bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Vibration Reduction in a Helicopter Blade With 2 Way Fluid-Structure Interaction
Authors: Sicim Mürüvvet Sinem , Kaya Metin Orhan
Published: November 2018

The main goal of this study is the optimization of vibration reduction on helicopter blade by using macro fiber composite (MFC) actuator under pressure loading. Due to unsteady aerodynamic conditions, vibration occurs mainly on the rotor blade during forward flight and hover. High level of vibration effects fatigue life of components, flight envelope, pleasant for passengers and crew. In this study, the vibration reduction phenomenon on helicopter blade is investigated. 3D helicopter blade model is used to perform the aeroelastic behavior of a helicopter blade. Blade design is created by Spaceclaim and finite element analysis is conducted by ANSYS 19.0. Generated model are solved via Fluent by using two-way fluid-solid coupling analysis, then the analyzed results (all aerodynamic loads) are directly transferred to the structural model. Mechanical results (displacement etc.) are also handed over to the Fluent analysis by helping fluid-structure interaction interface. Modal and harmonic analysis are performed after FSI analysis. Shark 120 unmanned helicopter blade model is used with NACA 23012 airfoil. The baseline of the blade structure consists of D spar made of unidirectional Glass Fiber Reinforced Polymer +45°/−45° GFRP skin. MFC, which was developed by NASA’s Langley Research Center for the shaping of aerospace structures, is applied on both upper and lower surfaces of the blade to reduce the amplitude in the twist mode resonant frequency. D33 effect is important for elongation and to observe twist motion. To foresee the behavior of the MFC, thermo-elasticity analogy approach is applied to the model. Therefore, piezoelectric voltage actuation is applied as a temperature change on ANSYS. The thermal analogy is validated by using static behavior of cantilever beam with distributed induced strain actuators. Results for cantilever beam are compared to experimental results and ADINA code results existing in the literature. The effects of fiber orientation of MFC actuator and applied voltage on vibration reduction on helicopter blade are represented. The study shows that torsion mode determines the optimum placement of actuators. Fiber orientation of the MFC has few and limited influences on results. Additionally, the voltage applied on MFC has strong effects on the results and they must be selected according to applied model.
The Reliability Testing and Fatigue Behavior Study of Micro Piezoelectric Energy Harvester
Authors: Yang Y. H. , Fu Y. H. , Chen C. T. , Lin S. C. , Shieh Jay , Veidt Martin , Wu W. J.
Published: November 2018

In this paper, a high performance micro piezoelectric energy harvester (PEH) fabricated on stainless substrates is presented. A PZT piezoelectric active layer with a thickness of about 10 μm was deposited on a stainless steel substrate by the aerosol deposition method. The cantilever beam-shaped PEH was then fabricated by metal-MEMS processing of the PZT/stainless steel composite structure. The size of the cantilever PEH transducer developed was about 1 cm2 and a proof mass was attached to tune its resonant frequency to around 120 Hz for harvesting mechanical vibrations from direct drive AC motors. The PEH transducer showed an output voltage and an output power of 8.9 Vp-p and 107.8 μW, respectively, when connected with optimal load and excited under 0.5 g acceleration level. In order to realize the fatigue behavior and reliability of the PEH in field applications, the PEH transducer was driven at its own resonant frequency and tested under 1.0 g acceleration level for millions of cycles and the vibration modes were measured with a laser scanning vibrometer. The PEH transducer had an operating lifetime of about 1.8 million cycles at 1.0 g cyclic loading based on the shift of its resonant frequencies and the decrease in electrical output. The experimental results show the resonant frequencies of the first, second and third modes were all shifted to lower frequencies with increasing operation cycle number due to the development of microcracks in the ceramic PZT active layer. However, the same PEH transducer could survive millions of cycles (in the high millions) at 0.5 g cyclic loading without any significant changes in the resonant frequencies and electrical output. The results confirm the operating limits of the PEH transducer and suggest further protection and reinforcement are required for the transducer to operate at high acceleration loadings.
Hybrid Mass Damper Experimental Analysis of Shock Response
Authors: Billon Kevin , Perez Matthias , Chesné Simon , Zhao Guoying , Collette Christophe
Published: November 2018

In this paper, an hybrid mass dampers (HMD) and its control law are studied. Based on a optimal tuned mass damper (TMD), it is a one degree of freedom (dof) mass-spring system associated with an electromagnetic system. The passive damping is provided by the coil-magnet combination coupled with a tunable load. The passive resonator has been modify to become “dual”, a second coil-magnet combination has been had on the same dof to create an active part. The control law is a modified velocity feedback with phase compensator. The proposed hybrid system controller is hyperstable and ensure a fail-safe behavior. The HMD is experimentally tested at 1:1 scale. It is carried out on a main structure suspended by flexible blades. The numerical model, with experimental parameters identification, provides good results. Under shock disturbance, experimental results show the ability of this system to react quickly and dissipate energy in comparison with the passive one.
Broadband Rotational Energy Harvesting Using Micro Energy Harvester
Authors: Chien Jui-Ta , Fu Yung-Hsing , Chen Chao-Ting , Lin Shun-Chiu , Shu Yi-Chung , Wu Wen-Jong
Published: November 2018

