bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydroxysafflor yellow A exerts beneficial effects by restoring hormone secretion and alleviating oxidative stress in polycystic ovary syndrome mice
Authors: Luo Man , Huang Ji‐Cheng , Yang Zhan‐Qing , Wang Yu‐Si , Guo Bin , Yue Zhan‐Peng
Published: December 2019

New Findings

What is the central question of this study?

What are the potential therapeutic roles of ginsenoside Rb1 and hydroxysafflor yellow A (HSYA) in polycystic ovary syndrome (PCOS).

What is the main finding and its importance?

HSYA restored the oestrous cycles of PCOS mice, reduced follicular cysts in ovaries and rescued abnormal hormone secretion; ginsenoside Rb1 did not ameliorate the main symptoms of PCOS mice. HSYA alleviated oxidative stress along with an enhancement of antioxidant enzyme activity. This highlights a potential role of HSYA in PCOS therapy.

Polycystic ovary syndrome (PCOS) is the most common endocrine disease resulting in female infertility. Hydroxysafflor yellow A (HSYA) and ginsenoside Rb1 have been shown to have antioxidant properties, but little is known about their impact in PCOS. Here dehydroepiandrosterone was used to induce PCOS in a mouse model that was characterized by an irregular oestrous cycle, cystic follicles and an elevated serum testosterone level. Supplementation of HSYA restored the oestrous cycle of PCOS mice, reduced follicular cysts in PCOS mouse ovaries and brought about a decline in serum testosterone level, while ginsenoside Rb1 did not ameliorate the above symptoms of PCOS mice. After HSYA treatment, there was elevation of serum oestradiol, progesterone, luteinizing hormone and anti‐Müllerian hormone levels and a reduction of follicle‐stimulating hormone level, but ginsenoside Rb1 only rescued the levels of follicle‐stimulating hormone and anti‐Müllerian hormone. Further analysis evidenced that HSYA reversed the expression of steroid hormone secretion‐related genes Star, Hsd3b1, Cyp11a1 and Cyp19a1. In PCOS mice HSYA weakened the elevation of ovarian malondialdehyde, which is regarded as a biomarker for oxidative stress. Moreover, HSYA improved reduced glutathione content accompanied by a simultaneous increase in reduced to oxidized glutathione ratio, and enhanced the activities of the antioxidant enzymes superoxide dismutase, glutathione peroxidase and catalase. Collectively, HSYA exerted beneficial effects on PCOS mice by restoring hormone secretion and alleviating oxidative stress.
Acute intermittent hypercapnic hypoxia and sympathetic neurovascular transduction in men
Authors: Stuckless Troy J. R. , Vermeulen Tyler D. , Brown Courtney V. , Boulet Lindsey M. , Shafer Brooke M. , Wakeham Denis J. , Steinback Craig D. , Ayas Najib T. , Floras John S. , Foster Glen E.
Published: December 2019

Key points

Intermittent hypoxia leads to long‐lasting increases in muscle sympathetic nerve activity and blood pressure, contributing to increased risk for hypertension in obstructive sleep apnoea patients.

We determined whether augmented vascular responses to increasing sympathetic vasomotor outflow, termed sympathetic neurovascular transduction (sNVT), accompanied changes in blood pressure following acute intermittent hypercapnic hypoxia in men.

Lower body negative pressure was utilized to induce a range of sympathetic vasoconstrictor firing while measuring beat‐by‐beat blood pressure and forearm vascular conductance.

IH reduced vascular shear stress and steepened the relationship between diastolic blood pressure and sympathetic discharge frequency, suggesting greater systemic sNVT.

Our results indicate that recurring cycles of acute intermittent hypercapnic hypoxia characteristic of obstructive sleep apnoea could promote hypertension by increasing sNVT.

Acute intermittent hypercapnic hypoxia (IH) induces long‐lasting elevations in sympathetic vasomotor outflow and blood pressure in healthy humans. It is unknown whether IH alters sympathetic neurovascular transduction (sNVT), measured as the relationship between sympathetic vasomotor outflow and either forearm vascular conductance (FVC; regional sNVT) or diastolic blood pressure (systemic sNVT). We tested the hypothesis that IH augments sNVT by exposing healthy males to 40 consecutive 1 min breathing cycles, each comprising 40 s of hypercapnic hypoxia (: +4 ± 3 mmHg above baseline; : 48 ± 3 mmHg) and 20 s of normoxia (n = 9), or a 40 min air‐breathing control (n = 7). Before and after the intervention, lower body negative pressure (LBNP; 3 min at –15, –30 and –45 mmHg) was applied to elicit reflex increases in muscle sympathetic nerve activity (MSNA, fibular microneurography) when clamping end‐tidal gases at baseline levels. Ventilation, arterial pressure [systolic blood pressure, diastolic blood pressure, mean arterial pressure (MAP)], brachial artery blood flow (BA), FVC (BA/MAP) and MSNA burst frequency were measured continuously. Following IH, but not control, ventilation [5 L min–1; 95% confidence interval (CI) = 1–9] and MAP (5 mmHg; 95% CI = 1–9) were increased, whereas FVC (–0.2 mL min–1 mmHg–1; 95% CI = –0.0 to –0.4) and mean shear rate (–21.9 s–1; 95% CI = –5.8 to –38.0; all P < 0.05) were reduced. Systemic sNVT was increased following IH (0.25 mmHg burst–1 min–1; 95% CI = 0.01–0.49; P < 0.05), whereas changes in regional forearm sNVT were similar between IH and sham. Reductions in vessel wall shear stress and, consequently, nitric oxide production may contribute to heightened systemic sNVT and provide a potential neurovascular mechanism for elevated blood pressure in obstructive sleep apnoea.
Direct Validation of Human Knee-Joint Contact Mechanics Derived From Subject-Specific Finite-Element Models of the Tibiofemoral and Patellofemoral Joints
Authors: Gu Wei , Pandy Marcus G.
Published: December 2019

