bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Creases in Polymers for Adaptive Origami Structures
Authors: Abbott Andrew C. , Buskohl Philip R. , Joo James J. , Reich Gregory W. , Vaia Richard A.
Published: December 2014

Techniques employed in origami are of interest for the design of actuating structures with multiple defined geometric states. Most research in this area has focused on manipulating material chemistry or geometry to achieve folding, but crease development through full material thickness has not been studied in detail. Understanding creasing is crucial for establishing material selection guidelines in origami engineering applications. Identification of the precise failure mechanisms is critical for understanding the residual fold angle and selecting optimal materials for specific origami applications. To characterize crease formation and development, polymer films were folded using a modified parallel plate bending technique which was successfully modeled with Euler beam theory in the elastic regime. Fold angles measured after creasing provided a means to quantitatively describe a material’s ability to retain a fold, and degree of plastic deformation incurred during folding. SEM micrographs of creased regions revealed tensile deformations on exterior crease surfaces while compressive deformations such as wrinkling occurred inside. Profilometry was performed on crease interiors to identify and measure wrinkle topology. It was found that increased dissipative plastic deformation led to retention of smaller fold angles. These characterization techniques can be used as a means of classifying and organizing polymers by potential usefulness in structural origami applications.
Hybrid Torsional Vibration Damper Incorporating Conventional Centrifugal Pendulum Vibration Absorber and Magnetorheological Damper
Authors: Abouobaia Ehab , Bhat Rama , Sedaghati Ramin
Published: December 2014

A hybrid torsional vibration damper is proposed in this study incorporating a conventional Centrifugal Pendulum Vibration Absorber (CPVA) and a Magnetorheological (MR) damper. While CPVAs are simple and reliable passive torsional vibration absorbers, their performance is limited to the designed tune conditions. MR dampers have recently received considerable attention due to their inherent fail-safe feature, low power requirement and capability to attenuate vibration under unpredictable environmental conditions. The present research aims at developing a novel hybrid torsional vibration damper combining conventional CPVA with the MR damper capable of suppressing torsional vibration at varying excitation frequencies. This research presents results from analytical investigation of rotor systems integrated with the proposed hybrid torsional vibration damper. The system under investigation consists of a rotor with attached hybrid torsional MR damper subjected to an external harmonic torque. The CPVA has been connected to the cylindrical housing of the MR damper. Different cases have been investigated including: 1- Rotor system without any damper, 2- Rotor system with only CPVA, 3- Rotor system with only torsional MR damper and 4- Rotor system with the hybrid torsional damper. Results for each case have been illustrated and compared against one another.
Development and Testing of a Hybrid SMA/MR Passive Clutch
Authors: Bucchi Francesco , Elahinia Mohammad , Forte Paola , Frendo Francesco
Published: December 2014

The reduction of consumption and emissions is a key factor in modern vehicle design. The overall vehicle efficiency is pursued in several ways, including the reduction of consumption of the auxiliary devices (e.g. water pumps, oil pumps, vacuum pumps etc.). In this paper, using two different smart materials (i.e. magnetorheological fluids and shape memory alloys) a device aimed at disengaging the vacuum pump was developed.

The conceived device is composed of a magnetorheological (MR) clutch excited by permanent magnets coaxially manufactured with a sliding spline sleeve moved by shape memory alloys (SMA) springs. In the MR clutch, the magnet can move under the effect of a passive pneumatic system. The magnetic field in the fluid varies with the magnets displacement and two steady positions are possible: the engaged clutch (ON) and the disengaged clutch (OFF). The torque in the ON configuration is high enough to drive the vacuum pump during normal operating conditions, whereas the low torque value in the OFF condition guarantees power saving up to 150 W.

In particular operating conditions (i.e. at low environmental temperatures) the torque necessary to start the vacuum pump may exceed the maximum transmissible torque of the MR clutch. For this reason a sliding spline sleeve, led by two SMA springs which counteract the force of two traditional springs was developed. A dummy plain sliding sleeve with SMA and conventional springs was numerically developed and tested. The fairly good agreement of the results confirmed the feasibility of the combined SMA/MR device.
Embedded Catalytic Healing Agents for the Repair of Fibre-Reinforced Composites
Authors: Everitt Daniel , Trask Richard , Wass Duncan , Bond Ian
Published: December 2014

The inclusion of latent catalytic healing agents (CHAs) during layup of fibre-reinforced polymer (FRP) composite specimens yields a functionalised composite material with the capability to self-repair. Strategies for preventing the reaction of CHAs with prepreg resins during curing of the host material are explored.

