Showing papers in "Smart Materials and Structures in 2022"

Analysis of magnetorheological clutch with double cup-shaped gap excited by Halbach array based on finite element method and experiment

Abstract: Abstract This work describes the magnetic analysis of an innovative double cup-shaped gap magnetorheological (MR) clutch featuring with three smart MR gels. Four kinds of Halbach array is used to excite the MR gel. The apparatus is designed by using a magneto/mechanical finite element method model, which is numerical calculated by COMSOL Multiphysics software. After describing the configuration, the transmittable torque in the designed MR clutch is derived based on the Bingham-Plastic field-dependent constitutive model of the MR gel. Considering the viscosity in the model building, such as the shear yield stress, which also various with change of magnetic flux density. The magnetic flux density distribution, the shear yield stress distribution, the dynamic viscosity distribution and the shear stress distribution inside the MR gel are obtained and carefully studied. Furthermore, the chain layer of internal cylindrical part, external cylindrical part, internal disc part and external disc part with lowest shear stress are found to calculate the transmission torque and slip torque. Then, the structure of the prototype is optimized based on multi-physics analysis. Finally, the optimal MR clutch is developed and the magneto-static torque is tested with detail analysis.

3D-printed bio-inspired zero Poisson’s ratio graded metamaterials with high energy absorption performance

Abstract: Abstract This study aims at introducing a number of two-dimensional (2D) re-entrant based zero Poisson’s ratio (ZPR) graded metamaterials for energy absorption applications. The metamaterials’ designs are inspired by the 2D image of a DNA molecule. This inspiration indicates how a re-entrant unit cell must be patterned along with the two orthogonal directions to obtain a ZPR behavior. Also, how much metamaterials’ energy absorption capacity can be enhanced by taking slots and horizontal beams into account with the inspiration of the DNA molecule’s base pairs. The ZPR metamaterials comprise multi-stiffness unit cells, so-called soft and stiff re-entrant unit cells. The variability in unit cells’ stiffness is caused by the specific design of the unit cells. A finite element analysis (FEA) is employed to simulate the deformation patterns of the ZPRs. Following that, meta-structures are fabricated with 3D printing of TPU as hyperelastic materials to validate the FEA results. A good correlation is observed between FEA and experimental results. The experimental and numerical results show that due to the presence of multi-stiffness re-entrant unit cells, the deformation mechanisms and the unit cells’ densifications are adjustable under quasi-static compression. Also, the structure designed based on the DNA molecule’s base pairs, so-called structure F‴, exhibits the highest energy absorption capacity. Apart from the diversity in metamaterial unit cells’ designs, the effect of multi-thickness cell walls is also evaluated. The results show that the diversity in cell wall thicknesses leads to boosting the energy absorption capacity. In this regard, the energy absorption capacity of structure ‘E’ enhances by up to 33% than that of its counterpart with constant cell wall thicknesses. Finally, a comparison in terms of energy absorption capacity and stability between the newly designed ZPRs, traditional ZPRs, and auxetic metamaterial is performed, approving the superiority of the newly designed ZPR metamaterials over both traditional ZPRs and auxetic metamaterials.

Coda wave interferometry-based very early stage bolt looseness monitoring using a single piezoceramic transducer

Abstract: Abstract The traditional monitoring methods can only give warnings for the bolts with severe looseness. However, it is essential for the safety of bolted joints to detect the looseness of bolts at the very early stage. To this end, in this paper, coda wave interferometry (CWI)-based high-resolution bolt preload monitoring using a single piezoceramic transducer is proposed. According to the CWI and acoustoelastic theories, a theoretical model is established and the linear relationship between the time shifts of coda waves and the preload variations of the bolt is derived. An experiment, in which a piezoceramic transducer simultaneously functions as the actuator and sensor, was carried out to verify the effectiveness of the proposed method. Three lead zirconium titanate transducers at different locations of a bolted specimen are tested. The experimental results show that the time shifts of coda waves increase linearly with the decrease of bolt preload and the detectable resolution of bolt preload (DRBP) is up to 0.326%. The DRBP value proves that the proposed technique can successfully monitor bolt looseness at the very early stage. In addition, a comparison study is carried out between the CWI-based method and the energy-based wavelet packet decomposition (WPD) method, and the result shows that the preload sensitivity of the CWI-based method is about six times higher than that of the WPD approach. Therefore, the CWI-based method is an effective way for the in situ monitoring of bolt looseness, especially in the embryonic stage.