The primary aim of this study was to validate predictions of human knee-joint contact mechanics (specifically, contact pressure, contact area, and contact force) derived from finite-element models of the tibiofemoral and patellofemoral joints against corresponding measurements obtained in vitro during simulated weight-bearing activity. A secondary aim was to perform sensitivity analyses of the model calculations to identify those parameters that most significantly affect model predictions of joint contact pressure, area, and force. Joint pressures in the medial and lateral compartments of the tibiofemoral and patellofemoral joints were measured in vitro during two simulated weight-bearing activities: stair descent and squatting. Model-predicted joint contact pressure distribution maps were consistent with those obtained from experiment. Normalized root-mean-square errors between the measured and calculated contact variables were on the order of 15%. Pearson correlations between the time histories of model-predicted and measured contact variables were generally above 0.8. Mean errors in the calculated center-of-pressure locations were 3.1 mm for the tibiofemoral joint and 2.1 mm for the patellofemoral joint. Model predictions of joint contact mechanics were most sensitive to changes in the material properties and geometry of the meniscus and cartilage, particularly estimates of peak contact pressure. The validated finite element modeling framework offers a useful tool for noninvasive determination of knee-joint contact mechanics during dynamic activity under physiological loading conditions.
Optimization of the Width of Vapor Chamber Regions by Using Particle Swarm Optimization Method
Authors: Hassan Hamdy , Harmand Souad
Published: December 2019

An optimization of vapor chamber (VC) region's width and its wick porosity to achieve the minimum temperature rise of the vapor chamber is studied in this paper. The optimization process is carried out by particle swarm optimization (PSO) method. The study is performed at various widths of the vapor chamber, cooling rates, and input powers. The vapor chamber includes two solid copper plates, two wick regions, and vapor region between them. The required chamber characteristics for the optimization process are obtained by solving a complete VC mathematical model, which couples the thermal and hydrodynamic models. The optimum vapor chamber regions' thicknesses and the fluid flow through the vapor chamber regions are studied. The results illustrate that to minimize the chamber temperature, the wick region width must be minimized. They also show that increasing the total width of the chamber from 3 to 7 mm does not have a great impact on the chamber optimized temperature. Moreover, the vapor chamber width does not have a great impact on the optimum wick region width. The optimum width of the vapor region and the chamber walls augments with increasing the total vapor chamber width. Additionally, the form of temperature, streamlines, and velocity distributions at liquid and vapor regions at optimum conditions are not greatly influenced by increasing vapor chamber width.
Soft Morphing Buttons Based on Actuator and Sensor Properties of Shape Memory Alloy Wires
Authors: Scholtes Dominik , Goergen Yannik , Motzki Paul , Seelecke Stefan , Scheiner Philipp
Published: December 2019

As a smart material thermal shape memory alloys (SMAs) feature actuator behavior combined with self-sensing capabilities. With their high energy density and design flexibility they are predestined to be used in soft robotics and the emerging field of morphing surfaces. Such shape changing surfaces can be used for novel human-machine interaction (HMI) elements based on mode-/situation-dependent interfaces that may be applied to all kind of machines, appliances and smart home devices as well as automotive interiors. Since many of those contain textile surfaces, it is of special interest to place SMA-based actuator-sensor-elements beneath a textile cover or integrated them in the textile itself. In this study, the unique features of SMAs are used to design a system which represents an active “morphing” button. It can lower into the surface it is integrated in, pops up to be used and shows a proportional signal output depending on the pushing stroke. The system is characterized concerning haptics and sensor technology. The button consists of a TPU structure, to which two NiTi wires are attached. When activated, the SMAs contract and the structure curves upwards. The user can now push on the device to use it as a button. In the future, the use of SMA wires and for example TPU fibers enables direct integration in the production process of a possible smart and functional textile.
Design-Oriented Multifidelity Fluid Simulation Using Machine Learned Fidelity Mapping
Authors: Fuchi Kazuko , Wolf Eric M. , Makhija David S. , Wukie Nathan A. , Schrock Christopher R. , Beran Philip S.
Published: December 2019