This paper proposes a broadband rotational energy harvesting setup by using micro piezoelectric energy harvester (PEH). When driven in different rotating speed, the PEH can output relatively high power which exhibits the phenomenon of frequency up-conversion transforming the low frequency of rotation into the high frequency of resonant vibration. It aims to power self-powered devices used in the applications, like smart tires, smart bearings, and health monitoring sensors on rotational machines. Through the excitation of the rotary magnetic repulsion, the cantilever beam presents periodically damped oscillation. Under the rotational excitation, the maximum output voltage and power of PEH with optimal impedance is 28.2 Vpp and 663 μW, respectively. The output performance of the same energy harvester driven in ordinary vibrational based excitation is compared with rotational oscillation under open circuit condition. The maximum output voltage under 2.5g acceleration level of vibration is 27.54 Vpp while the peak output voltage of 36.5 Vpp in rotational excitation (in 265 rpm).
Linear and Nonlinear Viscoelastic Behavior of MR Fluids: Effect of Temperature
Authors: Hemmatian Masoud , Sedaghati Ramin , Rakheja Subhash
Published: November 2018

This study aims to investigate the influence of temperature on the linear and nonlinear rheological behavior of a MR fluid, MRF 132DG, using a rotational rheometer. The experiments were designed to obtain properties of the fluid under oscillatory shear strain in the amplitude and frequency sweep modes, while maintaining different constant temperatures (−5, 0, 20 and 50 °C). The data were used to evaluate the storage and loss moduli under different levels of magnetic flux density considering the linear as well as nonlinear viscoelastic regions. The critical strain amplitudes were further obtained. Results showed enhanced linear viscoelastic region with increasing magnetic field density. Moreover, the effects of temperature and magnetic field on the frequency dependency of the fluid properties are illustrated for small and large amplitudes of shear strains.
Power Generation Amplification and Stack Toughening via Compliant Layer Interdigitation
Authors: Krech Ember D. , Barrett Ronald M. , Cadel Eileen S. , Friis Elizabeth A.
Published: November 2018

Energy harvesting from low frequency cyclic motion is possible in a variety of applications, but generating power with piezoelectric stacks at low, off-resonance frequencies is challenging. In this study, Compliant Layer Adaptive Composite Stacks (CLACS) were investigated as a toughened piezoelectric generator to increase efficiency at low frequencies and match the compliance of many commercial devices.

CLACS were manufactured with PZT discs, interdigitated epoxy layers of varying thicknesses, and encapsulated in epoxy. Energy production of each CLACS type as a function of compliant layer thickness was characterized. Power amplification of CLACS was modeled assuming discs remain planar, volume of epoxy was conserved, and total epoxy deformations were small. Shear lag theory demonstrated increases in positive in-plane strains induced by external through-thickness compression. This amplified sensitivity of the entire stack to through-thickness compressions, substantially increases power generation capability.

Experimental data showed that increases in compliant layer thickness resulted in increased power generation in all loading conditions. The shear lag structural mechanics model showed good correlation with theoretical predictions, assuming small deformation of the compliant layer. In addition to reducing composite stiffness, the CLACS generated 61% more power than conventional stack actuators with the same PZT volume via lateral strain amplification effects.
Electrospun PVDF Miniaturized Muscles for Bio Inspired Morphing Materials
Authors: Chinnam Krishna Chytanya , Fabriani Federico , Giovanna Iucci , Lanzara Giulia
Published: November 2018

Several biological creatures represent a great inspiration for the realization of advanced morphing materials. For instance, bat wing is extremely interesting because of its unique ability of drastically changing shape and size thanks to an embedded distributed array of ultra-small-in-size muscles. This is obviously done as a response to continuously detected external stimuli. Novel ultra-lightweight and non-invasive artificial muscles that can exploit a dual functionality and that can be integrated into hosting materials, are here investigated. The muscles are made of a piezoelectric (PVDF) single micro-fibre and a micro-fibre rope created using a simple electrospinning technique. The advantage of this technique is the less-complex in-situ fibres poling during electrospinning which makes them an attractive alternative compared to thin PVDF films that require an additional complicated poling step to achieve their piezoelectric properties. Muscles that possess an active and passive electromechanical response based on a ∼ 3-micron thick single PVDF fibre and ∼ 150-micron thick PVDF fibred rope, were realized. Preliminary results prove that these PVDF fibres have a highly accurate electromechanical response over an extremely wide frequency range. Fully constrained single fibres and fibre ropes, when actuated with the corresponding electric fields, show a midpoint displacement of ∼ 36 μm.
Self-Adaptable Carbon Fiber Composite
Authors: Casalotti Arnaldo , Chinnam Krishna C. , Lanzara Giulia
Published: November 2018