Shape memory performance of PETG 4D printed parts under compression in cold, warm, and hot programming

Abstract: Abstract The main novelty of this paper is the use of poly-ethylene terephthalate glycol (PETG) as a new shape memory polymer with excellent shape memory effect (SME) and printability. In addition, for the first time, the effect of programming temperature on PETG 4D printed samples has been studied. The amorphous nature of the PETG necessitates that molecular entanglements function as net points, which makes the role of programming temperature critical. SME comprehensively was conducted under compression loading for three programming conditions as well as various pre-strains. Significant results were obtained that summarized the gross differences exhibiting that the hot, cold, and warm programmed samples had the highest shape fixity, shape recovery, and stress recovery, respectively. The recovery and fixity ratios fell and rose, respectively, as the programming temperature increased. This effect intensified in hot programmed samples as the applied strain (loading time) expanded. So, the recovery ratio dropped from 68% to 50% by raising the pre-strain from 20% to 80%. The maximum stress recovery was 16 MPa, suggesting the fantastic benefit of warm programming conditions in PETG 4D printed parts. The locking mechanism (recovery force storage) for cold and hot programming is quite different. The dominant mechanism in cold programming is increasing internal energy by potential energy level enhancement. Contrary to this, in hot programming, the entropy reduction applies to the majority of the molecular segments, playing this role. By cooling, the state of the material changes from rubbery to glassy, and with this phase change, the oriented conformation of the deformed polymer chains is maintained under deformation. The results of this research can be used for various applications that require high shape fixity, recovery, or stress recovery.

Reversible energy absorption of elasto-plastic auxetic, hexagonal, and AuxHex structures fabricated by FDM 4D printing

Abstract: Abstract The present study aims at introducing reconfigurable mechanical metamaterials by utilising four-dimensional (4D) printing process for recoverable energy dissipation and absorption applications with shape memory effects. The architected mechanical metamaterials are designed as a repeating arrangement of re-entrant auxetic, hexagonal, and AuxHex unit-cells and manufactured using 3D printing fused deposition modelling process. The AuxHex cellular structure is composed of auxetic re-entrant and hexagonal components. Architected cellular metamaterials are developed based on a comprehension of the elasto-plastic features of shape memory polylactic acid materials and cold programming deduced from theory and experiments. Computational models based on ABAQUS/Standard are used to simulate the mechanical properties of the 4D-printed mechanical metamaterials under quasi-static uniaxial compression loading, and the results are validated by experimental data. Research trials show that metamaterial with re-entrant auxetic unit-cells has better energy absorption capability compared to the other structures studied in this paper, mainly because of the unique deformation mechanisms of unit-cells. It is shown that mechanical metamaterials with elasto-plastic behaviors exhibit mechanical hysteresis and energy dissipation when undergoing a loading-unloading cycle. It is experimentally revealed that the residual plastic strain and dissipation processes induced by cold programming are completely reversible through simple heating. The results and concepts presented in this work can potentially be useful towards 4D printing reconfigurable cellular structures for reversible energy absorption and dissipation engineering applications.

4D printed shape memory sandwich structures: experimental analysis and numerical modeling

Abstract: Abstract Additive manufacturing has provided a unique opportunity to fabricate highly complex structures as well as sandwich structures with various out-of-plane cores. The application of intelligent materials, such as shape memory polymers, gives an additional dimension to the three-dimensional (3D) printing process, known as four-dimensional (4D) printing, so that the deformed structures can return to their initial shape by the influence of an external stimulus like temperature. In this study, 4D printing of smart sandwich structures with the potential of energy absorption is investigated. The samples were fabricated considering various process parameters (i.e. layer height, nozzle temperature, printing velocity, and wall thickness) and tested mechanically. The experimental work reveals that the deformed sandwiches can fully recover their initial form by applying simple heating. Besides, a reliable finite element model (FEM) was developed to predict the functional behavior of the horseshoe sandwich structures in compression analysis. The experimental and simulation results show that among process parameters, wall thickness, layer height, and nozzle temperature are the most significant parameters to increase the compressive load and, consequently, the energy absorption rate. The concept, results, and modeling provided in this study are expected to be used in the design and fabrication of 4D printed sandwich structures for energy absorption applications.

Fluidic rolling robot using voltage-driven oscillating liquid

Abstract: Abstract Rolling motions have been observed in many animals and insects. In the previous fluidic rolling system, a deformed chamber and long cables were imperative to drive the soft rolling actuators, which required high pressure and a sophisticated controlling strategy. In this study, we propose a soft fluidic roller using a simple structure composed of a bendable and twistable electrohydrodynamic (EHD) pump and a layer of natural latex. To realize the rolling motion, we first optimized the electrode and channel height of the EHD pumps using different patterns and designs. We also examined the output power, efficiency, pressure loss, bending, and twisting performance. Subsequently, the optimized electrodes and channel height were selected to design the power source of the EHD roller. This roller was lightweight (0.7 g) with an amount of liquid (0.6 g). This EHD robot can roll as the EHD liquid oscillates under a duty-controlled voltage realized using a high-voltage circuit. Next,we investigated the influence of frictional forces on rolling performance. Finally, the rolling motion in the liquid was demonstrated. This study extends the EHD pumps to independent soft actuators integrated with a soft power source.

