bluuebunny/crossref_metadata_2025 huggingface dataset:
Forced Vibration Analysis of FG-Graphene Platelet Reinforced Polymer Composite Shells Bonded With Piezoelectric Layers Considering Electroelastic Nonlinearities
Authors: Rao M. N. , Schmidt R. , Schröder K.-U.
Published: November 2018

In the present article, we focus on the forced vibration and control analysis of functionally graded (FG) graphene-polymer composites bonded with piezoelectric layers considering strong electric fields. Different non-uniform gradient distributions of graphene platelets (GPLs) are assumed through the thickness direction. The Modified Halpin-Tsai micromechanics model is used to obtain the effective material properties of GPL/polymer composites. Electromechanical coupling of piezoelectric layers is described by two rotationally invariant non-linear constitutive relations. A four-node shell element considering transverse shear effect based on the Reissner-Mindlins hypothesis has been developed for forced vibration and control analysis of smart FG-GPL/composites using the principle of virtual work considering nonlinear material law for the piezoelectric layers. The developed element is verified and compared with the numerical results those available in the literature. Different configurations of FG-GPL composite shells have been analysed and discussed to compare in terms of settling time, first resonance frequency and absolute amplitude corresponding to first resonant frequency by carrying out time and frequency response analysis, and the effects of weight fraction of GPLs on vibration response of such shell structures are also discussed. The influence of electromechanical nonlinear constitutive relations is also presented and discussed by performing active control analysis on different FG-GPL composite shell structures. Moreover, the results show that the GPL distribution and weight-fraction of GPLs have a significant effect on the vibration and damping characteristics of the FG-GPL composite shell structures.
Impulsively-Excited Bistable Energy Harvester Combined With Electromagnetic Mechanism
Authors: Fang Shitong , Liao Wei-Hsin
Published: November 2018

Impulsive energy provides a promising source for energy harvesting techniques due to their high amplitude and abundance in a living environment. The sensitivity to excitation of bistable energy harvesters makes them feasible for impulsive-type events. In this paper, a novel impulsively-excited bistable energy harvester with rotary structure and plectrum is proposed to achieve plucking-based frequency up-conversion. The input excitation is converted to plucking force on the bistable energy harvester, so as to help it go into the high-energy orbit. The piezoelectric and electromagnetic transduction mechanisms are combined by incorporating a coil to the structure in order to overcome the increase of damping introduced by the bistable configuration. As a result, high-energy output and broadband performance could be realized. Impact mechanics is employed to develop a comprehensive model, which could be used to analyze the nonlinear dynamics and predict the system responses under various plucking velocities and overlap lengths. Numerical simulation shows that the bistable energy harvester could experience large-amplitude oscillation under impulsive excitation and the hybrid configuration outperforms the standalone ones under high damping ratio and low coupling coefficient. The proposed design is targeted to be applied on the turnstile gates of the subway station. Less human effort would be needed when passengers pass the turnstile gate due to the snap-through motion of bistability.
Horizontal Planform Morphing Tail for an Avian Inspired UAV Using Shape Memory Alloys
Authors: Haughn Kevin P. T. , Gamble Lawren L. , Inman Daniel J.
Published: November 2018

Unlike most modern aircraft, which have a vertical tail component, birds fly utilizing a purely horizontal tail. In order to provide control normally associated with a vertical rudder, bird’s tails are incredibly mobile, twisting, pitching, and widening to perform necessary aerial maneuvers. This research primarily focuses on the development and testing of a mechanical planform morphing horizontal control surface, aiming to emulate the tail-spread control action of birds. This horizontal control surface is implemented on a small, tailless, avian inspired unmanned aerial vehicle (UAV). In this research, the horizontal control surface, made entirely of 3D printed material, comprises a rigid overlapping top layer held together by a soft and elastic honeycomb bottom layer, allowing for shape morphing without compromising structural integrity required to withstand aerodynamic forces. Using the relatively large strain and strength offered by shape memory alloy (SMA) springs, the 3D printed horizontal tail undergoes a notable and consistent geometric change. To quantify the system’s performance, the tail width and center was measured while actuating the springs through a range of frequencies from 0.01 to 10 Hz. Preliminary experiments were conducted in a 1ft. × 1 ft. open loop wind tunnel at the University of Michigan at wind speeds of 5, 10 and 15 m/s to quantify the effects of aerodynamic loading on actuation magnitude and speed.
Energy Harvesting From Ankle: Generating Electricity by Harvesting Negative Work
Authors: Liu Mingyi , Tai Wei-Che , Zuo Lei
Published: November 2018