This article illustrates an approach to develop innovative smart materials based on carbon fiber composites. The proposed approach relies on the use of ultra-light strain sensors that are embedded into the composite and are adopted to monitor in real-time the actual material configuration. Such sensors are composed of electrospun PVDF fibers that exploit piezoelectricity to identify strain and thanks to their extreme lightweight can easily be embedded within the composite layers without affecting the structural integrity. On the other hand, the composite is equipped with a system of internal distributed heaters that can locally and globally vary the composite temperature. Since the adopted epoxy has a considerable temperature-dependent behaviour, it is possible to control its stiffness and thus to control the structural frequencies and damping. By coupling the sensing system with the control system, the structural properties are tuned to match prescribed working conditions, thus optimizing the performance of the proposed smart system. The proposed approach is investigated experimentally by manufacturing prototypes of the smart composite and by performing multiple tests to study the material response and evaluate the obtained performance.
Self-Powered Multifunctional Instrumented Knee Implant
Authors: Safaei Mohsen , Anton Steven R.
Published: November 2018

Computational modeling, instrumented linkages, optical technologies, MRI, and radiographic techniques have been widely used to study knee motion after total knee replacement (TKR) surgery. Information provided by these methods has helped designers to develop implants with better clinical performance and surgeons to obtain an improved understanding of the stability and mobility of the joint. Correspondingly, overall patient satisfaction with respect to the reduction in pain and recovery of normal functioning of the joint has been improving. However, about 20% of patients are still not fully satisfied with their surgical outcomes. The main obstacle in the current state-of-the-art is that a comprehensive post-operative understanding of knee balance is still unavailable, mostly due to a lack of in vivo data collected from the joint after surgery. This work presents an attempt to develop a self-powered instrumented knee implant for in vivo data acquisition. The knee sensory system in this study utilizes several embedded piezoelectric transducers in the tibial bearing of the knee replacement in order to provide sensing and energy harvesting capabilities. Through a series of analytical modeling, finite element simulation, and experimental testing, the performance of the suggested system is evaluated and a dimensionally optimized design of an instrumented TKR is achieved. More specifically, a comprehensive platform is established in order to combine the knowledge of embedded piezoelectric sensors and energy harvesters, musculoskeletal modeling of the knee joint, multiphysics finite element modeling, additive manufacturing techniques, image processing, and experimental knee loading simulation in order to achieve the experimentally validated and optimized instrumented knee implant design. The cumulative work presented in this article encompasses three main studies performed on the sensing performance of the proposed design: first, preliminary parametric studies of the effect of local dimensional and material parameters on the electromechanical behavior of the embedded sensory system; second, investigation of the ability to sense total force and center of pressure location; and third, evaluation of an enhanced system with the ability to sense compartmental forces and contact locations. Additionally, the energy harvesting capacity of the system is investigated to ensure the achievement of a fully self-powered sensory system. Results obtained from the experimental analysis of the system demonstrate the successful sensing and energy harvesting performance of the designs achieved in this study.
Effects of Bandgap Formation on the Aeroelastic Behavior of a Plate-Like Wing
Authors: Dainezi João Henrique Ribeiro , Schiavon Gabriel Bellomi , De Marqui Carlos
Published: November 2018

In this work the aeroelastic behavior of locally resonating periodic structures is investigated. The plate-like wing behavior will be obtained from the Love-Kirchhoff plate model with a finite number of mechanical resonators periodically distributed along its surface and using assumed-modes expansion. The unsteady aerodynamic loads are obtained from the doublet lattice model. By combining the structural and aerodynamic models, the aeroelastic behavior of the wing over a range of airflow speeds is discussed. Frequency response functions due to simultaneous base and flow excitations are calculated from the absence of flow speed to the linear flutter speed of the system without resonators. The effects of bandgap presence on the flutter boundary of the wing are also discussed.
An Investigation of the Electroaeroelastic Behavior of a Locally Resonant Piezoelectric Metastructure
Authors: Schiavon Gabriel B. , Dainezi Joao H. R. , De Marqui Carlos
Published: November 2018

The literature of aeroelasticity includes the use of smart materials to modify the aeroelastic behavior of fixed or rotary wings. In some cases, they are employed as actuators in active control systems while in others the use of smart materials in passive control schemes is investigated. In this work a different approach is investigated. The aeroelastic behavior of a locally resonant electromechanical metastructure made from flexible substrates with piezoelectric layers connected to resonant shunt circuits is investigated. An electromechanically coupled finite element plate model is employed for predicting the electroelasatic behavior of the wing. The unsteady aerodynamic loads are obtained from the doublet lattice model. By combining the structural and aerodynamic models, the aeroelastic behavior of the metastructure over a range of airflow speeds is studied.
Multi-Modal Morphing Wing Flaps for Next Generation Green Regional Aircraft: The CleanSky Challenge
Authors: Pecora Rosario
Published: November 2018

Regional aviation is an innovation driven sector of paramount importance for the European Union economy.

Large resources and efforts are currently spent through the CleanSky program for the development of an efficient air transport system characterized by a lower environmental impact and unequalled capabilities of ensuring safe and seamless mobility while complying with very demanding technological requirements. The Green Regional Aircraft (GRA) panel, active from 2006, aims to mature, validate and demonstrate green aeronautical technologies best fitting the regional aircraft that will fly from 2020 onwards with reference to specific and challenging domains: from advanced low-weight and high performance structures up to all-electric systems and bleed-less engine architectures, from low noise/high efficiency aerodynamic up to environmentally optimized missions and trajectories management.