Machine learning-driven performance-based seismic design of hybrid self-centering braced frames with SMA braces and viscous dampers

Abstract: Abstract A hybrid self-centering braced frame equipped with shape memory alloy-based self-centering braces (SMA-SCBs) and viscous dampers is proposed to achieve enhanced seismic performance. Based on the proposed hybrid strategy combining the contributions of SMA-SCBs and viscous dampers, this paper investigates the advantages of such hybrid self-centering braced frames in achieving the desired maximum inter-story drift under a considered seismic intensity. To this end, the influence of design parameters of SMA-SCBs and viscous dampers on hybrid self-centering braced frames is examined through parametric dynamic analyses of equivalent single-degree-of-freedom systems. The analysis results indicate that the post-yield stiffness ratio α and energy dissipation factor β of SMA-SCB, and the contribution of viscous damper show significant influence on the peak displacement responses of hybrid self-centering braced frames. The constant inelastic displacement ratio prediction model for hybrid self-centering braced frames is developed using machine learning algorithms. A performance-based seismic design method is subsequently proposed for the hybrid self-centering braced frames to achieve the target displacement responses based on the developed machine learning models. Two hybrid self-centering braced frames are designed based on the proposed design method. Nonlinear dynamic analyses are conducted to investigate the seismic performance of the designed structures. To highlight the advantages of the hybrid self-centering braced frames, another six-story self-centering braced frame with SMA-SCBs only is also studied in this paper. The analysis results indicate that all the designed hybrid self-centering braced frames can achieve the desired performance objective. Compared to the self-centering braced frame with SMA-SCBs only, the hybrid self-centering braced frames can achieve much smaller base shear demand and absolute floor acceleration responses.

Experimental and numerical investigations on hysteretic response of a multi-level SMA/lead rubber bearing seismic isolation system

Abstract: Abstract This study investigates the response of a shape memory alloy (SMA)-based isolation system that combines multiple groups of SMA cables and a lead rubber bearing (LRB). The isolation device, named as multi-level SMA/lead rubber bearing (ML-SLRB), is designed such that it maintains its efficiency under frequent, design and extreme levels of seismic events. Two large-size ML-SLRB isolation devices were designed and fabricated. The response of the proposed isolation systems was evaluated together with a conventional LRB under increasing amplitudes of cyclic loads. The effects of loading rate and vertical pressure on the response of the ML-SLRB isolator were evaluated. Finite element models of the fabricated ML-SLRB isolators were developed and analyzed to assess the response of the different SMA cable groups at different stages of the loading. The test results, supported by the finite element analyses, revealed that the SMA cable groups used in a loop configuration in the ML-SLRB isolator are prone to stress concentrations and early damage. The ML-SLRB isolators that employed its main SMA cable groups in a straight configuration successfully achieved a multi-level performance where the stiffness of the isolator increased as the demands of the displacement increased. The developed isolator also exhibited lower residual drifts compared to the LRB isolator.

Effects of soft and hard magnetic particles on the mechanical performance of ultra-soft magnetorheological elastomers

Abstract: Abstract Magnetorheological elastomers (MREs) mechanically respond to external magnetic stimuli by changing their mechanical properties and/or changing their shape. Recent studies have shown the great potential of MREs when manufactured with an extremely soft matrix and soft-magnetic particles. Under the application of an external magnetic field, such MREs present significant mechanical stiffening, and when the magnetic field is off, they show a softer response, being these alternative states fully reversible. Although soft-magnetic particles are suitable for their high magnetic susceptibility, they require the magnetic actuation to remain constant in order to achieve the magneto-mechanical stiffening. Here, we present an alternative solution based on hard-magnetic MREs to provide stiffening responses that can be sustained along time without the need of keeping the external magnetic field on. To this end, we manufacture novel extremely soft hard-magnetic MREs (stiffness in the order of 1 kPa) and characterise them under magneto-mechanical shear and confined magnetic expansion deformation modes, providing a comparison framework with the soft-magnetic counterparts. The extremely soft nature of the matrix allows for easily activating the magneto-mechanical couplings under external magnetic actuation. In this regard, we provide a novel approach by setting the magnetic actuation below the fully magnetic saturating field. In addition, free deformation tests provide hints on the microstructural transmission of torques from the hard-magnetic particles to the viscoelastic matrix, resulting in macroscopic geometrical effects and intricate shape-morphing phenomena.