Portable, wearable, and mobile devices are becoming more and more popular in the past two decades. Those devices rely on batteries heavily as power source. However, the limited life span of batteries constitutes a limitation. Human body energy harvesting has the potential to power those devices, thus replacing batteries or extending battery life. Harvesting positive muscle work from human body can be a burden, and exhausts the wearer. In this paper, we developed a biomechanical energy-harvesting device that generates electricity by harvesting negative work during human walking. The energy harvester mounts on the ankle and selectively engages to generate power between the middle stance phase and terminal stance phase, during which the calf muscles do negative work. The device harvests negative energy by assisting muscles in performing negative work. Test subjects walking with the device produced an average of 0.94 watts of electric power. From treadmill test, the device was shown to harvest energy only during the negative work phase, as a result it has the potential to not to increase the metabolic cost. Producing substantial electricity without burden on the wearer makes this harvester well suited for powering wearable, portable, and mobile devices.
Tensile Properties of 3D-Printed Polycarbonate/Carbon Nanotube Nanocomposites
Authors: Kalia Karun , Ameli Amir
Published: November 2018

Fused deposition modeling (FDM) is highly commercialized Rapid Prototyping (RP) technology for its ability to build complex parts with low cost in a short period of time. The process parameters in the FDM play a vital role in the mechanical properties of the polymeric parts. Most of the research studies show that the variable parameters such as orientation, layer thickness, raster angle, raster width, and air gap are some of the key parameters that affect the mechanical properties of FDM-processed polymeric parts. However, no reports have been made regarding the influence of nozzle diameter with raster width on the tensile properties of FDM fabricated polymeric parts.

This work was devoted to achieving improved and isotropic mechanical properties in polycarbonate (PC) and PC/carbon nanotube (PC/CNT) nanocomposites by investigating the effect of printing parameters in FDM process. The nozzle diameter to raster width ratio, α was found to significantly affect the mechanical properties. The printing direction dependency in tensile properties were studied with the ratio α < 1 and α≥ 1 at three different raster angles of 0°, 45°/−45° and 90°. For α < 1, Ultimate tensile strength and modulus of elasticity were higher for 0°, compared to 45°/−45° and 90° raster angles. However, for α ≥ 1, the ultimate tensile strength and the modulus of elasticity showed little dependency to print direction. This certainly determines the decrease in anisotropy at higher values of α. Mesostructure characterization with microscopy and image analysis were used to further explain the printing behavior and the resultant properties of the printed samples.
Design of a Variable Stiffness Wrist Brace With an Origami Structural Element
Authors: Oliveira Marcos B. , Liu Chang , Zhao Mengtao , Felton Samuel M.
Published: November 2018

This paper presents a motor driven wrist brace that can adjust its stiffness by changing its mesoscale geometry. The design involves a plate structure that folds from a flexible flat shape to a stiff corrugated shape by means of a motor driven tendon. The structure is built using a laminate of rigid and flexible layers, with embedded flexural hinges that allow it to fold. The paper proposes a simplified analytical model to predict stiffness, and physical three-point bending tests indicate that the brace can increase its stiffness up to fifty times by folding.
Design of a Beam-Based Variable Stiffness Actuator via Shape Optimization in a CAD/CAE Environment
Authors: Bilancia Pietro , Berselli Giovanni , Scarcia Umberto , Palli Gianluca
Published: November 2018

Industrial robots are commonly designed to be very fast and stiff in order to achieve extremely precise position control capabilities. Nonetheless, high speeds and power do not allow for a safe physical interaction between robots and humans. With the exception of the latest generation lightweight arms, purposely design for human-robot collaborative tasks, safety devices shall be employed when workers enter the robots workspace, in order to reduce the chances of injuries. In this context, Variable Stiffness Actuators (VSA) potentially represent an effective solution for increasing robot safety. In light of this consideration, the present paper describes the design optimization of a VSA architecture previously proposed by the authors. In this novel embodiment, the VSA can achieve stiffness modulation via the use of a pair of compliant mechanisms with distributed compliance, which act as nonlinear springs with proper torque-deflection characteristic. Such elastic elements are composed of slender beams whose neutral axis is described by a spline curve with non-trivial shape. The beam geometry is determined by leveraging on a CAD/CAE framework allowing for the shape optimization of complex flexures. The design method makes use of the modeling and simulation capabilities of a parametric CAD software seamlessly connected to a FEM tool (i.e. Ansys Workbench). For validation purposes, proof-concept 3D printed prototypes of both non-linear elastic element and overall VSA are finally produced and tested. Experimental results fully confirm that the compliant mechanism behaves as expected.
Essentially Nonlinear Piezoelectric Attachment for Aeroelastic Flutter Suppression
Authors: Otsubo Gabriela Mayumi de Freitas , De Marqui Carlos
Published: November 2018

Various researchers have investigated the behavior of a linear mechanical oscillator weakly coupled to a nonlinear mechanical attachment that has essential stiffness nonlinearity. Under certain conditions, the essentially nonlinear attachment acts as a nonlinear energy sink (NES) and one-way energy transfer from the main structure to the attachment can be achieved. Since an essentially nonlinear attachment does not possess any preferential resonance frequency, they have increased robustness against detuning, enabling frequency-wise wideband performance. In this work, the interactions between an essentially nonlinear piezoelectric attachment and an electromechanically coupled two-degree-of-freedom (2-DOF) aeroelastic typical section are studied. The governing equations of the electromechanically coupled typical section with piezoelectric coupling added to the plunge DOF are presented. An equivalent electrical model of the coupled aeroelastic system is presented and combined to a nonlinear shunt circuit. The performance of the piezoelectric NES to modify the aeroelastic behavior of the typical section is discussed using the short-circuit condition as a reference case. Furthermore, the robustness of the piezoelectric NES against detuning is also investigated by changing some parameters of the typical section.
Numerical Techniques to Model Fractional-Order Nonlinear Viscoelasticity in Soft Elastomers
Authors: Miles Paul , Pash Graham , Oates William , Smith Ralph C.
Published: November 2018