The inclusion of catalyst as an interleave on the composite mid-plane was found to be detrimental to the fracture toughness of the double cantilever beam (DCB) specimens. A potential application for this effect includes damage redirection, whereby propagating damage is steered into self-healing features. This will be an area of interest for future investigation.

Upon failure of the composite, healing is achieved by addition of a low-viscosity epoxide monomer and heating the material to activate the curing agent. Specimens featuring embedded Sc(OTf)3 healed for 2 hours at 200°C showed a mean recovery in peak load of 79%.
Probing Multiferroic Heterostructures of BiFeO3-LiMn2O4 Using Magnetic, Piezoelectric and Piezomagnetic Force Microscopies
Authors: Eshghinejad Ahmadreza , Liang Wen-I , Chen Qian Nataly , Ma Feiyue , Chu Ying-Hao , Li Jiangyu
Published: December 2014

In this study magnetic force microscopy (MFM), piezoresponse force microscopy (PFM), and the newly developed piezomagnetic force microscopy (PmFM) techniques are used to probe the ferroelectric and ferromagnetic properties of BiFeO3-LiMn2O4 (BFO-LMO) heterostructures at nano-scale. The PmFM technique is also used to probe the ferromagnetic properties of CoFe2O4 (CFO) as a case study. The PFM and PmFM mappings of the BFO-LMO heterostructures clearly distinguish the BFO matrix and LMO nanopillars while the MFM mapping is ambiguous. The relatively high piezomagnetic response of BFO matrix is believed to be due to the Mn doping while the piezoelectric-like response of LMO nanopillars is due to the ionic activities and the vertical geometry of its heterostructure. Lastly, limitations of the PmFM technique are discussed.
Stability Analysis of the Wing Leading Edge Spar of a Passively Morphing Ornithopter
Authors: Wissa Aimy , Calogero Joseph , Hubbard James E. , Frecker Mary
Published: December 2014

This paper presents a stability model for the wing leading edge spar of a test ornithopter. The long-term goal of this research effort is to passively improve the performance of ornithopters during steady level flight by implementing a set of wing kinematics found in natural flyers. The desired kinematics is achieved by inserting a compliant mechanism called a compliant spine into the wing leading edge spar to mimic the function of an avian wrist. The stiffness of the compliant spine is time varying and given the nature of flapping flight, it is periodic. Introducing a variable stiffness compliant mechanism into the leading edge spar of the ornithopter affects its structural stability. Therefore, a stability analysis is required. In order to start the stability analysis, an analytical model of the ornithopter wing leading edge spar with a compliant spine inserted in is necessary. In the model, the compliant spine is modeled as a torsional spring with a sinusoidal stiffness function. Moreover, the equations of motion of the wing leading edge spar-spine system can be written in the form of non-homogeneous Mathieu’s equations, which has well-known stability criteria. The analytical system response is then validated using experimental data taken at NASA Langley Research Center. Results show that the analytical spine angular deflection agrees with the experimental angular deflection data within 11%. Stability was then demonstrated using both analytical and graphical proving that the response of leading edge spar with a compliant spine design inserted at 37% of the wing half span is bounded.
Design and Realization of a Compliant Adaptable Wing
Authors: Molinari G. , Quack M. , Arrieta A. F. , Morari M. , Ermanni P.
Published: December 2014

This paper presents the design, optimization, realization and testing of a novel wing morphing concept based on compliant structures actuated by Macro Fiber Composites. The geometry of the compliant morphing ribs is determined through multidisciplinary optimizations. The static and dynamic behavior of the wing, and the effect of activating the actuators, is assessed using 3-D aeroelastic simulations. The performance and manufacturability of a wing designed according to this approach are investigated. The achieved active deformations produce sufficient roll control authority to replace conventional ailerons.

The numerical simulation for the conformal shape adaptation of the wing is compared to experimental results, showing good agreement. The aerodynamic and structural behavior of the introduced concept is investigated through a validated finite element model, revealing the potential of the presented morphing wing.