A comparative study of electrical interfaces for tunable piezoelectric vibration energy harvesting

Abstract: Abstract The present work deals with tunable electrical interfaces able to enhance both the harvested power and bandwidth of piezoelectric vibration energy harvesters. The aim of this paper is to propose a general, normalized, and unified performance evaluation (with respect to the harvested power and bandwidth) of the various electrical strategies that can tune the harvester’s frequency response. By mean of a thorough analysis, we demonstrate how such interfaces influence the electromechanical generator response through an electrically-induced damping and an electrically-induced stiffness. The choice of the strategy determines these two electrical quantities, and thus the achievable frequency response of the system. Thereafter, we introduce a collection of graphical and analytical tools to compare and analyze single- and multi-tuning electrical strategies, including a qualitative performance evaluation of existing strategies. Finally, we establish a unified comparison of single- and multiple-tuning strategies which is supported by the definition and evaluation of a new optimization criterion. This comparison reveals which strategy performs best depending on the electromechanical coupling of the piezoelectric harvester and on the losses in the electrical interface. Furthermore, it quantifies the power and bandwidth gain brought by single- and multi-tuning strategies. Such quantitative criterion provides guidance for the choice of a harvesting strategy in any specific applicative case.

Design and performance of a compact stick-slip type piezoelectric actuator based on right triangle flexible stator

Abstract: Abstract In the field of stick-slip type piezoelectric actuators, the actuator with simple and compact structure has been given significant research and design value. A compact stick-slip piezoelectric actuator based on right triangle flexible stator is proposed and evaluated in this work. The proposed actuator only includes a right triangular type stator inserted with a PZT stack and it has the merit of simple structure. The PZT stack is excited under a sawtooth waveform voltage, and the elongation deformation of the PZT stack makes the driving foot move obliquely due to the right triangular stator. The slider is pressed under the vertical component of the oblique movement, while the slider is actuated under the horizontal component simultaneously. The working principle of the proposed actuator is illustrated by theoretical and simulation methods in detail. The proposed actuator is fabricated and its output characteristics are measured. The experimental results show that the maximum output speed of the developed actuator is 4.6 mm s −1 when the voltage and frequency are 100 V and 720 Hz. It has the merit of simple design and relatively better performance by series of comparisons with some existing works.

A novel re-entrant honeycomb metamaterial with tunable bandgap

Abstract: Abstract An auxetic metamaterial consisting of a re-entrant honeycomb structure with hierarchical characteristics (RHS-H) is proposed. The new structure is constructed by attaching small re-entrant structural unit cells to the nodes of the traditional re-entrant structures. Not only can the overall stiffness and stability of the proposed structure be tuned during compression and tension, but a better acoustic performance is also obtained compared with traditional re-entrant honeycomb structures. Firstly, the deformation mechanism of the bandgap is numerically explored by analyzing the dispersion curve of the microstructure as well as the upper and lower bounds of the bandgap vibrational modes. Secondly, the bandgap tunability of the designed structure under uniaxial compression or tension is discussed. Finally, the transmittance of finite period size is calculated to verify the numerical results of the bandgap. Numerical simulation results show that the proposed novel RHS-H has attenuation characteristics of a tunable low-frequency plane wave through a reasonable selection of compressive strain, tensile strain and geometric parameters. The vibration damping strength of the bandgap increases under tensile strain. When the auxetic effect is enhanced, the first and second bandgaps become lower and wider. The novel metamaterial has potential applications in vibration and noise reduction and the design of acoustic devices in dynamic environments, while providing new ideas and a methodology for the real-time adjustment of bandgaps.

Medical applications of magnetorheological fluid: a systematic review

Abstract: Abstract Magnetorheological (MR) fluid, whose rheological properties can be changed reversibly by applied magnetic field, offers superior capabilities and opportunities since its invention. The most crucial feature of MR fluid is its controllable and continuous yield stress. Taking this advantage, MR fluid is gaining popularity in various medical applications to meet their force/torque requirements. In this review article, progress of medical applications of MR fluid in the last two decades are systematically reviewed, mainly focused on six categories: lower limb prosthesis, exoskeleton, orthosis, rehabilitation device, haptic master, and tactile display. With MR fluid, natural and stable limb motions in lower limb prostheses, exoskeletons, and orthoses, flexible muscle trainings in rehabilitation devices, and high transparency and resolution haptic feedback can be realized. Relevant discussions and future perspectives are also provided.