Dielectric elastomers are employed on a wide variety of adaptive structures. Many of these soft elastomers exhibit significant rate-dependencies in their response. Accurately quantifying this viscoelastic behavior is non-trivial and in many instances a nonlinear modeling framework is required. Fractional-order operators have been applied to modeling viscoelastic behavior for many years, and recent research has shown fractional-order methods to be effective for nonlinear frameworks. This implementation can become computationally expensive to achieve an accurate approximation of the fractional-order derivative. In this paper, we demonstrate the effectiveness of using quadrature techniques in approximating the Riemann-Liouville definition for fractional derivatives in the context of developing a nonlinear viscoelastic model.
An Adaptive Structure Topology Optimization Approach Applied to Vertebral Bone Architecture
Authors: DiCarlo Anthony A. , Gallagher John A.
Published: November 2018

Bone is a highly adaptive biological structure. Following Wolff’s law, bone realigns and grows to adapt to its mechanical environment. This leads to structural heterogeneity of trabecular bone and orthotropic symmetry of the elastic properties. Determining the bone alignment and material properties for living patients is difficult and involves implantation of force and displacement sensors on the bone to determine the compliance and stiffness properties. Micro-computed tomography along with finite element modeling have been limited to the vertebrae of donor cadavers to evaluate trabecular architecture, material properties, and density. Here, an adaptive structure topology optimization algorithm is presented and used to predict trabecular architecture. The algorithm predicts the optimal structure by minimizing the global compliance. The lumbar 1 (L1) vertebra is used as an example. Loads common to L1 vertebrae are applied and bone volume fraction measurements that can be taken easily from living patients through bone mineral density scans are used as the only inputs. The mathematical model is an adaptation of “99 Line Topology Optimization Code Written in Matlab” developed by Sigmund (2001). Bone is locally assumed to be isotropic with an elastic modulus of 13 GPa and the Poisson ratio of 0.3 applied to each element. The resulting structural heterogeneity results in global orthotropic relations. The model uses bone volume fraction and the loading orientation as inputs and gives the corresponding ideal bone structure geometry as an output. The trabecular structure can be predicted solely from the results of a bone mineral density scan. Finite element analysis of the optimized structure is then conducted and the global material properties are determined. While this model is for two-dimensional examples representing planes within the vertebral bone, it is extended to three-dimensional modeling to develop the cortical bone geometry and define the total volume. Matlab is then used to run the topology optimization simulation. The ideal structure is defined by optimizing for a prescribed displacement field of the system following the implementation of a gradient descent optimization method. The results are compared to published values from a combined experimental and numerical procedure. The procedure on sectioned vertebrae reported average ratios between elastic moduli of E1/E2 = 5.2, E1/E3 = 8.8, and E2/E3 = 1.4. Results between the models and the previously published data yield similar transversely isotropic symmetry in the elastic moduli of trabecular bone. However, the elastic moduli ratios are not quite in agreement. Improving the accuracy of the boundary conditions and loading of the finite element model may improve the correlation between the optimization models and published data.
Investigation of Elastic Meta-Structures With Periodic Localized Stress-Fields
Authors: Albakri Mohammad I. , Tarazaga Pablo A.
Published: November 2018

Elastic meta-structures, with wave propagation control capabilities, have been widely investigated for mechanical vibrations suppression and acoustics attenuation applications. Periodic architected lattices, combined with mechanical or electromechanical resonators, are utilized to form frequency bands over which the propagation of elastic waves is forbidden, known as bandgaps. The characteristics of these bandgaps, in terms of frequency range and bandwidth, are determined by the local resonators as well as characteristics of the individual cells out of which the structure is composed.

In this study, the effectiveness of local stress fields as a tool for bandgap tuning in active, elastic meta-structures is investigated. A finite beam undergoing axial and flexural deformations, with a spatially periodic axial loads acting on it, is chosen to demonstrate the concept. The beam is first divided into several sections where localized stress-fields are varied periodically. Lateral and longitudinal deformations of the beam are described, respectively, by the Timoshenko beam theory and the Elementary rod theory. The Frequency-domain Spectral Element Method is then employed to calculate the forced-vibration response of the structure. The effects of the local state-of-stress on the width and frequency of the resulting bandgaps are investigated.
Prediction of Dielectric Electroactive Polymer Material Functionality
Authors: Newell Brittany , Garcia Jose , Vindrola Angello
Published: November 2018

Dielectric electroactive actuators (DEAs) are polymer materials capable of reallocating their shapes mechanically due to an electric stimulus [1]. They can also be used as sensors by producing an electrical change from an induced mechanical deformation [2]. However, production of these materials using traditional manufacturing methods is a challenging process. The use of additive manufacturing promises to be an improved method to overcome those challenges. In addition, selection of dielectric materials that can function as DEAs and are capable of being produced through additive manufacturing is challenging.