A machine learning algorithm that performs multifidelity domain decomposition is introduced. While the design of complex systems can be facilitated by numerical simulations, the determination of appropriate physics couplings and levels of model fidelity can be challenging. The proposed method automatically divides the computational domain into subregions and assigns required fidelity level, using a small number of high fidelity simulations to generate training data and low fidelity solutions as input data. Unsupervised and supervised machine learning algorithms are used to correlate features from low fidelity solutions to fidelity assignment. The effectiveness of the method is demonstrated in a problem of viscous fluid flow around a cylinder at Re ≈ 20. Ling et al. built physics-informed invariance and symmetry properties into machine learning models and demonstrated improved model generalizability. Along these lines, we avoid using problem dependent features such as coordinates of sample points, object geometry or flow conditions as explicit inputs to the machine learning model. Use of pointwise flow features generates large data sets from only one or two high fidelity simulations, and the fidelity predictor model achieved 99.5% accuracy at training points. The trained model was shown to be capable of predicting a fidelity map for a problem with an altered cylinder radius. A significant improvement in the prediction performance was seen when inputs are expanded to include multiscale features that incorporate neighborhood information.
Evaluation of SHM With the Electromechanical Impedance Method Using a High Voltage Excitation Signal in High Frequencies
Authors: Nolan Eric C. , Safaei Mohsen , Anton Steven R.
Published: December 2019

Structural health monitoring (SHM) has originally been used for static structures. With the development of high-speed data acquisition technology, SHM systems can monitor structures in seconds. Advanced SHM systems for use in dynamic environments require operation in the microsecond timescale. One promising approach is the electromechanical impedance (EMI) technique. The EMI method monitors the impedance of a structure, and damage is indicated by changes in the impedance. Standard impedance measuring hardware are not practical for microsecond detection due to their slow sampling speeds. Faster impedance measuring techniques have been developed and allow for customizable excitation signals. Researchers have also considered taking measurements at higher frequencies to decrease the measurement time. Past works indicate sensitivity to damage is limited above 600 kHz. The goal of this study is to evaluate the sensitivity of the EMI method to damage with a high voltage excitation signal. It was hypothesized that increasing the voltage would increase damage sensitivity at higher frequencies. In this study, the amplitude of the excitation signal was increased using a high frequency voltage amplifier. A PZT disk bonded to a cantilevered aluminum beam was used as the test structure. Damage was created by decreasing the length of the beam. Finite element (FE) simulation was also employed to achieve a better understanding of the experiment. From the results of the experiment and FE model, using a higher excitation voltage has proven not to increase the sensitivity level of the EMI method. Higher voltages do improve the precision of the measurement by increasing the signal to noise ratio.
A Piezocomposite Solid-State Rotor: Theoretical Analysis of Thrust and Efficiency Metrics
Authors: Carneiro Ferreira de Castro Taís , Bilgen Onur
Published: December 2019

This paper presents a summary on the ongoing research and development of a solid-state piezoelectric composite rotor design for use in rotary systems. The paper focuses on the theoretical analysis of a two-bladed rotor with varying parameters such as flight speed, blade pitch angle, and rotational speed. XROTOR, a blade element method based software, is used for analysis. The two-dimensional aerodynamic characteristics are acquired from the previous research on a Macro-Fiber Composite actuated simply supported thin airfoil. A set of simulations are conducted to determine the best geometric configuration, so the piezoelectric increase in thrust is maximized. The proposed hub-rotor system has the potential to be implemented in unmanned-aerial-vehicles such as single-rotor, tandem-rotor, multi-copter, and ducted-fan rotorcraft, or other rotating systems such as wind turbines, turbine engines, and marine propellers. This paper presents a summary of previous findings on a solid-state rotor prototype, and a new investigation on the theoretical aerodynamic behavior.
Initial Analysis of a Novel Biomimetic Span-Wise Morphing Wing Concept
Authors: Stacey Benjamin J. , Thomas Peter
Published: December 2019

Morphing wings and the adaptive systems they form have been developed significantly over recent decades. Increased efficiency and control performance can be achieved with their implementation, while advances in material technology, system integration and control, have allowed concepts to present a realistic alternative to fixed-wing and aft-tail aircraft. Set out in this paper is the preliminary design and development for a novel span-wise morphing concept which employs and heavily implements biomimetic design. Specifically, the skeletal structure of the bird wing by mimicking the humerus, ulna/radius, and carpometacarpus of birds of prey as they exhibit the most versatile wing shape enabling multiple manoeuvre and flight types. The concept comprises three sections corresponding to the skeletal structure, each consisting of a leading edge D-spar and an internal structural member onto which trailing edge plates are mounted. Pneumatic artificial muscle (PAM) actuators are presented as a drive for a biologically derived ‘drawing-parallels’ mechanism, through which a 75% semi-span length change and variable sweep angle, can be obtained. Analysis of initial CFD results is discussed in comparison with similar concepts in the field and a proposal for small scale wind tunnel verification put forward. While a rapid prototype is printed to confirm the viability of the concept.
Modeling and Design of an Experimental Demonstrator of Blade Twist Through the SMA Technology
Authors: Ameduri Salvatore , Concilio Antonio , Galasso Bernardino
Published: December 2019

