查看更多>>摘要：Origami and kirigami are effective approaches to fabricate lightweight cellular metamaterials with extraordinary mechanical properties. However, the novel designs of such metamaterials are still limited. In this paper, a novel metamaterial similar to typical Kelvin foams is proposed and fabricated via origami and kirigami methods, and its mechanical properties are investigated. Quasi-static compression tests are first conducted to analyze the deformation characteristics and stress-strain responses. Numerical simulations are then carried out to simulate the tests. Furthermore, two methods including adjusting the wall thickness and introducing openings are adopted to alter the relative density of the metamaterials, and their influences on the plateau stress and specific energy absorption (SEA) are explored. Finally, analytical studies are conducted to predict the plateau stress, and good agreement between the analytical, numerical, and experimental results are obtained. The results reveal that the kinetic energy is primarily dissipated by unfolding the constitutive elements along the creases, and three typical stages of linear-like elastic, plateau, and densification are generated in the stress-strain curves. Increasing the wall thickness significantly improves the plateau stress and SEA. Introducing smaller openings has minor influences on the plateau stress, while the stress level drops remarkably when the opening size exceeds a critical value. By adopting an appropriate opening size, the increment of the SEA can be up to 29% in comparison with non-opening counterparts. The findings of the present study provide an alternative to fabricating cellular materials with outstanding performance.
查看更多>>摘要：When considering durability and reliability, flexible piezoelectric materials, such as PVDF and macro-fiber composite, are preferable to piezoceramics due to the brittleness of piezoceramics. However, flexible piezoelectric materials cannot sustain compressive loads so they need to be operated in either tensile or bending mode. The tensile mode has the advantage of uniform strain distribution over the bending mode. This study proposes a novel tensile-mode piezoelectric energy harvester based on a three-hinged force amplification mechanism. The proposed design consists of a rigid beam and an elastic PVDF film connected to each other via a revolute joint. The assembly is attached to a base via revolute joints with the PVDF film pre-stretched. The PVDF film bears a dynamic tensile load when the harvester is under harmonic excitations. A theoretical model of the proposed harvester is developed and experimentally validated. The simulation and experimental results show that the proposed design exhibits a strong hardening effect due to the nonlinear geometry of the three-hinged mechanism. The effect of preloads and mass distributions are explored to see their impact on the harvesting performance. It is shown that the peak voltage and bandwidth of the harvester decline as the preload increases. By properly tuning the mass distribution, the performance of the harvester can be enhanced. Compared with a bending-mode cantilevered harvester, the voltage output and harvesting bandwidth of the proposed harvester can be improved by 500% and 1250%, respectively.
James, Stephen W.Kissinger, ThomasWeber, SimoneMullaney, Kevin...
13页
查看更多>>摘要：Optical fibre strain and shape measurement sensors were deployed on a 5-m long rotor blade during a full-speed (rotation rate 6.6 Hz) helicopter ground run, with real-time data wirelessly streamed from rotor hub-mounted sensor interrogators. In Part 1 of a 2-part paper series, the strain sensing capabilities of the two optical fibre-based sensing techniques, optical fibre Bragg grating (FBG) and fibre segment interferometry (FSI), are compared, while Part 2 (Kissinger et al 2022 Smart Mater. Struct. accepted) specifically investigates the blade shape measurement based on the FSI approach. In part 1, the rotor hub-mounted instrumentation is described, and data on the dynamics of the blade obtained from a sequence of controlled pilot inputs are analysed both in the time and spectral domains. It is shown that this can provide insights into the aeroelastic properties of the blade. Noise standard deviations of 0.2 n epsilon/root Hz and 30 n epsilon/root Hz for the FSI and FBG-based sensing approaches, respectively, were observed over a strain range of 3500 mu epsilon.
查看更多>>摘要：The breakthrough invention of conducting polymers (CPs) initiates a new pathway for the researchers to make use of their properties in thermoelectric (TE) applications. They are considered to be potential candidates in TE application when combined with inorganic counterparts. Different strategies were undertaken to enhance structural order and hence the TE performance of the CPs which trigger the scientific community to focus more on this area. Consequently, the use of nano filler in the polymer matrix proved to be a better way to improve the TE properties and chalcogenide materials could be the best candidates to be used as nano filler due to their high TE parameters. Thus, composites of CPs with different chalcogenides have been drawing attention in the field of TEs in recent years. The present work points towards a comprehensive update on different synthesis process of composites of various CPs with a number of chalcogenides along with a state-of-art review of these promising materials in TEs for device applications with the expectation that this work will surely motivate the researchers to optimize the best candidate.