The development of such technologies addresses two different aircraft concepts, identified by two seat classes, 90-pax with Turboprop (TP) engine and 130-pax, in combination with advanced propulsion solutions, namely, the Geared Turbofan (GTF), the Advanced Turbofan (ATF) and the Open Rotor (OR) configuration.

Within the framework of the Clean Sky program, and along nearly 10 years of research, the design and technological demonstration of a novel wing flap architecture was addressed. Research activities aimed at demonstrating the industrial feasibility of a morphing architecture enabling flap camber variation in compliance with the demanding safety requirements applicable to the next generation GRA in both open rotor and turboprop configurations. The driving motivation was found in the opportunity to replace a conventional double slotted flap with a single slotted morphing flap assuring improved high lift performances — in terms of maximum attainable lift coefficient and stall angle — while lowering emitted noise, fuel-burnt and deployment system complexity. Additional functionalities for load control and alleviation were then considered and enabled by a smart architecture allowing for an independent shape-control of the flap tip region during cruise.

The entire process moving from concept definition up to the experimental qualification of true scale prototypes, characterized by global and multi-zone differential morphing capabilities, is here described with specific emphasis on the adopted design philosophy and implemented technological solutions. Paths to improvements are finally outlined in perspective of a low-term item certification and series production.
Shuttered Passive Infrared Sensor for Occupancy Detection: Exploring a Low Power Electro-Mechanical Driving Approach
Authors: Wu Libo , Wang Ya
Published: November 2018

Passive infrared (PIR) sensors are the most popular deployed sensors in building lighting control for individual presence detection. However, PIR sensors are motion detectors in nature, responding only to incident radiation variation, which lead to false negative detections, inaccurate occupancy estimation, and uncomfortable lighting swings, short lifetime of the equipment, and waste of energy. In this study, a shutter driven by a Lavet motor PIR (LAMPIR) sensor is developed for presence detection for both stationary and moving occupants. Building off our previous work on chopped PIR (C-PIR) and rotationally-chopped PIR (Ro-PIR) sensors, Lavet motor, a single-phase electro-mechanical vibrator, is introduced, which has many advantages over traditional servo motors and stepper motors in terms of power consumption, size, weight and noise level. Driven by pulsed signal from a microcontroller unit (MCU), the electro-mechanical vibrator drives a semi-transparent long-wave infrared (LWIR) optical shutter to shutter the field of view (FOV) of a PIR sensor periodically. Output voltage generated by a LAMPIR senor for occupied and unoccupied scenarios can be monitored and analyzed to identify presence accurately. Parametric studies are conducted to find the optimal setting of driving signal frequency, shutter width and shuttering period. The LAMPIR sensor reaches an accuracy of 100% for detecting stationary occupants up to a range of 4.5 m and moving occupants up to a range of 10 m, which improves the detection range of both C-PIR and Ro-PIR sensors (4.0 m for stationary and 8.0 m for moving occupancy detection). LAMPIR has a FOV of 90° in horizontal and 100° in vertical, which is reasonable for most applications. For a 17-hour-long presence detection test, LAMPIR can reach an accuracy of 93.52% to classify unoccupied, stationary and moving occupant scenarios. More importantly, the average power consumption of LAMPIR is 0.19 W, which is 82% less than that of the C-PIR sensor and 89% less than that of the Ro-PIR sensor.
Experimental Validation of Neo-Hookean Fiber Reinforced Elastic Solids
Authors: Erel Veysel , Jiang Mingliang , Moreno Michael R. , Freed Alan D.
Published: November 2018

There have been various theoretical studies done on anisotropic neo-Hookean models; however, there have been limited experimental validations of these theories. In this study, a silicone/silicone laminate with a fiber volume fraction of 18% has been parameterized. Conventional neo-Hookean models have been modified for compressible in-plane deformations. Two-dimensional deformation limitations and a compressible constraint have been discussed. Material parameters have been calculated for three different anisotropic, neo-Hookean models from the literature.
Data-Driven Modeling Techniques to Estimate Dispersion Relations of Structural Components
Authors: Malladi Vijaya V. N. Sriram , Albakri Mohammad I. , Tarazaga Pablo A. , Gugercin Serkan
Published: November 2018

Dispersion relations describe the frequency-dependent nature of elastic waves propagating in structures. Experimental determination of dispersion relations of structural components, such as the floor of a building, can be a tedious task, due to material inhomogeneity, complex boundary conditions, and the physical dimensions of the structure under test.