The paper at hand focuses on the modeling and design of an experimental demonstrator of a blade segment, twisted through Shape Memory Alloy technology. The demonstrator will be used for the wind tunnel tests planned within the Project of SABRE (H2020 Eu Program), aimed at investigating the effects produced by blade oriented morphing technologies, both in fixed and rotary wing configurations. The design approach adopted for a SMA twist concept is herein described in its different phases, moving from the definition of the preliminary layout, its fitting to the reference blade mechanical features, the preliminary structural analysis to confine its operational envelope, up to the simulation of the SMA actuation through a SMA torque element. The results are presented in terms of operational envelope limits and transmitted twist.
Integrated Rotor Performance Improvement and Vibration Reduction Using Active Camber Morphing
Authors: Kumar Sumeet , Komp Dominik , Hajek Manfred , Rauleder Jürgen
Published: December 2019

This paper discusses open-loop and closed-loop active control investigations of a full-scale Bo 105 helicopter rotor with active camber morphing. The potential of an active camber morphing concept to reduce non-rotating vibratory hub loads and rotor power using active control was investigated. The mechanism employed was a dynamically actuated airfoil camber morphing concept known as Fish Bone Active Camber (FishBAC) that smoothly deforms the camber over the aft section of the airfoil. A comprehensive rotorcraft aeromechanics analysis was used that modeled the blade elastic motion using one-dimensional finite beam elements combined with multibody dynamics. Aerodynamic forces were calculated with a free-vortex wake model together with lifting line theory for the blade aerodynamics. The open-loop investigation comprised of a parametric study of relevant control parameters that govern the active camber deflection cyclic actuation profile and their effects on rotor performance and hub vibration. It was found that active camber morphing using superimposed once-per-revolution (1P) and 2P control inputs was able to simultaneously reduce rotor power by 4.3% and overall vibratory hub loads by 27%. Additionally, a closed-loop adaptive multicyclic controller was used to identify the potential of this morphing concept for hub vibration reduction using multicyclic active control inputs. Active camber actuation using a sum of four control harmonic inputs, i.e. 1-4P, resulted in a maximum hub vibration reduction of 50%.
Graph-Based Interpretation of L-System Encodings Toward Aeroelastic Topology Optimization of a Morphing Airfoil in Supersonic Flow
Authors: Bielefeldt Brent R. , Hartl Darren J. , Hodson Joshua D. , Reich Gregory W. , Beran Philip S. , Pankonien Alexander M. , Deaton Joshua D.
Published: December 2019

This work details the preliminary design of a morphing airfoil in supersonic flow using evolutionary design principles. The structural topology of the airfoil includes a fixed outer mold line, fixed spars, and designable internal stiffeners and actuators. The designable components are generated using a bio-inspired model known as a Lindenmayer System (L-System), which encodes design variables and governs the development of a structural topology when coupled with an interpretation algorithm. Here, we utilize a graph-based interpretation scheme known as Spatial Interpretation for the Development of Reconfigurable Structures (SPIDRS), which has been shown to effectively explore the mechanism design space using a limited number of design variables. The optimization process behind this preliminary design problem is discussed, and optimal airfoil topologies capable of meeting specified aerodynamic performance criteria are presented in hopes of gaining a better understanding of how actuation systems could be integrated into the next generation of aircraft.
Quantitative Measurement of Thin Film Adhesion Force
Authors: Tsai Li-Chih , Rezaee Maysam , Haider Muhammad Istiaque , Yazdi Armin , Salowitz Nathan P.
Published: December 2019

Thin film and micro-fabricated devices are increasingly being used in actuators, sensors, and processors deployed in smart materials. The physical survival of these devices is paramount to their usefulness but existing methods for testing and analysis are limited and challenging due to their properties. The most common test involve the manual application and removal of (unspecified) tape but does not provide a result in scientific units and has large variation (> 35%). This paper presents a study into the effects of parameters of tape application and peeling on the adhesion strength of the tape. This information was then used to create a test methodology using commonly available laboratory equipment, which would control these parameters to minimize variation and produce repeatable quantitative results. Experiments using this test methodology were performed with tape directly adhered to several different substrates as well as tape adhered to a thin film which was then peeled off of a backing. Ongoing work is seeking to identify and address different forms of failure including adhesive failure, cohesive failure, or survival.
Mechanics of Post Constrained Recovery Residual Stress Produced by NiTi
Authors: Haider Muhammad Istiaque , Yazdi Armin , Rezaee Maysam , Tsai Li Chih , Salowitz Nathan
Published: December 2019

Recent research has revealed that Nickel Titanium (NiTi) shape memory alloys can produce residual stresses after undergoing constrained recovery and returning to their low temperature, martensitic state while still constrained. The nature and underlying mechanisms that cause this post constrained recovery residual stress (PCRRS) are not well understood. This paper presents experimental research and results seeking to further understand the PCRRS. Experiments were performed on multiple formulations of NiTi subjected to: 1) Cyclic loading and training before producing PCRRS, 2) Repeated thermomechanical loading with large strains followed by a thermal cycle to create and re-generated the PCRRS, and 3) Creation of the PCRRS followed by repeated cycles of small, 0.5% strains.

