to offer an improved security measure in VLC through tracking the legitimate receiver (i.e., via face recognition) and uses the feedback to steer the focused light onto the targeted device. The joint use of focusing and steering features allows for the legitimate receiver to roam within the room while enjoying the improved secrecy due to the focused light. We calculate the secrecy capacity for the demonstrated approach, which compares favorably with a number of jamming, spatial modulation, and beam-forming counterparts. The presented actuator can be used with larger room dimensions, yet upscaling to larger illumination units will require the use of a lens having smaller focus to address a larger total steering angle.

Analysis of free vibration of tapered cracked double nanobeams using Maclaurin series

In the study, the Maclaurin series technique is presented to analyse the vibration of cracked tapered double nanobeams. The equation of motion is derived from the Euler–Bernoulli beam theory based on the Hamiltonian principle and Eringen’s nonlocal theory of elasticity. The double-nanobeam system consists of two parallel nanobeams attached by a Winkler elastic layer. Both beams are identical and their widths vary along the x-axis. A single crack is considered at the upper beam of the system. The mechanical behaviour of cracked cross-sections is simulated by the local stiffness model. According to the model, the cracked double-beam system is divided into two intact segments. A numerical investigation is carried out to scrutinize the effects of nonlocal parameters, crack severity, taper ratio, and spring constant on the vibration of the double nanobeam. The results reveal that the effects of crack depth, crack location, nonlocal parameters, taper ratio, and spring constant influence the natural frequency and dynamic response of the system significantly. This study highlights that a crack at the upper beam influences the mode shape of the upper beam as well as the intact lower beam. Numerical results have been examined with the previously published works and found a good agreement with them.

Interplay between disorder and hardening during tensile fracture of a quasi-brittle solid

We examine the specific role of the interplay between hardening and disorder characteristics of a representative quasi-brittle material on its failure mechanisms using a random spring network model. The model incorporates quasi-brittleness in its spring constants and disorder in the failure strain threshold and is shown to be effective in simulating the experimentally observed tensile and fracture behaviour of a quasi-brittle epoxy resin-based polymer. It is shown that rapid localization of deformation and associated damage growth occurs for a weakly hardening solid while for a linear elastic material, damage nucleates at multiple independent sites, and there is significant growth of damage, independent of other nucleating sites, prior to maximum load. The failure mechanism is shown to crossover from an avalanche-dominated fracture for a linear elastic material to nucleation-dominated fracture for a weakly hardening material.

Effects of Plan Irregularities of Multi-Storeyed Structure Resting on Sloping Terrain with Soil Structure Interaction

Abstract: Structures resting on sloping ground are highly vulnerable to earthquakes due to irregularities in plan and elevation. Structures are often analysed under earthquake loadings, without considering the effect of soil–structure interaction (SSI).In the present study the irregular G+4 storey structure has resting on sloping terrain. The influence of the soil structure interaction in the dynamic behaviour of the structure is reflected in an increase in the vibration period as well as increase in the system damping in comparison with the fixed-base model, which does not consider the supporting soil. 4 types of sloping angles are considered in the present study. The considered structure have been modelled and analysed in ETAB2016 software. The considered building has been subjected to earthquake forces. Non linear time history method is considered to perform on structures models. Performing soil structure interaction for all three types of soil Hard, Medium and Soft by applying point spring at the footing. The design and analysis of structure is carried out in ETABS2016 and calculation of spring constants are carried out manually with standard data of it. Keywords: Multi storied RC structures, Plan irregularities, Sloping Terrain, Soil Structure Interaction(SSI), Non linear Time History Method(NLTHM)

Atomic resolution with high-eigenmode tapping mode atomic force microscopy

Atomic surface structure imaging is instrumental for the understanding of surface-related phenomena. Here, we show that conventional tapping mode atomic force microscopy with high cantilever eigenmodes and subnanometer amplitudes allow routine atomic imaging at atmospheric pressures. We identify the reasons for failure of atomic resolution imaging employing low eigenmodes. Strong tip-surface interactions cause significant differences between the oscillatory behaviors of the inclination of the cantilever as detected by conventional instruments and of the vertical position of the tip, which prevents correct functioning of instrumental feedback control loops. However, high effective spring constants of high eigenmodes make it possible to overcome the problem. Furthermore, the combination of high effective elastic constants of high cantilever eigenmodes with the high flexibility of the cantilever substantially enhances the imaging stability, thereby universally allowing atomic imaging of solid surfaces in gaseous environments and at elevated temperatures. Demonstrated imaging examples include single sulfur vacancies at the surface of ${\mathrm{MoS}}_{2}$ crystals imaged at temperatures ranging from room temperature to 250\ifmmode^\circ\else\textdegree\fi{}C and potassium ions on hydrophilic and highly adhesive muscovite mica surfaces. Moreover, the high imaging stability allows knocking atoms off the ${\mathrm{MoS}}_{2}$ surface by hard tapping, indicating the potential for ultrahigh resolution lithography.