The actuation capabilities of the DEA depend heavily on the electrical and mechanical material properties of the dielectric material used to build it, and not all dielectric materials have the capacity to function as DEAs. The likelihood of a material functioning as a DEA is difficult to predict due to the large number of variables. Therefore, this paper introduces a simple method for comparing materials, particularly 3-D printed materials for their viability to be used as DEAs.

The study proposes a method to compare 3-D printable materials by using coefficients calculated from the materials’ electromechanical properties. This value is then compared to an ideal DEA material. The higher the value, the better the 3-D printable material will be in comparison to a selected optimal DEA material. The coefficient is based on a linear elastic model that describes the strain of the material in relation to the electromechanical pressure applied as a result of supplied voltage.

This study tested three materials using a quantitative method along with experimental verification. The study demonstrates the relationship between the predictive coefficients and the physical actuation responses with disc-type actuators providing a simple method for predicting actuation potential of 3-D printable DEA material candidates.
Composite Laminate Fatigue Damage Detection and Prognosis Using Embedded Fiber Bragg Gratings
Authors: Todd Michael , Gregory William , Key Christopher , Yeager Michael , Ye Jordan
Published: November 2018

In many structural applications the use of composite material systems in both retrofit and new design modes has expanded greatly. The performance benefits from composites such as weight reduction with increased strength, corrosion resistance, and improved thermal and acoustic properties, are balanced by a host of failure modes whose genesis and progression are not yet well understood. As such, structural health monitoring (SHM) plays a key role for in-situ assessment for the purposes of performance/operations optimization, maintenance planning, and overall life cycle cost reduction. In this work, arrays of fiber Bragg grating optical strain sensors are attached to glass-epoxy solid laminate composite specimens that were subsequently subjected to specific levels of fully reversed cyclic loading. The fatigue loading was designed to impose strain levels in the panel that would induce damage to the laminate at varying numbers of cycles. The objectives of this test series were to assess the ability of the fiber Bragg grating sensors to detect fatigue damage (using previously developed SHM algorithms) and to establish a dataset for the development of a prognostic model to be applied to a random magnitude of fully reversed strain loading. The prognostic approach is rooted in the Failure Forecast Method, whereby the periodic feature rate-of-change was regressed against time to arrive at a failure estimate. An uncertainty model for the predictor was built so that a probability density function could be computed around the time-of-failure estimate, from which mean, median, and mode predictors were compared for robustness.
Traveling Waves As a De-Powdering Process for Additively Manufactured Parts
Authors: Tenney Charles M. , Malladi Vijaya V. N. Sriram , Musgrave Patrick F. , Williams Christopher B. , Tarazaga Pablo A.
Published: November 2018

Steady-state traveling waves in structures have been previously investigated for a variety of purposes including propulsion of objects and agitation of a surrounding medium. In the field of additive manufacturing, powder bed fusion (PBF) is a commonly used process that uses heat to fuse regions of metallic or polymer powders within a loose bed. PBF processes require post-process removal of loose powder, which can be difficult when blind holes or complex internal geometry are present in the fabricated part. Here, a preliminary investigation of a simple part is conducted examining the use of traveling waves for post-process de-powdering of additively manufactured specimens.

The generation of steady-state traveling waves in a structure is accomplished through excitation at a frequency between two adjacent resonant frequencies of the structure, resulting in two-mode excitation. This excitation can be generated by bonded piezoceramic elements actuated by a sinusoidal voltage signal. The response of the structure is affected by the parameters of the excitation, such as the particular frequency of the voltage signal, the placement of the piezoceramic actuators, and the phase difference in the signals applied to different actuators. Careful selection of these parameters allows adjustment of the quality, wavelength, and wave speed of the resulting traveling waves.

In this work, open-top rectangular box specimens composed of sintered nylon powder and coated with fine sand are used to represent freshly fabricated parts yet-to-be cleaned of un-sintered powder. Steady-state traveling waves are excited in the specimens while variations in the frequency content and phase differences between actuation points of the excitation are used to affect the characteristics of the dynamic response. The effectiveness of several response types for the purpose of moving un-sintered nylon powder within the specimens is investigated.
Design and Analysis of SMA Woven Fabric
Authors: Skalitzky Amanda , Gurley Austin , Beale David , Kubik Kyle
Published: November 2018