Experiments found that the training in 1) did not significantly alter the ability to produce PCRRS or its magnitude. Straining samples from the PCRRS state could reduce the residual stress state to zero stress, but the PCRRS could be recreated by repeating thermal actuation with the only significant variation being a reduction in magnitude for the first to second cycle. Multiple small strain cycles applied from the PCRRS state caused an incremental reduction in residual stress. The full PCRRS could be re-created by repeating the initial thermomechanical cycle. The values of the residual stress varied across the first 3 sets of cycles, but from the third set onward the response stabilized.

These results indicate that the primary mechanisms for generating a PCRRS are stable and recoverable with only minor and diminishing variations due to training or repeated regeneration of the PCRRS. Grain boundary stabilization and similar mechanisms may be responsible for the minor variation between the first few regenerations of the PCRRS. The incremental reduction in the residual stress after exposure to small 0.5% strains must be due to a recoverable process like partial and accumulating detwinning of the NiTi with each load cycle.

Further work is underway to perform microstructural analysis of samples in the various states to further the theorized material states.

The ability to generate and control PCRRS has the potential to find new application and advance capabilities in fields like self-healing and fatigue resistant materials by generating stresses without the continuous application of heat energy. New forms of actuation could also be developed based on the potential energy stored in a structure through PCRRS.
Chord Morphing for Helicopter Rotor Blades
Authors: Riemenschneider Johannes , Balzarek Christoph , van der Wall Berend G. , Majeti Rohin Kumar
Published: December 2019

Since helicopter rotors have different demands from different flight stats, the final design is always a compromise between flight stats such as hover and fast forward flight. Two of the design parameters are twist and chord length. This paper is giving some reasoning from rotor simulations on what twist and chord length should look like in order to increase performance in hover or forward flight. The result is, that the inboard chord length should be much larger for hover than for forward flight. This paper is presenting a structural concept, that can enable a helicopter rotor blade to change its chord length.
Ultrasonic De-Icing System for Leading Edge in Composite Material
Authors: Maio Leandro , Ameduri Salvatore , Memmolo Vittorio , Ricci Fabrizio , Concilio Antonio
Published: December 2019

The paper presents a numerical study about a de-icing system using ultrasonic waves. The activity is developed within the project “SMart On-Board Systems” (SMOS), which is part of Italian Aerospace National Research Program, funded by the Italian Ministry of Education (MIUR) and Research and coordinated by Italian Aerospace Research Centre (CIRA). The system is conceived for an aircraft wing leading edge and it shall be extended to other aircraft components, once its efficiency and reliability will be demonstrated. In this work, a numerical study about a 0012 NACA profile in composite material is discussed and the simulations results coming from finite element analyses in frequency and time domains are presented.
Pneumatic Artificial Muscle Actuators With Integrated Controls for Space Flight Applications
Authors: Netwall Christopher J. , Thomas James P. , Kubista Michael S. , Griffith Kerry A. , Kindle Christopher , Schlater Jordan , Hays Joseph T. , Feerst Phillip A. , Wereley Norman
Published: December 2019

The U.S. Naval Research Laboratory (NRL) has been developing a space-rated 7 degree of freedom (DOF) robot arm with a high payload-to-mass ratio as an alternative design to motor-gear driven robotic manipulators. The robot arm employs antagonistic pairs of pneumatic artificial muscle (PAM) actuators to control each degree-of-freedom (DOF) to achieve large force outputs relative to the PAM component masses. A novel feature of the NRL PAM actuator was the integration of the pneumatic control components inside the pressure-bladder, which not only reduces the volume of the robotic arm hardware but also reduces the pressurized-gas actuation volume in the PAM enabling significant reductions in gas consumption during actuation. This multifunctional design enables reductions in launch-weight costs and increases in operational endurance for space applications. The integration of these PAMs into a well-designed robotic-arm structure, in tandem with a newly developed control algorithm, has the potential to exceed the performance metrics of traditional motor-driven robot arms. This paper describes the development of the improved efficiency PAM design that is advancing this technology towards space flight readiness.
A Wearable Biomedical Motion Sensor Employing a Vibration Energy Harvester
Authors: Sharghi Hesam , Daneault Jean-François , Bilgen Onur
Published: December 2019

Wearable motion sensors find a great number of applications in the biomedical field by recording real-time movements and transferring data to mobile electronics. Patients with hyperkinetic movements is a group of interest for such sensors to survey their conditions for long periods. Longer and more frequent recording intervals are necessary to diagnose and treat patients’ disease. Mobile battery-operated motion sensors have a limited recording span, and they need to be charged frequently, which is inconvenient for most of the patients. In this study, vibration energy harvesters are employed to extend the battery life of motion sensors: one step closer to make autonomous sensors without chargers. A vibration energy harvester is designed for a motion sensor to harvest energy from involuntary movements of patients with hyperkinetic movements. An analytical model for charging and discharging cycles is developed to predict the battery life based on the amount of harvested power. Preliminary data from commercial devices are used as a foundation for the design and the current feasibility study.
Continuous Operating Elastocaloric Heating and Cooling Device: Model-Based Parameter Study With Airflow Losses
Authors: Welsch Felix , Kirsch Susanne-Marie , Michaelis Nicolas , Motzki Paul , Schütze Andreas , Seelecke Stefan
Published: December 2019

Elastocaloric cooling uses solid-state NiTi-based shape memory alloy (SMA) as a non-volatile cooling medium and enables a novel environment-friendly cooling technology. Due to the high specific latent heats activated by mechanical loading/unloading, substantial temperature changes are generated in the material. Accompanied by a small required work input, a high coefficient of performance is achievable.