High-dimensional data analytics in structural health monitoring and non-destructive evaluation: a review paper

Abstract: Abstract This paper aims to review high-dimensional data analytic (HDDA) methods for structural health monitoring (SHM) and non-destructive evaluation (NDE) applications. High-dimensional data is a type of data in which the number of features for each observation is much larger than the number of all observations. High-dimensional data may violate assumptions of the classic methods for statistical modeling and data analysis. Then, classic statistical modeling will no longer be applicable. HDDA methods were developed to overcome this challenge and analyze these types of data. In the field of SHM/NDE, there are several sources of high-dimensionality. Examples include a large number of data points in continuous waves/signals or high-resolution images/videos. HDDA methods are used as a dimension-reduction tool to preprocess data for further analysis, or they are directly implemented for damage detection and localization. This paper reviews six HDDA methods as well as existing and potential applications in SHM/NDE. Particularly, this paper discusses the vast range of implemented SHM/NDE applications from crack detection to missing data imputation. Furthermore, experimental and simulated datasets have been used to show the application of HDDA methods as hands-on examples. It is shown that the potential of HDDA for SHM/NDE studies is significantly more than the existing studies in the literature, and these methods can be used as a powerful tool that provides vast opportunities in SHM/NDE.

Highly sensitive and flexible three-dimensional force tactile sensor based on inverted pyramidal structure

Abstract: Abstract To improve the haptic sensing performance of electronic skin (e-skin), this study designed a capacitance-based highly sensitive three-dimensional (3D) force tactile sensor with an inverted pyramidal structure with high electrical stability and mechanical repeatability. The working mechanism of the sensor was verified by finite element simulation, and it was fabricated by low-cost 3D printing technology and layer-by-layer self-assembly process. A capacitive signal acquisition system and an application test platform were constructed. The results revealed that the proposed 3D-force tactile sensor had a normal force sensitivity of 0.551 N −1 at 0–7 N and 0.107 N −1 at 7–35 N. The results for tangential force were 0.404 N −1 at 0–4 N and 0.227 N −1 at 4–14 N, with a low hysteresis of 4.17% and a fast response/recovery time of 56/30 ms. High sensitivity and reliability of the device were demonstrated experimentally. The proposed capacitive flexible 3D-force haptic sensor can be used in applications such as robotic gripping, gamepad control and human motion detection, and its feasibility for application as e-skin was confirmed.

Light controlled bending of a holographic transmission phase grating

Abstract: Abstract We recorded a permanent phase transmission grating on a thin film made by using a recently developed holographic photomobile mixture. The recorded grating pitch falls in the visible range and can be optically manipulated by using an external coherent or incoherent low power light source. When the external light source illuminates the grating the entire structure bends and, as a consequence, the optical properties of the grating change. This peculiarity makes it possible to use the recorded periodic structure as an all-optically controlled free standing thin colour selector or light switch depending on the source used to illuminate the grating itself. Additionally, it could open up new possibilities for stretchable and reconfigurable holograms controlled by light as well as thin devices for optically reconfigurable dynamic communications and displays.

Metamaterials with enhanced mechanical properties and tuneable Poisson’s ratio

Abstract: Abstract This paper reports a structural modification of an auxetic metamaterial with a combination of representative re-entrant and chiral topologies, namely, a re-entrant chiral auxetic (RCA) metamaterial. The main driving force for the structural modification was to overcome the undesirable properties of the RCA metamaterial such as anisotropic mechanical response under uniaxial compression. Additively manufactured polyamide 12 specimens via Multi Jet Fusion were quasi-statically compressed along the two in-plane directions. The experimental results confirmed that the modified structure was less sensitive to the loading direction and the deformation was more uniform. Moreover, similar energy absorptions were obtained when the modified metamaterial was crushed along the two in-plane directions. The energy absorption per unit volume was improved from 390 to 950 kJ m −3 and from 500 to 1000 kJ m −3 compared with the RCA when they were crushed along the X and Y directions, respectively. The absorbed energy per unit mass (specific energy absorption) also improved from 1.4 to 2.9 J g −1 and from 1.78 to 3.1 J g −1 compared with that of the RCA under the axial compression along the X and Y directions. Furthermore, parametric studies were performed and the effects of geometric parameters of the modified metamaterial were numerically investigated. Tuneable auxetic feature was obtained. The energy absorption and Poisson’s ratio of the modified metamaterial offer it a good candidate for a wide range of potential applications in the areas such as aerospace, automotive, and human protective equipment.