In this work, data-driven modeling techniques are utilized to reconstruct dispersion relations over a predetermined frequency range. The feasibility of this approach is demonstrated on a one-dimensional beam where an exact solution of the dispersion relations is attainable. Frequency response functions of the beam are obtained numerically over the frequency range of 0–50kHz. Data-driven dynamical model, constructed by the vector fitting approach, is then deployed to develop a state-space model based on the simulated frequency response functions at 16 locations along the beam. This model is then utilized to construct dispersion relations of the structure through a series of numerical simulations. The techniques discussed in this paper are especially beneficial to such scenarios where it is neither possible to find analytical solutions to wave equations, nor it is feasible to measure dispersion curves experimentally. In the present work, actual experimental data is left for future work, but the complete framework is presented here.
Gripping Force Measurement of a Bioinspired Wall-Climbing Robot With Spiny Toe Pads
Authors: Chen Haofeng , Zhang Yanan , Wu Xuan , Wang Xiaojie , Xu Linsen , Zhang Ningning , Li Zhaochun
Published: November 2018

This paper presents a method to measure gripping force of a bipedal wall-climbing robot (WCR) with spiny toe pads. The spiny toe pad is designed based on inspiration of an insect’s tarsal system. Each foot of the robot consists of a pair of opposed linear spiny arrays. The foot employs a pulley system to actuate the arrays via four pairs of tension and compression springs. Two Hall effect sensors are embedded into the robot feet to sense the gripping force by detecting the linear deformation of the springs. The two Hall effect sensors are calibrated and the relationship between the voltage signal output of the sensors and displacement is established before measuring gripping force. Then the consistency and accuracy of Hall effect sensor measurement method are verified by comparing with a commercial force sensor. A horizontal crawling test of the WCR is carried out and the gripping force verse time when the WCR moves. The experimental results show that the measured force history is in accordance with the actual movement states.
Active Load Control of a Regional Aircraft Wing Equipped With Morphing Winglets
Authors: Fonte Federico , Iannaccone Giuseppe , Cimminiello Nicola , Dimino Ignazio , Ricci Sergio
Published: November 2018

Morphing winglets are innovative aircraft devices capable to adaptively enhance aircraft lift distribution throughout the flight mission while providing augmented roll and yaw control capability. Within the scope of the Clean Sky 2 REG IADP, this paper deals with nonlinear simulations of a regional aircraft wing equipped with active morphing winglets in manoeuvring conditions. The fault tolerant morphing winglet architecture is based on two independent and asynchronous control surfaces with variable camber and differential settings capability. The mechanical system is designed to face different flight static and dynamic situations by a proper action on the movable control tabs. The potential for reducing wing and winglet loads by means of the winglet control surfaces is numerically assessed by means of static aeroelastic analyses, using a feedforward manoeuvre load alleviation controller. An electro-mechanical Matlab/Simulink model of the actuation architecture is used as design tool to preliminary evaluate the complete system performance and the ability to cope with the expected morphing aeroshapes. Then, the aeroelastic model of the aircraft is combined with the nonlinear simulator of the response of the winglet actuation system to evaluate a symmetric and asymmetric manoeuvres obtained by a sudden deflection of the main control surfaces. The use of the morphing winglet tabs shows to alleviate the wing loads in such conditions. The introduction of the dynamic actuator model leads to a reduction of the performances with respect to predictions of the static analyses but a reduction of the manoeuvre loads can still be observed.
Functionally Graded Cellular Contact-Aided Compliant Mechanism for Energy Absorption
Authors: Jovanova Jovana , Nastevska Angela , Frecker Mary
Published: November 2018

Cellular contact-aided compliant mechanisms (C3M) are cellular structures with integrated self-contact mechanisms, i.e. the segments can come into contact with each other during deformation. The contact changes the load path and can influence on the mechanism’s performance. Cellular contact-aided compliant mechanisms can be tailored for a specific structural application, such as energy absorption. Nickel Titanium compliant mechanisms can exploit the superelastic effect to improve performance and increase energy absorption. The potential for compliant mechanisms designed specifically for metal additive manufacturing opens the possibility of functional grading and tailoring the material properties locally for achieving overall performance. The combined effort of the geometry and the nonlinear material property increases the local compliance of the unit cell, resulting in higher energy absorption. A functionally graded 3D energy absorbing contact-aided compliant mechanisms cell with curved walls is analyzed. Functionally graded zones of higher flexibility are explored with different superelastic material properties. Introducing different moduli of elasticity as a function of the critical transformation stress results in different energy absorption. This approach can be used for tailoring the overall performance based on the application.
Crack Growth Behavior in NiTi Shape Memory Alloys Under Mode-I Isothermal Loading: Effect of Stress State
Authors: Haghgouyan Behrouz , Karaman Ibrahim , Jape Sameer , Solomou Alexandros , Lagoudas Dimitris C.
Published: November 2018

Fracture behavior in nickel-titanium (NiTi) shape memory alloys (SMAs) subjected to mode-I, isothermal loading is studied using finite element analysis (FEA). Compact tension (CT) SMA specimen is modeled in Abaqus finite element suite and crack growth under displacement boundary condition is investigated for plane strain and plane stress conditions. Parameters for the SMA material constitutive law implemented in the finite element setup are acquired from characterization tests conducted on near-equiatomic NiTi SMA. Virtual crack closure technique (VCCT) is implemented where crack is assumed to extend when the energy release rate at the crack-tip becomes equal to the experimentally obtained material-specific critical value. Load-displacement curves and mechanical fields near the crack-tip in plane strain and plane stress cases are examined. Moreover, a discussion with respect to the crack resistance R-curves calculated using the load-displacement response for plane strain and plane stress conditions is presented.
Smart Material Composites for Discrete Stiffness Materials
Authors: Allen Emily A. , Taylor Lee D. , Swensen John P.
Published: November 2018