Recently, a fully-functional and illustrative continuous operating elastocaloric air cooling system based on SMA was developed and realized. To assist the design process of an optimized device with given performance and efficiency requirements, a fully coupled thermo-mechanical system-level model of the multi-wire cooling unit was developed and implemented in MATLAB. The resulting compact simulation tool is qualified for massively parallel computation on modern multi-core computers, which allows fast and comprehensive parameter scans.

The comparison of first measurements and simulation results showed differences in the system performance. As the airflow rate influences the thermal power and the outlet temperature significantly, the demonstrator is extended with a spatial airflow measurement system to analyze the crossflow between the hot and cold side. Following, the fluid transport model is advanced by the effect of cross-flow losses, and first modeling results with the variation of airflow rate and rotation frequency are presented.
Controlled Operation of Lithium Ion Batteries Using Reversible Shutdown Membrane Separators
Authors: Hery Travis , Sundaresan Vishnu Baba
Published: December 2019

In this paper, we demonstrate the application of the ionic redox transistor as a reversible shutdown membrane separator (RSMS) in a custom designed Li-ion battery (LIB). The oxidized state corresponds to the OFF state and reduced state corresponds to the ON state of the RSMS in the LIB. It is demonstrated that RSMS reversibly enables and disables the LIB from charging/discharging as it is switched between its reduced (ON) and oxidized (OFF) state, respectively. The operation of the LIB with RSMS is compared with a standard LIB fabricated from identical cathodes and anodes at various C-rates.

The specific capacity of the standard LIB is 144, 132, and 50 mAh/g at C/12, C/4, and C/2 rates, respectively. The specific capacity of the LIB with RSMS in the reduced state is 134, 108, and 48 mAh/g at C/12, C/4, and C/2 rates, respectively, showing similar capacity to the standard LIB at all C-rates. The specific capacity of the LIB with RSMS in the oxidized state is 125, 11, and 5 mAh/g at C/12, C/4, and C/2 rates, respectively, demonstrating a capacity decrease compared to the reduced state at all C-rates.
Self-Sensing Characterization of GNP and Carbon Black Filled Cementitious Composites
Authors: Jiang Zhangfan , Ozbulut Osman E. , Xing Guohua
Published: December 2019

Over the past decades, a number of structural health monitoring methods have been developed for condition assessment of concrete structures. Most of these methods require the installation of external sensors. Accelerometers are commonly used for vibration-based damage detection for the entire structure, while strain gauges are installed in order to detect cracking and damage at the component level. Conventional strain sensors, such as metal foil strain gauges, have been widely used to monitor local conditions in concrete structures. However, all of these sensors have certain shortcomings such as exhibiting limited durability and low gauge factor, and providing only pointwise strain measurements. Multifunctional cement-based composites that can determine their own strain and damage can overcome the limitations of these traditional sensors.

This study explores the use of two different nanomaterials, namely graphene nanoplatelets (GNP) and carbon black (CB) for the development of self-sensing cementitious composites and the synergetic effects in their hybrid utilization. A simple fabrication method that does not require special treating procedures such as ultrasonication for dispersing nanomaterials is pursued. Twelve batches of mortar specimens reinforced with only GNP or CB at different concentrations, or with both GNP and CB fillers are prepared. A polycarboxylate-based superplasticizer is used to disperse nanomaterials and to increase the workability of the nano-reinforced mortar. Scanning electron microscope (SEM) is utilized to assess the distribution quality of nanomaterials. Standard cubic specimens are tested for compressive strength at 28 days. The bulk resistivity of the standard prismatic specimens is measured using the four-point probe method. The piezoresistive response of nano-reinforced cement composites is evaluated under the cyclic compressive loads.
Experimental Investigation of the Mechanisms and Performance of Active Auxetic and Shearing Textiles
Authors: Granberry Rachael , Holschuh Brad , Abel Julianna
Published: December 2019