查看更多>>摘要：Piezoelectric metamaterials with shunt resonant circuits have been extensively investigated for their tunability in bandgaps. However, the vibration attenuation ability induced by the electromechanical coupling is generally weaker than that of mechanical metamaterials, limiting their applications in engineering practice. This research presents a non-uniform piezoelectric metamaterial beam with shunt circuit parameters optimized by an adaptive genetic algorithm (AGA) for tailoring the vibration attenuation zone. First, the non-uniform piezoelectric metamaterial beam is modeled for transmittance analysis and verified by the finite element method. By simultaneously tuning the resonance frequencies and the resistance of the shunt circuits, it is conceptually demonstrated that the attenuation zone can be broadened, and the undesired localized vibration modes can be mitigated. Subsequently, two optimization strategies are proposed respectively for two typical vibration scenarios. The inductances and the load resistance in the shunt circuits constitute the set of design variables and are optimized by the AGA. Dedicated case studies are carried out, and the results show that the objective-oriented circuitry parameters can greatly enrich the design freedom, and tailor the transmittance profile according to a given vibration spectra. As compared to the conventional uniform and the graded piezoelectric metamaterial beams, the proposed design provides superior vibration attenuation performance and demonstrates a promising approach for tailoring piezoelectric metamaterials systems.
查看更多>>摘要：Lamb wave-based damage detection is one of the most promising structural health monitoring (SHM) technologies for aircraft structures. In this paper, a Lamb wave-based deep transfer learning network is developed for multi-level damage classification of plate-type structures. A one-dimensional convolutional neural network (1D-CNN) is employed to deeply mine the damage characteristics of complex Lamb wave signals with multiple modes and multiple boundary reflections. The concept of multi-level damage classification is carried out to get different results for different engineers, and a multi-task cascaded 1D-CNN architecture is established for three levels of damage classifications, which is corresponding to different SHM levels, i.e. identifying the damage presence, location, and severity, respectively. In the multi-task cascaded architecture, a fine-tune transfer learning concept is adopted to share partial structures and weight values among different classification models, which could greatly improve the efficiency of the model calculation. In the multi-level damage classification model, the one-dimensional Lamb wave scattering signals with different damage locations and sizes are used as the input without any preprocessing steps, while the classifications of the damage presence, location and size are designated as output of different levels. An experiment has been conducted to verify the proposed multi-level damage classification model. The experimental results show that the training time of this model is reduced by 35% and the accuracy of the proposed model is greater than 99%, which verifies the effectiveness and reliability of the proposed technique.
查看更多>>摘要：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.
查看更多>>摘要：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.
查看更多>>摘要：Modeling dynamic heterogeneity in amorphous shape memory polymers (SMPs) is a huge challenge due to the complex statistics of strain energy distributions during their thermodynamic relaxations. In this study, based on the dynamic heterogeneity of strain energy distribution, we have considered, for the first time, the influences of different temperature rates and strain rates on strain energy evolution as a dynamic equilibria, rather than a quasi-static problem. We propose a phase transition model incorporated with Gaussian distribution statistics to investigate the dynamic equilibria with glass transition heterogeneity and tailorable mechanics for the amorphous SMPs. The Gaussian distribution statistics is firstly applied to characterize the heterogeneity of strain energy distributions in the amorphous polymers. Phase transition theory is then developed to describe working principles of strain energy evolution, glass transition heterogeneity, thermodynamic relaxation and tailorable mechanics. Finally, the dynamic equilibria of heterogeneity about the statistics of strain energy distribution are formulated based on the one dimensional Maxwell multi-branch model. The analytical results are compared with the experimental data of epoxy, polyamide and vinylester SMPs reported in literature, and good agreements between them are demonstrated. This study provides a new insight into the dynamic heterogeneity in the mechanics of amorphous SMPs.
查看更多>>摘要：Ceramic-ceramic composite structures are a viable solution to improve the electromechanical response of lead-free ferroelectrics (FEs) through tuning of the local electrical and mechanical fields. The origin of the enhanced properties, however, remains unclear, as many of the possible effects, such as polarization and strain coupling (PSC) as well as interface diffusion, are interrelated and difficult to separate or directly investigate. In this study, we use a custom-built digital image correlation system to directly investigate the influence of strain coupling on 2-2 composites consisting of 0.90Na(1/2)Bi(1/2)TiO(3)-0.06BaTiO(3)-0.04K(0.5)Na(0.5)NbO(3) (NBT-6BT-4KNN) and 0.94Na(1/2)Bi(1/2)TiO(3)-0.06BaTiO(3) (NBT-6BT) by varying the mechanical interface contacts between end members. Specifically, two model cases were utilized to separate the relative contributions of the PSC mechanisms: (a) electrically connected and (b) mechanically and electrically connected. The local strain gradient was characterized through the thickness of the composite across different layers as well as the interface, where the macroscopic large signal longitudinal and transverse FE response was determined. Experimental results reveal an enhancement of the large signal piezoelectric coefficient d33* <i by approximately 10% from 390 to 440 pm V-1 due to strain coupling.
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