Shape Memory Alloys (SMAs) are often used for robotic, biomedical, and aerospace applications because of their unique ability to undergo large amounts of stress and strain during thermomechanical loading compared to traditional metals. While SMAs such as NiTi have been used in wire, plate, and tubular forms, NiTi as a woven dry fabric has yet to be analyzed for use as protective materials and actuators. Applications of SMA fabric as a “passive” material include shields, seatbelts, watchbands and window screens. Applications as an “active” material include robotic actuators, wearable medical and therapy devices, and self-healing shields and screens. This paper applies a macro-mechanical model from composites analysis to NiTi plain woven fabric to determine the effective elastic constants. The fabric model is based on actual weave geometry, including the presence of open gaps and wire cross-sectional area, and with the same diameter and alloy in the warp and weft. A woven NiTi ribbon has been manufactured (Figure 1) using a narrow weaving machine and has been tested in uniaxial tension. Planar fabric constants were measured at a range of temperatures. The analytically and experimentally derived constants for various weave patterns and cover factor combinations are presented and compared. It was determined that in uniaxial tension the fabric behaves like a collection of unidirectional wires, but has 78% of the rigidity, on average, across all test temperatures. This result is predicted by the fabric model with a 16% error, demonstrating that the proposed analytical model offers a useful tool for design and simulation of SMA fabrics.
Switchable Bistability in 3D Printed Shells With Bio-Inspired Architectures and Spatially Distributed Pre-Stress
Authors: Ang Karl Jin , Riley Katherine S. , Faber Jakob , Arrieta Andres F.
Published: November 2018

Using fused deposition modeling (FDM) 3D printing, we combine a bio-inspired bilayer architecture with distributed pre-stress and the shape memory behavior of polylactic acid (PLA) to manufacture shells with switchable bistability. These shells are stiff and monostable at room temperature, but become elastic and bistable with fast morphing when heated above their glass transition temperature. When cooled back down, the shells retain the configuration they were in at the elevated temperature and return to being stiff and monostable. These programmed deformations result from the careful design and control of how the filament is extruded by the printer and therefore, the resulting directional pre-stress. Parameter studies are presented on how to maximize the pre-stress for this application. The shells are analyzed using nonlinear finite element analysis. By leveraging the vast array of geometries accessible with 3D printing, this method can be extended to complex, multi-domain shells, including bio-inspired designs.
Progress of Active Thermometry Method in Submarine Pipeline Scour Monitoring
Authors: Zhao Xuefeng , Yan Xu , Zhang Xinwang , Li Weijie , Ba Qin , Li Le
Published: November 2018

Scour is one of the most important problems lead to submarine pipeline failure. In this paper, several scour monitoring techniques based on active thermometry method was introduced. Firstly, DS18B20 digital temperature sensor was used to monitor the surface heat change pattern in the heating process in different media like sand and water. The test results validated the feasibility of the active thermometry method. Then, the submarine pipeline scour monitoring system based on Brillouin distributed optical fiber sensing technique was developed. Due to the high cost of monitoring system of distributed Brillouin fiber optical sensing technology. In order to reduce costs, common armed fiber optic cable was used as both heating and sensing unit, and Raman sensing with relatively lower cost was utilized for distributed temperature sensing for scour monitoring. Laboratory test results shown there is good potential of active thermometry method for scour monitoring in practical field.
AIRGREEN2 - Clean Sky 2 Programme: Adaptive Wing Technology Maturation, Challenges and Perspectives
Authors: Ameduri Salvatore , Concilio Antonio , Dimino Ignazio , Pecora Rosario , Ricci Sergio
Published: November 2018

By introducing the progresses on Morphing currently achieved within the European Project “AIRGREEN2”, in Clean-Sky 2 GRA platform, this work presents a review of the research step forwards accomplished in the last decade by three Italian Partners largely active in the field: the Italian Aerospace Research Centre, the University of Naples “Federico II” and the Politecnico of Milano. A chronologic overview is at first presented, revisiting the research programs and the achieved results; an organic development path has been then built, starting from low TRL achievements up to arrive at the most complete technical accomplishments, characterized by a high level of integration and targeting specific aerospace applications.
Color Changing Actuators: A Review Towards Designing Cyanosis in a Baby Manikin Simulator
Authors: Azmi Nur Fatihah Binti , Delbressine Frank , Feijs Loe , Andriessen Peter , Pols Tessa
Published: November 2018

This paper reports on the realistic color generation and color change due to cyanosis which refers to the blue coloration around the lips’ area. The design requirements for the manikin were identified based on the color measurement and corrections of cyanosis in images of real babies. The classification of the literature study is according to physics working principles based on energy. A reversible color changing mechanism is achievable by stimuli of external energy such as electric, heat, mechanical, light and magnetic energy. Here, the overview of cyanosis coloration is presented to serve as a basis for a new design of a physiologically-inspired color change actuator for cyanosis in a baby manikin. A state-of-the-art review of color change actuators in the desired color ranges, switching time, dimensions and shape, including the safety issues of each actuating working principle, is presented. Employing a simplified version of the Weighted Objectives method, the practical value of the actuator types was evaluated by assigning scores to each actuator’s type, which indicates their criteria. This work highlights the design’s specifications which aim to design a cyanosis color change actuator in the near future. Ultimately, the envisioned system will increase the efficiency of the visual evaluation and assessment of cyanosis coloration in medical training.
Structural Health Monitoring of Solid Rocket Propellants Using Piezoresistive Properties of Dispersed Carbon Nano-Tube Sensing Networks
Authors: Shirodkar Nishant , Rocker Samantha , Seidel Gary D.
Published: November 2018