Anisotropic textiles are commonly used in wearable applications to achieve varied bi-axial stress-strain behavior around the body. Auxetic textiles, specifically those that exhibit a negative Poisson’s ratio (v), likewise exhibit intriguing behavior such as volume increase in response to impact or variable air permeability. Active textiles are traditional textile structures that integrate smart materials, such as shape memory alloys, shape memory polymers, or carbon nanotubes, to enable spatial actuation behavior, such as contraction for on-body compression or corrugation for haptic feedback. This research is a first experimental investigation into active auxetic and shearing textile structures. These textile structures leverage the bending- and torsional-deformations of the fibers/filaments within traditional textile structures as well as the shape memory effect of shape memory alloys to achieve novel, spatial performance. Five textile structures were fabricated from shape memory alloy wire deformed into needle lace and weft knit textile structures. All active structures exhibited anisotropic behavior and four of the five structures exhibited auxetic behavior upon free recovery, contracting in both x- and y-axes upon actuation (v = −0.3 to −1.5). One structure exhibited novel shearing behavior, with a mean free angle recovery of 7°. Temperature-controlled biaxial tensile testing was conducted to experimentally investigate actuation behavior and anisotropy of the designed structures. The presented design and performance of these active auxetic, anisotropic, and shearing textiles inspire new capabilities for applications, such as smart wearables, soft robotics, reconfigurable aerospace structures, and medical devices.
DfAM of Nonlinear Cellular Flexible Structures
Authors: Djokikj Jelena , Jovanova Jovana
Published: December 2019

Nonlinear cellular structures are defined as structures with multiple scale unit cells patterned through the volume of the structure. The geometrical nonlinearity allows local high flexibility in the movement and also in the sense of strength of materials.

The focus of this paper is to create a framework for design for additive manufacturing (DfAM) of a modular nonlinear cellular structure with high level of flexibility. The flexibility will be exploited in skin-like structures adaptable to freeform geometries or utilize flat printed designs for voluminous and structural 3D shapes.

For the modeling of the structure CAD software is used and for the fabrication of the structure additive manufacturing (AM) is applied. These technologies work by adding the material in layers, which enables fabrication of parts with complex geometries. The working principal of AM which is opposite to the traditional manufacturing requires for changes in the design process. These changes are applied in the DfAM that we are presenting with this study. The DfAM is used to develop a systematic design approach to support the fabrication of unique structure shapes by AM.
Experimental Studies of the Actuation of Carbon Nanotube-Based Materials
Authors: Geier Sebastian , Mahrholz Thorsten , Wierach Peter , Sinapius Michael
Published: December 2019

Carbon nanotubes (CNTs) show an active behavior when they are positioned within an electric field, immersed into an electrolyte and charged. Several explanations are given, ranging from nanoscopic to macroscopic effects. This paper presents experimental proven explanations of the paper actuation and results using continuous CNTs of a CNT-array.

For the first test series specimens are cut off a paper manufactured of single-walled, μ-long CNTs working in series. The second test series uses specimens which are prepared of free standing multi-walled CNTs. Their CNT lengths reach macroscopic dimensions of almost 3 mm and they can be considered as connected in parallel. Both series are electromechanically tested.

The paper tests reveal their strong condition-dependent microstructure. Generally, the observed effects can be explained by diffusion of ions into the flexible CNT microstructure.

In contrast, the CNT-array based specimens show almost no condition dependency which can be explained by the strong carbon bonds. Due to specimen orientation and test set-up, macroscopic effects can be excluded. The found actuation can be attributed to an elongation of the carbon structure as result of ion-interaction. However, it must be assumed that there are further superimposing effects which might not be distinguished from each other down to the last detail.
Structure Integrated Supercapacitors for Space Applications
Authors: Geier Sebastian , Petersen Jan , Wierach Peter
Published: December 2019

The increasing electrification places great demands on the supply and storage of electrical energy. Beside batteries, supercapacitors are a second storage technology with clear advantages compared to batteries in terms of charging time, energy density and cycle stability.

This publication deals with the structurally compliant integration of pouch supercapacitor cells which are developed for integration into fiber-reinforced composites. The energy storage components are designed to transmit mechanical stresses. The aim is to qualify a space structure with integrated supercapacitors for use under space conditions. For a special peak power application, 14 supercapacitors are integrated into the lay-up of a glass fiber-reinforced structure. This structure connects electronic components and is therefore designed load-bearingly.

Thermal cycling under high vacuum between −22°C and +67°C shows temperature effects, as result of the temperature dependence of the ion mobility. During the other mechanical tests (sinus vibration, random vibration, pyroshock) and irradiation with a Co60 source the electrical performance keeps at the same level.

The structure featuring 14 integrated supercapacitors exhibits a specific capacitance of 1.12 F/g compared to a specific capacitance of 0.35 F/g of a structure using 16 commercial supercapacitors (FastCap EE350). These results demonstrate the great weight- and volume-saving potential of this approach.
Coupled Electro-Thermo-Mechanical Modeling of Shape Memory Polymers
Authors: Siwakoti Midhan , Mailen Russell W.
Published: December 2019

Shape memory polymers (SMPs) are extensively studied for self-folding origami due to their large strain recovery, low cost, and low activation energy. SMPs utilize viscoelastic material behavior to change shape in response to an applied stimulus, for instance light or electricity. Electrical actuation is desirable due to its higher energy density and shorter response time. Previous studies reported empirical results on shape recovery of conductive polymer composites actuated by specific applied voltage or current conditions, which required rigorous experimentation. Here, we introduce a finite element framework capable of predicting the coupled electro-thermo-mechanical response of electrically actuated SMPs. As inputs, this framework requires material properties, such as electrical conductivity and viscoelastic parameters. The viscoelastic response is implemented using a Prony series model that is fit to experimental dynamic mechanical analysis (DMA) data. Using this framework, we predict the shape recovery behavior of electrically actuated SMPs subject to various thermal, electrical, and mechanical loads and evaluate the sensitivity of the response to the material properties. Additionally, we show the effects of material pre-straining conditions and localized conductive pathways on shape recovery and self-folding. This computational framework provides a fundamental understanding of the electro-thermo-mechanical response of electrically actuated SMPs and can be used to design electrically actuated self-folding origami for aerospace applications.
Structural Health Monitoring of Composite Structures via Machine Learning of Mechanoluminescence
Authors: Gupta Sujasha , Krishnan Srivatsava , Sundaresan Vishnubaba
Published: December 2019