Novel ionic bioartificial muscles based on ionically crosslinked multi-walled carbon nanotubes-mediated bacterial cellulose membranes and PEDOT:PSS electrodes

Abstract: Abstract High-performance bioartificial muscles with low-cost, large bending deformation, low actuation voltage, and fast response time have drawn extensive attention as the development of human-friendly electronics in recent years. Here, we report a high-performance ionic bioartificial muscle based on the bacterial cellulose (BC)/ionic liquid (IL)/multi-walled carbon nanotubes (MWCNT) nanocomposite membrane and PEDOT:PSS electrode. The developed ionic actuator exhibits excellent electro-chemo-mechanical properties, which are ascribed to its high ionic conductivity, large specific capacitance, and ionically crosslinked structure resulting from the strong ionic interaction and physical crosslinking among BC, IL, and MWCNT. In particular, the proposed BC-IL-MWCNT (0.10 wt%) nanocomposite exhibited significant increments of Young’s modulus up to 75% and specific capacitance up to 77%, leading to 2.5 times larger bending deformation than that of the BC-IL actuator. More interestingly, bioinspired applications containing artificial soft robotic finger and grapple robot were successfully demonstrated based on high-performance BC-IL-MWCNT actuator with excellent sensitivity and controllability. Thus, the newly proposed BC-IL-MWCNT bioartificial muscle will offer a viable pathway for developing next-generation artificial muscles, soft robotics, wearable electronic products, flexible tactile devices, and biomedical instruments.

Preparation and performance of graphene oxide/self-healing microcapsule composite mortar

Abstract: Abstract In order to solve the special needs for the durability and resistance of concrete materials in power transmission projects in Northwest China. Using sodium silicate and bentonite as capsule core and ethyl cellulose as capsule wall, microcapsules were synthesized by physical method. Standard specimens of cement-based materials were prepared by adding graphene oxide as conductive medium. Indoor experiments and micro technology were used to determine the optimal ratio of graphene-microcapsules, study the effects of graphene content, microcapsule content, and curing age on compressive strength, resistance, and self-repairing effect of the composite material. The results show that the average size of microcapsules was about 1.25 mm. The microcapsule was a relatively regular sphere with rough surface and dense structure. The recommended content was 2% microcapsules and 0.1% graphene oxide. With the increase of microcapsules and graphene oxide, the compressive strength first increased and then decreased, and the resistance increased gradually. After the cracks were repaired, the repairing rate of compressive strength was 57% and the recovery rate was 81%.

Design of novel 3D auxetic structures based on S-shaped unit-cells

Abstract: Abstract In this study, four novel three-dimensional (3D) warp and woof structures with negative Poisson’s ratio (NPR) were designed and assembled using the interlocking assembly method. The designed structures, including S-shaped auxetic unit-cells (UCs), exhibited NPR properties in two perpendicular planes. Because of the lower stress concentration of S-shaped than conventional re-entrant UCs, this UC was suggested for use in energy absorber structures. Furthermore, the mechanical behavior of the designed structures under quasi-static loading was simulated using the finite element method. In addition, two designed structures were fabricated using fused deposition modeling 3D printing technology and subjected to quasi-static compressive loading. The results of FE simulation and experimental work were verified and good agreement was found between them. Stress–strain diagrams, values of energy absorption ( W ), specific energy absorption ( W s ), and NPRs in two perpendicular planes were evaluated. The results showed that four designed auxetic structures had NPR in two perpendicular directions. In addition, stress concentration contours of the structures were investigated using FE simulation. Finally, considering the results of energy absorption and stress concentration for designed structures, the proposed structure to be utilized for energy-absorbing systems was introduced.

Study on mechanical properties of an isotropic negative Poisson’s ratio Voronoi foam and its foam-filled tube

Abstract: Abstract Based on a modified Voronoi tessellation technique, a series of isotropic negative Poisson’s ratio (NPR) Voronoi foam models were proposed via finite element method (FEM). And the proposed models were prepared by reverse modeling method. Poisson’s ratio and stress–strain relationship of the proposed models were studied via FEM and experimental method. Results showed that the structure exhibited NPR and isotropic behavior. With the increased of the relative density of the model, the absolute value of Poisson’s ratio decreased gradually. The results of FEM and experiment showed good consistency. Then, a foam-filled structure was built by filling the proposed NPR Voronoi foam into a square tube. And its energy absorption ability was studied and compared with an isotropic chiral lattice foam-filled tube. Results showed that the energy absorption ability of the proposed NPR Voronoi foam-filled structure was 11% higher than that of the isotropic NPR chiral lattice foam-filled tube with the same relative density. The research was expected to be meaningful for the further research and application of the isotropic NPR foam.

Decade of bio-inspired soft robots: a review

Abstract: Abstract Soft robotics is an emerging field of robotics that focuses on the design of soft machines and devices with effective human-machine interaction, high conformity, and environmental adaptability. The conventional robots made of hard materials have already achieved precision and accuracy, but they lack in reachability, adaptability, degree of freedom, and safe interaction. Moreover, soft robots mimic the behavior of biological creatures by mimicking their locomotive patterns. The actuation or the locomotion of the soft robots is achieved by soft actuators which are a very important part of soft robotic systems. Herein, a comprehensive review based on the evolution of six actuation methodologies is presented. Various approaches used for the design and fabrication of soft robots such as pneumatic, shape memory alloy, dielectric elastomers, chemical-reaction enforced, and pneumatic and magneto-rheological elastomers-based actuation methods reported in the last decade. Furthermore, the advancement of these approaches has been rigorously discussed in chronological order for parameters like efficiency, power requirement, frequency, and possible applications. Future challenges and directions toward the advancement in soft robotics are also discussed for achieving the remarkable performance of soft robots in a real-time environment. Furthermore, we believe, this is a complete review package for the young researchers which can help them to understand, how this field has evolved from a performance, application, and efficiency point of view.