This paper presents an initial step towards a new class of soft robotics materials, where localized, geometric patterning of smart materials can exhibit discrete levels of stiffness through the combinations of smart materials used. This work is inspired by a variety of biological systems where actuation is accomplished by modulating the local stiffness in conjunction with muscle contractions. Whereas most biological systems use hydrostatic mechanisms to achieve stiffness variability, and many robotic systems have mimicked this mechanism, this work aims to use smart materials to achieve this stiffness variability. Here we present the compositing of the low melting point Field’s metal, shape memory alloy Nitinol, and a low melting point thermoplastic Polycaprolactone (PCL), composited in simple beam structure within silicone rubber. The comparison in bending stiffnesses at different temperatures, which reside between the activation temperatures of the composited smart materials demonstrates the ability to achieve discrete levels of stiffnesses within the soft robotic tissue.
Static and Dynamic Characterization of Magnetorheological Elastomers Under Shear Mode Operation
Authors: Dargahi Ashkan , Sedaghati Ramin , Rakheja Subhash
Published: November 2018

Static and dynamic properties of six magnetorheological elastomers (MRE) with iron particles volume fraction ranging from 12.5% to 40% were experimentally characterized under shear mode operation. The experiments were designed on the basis of standardized methods defined in ISO-1827 and ISO-4664. The static shear stress-shear strain data obtained under strains up to 30% were used to quantify absolute and relative MR effects of the MREs as functions of magnetic flux density in the 0 to 450 mT range. The MRE specimen with highest iron particles fraction and a softening agent revealed greatest MR effect. The dynamic characteristics of this MRE specimen were then evaluated under harmonic excitations in the 0.1–50 Hz frequency range with shear strain amplitude and magnetic flux density ranging from 2.5 to 20%, and 0 to 450 mT, respectively. The data were then utilized to evaluate elastic and loss shear moduli of the specimen.
Feasibility of Triboelectric Energy Harvesting and Load Sensing in Total Knee Replacement
Authors: Ibrahim Alwathiqbellah , Jain Manav , Salman Emre , Willing Ryan , Towfighian Shahrzad
Published: November 2018

The main goal of this paper is to investigate the feasibility of a triboelectric mechanism to harvest electrical energy for powering a knee implant load measurement sensor under walking activity of daily living. A triboelectric energy harvester is proposed to be placed in between the tibial tray and the UHMWPE bearing of the TKR. To characterize the triboelectric generator, the walking tibiofemoral axial load is approximated as a 1 Hz sine wave signal. An MTS 858 II servo-hydraulic load frame setup is used to transfer the axial load to the triboelectric generator. The optimal resistance is extracted experimentally and found to be 58MΩ. With an applied cyclic load of 2.3 kN at 1 Hz, which is equivalent to the load from normal walking, the generator generated a maximum output of 18 V, and 6 μW of power at the optimal resistance. A power management and digitization circuit is designed based on the harvester output that consumes about 4.74 μW power, which is less than the generated power. Thus, the power harvested from the triboelectric energy harvester can power the load sensing circuitry.
Manufacture of Ultra-Dense Knitted Superelastic Structures
Authors: Koon Henry , Laven Jack , Abel Julianna
Published: November 2018

Knitted Textiles made from Nickel-Titanium (NiTi) shape memory alloy wires are a new structural element with enhanced properties for a variety of applications. Potential advantages of this structural form include enhanced bending flexibility, tailorable in-plane, and through-thickness mechanical performance, and energy absorption and damping. Inspection of the knit pattern reveals a repeating cell structure of interlocking loops. Because of this repeating structure, knits can be evaluated as cellular structures that leverage their loop-based architecture for mechanical robustness and flexibility. The flexibility and robustness of the structure can be further enhanced by manufacturing with superelastic NiTi. The stiffness of superelastic NiTi, however, makes traditional knit manufacturing techniques inadequate, so knit manufacturing in this research is aided by shape setting the superelastic wire to a predefined pattern mimicking the natural curve of a strand within a knit fabric. This predefined shape-set geometry determines the outcome of the knit’s mechanical performance and tunes the mechanical properties. In this research, the impact of the shape setting process on the material itself is explored through axial loading tests to quantify the effect that heat treatment has on a knit sample. A means of continuously shape setting and feeding the wire into traditional knitting machines is described. These processes lend themselves to mass production and build upon previous textile manufacturing technologies. This research also proposes an empirical exploration of superelastic NiTi knit mechanical performance and several new techniques for manufacturing such knits with adjustable knit parameters. Displacement-controlled axial loading tests in the vertical (wale) direction determined the recoverability of each knit sample in the research and were iteratively increased until failure resulted. Knit samples showed recoverable axial strains of 65–140%, which could be moderately altered based on knit pattern and loop parameters. Furthermore, this research demonstrates that improving the density of the knit increases the stiffness of the knit without any loss in recoverable strains. These results highlight the potential of this unique structural architecture that could be used to design fabrics with adjustable mechanical properties, expanding the design space for aerospace structures, medical devices, and consumer products.
Plane Strain Sliding Contact Between a Rigid Cylinder and a Pseudoelastic Shape Memory Alloy Half-Space
Authors: Fernandes Ralston , Boyd James G. , Lagoudas Dimitris C. , El-Borgi Sami
Published: November 2018