There has been increasing focus in the area of in-situ structural health monitoring since the advent of embedded nano-composites. This experimental research investigates the structural health monitoring abilities of polymer bonded energetics embedded with a uniformly dispersed but randomly oriented carbon nanotube (CNT) sensing network within the polymer binder. A common formulation of the recent solid propellants consists of ammonium perchlorate (oxidizer) and aluminum powder (combustive fuel)-often shaped using a polymer binder, rather than the older techniques of power pressing. Since this study focuses on the structural health of the material and not its thermal properties, monoclinic sugar crystals were used as a substitute for ammonium perchlorate as it has very similar mechanical properties and is much safer in terms of material handling. Thus, a combination of sugar crystals and aluminum powder bound by a Polydimethylsiloxane (PDMS) binder is fabricated in varying concentrations to simulate actual solid rocket propellants. The main focus of this study lies in characterizing the mechanical and electrical properties of the CNT embedded energetic material through subjecting it under mechanical loads; followed by a detailed observation and study of the real time electro-mechanical response under tension and compression. The addition of carbon nanotubes to the polymer binder, thus translates to a real time sensing technique for detection of multi-scale damage in polymer bonded energetics. The results of this study aim to establish a proof of concept for CNT embedded structural health monitoring systems.
Monolithic Morphing Rib With Selective Stiffness From Embeddable Bi-Stable Elements
Authors: Boston D. Matthew , Arrieta Andres , Rivas-Padilla Jose
Published: November 2018

A trade-off exists in compliant morphing structures between weight, adaptability, and load-carrying capacity. A truss-like structure utilizing a selectively stiff, bi-stable element is proposed to provide a solution to this problem. The design space of the element is explored in a parameter study using a finite element model. The element is embedded in a rib to correlate its behavior to that of the element in isolation. Finally, an aeroelastic analysis is conducted on the rib to determine the response of the structure to aerodynamic loading.
Development of Thermal Switches Based on Shape Memory Alloy Actuators
Authors: Voigt Immanuel , Drossel Welf-Guntram , Eppler Christoph , Pagel Kenny , Bucht André
Published: November 2018

In machine tool engineering, the impact of thermal issues on machine precision and efficiency has been outlined in numerous studies. One of the major challenges is the energy-efficient distribution of heat within the machine structure. In order to control occurring heat fluxes without additional energy input into the machine tool, smart materials can be used for load-dependent adjustment of heat transfer characteristics.

The present study illustrates the development and examination of heat transfer switch mechanisms using shape memory alloys. Experimental and numerical results demonstrate how different types of actuators can be used to enable an energy self-sufficient thermal switch function between heat source and heat sink. Different scenarios are considered and the combination of thermal switches with highly conductive heat-transfer devices and latent heat storages is evaluated.
Feature Recognition and Detection for Common Maintenance Tools Based on Deep Learning
Authors: Liu Chengcheng , Zhang Kuan , Li Peigang , Li Shengyuan , Zhao Xuefeng
Published: November 2018

With the rapid development of rail traffic, the importance of railway overhaul is becoming increasingly prominent. Making an inventory on tools is an important step that railway workers must take before and after railway inspection. The tools left on the railway will cause great harm to train safety. To avoid this happening, the commonly used method is manual inventory at present, which is time-consuming, laborious and easily leads to omissions. In order to overcome these shortcomings, this paper proposes a Faster Region-based Convolutional Neural Network (Faster R-CNN)-based method for tools inventory. To realize the method, a Faster R-CNN architecture based on ZF-Net is modified and a database including a large number of images for 10 types of tools is built. Then the Faster R-CNN is trained and validated using the built database. The performance of the trained Faster R-CNN is evaluated using some new images which are not be used for training process. The result shows 95.0325% average precision (AP) ratings for 10 different types of tools and proves the proposed method is effective.
Measuring Physical Load in Soccer: Strengths and Limitations of 3 Different Methods
Authors: Fischer-Sonderegger Karin , Taube Wolfgang , Rumo Martin , Tschopp Markus
Published: November 2018