In Situ Supramolecular Polymerization via Organometallic-Catalyzed Macromolecular Metamorphosis

In Situ Supramolecular Polymerization via Organometallic-Catalyzed Macromolecular Metamorphosis

Measuring biological materials mechanics with atomic force microscopy - Mechanical unfolding of biopolymers.

Biopolymers, such as polynucleotides, polypeptides and polysaccharides, are macromolecules that direct most of the functions in living beings. Studying the mechanical unfolding of biopolymers provides important information about their molecular elasticity and mechanical stability, as well as their energy landscape, which is especially important in proteins, since their three‐dimensional structure is essential for their correct activity. In this primer, we present how to study the mechanical properties of proteins with atomic force microscopy and how to obtain information about their stability and energetic landscape. In particular, we discuss the preparation of polyprotein constructs suitable for AFM single molecule force spectroscopy (SMFS), describe the parameters used in our force‐extension SMFS experiments and the models and equations employed in the analysis of the data. As a practical example, we show the effect of the temperature on the unfolding force, the distance to the transition state, the unfolding rate at zero force, the height of the transition state barrier, and the spring constant of the protein for a construct containing nine repeats of the I27 domain from the muscle protein titin.Highlights1. Atomic force microscopy (AFM) can be used to study the mechanical unfolding of polymers.2. AFM provides a direct measurement of unfolding (unbinding) forces.3. Force measurements for different rates provide information about the distance to the transition state and the unfolding rate at zero force.

Customizable and highly sensitive 3D micro-springs produced by two-photon polymerizations with improved post-treatment processes

Springs are ubiquitous in a variety of scientific and engineering fields. However, the comprehensive study on mechanical properties of micro-spring has not been fully conducted yet due to a lack of reliable productions of varied-shaped micro-springs. Here, we report the design and manufacturing of triple-helix-shaped springs employing two-photon polymerization (TPP) technologies and present a systemic study on the mechanical properties of micro-springs particularly involving spring constants of k. To construct high-quality hollow microstructures, we optimize the TPP process by combining violet light post-treatment with a proper selection of cleaning liquid. Consequently, we demonstrate that the sensitives k can be actively tuned over a range of two orders of magnitude, from ∼1.5 to ∼108.2 μN/μm while maintaining a high resolution of ∼1 μN/μm. Furthermore, compression tests showcase an excellent agreement among all force-vs-displacement lineshapes, resulting in a small k fluctuation of &amp;lt;1%. On the whole, we expected that the modified TPP technique along with proposed helical springs opens an alternative avenue toward micro-scale force detection, leading to potential applications in the field of bio-sensing, where typical forces to be measured exist within a broad range from several piconewtons to several micronewtons.

Effects of gripper location and blank geometry on the thermoforming of a carbon-fiber woven-fabric/polyphenylene sulfide composite sheet

The effects of gripper location and blank geometry on the thermoforming of a pre-consolidated carbon-fiber woven-fabric/polyphenylene sulfide (PPS) thermoplastic composite sheet (deformed into a U-beam geometry) are investigated both experimentally and numerically. The thermoforming experiments and simulations are performed at constant tool (160oC) and sheet (315oC) temperatures by using four thermoplastic composite blanks, which are different in geometry and inserted into the blank holder using gripping springs. Thermocouples are inserted on the composite sheet and forming molds in order to monitor the temperature variations during thermoforming. Thermoforming process is simulated in Ls-Dyna; the composite sheet is modeled using the Anisotropic Hyperelastic Material Model (MAT_249). An optimum punch speed and a spring constant are initially determined through numerical simulations. Afterward, the numerical thermoforming processes of four different blanks are implemented separately. Results reveal that the simulations show good agreements with the experiments in terms of defects formation and the maximum shear angles between the fiber directions on the final thermoformed U-beam geometry. When the blank is attached with eight springs from the lugs to the blank holder, the deformation and distortion of the net edge of the sheet are avoided, resulting in significant reductions in the extent of defect formation.