A nonlinear piezoelectric shunt absorber with 2:1 internal resonance: experimental proof of concept

Abstract: Abstract An experimental proof of concept of a new semi-passive nonlinear piezoelectric shunt absorber, introduced theoretically in a companion article, is presented in this work. This absorber is obtained by connecting, through a piezoelectric transducer, an elastic structure to a resonant circuit that includes a quadratic nonlinearity. This nonlinearity is obtained by including in the circuit a voltage source proportional to the square of the voltage across the piezoelectric transducer, thanks to an analog multiplier circuit. Then, by tuning the electric resonance of the circuit to half the value of one of the resonances of the elastic structure, a two-to-one internal resonance is at hand. As a result, a strong energy transfer occurs from the mechanical mode to be attenuated to the electrical mode of the shunt, leading to two essential features: a nonlinear antiresonance in place of the mechanical resonance and an amplitude saturation. Namely, the amplitude of the elastic structure oscillations at the antiresonance becomes, above a given threshold, independent of the forcing level, contrary to a classical linear resonant shunt. This paper presents the experimental setup, the designed nonlinear shunt circuit and the main experimental results.

Investigation on rheological characteristics of magnetorheological shear thickening fluids mixed with micro CBN abrasive particles

Abstract: Abstract The novel magnetorheological shear thickening polishing fluids (MRSTPFs) were developed by mixing micro cubic boron nitride (CBN) abrasive particles into traditional magnetorheological shear thickening fluids. MRSTPFs were constructed by uniformly fumed silica and polyethylene glycol as shear thickening fluids, carbonyl iron particles (CIPs) as ferromagnetic phase and CBN particles as abrasive phase. In this work, various MRSTPFs were prepared to explore their rheological characteristics. Sweeps of steady shear rate and dynamic shear frequency were conducted under different magnetic flux densities, respectively. A mathematical model was presented to explain shear rate variation with shear stress. The magnetorheological shear thickening mechanism was well described. The rheological experiment results have revealed that shear thickening effect was still existing in magnetic flux density. However, the increased magnetic flux density played a negative role on the shear thickening effect. Particle size optimization of CIPs was thus essential to maximize the shear thickening effect. On the other hand, with increased shear frequency, the viscoelastic feature of MRSTPFs was converted from linear to non-linear. It was found that the shear yield stress of the MRSTPFs was magnified with the stronger magnetic flux density and larger CIPs size. The investigation of rheological characteristics demonstrated that MRSTPFs could enhance polishing performance, which contributed to developing a high-efficiency and ultra-precision polishing process.

Neural network-based motion modeling and control of water-actuated soft robotic fish

Abstract: Abstract Soft actuator has broad application prospects due to its good compliance to different environments. However, its deformation is difficult to be described by the traditional method, so it is impossible to establish an accurate model of its motion, resulting in the difficulty of motion control of the software actuator. In this study, a soft robotic fish is designed, and a motion modeling method is proposed applying the neural network. The neural network-based motion model of the water-actuated soft robotic fish is constructed through neural network training with data collected by visual sensor. Further, a data set of control signals about the desired swing angle of robotic fish is established based on the motion model and stochastic algorithm, and the accurate motion control of the robot is implemented. The accuracy of the motion control method and the free swimming ability of the soft robotic fish using the control method in the water are analyzed quantitatively and qualitatively through the static and dynamic swing experiments of the robotic. This study provides a new idea for the motion modeling of soft actuators, which can effectively promote the development of modeling methods and theories of soft robots.

Energy harvesting from gravity-induced deformation of rotating shaft for long-term monitoring of rotating machinery

Abstract: Abstract Energy harvesting from rotating machines for self-powered sensor networks has attracted increasing attentions in the last decade. In this work, an energy harvester employing piezoelectric stacks for rotating machinery is proposed, which cannot only harvest kinetic energy from bending deformation of rotating shaft but also has the capability of rotor fault detection. The structure and working concept of the energy harvester are initially presented. Afterward, a theoretical model for the energy harvester is established to clarify its output characteristics. Then, vibration tests under different rotating speeds are carried out with a prototype mounted on a rotor test rig. The effects of electrical connections of piezoelectric stacks, rotor geometry, energy harvester location, and fastener preload on the output performance of energy harvester are evaluated. Finally, the applications of powering a scientific calculator and detecting typical faults of rotor systems including rotor crack and rub impact faults are demonstrated. Apart from fault detection capability, the proposed energy harvester has the advantages of long lifespan and causing little interference with the rotational motion, which overcomes the inherent deficiencies of commonly studied beam-type energy harvesters and manifest the potential of proposed energy harvester for the long-term condition monitoring of rotating machines.