Purpose: To investigate the strengths and limitations of different indicators to measure physical load. Furthermore, indicators were evaluated for discrimination between performance levels and playing positions. Methods: Ninety positional match files from 70 elite players and 91 match files from 69 subelite players were collected during 14 official under-18 matches using a local position measurement system. Indicators are calculated from speed, absolute acceleration (acc-abs), or percentage acceleration (acc-%). The acc-% describes the level of acceleration depending on the maximal voluntary acceleration (amax) for each initial running speed. Effect sizes (ES) were used to determine discriminative ability. Results: The number of high accelerations largely depended on the method (absolute threshold [>3 m·s−2 and >4 m·s−2] 120 and 59 efforts; high percentage threshold [>75% amax] 84 efforts). Only a small number of highly accelerated efforts reached speeds considered high-speed running (>19.8 km·h−1: 32.6%). More high acc-% exists from initial running speed >2 m·s−1 (23.0) compared with acc-abs (>3 m·s−2 14.4, >4 m·s−2 5.9). Elite players achieve higher values in most performance indicators, with ES being highest for the number of high acc-% (ES = 0.91) and high acc-abs (>3 m·s−2 ES = 0.86, >4 m·s−2 ES = 0.87), as well as for covered distance in jogging (ES = 0.94). Conclusions: Estimated physical load, discriminative ability of physical indicators, and positional requirements largely depend on the applied method. A combination of speed-based and acc-% methods is recommended to get a comprehensive view.
Impaired Heat Adaptation From Combined Heat Training and “Live High, Train Low” Hypoxia
Authors: McCleave Erin L. , Slattery Katie M. , Duffield Rob , Saunders Philo U. , Sharma Avish P. , Crowcroft Stephen , Coutts Aaron J.
Published: November 2018

Purpose: To determine whether combining training in heat with “Live High, Train Low” hypoxia (LHTL) further improves thermoregulatory and cardiovascular responses to a heat-tolerance test compared with independent heat training. Methods: A total of 25 trained runners (peak oxygen uptake = 64.1 [8.0] mL·min−1·kg−1) completed 3-wk training in 1 of 3 conditions: (1) heat training combined with “LHTL” hypoxia (H+H; FiO2 = 14.4% [3000 m], 13 h·d−1; train at <600 m, 33°C, 55% relative humidity [RH]), (2) heat training (HOT; live and train <600 m, 33°C, 55% RH), and (3) temperate training (CONT; live and train <600 m, 13°C, 55% RH). Heat adaptations were determined from a 45-min heat-response test (33°C, 55% RH, 65% velocity corresponding to the peak oxygen uptake) at baseline and immediately and 1 and 3 wk postexposure (baseline, post, 1 wkP, and 3 wkP, respectively). Core temperature, heart rate, sweat rate, sodium concentration, plasma volume, and perceptual responses were analyzed using magnitude-based inferences. Results: Submaximal heart rate (effect size [ES] = −0.60 [−0.89; −0.32]) and core temperature (ES = −0.55 [−0.99; −0.10]) were reduced in HOT until 1 wkP. Sweat rate (ES = 0.36 [0.12; 0.59]) and sweat sodium concentration (ES = −0.82 [−1.48; −0.16]) were, respectively, increased and decreased until 3 wkP in HOT. Submaximal heart rate (ES = −0.38 [−0.85; 0.08]) was likely reduced in H+H at 3 wkP, whereas CONT had unclear physiological changes. Perceived exertion and thermal sensation were reduced across all groups. Conclusions: Despite greater physiological stress from combined heat training and “LHTL” hypoxia, thermoregulatory adaptations are limited in comparison with independent heat training. The combined stimuli provide no additional physiological benefit during exercise in hot environments.
The Influence of Hamstring Muscle Peak Torque and Rate of Torque Development for Sprinting Performance in Football Players: A Cross-Sectional Study
Authors: Ishøi Lasse , Aagaard Per , Nielsen Mathias F. , Thornton Kasper B. , Krommes Kasper K. , Hölmich Per , Thorborg Kristian
Published: November 2018

Purpose: To investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development, RTD) vs sprint performance in elite youth football players. Methods: Thirty elite academy youth football players (16.75 [1.1] y, 176.9 [6.7] cm, 67.1 [6.9] kg) were included. Isometric peak torque (in Newton meters per kilogram) and early- (0–100 ms) and late- (0–200 ms) phase RTD (RTD100, RTD200) (in Newton meters per second per kilogram) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m-sprint trial. Mechanical sprint variables (maximal horizontal force production [FH0, in Newtons per kilogram], maximal theoretical velocity [V0, in meters per second], maximal horizontal power output [Pmax, in watts per kilogram]) and sprint split times (0–5, 0–15, 0–30, and 15–30 m, in seconds) were derived as dependent variables. Subsequently, linear-regression analysis was conducted for each pair of dependent and independent variables. Results: Positive associations were observed between hamstring RTD100 and FH0 (r2 = .241, P = .006) and Pmax (r2 = .227, P = .008). Furthermore, negative associations were observed between hamstring RTD100 and 0- to 5-m (r2 = .206, P = .012), 0- to 15-m (r2 = .217, P = .009), and 0- to 30-m sprint time (r2 = .169, P = .024). No other associations were observed. Conclusions: The present data indicate that early-phase (0–100 ms) rapid force capacity of the hamstring muscles plays an important role for acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity. This indicates that strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.
Effects of Drop Height on Jump Performance in Male and Female Elite Adolescent Handball Players
Authors: Prieske Olaf , Chaabene Helmi , Puta Christian , Behm David G. , Büsch Dirk , Granacher Urs
Published: November 2018