This study uses the finite element method to analyze the sliding contact behavior between a rigid cylinder and a shape memory alloy (SMA) semi-infinite half-space. An experimentally validated constitutive model is used to capture the pseudoelastic effect exhibited by these alloys. Parametric studies involving the maximum recoverable transformation strain and the transformation temperatures are performed to analyze the effects that these parameters have on the stress fields during indentation and sliding contact. It is shown that, depending on the amount of recoverable transformation strain possessed by the alloy, a reduction of almost 40 % of the maximum stress in the pseudoelastic half-space is achieved when compared to the maximum stress in a purely elastic half-space. The studies also reveal that the sliding response is strongly temperature dependent, with significant residual stress present in the half-space at temperatures below the austenitic finish temperature.
Viscoelastic Eshelby Analysis of Cardiomyocyte Contraction in the Cell-in-Gel System
Authors: Kazemi-Lari Mohammad , Shaw John , Wineman Alan , Shimkunas Rafael , Izu Leighton , Chen-Izu Ye
Published: November 2018

We present a mathematical model to guide and interpret ongoing Cell-in-Gel experiments, where isolated cardiac myocytes are embedded in a constraining viscoelastic hydrogel, to study mechano-chemo-transduction mechanisms at the single cell level. A recently developed mathematical model, based on the elastic Eshelby inclusion problem, is here extended to account for viscoelasticity of the inclusion (cell) and the matrix (gel). This provides a tool to calculate time-dependent 3D stress and strain fields of a single myocyte contracting periodically inside a viscoelastic matrix, which is used to explore the sensitivity of the cell’s mechanical response to constitutive properties and geometry. A parametric study indicates that increased gel crosslink concentration significantly alters the strain and stress fields inside the cell and creates an increased time-lag in the mechanical response of the cell during contraction.

It is also found that autoregulation at the cellular level in response to afterload, potentially in the form of increased cell stiffness, has a strong influence on cell contraction.
Role of the reactive sputtering deposition power in the phase control of cobalt oxide films
Authors: Azevedo Neto Nilton Francelosi , Leite Douglas M. G. , Lisboa-Filho Paulo N. , da Silva José H. D.
Published: November 2018

The influence of the reactive magnetron sputtering deposition power on determining the stoichiometry and structure of cobalt oxide polycrystalline films is investigated using experimental and simulated data. Direct current discharges with powers in the 80−240W range are tested using a metallic Co target and an Ar+O2 plasma. X-ray diffraction results show that lower deposition powers favor the spinel Co3O4 phase, while higher powers produce films presenting the rocksalt CoO phase. Computer simulations indicate that lower power processes occur in the poisoned target regime, while higher power depositions favor the metallic target regime. Consistent with the simulations, oxygen optical emissions (OI=777.3m) from the plasma show a significant decrease while the cobalt emissions (e.g., the CoI=340.5nm line) are significantly increased when the deposition power is increased. The results show that the film stoichiometry and structure are directly related to the deposition power, at constant O2 flow.
Visualization of organic/inorganic hybridization of UV-cured films with trimethylaluminum by scanning transmission electron microscopy and energy dispersive x-ray spectroscopy
Authors: Nakagawa Masaru , Uehara Takuya , Ozaki Yuki , Nakamura Takahiro , Ito Shunya
Published: November 2018

The organic/inorganic hybridization of photopolymerized resist films for ultraviolet nanoimprint lithography (UV-NIL) through chemical vapor modifications of atomic layer deposition (ALD), sequential infiltration synthesis (SIS), and saturated vapor infiltration (SVI) with an inorganic precursor of trimethylaluminum (TMA) and an oxidant of water was investigated. The hybridization of the bisphenol A-based polymethacrylate resist films was compared between resin-A comprising a monomer with hydroxy groups and resin-B comprising another monomer without hydroxy groups. The elemental depth profiles by scanning transmission electron microscopy and energy dispersive x-ray spectroscopy revealed the following three things. ALD and SIS caused the hybridization of the organic resist films with inorganic alumina near the film surfaces, while SVI caused the hybridization of the resist films entirely. The hydroxy-free resin-B physically adsorbed and chemically fixed more TMA molecules than the hydroxy-containing resin-A. Although SIS progressed the entire hybridization of the resist films, different behaviors of segregation of alumina between the hydroxy-containing resin-A and hydroxy-free resin-B films were confirmed near the film surface, inside, and interface with a silicon substrate. The organic/inorganic hybridization enabled the tuning of the etching rate of the NIL resist masks with a thickness of no thicker than 20 nm in oxygen reactive ion etching often used for the removal of residual layers from imprint patterns in UV-NIL processes.
Individual Factors Affecting Rugby Sevens Match Performance
Authors: Henderson Mitchell J. , Fransen Job , McGrath Jed J. , Harries Simon K. , Poulos Nick , Coutts Aaron J.
Published: November 2018