Protocol for Directing Nudged Elastic Band Calculations to the Minimum Energy Pathway: Nurturing Errant Calculations Back to Convergence.

The combination of density functional theory (DFT) and the nudged elastic band (NEB) method offers a practical tool for the discovery of underlying reaction mechanisms related to the synthesis of functional materials. However, in practice, the lack of a standardized protocol for minimum energy pathway determination too often leads to an inefficient and computationally intensive design process. To that end, we define a verifiable DFT+NEB protocol for efficiently locating and confirming the transition state of a reaction. To test this assertion, we curate 226 unique reactions within 14 classes of reactions and investigate their performance in terms of the number of NEB iterations they require to locate the transition state and an estimate of the associated mean absolute error. Leveraging this protocol, we demonstrate its application for an initial set of parameters: number of frames, Nframes = 11; maximum step size, Smax = 0.04 Å; optimizer = LBFGS; and spring constant, kspr = 0.1 eV/Å2. We report a convergence rate of 73% and find that a root-mean-square force (FRMS) of 0.01 eV/Å provides a "rule of thumb" below which NEB simulations are likely to converge. Venturing beyond this baseline enquiry, we delineate the effect on performance of altering the number of frames, maximum step size, choice of optimizer and spring constant. We find improvements in performance with increasing Nframes and Smax, ostensibly approaching some asymptotic limit. We also see substantial improvement in efficiency with the LBFGS optimizer and a clear minimum in performance for the spring constant value of 0.1 eV/Å2. Finally, we provide five case studies that demonstrate typical convergence issues for NEB simulations and suggest methods to overcome them. Our results provide specific and transferable recommendations, offering a transparent and practical tool for beginner and expert researchers alike toward a more rational NEB simulation design.

STABILITY AND DYNAMIC ANALYSES OF PIPE CONVEYED FLUID STIFFENED BY LINEAR STIFFNESS ELEMENT USING FINITE ELEMENTS METHOD

Different types of dynamic instability of the system occur when the flow velocity exceeds a specific value; thereby the problem of dynamic instability of the pipe conveyed flow became shining. Several effective parameters play an important role in stabilizing the system, such as stiffness addition. In this search, dynamic analysis of pipe conveying fluid stiffened by linear spring was studied using the finite element method. The effect of stiffness addition (linear spring) and the effect of spring location was deeply studied. Also, the effect of flow velocity on the dynamic stability of the system was taken into the consideration. It was observed that there is a critical flow velocity after which the system loses its stability. There is a critical spring constant at which the dynamic behavior becomes more sensitive. Also, there is a specific spring location (effective location) so the spring offers the best results for the frequency of the system. Effective spring locations depend on the flow velocity and spring constant itself. The effective spring location was found to be arranged from x/l= 0.7 to 1.

Elastic property of sickle and normal hemoglobin protein: Molecular dynamics

This work focuses on identifying the conformational stability and binding components in sickle and normal hemoglobin to explore the elastic properties and realize the stiffness by using molecular dynamics simulation. Our investigation shows that a larger force is required to separate the beta chain of normal hemoglobin in comparison to the sickle hemoglobin by using steered molecular dynamic. In sickle hemoglobin protein (HbS), the hydrogen bond binding force of the beta chain is 7073.74–12 646.80 pN for pulling velocities of 0.000 20–0.000 40 nm/ps with the spring constant of 800 kcal mol−1 nm−2. Similarly, in normal hemoglobin protein, the hydrogen bond binding force in the beta chain ranges from 12 005.00 to 17 753.70 pN for the same values of pulling velocities and spring constant. This indicates that the normal hemoglobin is stiffer than sickle hemoglobin. We have also analyzed the solvent accessible surface area (SASA) of both proteins, and our investigation shows that the SASA of normal hemoglobin is much less than that of sickle hemoglobin because of the sickled structure of HbS. We have also studied the van der Waals (vdW), electrostatic, hydrophobic, and salt bridge interactions in both kinds of hemoglobin. The sum of vdW, electrostatics, and hydrophobic interactions in HbS is higher, whereas salt bridge interactions are found lower in sickle normal hemoglobin proteins than in normal hemoglobin protein.