Development and experiment evaluation of a compact inchworm piezoelectric actuator using three-jaw type clamping mechanism

Abstract: Abstract A compact inchworm piezoelectric actuator using three-jaw type clamping mechanism is developed in this study. Different from the previous inchworm piezoelectric actuators constructed with guiding structures, the proposed actuator can drive an output shaft to realize linear motion without other auxiliary structures based on the automatic centering and guidance functions of the designed three-jaw type clamping mechanism, and a compact structure is obtained. The configuration of the actuator is presented to describe the operating principle in detail. Then the structures of the clamping and actuating units are designed by the assistance of finite element simulations. A prototype is fabricated and a compact structure is achieved with outer diameter of 34 mm and length of 40 mm. The experiments are performed to investigate the characteristics, a maximum speed of 155.5 μ m s −1 and a thrust force of 12.3 N are achieved. The experimental results confirm that the proposed inchworm actuator can achieve a compact structure by adopting the designed three-jaw type clamping mechanisms, it has great potential in integration with precision equipment, which is conductive to apply in the fields of biological manipulation robots and aerospace devices.

Singular spectrum analysis and fuzzy entropy-based damage detection on a thin aluminium plate by using PZTs

Abstract: Abstract In this research, a new method based on singular spectrum analysis (SSA) and fuzzy entropy is developed for damage detection on thin wall-like structures, and the normalized fuzzy entropy is employed as an indicator to identify the severity of the damage. The lead zirconate titanate (PZT) transducers are used in this research to generate and detect the Lamb waves. During the detection, the collected signals from the PZT sensors are firstly decomposed and reconstructed by SSA to extract the feature of the damage, and then the reconstructed signals with the feature of the damage are processed to obtain the normalized fuzzy entropy. An experimental setup of an aluminium plate with added magnets is fabricated to validate the proposed method. The experimental results show that when magnets are attached on the aluminium plate, the normalized fuzzy entropy is smaller than that when there are no magnets. That is because when magnets are placed on the plate, the movement and some vibration modes of Lamb waves are disturbed by the added magnets and this disturbing effect can be enhanced by increasing the number and locations of the added magnets, and eventually the complexity and nonlinearity of the waves are weakened. The experimental results of a single damage with different number of magnets indicate that the normalized fuzzy entropy decreases linearly as the number of the added magnets increases, which demonstrates that the proposed method can be used to detect the severity of the damage. Moreover, the experimental results of multi-damage on different locations indicate that the normalized fuzzy entropy is relevant with both the total number and locations of the added magnets. The normalized fuzzy entropy decreases linearly as the total number of the magnets increases, and the entropy of a single damage is smaller than that of the multi-damage with the same total number of magnets, which demonstrates that the proposed method also can be used for multi-damage detection on a thin plate. This study provides us a new approach to identifying a single or multiple damages on thin wall-like structures.

Silicon-based soft parallel robots 4D printing and multiphysics analysis

Abstract: Abstract Four-dimensional printing has set the stage for a new generation of soft robotics. The applications of rigid planar parallel robotic manipulators are also significant because of their various desirable characteristics, such as lower inertia, higher payload, and high accuracy. However, rigid planar parallel robots are heavy and require different actuators and components. This study introduces a novel technique to produce a light three degrees of freedom soft parallel manipulator at a low cost, which can be stimulated easily. This technique allows researchers to customize the actuator’s design based on the requirement. The robot is made by 3D printing based on fused deposition modelling and a direct ink writing process. The design, development, and additive manufacturing of a soft parallel robot electrothermally driven by a linear silicon-based actuator and polylactic acid parts are presented. Silicon-based soft actuators replace the rigid conventional linear actuators in this study to drive the planar parallel manipulator. The actuation of actuators is conducted using simple heating compared to the conventional rigid actuator. Various heating approaches and configurations are compared and analysed to find the most suitable one for the effective linear stroke of the soft actuator. The finite element model is used to analyse the performance of the electrothermally silicon-ethanol soft actuators in ABAQUS. The kinematics of the planar parallel robotic manipulator are simulated in MATLAB to achieve its workspace. The final soft parallel robot mechanism and the active and passive links are fabricated and tested experimentally.