The goal of this paper is to develop a machine learning algorithm for structural health monitoring of polymer composites with mechanoluminescent phosphors as distributed sensors. Mechanoluminescence is the phenomenon of light emission from organic/inorganic materials due to mechanical stimuli. Distributed sensors collect a large amount of data and contain structural response information that is difficult to analyze using classical or continuum models. Hence, approaches to analyze this data using machine learning or deep learning is necessary to develop models that describe initiation of damage, propagation and ultimately structural failure.

This paper focuses on developing a machine learning algorithm that predicts the elastic modulus of a structure as a function of input parameters such as stress and measured light output. The training data for the algorithm utilizes experimental results from cyclical loading of elastomeric composite coupons impregnated with ML particles. A multivariate linear regression is performed on the elastic modulus within the training data as a function of stress and ML emission intensity. Error in predicted elastic modulus is minimized using a gradient descent algorithm. The machine learning algorithm outlined in this paper is expected to provide insights into structural response and deterioration of mechanical properties in real-time that cannot be obtained using a finite array of sensors.
Strain Mapping and Large Strain Measurement Using Biaxial Skin Sensors
Authors: Donica Thomas , Gray Jonathan , Zegeye Ephraim F.
Published: December 2019

Electronic skins, or e-skins, are electronic devices capable of sensing physical interactions such as strain, temperature, or pressure. These e-skins are of interest in a variety of fields including robotics, structural health monitoring, and medicine. E-skins should measure strains over a larger range of elongation than traditional strain sensors could. This paper explores the synthesis of a flexible biaxial strain sensor for large surface strain measurement. The sensor is made by spraying an exfoliated graphite and latex mixture onto a latex substrate to form a 4 × 4 grid of electrically conductive strips. Electrodes are connected to each sensor to collect data on deformation induced voltage difference. Two setup geometries were characterized, the behavior of a single strip in each direction in a one by one configuration as well as the behavior of a four by four setup that can measure a two-dimensional strain field. The characteristics of the sensor is studied by attaching it on a tensile testing specimen. When the sensor is subjected to strain along one or both of the two measurement axes, the voltage difference can be recorded using Arduino. The voltage drop was normalized and used to construct a strain distribution plot in MATLAB to determine the highly strained location. In addition to characterizing the behavior of the sensor, the dispersion of the exfoliated graphite in the latex is also studied using optical microscopy. The sensor is made from inexpensive materials and was able to measure large strain that cannot be achieved with commercially available strain gauges.
Investigation of Variable Stiffness Effects on Radial Pulse Measurements Using Magneto-Rheological Elastomers
Authors: Weaver Kyle , Shumway Dylan , Yang Tae-Heon , Kim Young-Min , Koo Jeong-Hoi
Published: December 2019

Current wearable technologies strive to incorporate more medical functionalities in wearable devices for tracking health conditions and providing information for timely medical treatments. Beyond tracking of a wearer’s physical activities and basic vital signs, the advancement of wearable healthcare devices aspires to continuously monitor health parameters, such as cardiovascular indicators. To properly monitor cardiovascular health, the wearables should accurately measure blood pressure in real-time. However, current devices on the market are not validated for continuous monitoring of blood pressure at a clinical level. To develop wearable healthcare devices such applications, they must be validated by considering various parameters, such as the effects of varying skin properties. Being located between the blood vessel and the wearable device, the skin can affect the sensor readings of the device. The primary goal of this study is to investigate the effect of skin property on the radial pulse measurements. To this end, a range of artificial vein-inserted skin samples with varying properties is fabricated using Magneto-Rheological Elastomers (MRE), materials whose mechanical properties can be altered by external magnetic fields. The samples include layers to simulate the structure of skin and a silicone vein for the pulse to pass through. Note that they are not intended to represent real human skin-vein properties but created to vary a range of stiffness properties to carry out the study. Experiments are performed using a cam system capable of generating realistic human pulse waveforms to pass through the samples. During the indentation testing, the sample is compressed using a dynamic mechanical analyzer (DMA) to record experienced surface pressure, allowing the pulse patterns to be studied. Various samples are used to probe the effects of base resin hardness, iron content, and magnetic field. A pressure sensor incorporated in the cam simulator is used to benchmark the internal pulse pressure of the vein while the DMA indents the sample in order to note the pulse pressures being passed through the sample. Test results show that the properties of the skin influence the resulting pulse behaviors, particularly the ratio of the recorded pulse pressures from the sensor and the DMA.