Purpose: To examine the effects of drop height on drop-jump (DJ) performance and on associations between DJ and horizontal-jump/sprint performances in adolescent athletes. Methods: Male (n = 119, 2.5 [0.6] y post-peak-height velocity) and female (n = 120, 2.5 [0.5] y post-peak-height velocity) adolescent handball players (national level) performed DJs in randomized order using 3 drop heights (20, 35, and 50 cm). DJ performance (jump height, reactive strength index [RSI]) was analyzed using the Optojump Next system. In addition, correlations were computed between DJ height and RSI with standing-long-jump and 20-m linear-sprint performances. Results: Statistical analyses revealed medium-size main effects of drop height for DJ height and RSI (P < .001, 0.63 ≤ d ≤ 0.71). Post hoc tests indicated larger DJ heights from 20 to 35 and 35 to 50 cm (P ≤ .031, 0.33 ≤ d ≤ 0.71) and better RSI from 20- to 35-cm drop height (P < .001, d = 0.77). No significant difference was found for RSI between 35- and 50-cm drop height. Irrespective of drop height, associations of DJ height and RSI were small with 5-m-split time (−.27 ≤ r ≤ .05), medium with 10-m-split time (−.44 ≤ r ≤ .14), and medium to large with 20-m sprint time and standing-long-jump distance (−.57 ≤ r ≤ .22). Conclusions: The present findings indicate that, irrespective of sex, 35-cm drop heights are best suited to induce rapid and powerful DJ performance (ie, RSI) during reactive strength training in elite adolescent handball players. Moreover, training-related gains in DJ performance may at least partly translate to gains in horizontal jump and longer sprint distances (ie, ≥20-m) and/or vice versa in male and female elite adolescent athletes, irrespective of drop height.
Physiologic, Metabolic, and Nutritional Attributes of Collegiate Synchronized Swimmers
Authors: Costa Paula B. , Richmond Scott R. , Smith Charles R. , Currier Brad , Stecker Richard A. , Gieske Brad T. , Kemp Kimi , Witherbee Kyle E. , Kerksick Chad M.
Published: November 2018

Synchronized swimming is a sport that requires high levels of strength, power, and endurance, as well as artistic skill to perform in an aquatic environment. Purpose: The purpose of this study was to identify physiological characteristics and dietary habits of collegiate synchronized swimmers. Methods: A total of 21 female participants (mean [SD] age = 20.4 [1.6] y, height = 168.0 [4.9] cm, and weight = 64.4 [8.7] kg) performed resting metabolic rate test. Body composition was determined using skinfolds (4-site and 7-site) and dual-energy X-ray absorptiometry (DEXA). Dietary intake was assessed using 4-d dietary records. Results: Resting metabolic rate was 110.9 (10.5) kJ/kg normalized to body weight and calculated relative daily caloric intake was 121.4 (42.3) kJ/kg. Estimated energy availability ranged from 109.1 (52.1) to 126.7 (52.6) kJ/kg fat-free mass per day and was correlated (P = .045) to resting metabolic rate. Percentage body fat measured using DEXA (28.7% [4.8%] fat) was higher than both 4-site (25.7% [4.8%] fat, P = .001) and 7-site (25.3% [4.7%] fat, P = .001) skinfold values. No significant correlations were reported between bone mineral density, body composition, and dietary intake data. Conclusions: Synchronized swimmers have similar body composition and training habits as other competitive aquatic athletes. Dietary intake data revealed low energy availability and lower than recommended macronutrient levels.
Ingesting a Bitter Solution: The Sweet Touch to Increasing Short-Term Cycling Performance
Authors: Etxebarria Naroa , Ross Megan L. , Clark Brad , Burke Louise M.
Published: November 2018

Purpose: The authors investigated the potential benefit of ingesting 2 mM of quinine (bitter tastant) on a 3000-m cycling time-trial (TT) performance. Methods: Nine well-trained male cyclists (maximal aerobic power: 386 [38] W) performed a maximal incremental cycling ergometer test, three 3000-m familiarization TTs, and four 3000-m intervention TTs (∼4 min) on consecutive days. The 4 interventions were (1) 25 mL of placebo, (2) a 25-mL sweet solution, and (3) and (4) repeat 25 mL of 2-mM quinine solutions (Bitter1 and Bitter2), 30 s before each trial. Participants self-selected their gears and were only aware of distance covered. Results: Overall mean power output for the full 3000 m was similar for all 4 conditions: placebo, 348 (45) W; sweet, 355 (47) W; Bitter1, 354 (47) W; and Bitter2, 355 (48) W. However, quinine administration in Bitter1 and Bitter2 increased power output during the first kilometer by 15 ± 11 W and 21 ± 10 W (mean ± 90% confidence limits), respectively, over placebo, followed by a decay of 34 ± 32 W during Bitter1 and Bitter2 during the second kilometer. Bitter2 also induced a 11 ± 13-W increase during the first kilometer compared with the sweet condition. Conclusions: Ingesting 2 mM of quinine can improve cycling performance during the first one-third of a 3000-m TT and could be used for sporting events lasting ∼80 s to potentially improve overall performance.