Purpose: To examine the collective independent influence of a range of individual characteristics on physical and technical match performance during international rugby sevens matches. Methods: Data were collected from 20 international rugby sevens players from 1 team across 1 season. Activity profiles were measured using wearable microtechnology devices, and technical performance measures were collected from match video analysis. Subjective well-being measures were collected using a well-being questionnaire completed on the morning of main training days, and groin-squeeze assessments at 0° and 60° knee flexion were also conducted using a sphygmomanometer. Assessments of aerobic fitness were completed periodically across the season, including time to complete a 2-km run and final velocity during the 30:15 Intermittent Fitness Test (VIFT). A principal-components analysis was conducted to reduce the dimensionality of the physical and technical variables into single-factor values. Linear mixed models were then constructed to examine the collective influence of a range of individual contextual variables on physical and technical performance factors. Results: Increased muscle soreness, stress, and VIFT were associated with trivial to small increases in physical and technical performance values, whereas trivial to small decreases were associated with higher perceived recovery, body weight, and groin squeeze (0° knee flexion). Conclusions: A range of well-being metrics are required to account for a significant portion of the variance in physical and technical performance. These factors may be manipulated by coaches or practitioners to achieve favorable physiological readiness that may lead to improved match performance.
Single-Nucleotide-Polymorphism-Panel Population-Genetics Approach Based on the 1000 Genomes Database and Elite Soccer Players
Authors: Monnerat Gustavo , Maior Alex S. , Tannure Marcio , Back Lia K.F.C. , Santos Caleb G.M.
Published: November 2018

Purpose: Soccer is one of the most popular sports worldwide, a physical activity of great physiological demand and complexity. Currently, numerous trials involving physiological responses such as hypertrophy, energy expenditure, vasodilation, cardiac output, VO2max, and recovery have supported the possibility of genomic predictors’ affecting performance. In a complementary way to association studies with single nucleotide polymorphisms (SNPs), the objective was to evaluate if the use of population genetics data from human-genomics databases can provide information for a better understanding of the relationship between heritability and sport performance. Methods: The study included 25 healthy male professional soccer players (25.5 [4.3] y, 177.4 [6.4] cm, 76.4 [6.4] kg, body fat 10.5% [4.3%]) from the Brazilian first-division soccer club. Anthropometric measurements and field and isokinetic tests were performed to evaluate performance and physiologic parameters of subjects. Moreover, 10 genetic polymorphisms previously related to performance were genotyped. The genotypes of the same polymorphisms were obtained for 2504 individuals from the populations deposited in the 1000 Genomes database. A principal-component analysis and matrix genetic-distances approach (Fst) were evaluated. Results: As expected, the admixture Brazilian population has numerous genetic similarities with the European and American populations from genomic databases. Although the African component is absolutely recognized in genomes from the Brazilian population, using the specific performance-related SNPs, surprisingly the African population was one of the most genetically distant of the players (P < .00001). Conclusions: The early results suggest a selective pressure on genes of elite soccer players, possibly related simultaneously to physical-performance, environmental, cognitive, and sociocultural aspects.
Single-Leg Squat Delicacies—The Position of the Nonstance Limb is an Important Consideration
Authors: Olivier Benita , Quinn Samantha-Lynn , Benjamin Natalie , Green Andrew Craig , Chiu Jessica , Wang Weijie
Published: November 2018

Context: The single-leg squat task is often used as a rehabilitative exercise or as a screening tool for the functional movement of the lower limb. Objective: To establish the effect of 3 different positions of the nonstance leg on 3-dimensional kinematics, muscle activity, and center of mass displacement during a single-leg squat. Design: Within-subjects, repeated-measures design. Setting: Movement analysis laboratory. Participants: A total of 10 participants, aged 28.2 (4.42) years performed 3 squats to 60° of knee flexion with the nonstance (1) hip at 90° flexion and knee at 90° flexion, (2) hip at 30° flexion with the knee fully extended, or (3) hip in neutral/0° and the knee flexed to 90°. Main Outcome Measures: Trunk, hip, knee and ankle joint angles, and center of mass displacement were recorded with inertial sensors while muscle activity was captured through wireless electromyography. Results: Most trunk flexion (21.38° [18.43°]) occurred with the nonstance hip at 90° and most flexion of the stance hip (23.10° [6.60°]) occurred with the nonstance hip at 0°. Biceps femoris activity in the 90° squat was 40% more than in the 0° squat, whereas rectus femoris activity in the 0° squat was 29% more than in the 90° squat. Conclusion: The position of the nonstance limb should be standardized when the single-leg squat is used for assessment and be adapted to the aim when used in rehabilitation.