A closed-loop controller driving high-voltage electronics counteracts the nonlinearity and hysteresis of the piezoelectric actuators, allowing for controlling the wings’ morphing level.
A Soft Combustion-Driven Pump for Soft Robots
Authors: Stergiopulos Constantinos , Vogt Daniel , Tolley Michael T. , Wehner Michael , Barber Jabulani , Whitesides George M. , Wood Robert J.
Published: December 2014

This paper describes the design and manufacture of a monolithic high-pressure diaphragm pump made entirely of soft elastomer material and driven by a combustion chamber incorporated within the soft pump structure. The pump can deliver pressures up to 60 kPa and can reach output flows up to 40 ml/min. Methane (CH4) combustion is used as the actuation source. The pump uses two soft flap-structured check valves for directing the flow. Pumping pressure and frequency dependence were measured and analyzed. Results show that controlled and repeatable combustion of methane is possible without damaging the soft structure. Experimentally, 6–10% methane is identified as the ideal air-fuel ratio for combustion. With continuous delivery of reactants, a 1 Hz pumping frequency was achieved. The volume of the combustion chamber and the material stiffness are identified to be major determinants of the stroke volume.
Thermodynamically Consistent Thermomechanical Modeling of Kinetics of Macroscopic Phase Transition in SMA Using Phase Field Theory
Authors: Agboola Babatunde O. , Baxevanis Theocharis , Lagoudas Dimitris C.
Published: December 2014

Experimental observations have shown that polycrystalline NiTi wires, strips and tubes develop inelastic strain via nucleation and growth of macroscopic martensitic domains under mechanical loading. These domains consist of almost fully-transformed grains, which result from micro-domains that are formed at the grain-size level. Evolution of these macroscopic domains via transformation front propagation is accompanied by complex interactions between mechanical work, latent heat, heat transfer, and loading rates. These interactions could affect the performance reliability or controllability of the material when deployed. Therefore, modeling effort is necessary to describe these interactions so as to improve the design and application of SMA devices. A 3-D thermodynamically consistent thermomechanical macroscopic model, which is able to describe phase transition kinetics in shape memory alloys, is proposed in this work. The model employs a Ginzburg-Landau-type kinetic law resulting from the notion of configurational forces associated with the gradient of an order parameter (a field variable). As a first attempt to demonstrate the capability of the model, 1-D simplification of the model is implemented within a finite element framework. Kinetics of phase transition and the effects of heat production associated with the thermomechanical coupling on the stress-strain response of an SMA are examined. In particular, the roles of external loading rate and heat transfer boundary conditions on the stress-strain response are investigated for displacement-controlled loading. Results obtained are in good agreement with experimental trends.
Experimental Investigation on the Efficiency of a Control Dependent NiTi-Based Cooling Process
Authors: Schmidt Marvin , Schütze Andreas , Seelecke Stefan
Published: December 2014

Energy efficient systems and environmentally friendly solutions are the focus of many commercial development projects. Current refrigeration technology carries a significant share of global energy consumption and exploring alternative refrigeration principles has become increasingly important. Shape memory alloys (SMA’s), especially Nickel-Titanium (NiTi) alloys, generate a large amount of latent heat during solid-state phase transformations, which can lead to a significant cooling effect in the material. These materials not only provide the potential for an energy efficient cooling process, they also minimize the impact on the environment by reducing the need for conventional ozone-depleting refrigerants.

This paper presents the first experimental results obtained in a project within the DFG Priority Programme SPP 1599 “Ferroic Cooling”. It focuses on the performance of a control-dependent process of a NiTi-based cooling system. First, a suitable cooling process is introduced and the underlying mechanisms of the process are explained. Then different process variations are developed, which influence the efficiency of the cooling process. These process variations are systematically analyzed with a novel, experimental testing system capable of tuning process parameters independently. The testing system is able to measure force, displacement, temperature distribution and heat simultaneously. The coefficient of performance (of the cooling process) can then be determined by which the influence of the control process on the efficiency can be observed.
Self-Post-Tensioning for Concrete Beams Using Shape Memory Alloys
Authors: Sherif Muhammad , Ozbulut Osman , Landa Asheesh , Hamilton Reginald F.
Published: December 2014

This study explores the use of shape memory alloys for self-post-tensioning concrete beams. SMAs have the ability to regain their original shape after being deformed up to 6–8% strain. This shape recovery is a result of an underlying reversible solid-solid phase transformation, which can be induced by either a stress (superelastic effect) or a temperature change (shape memory effect). The shape memory effect can be exploited to prestress concrete. The heat of hydration of grout can thermally activate SMA tendons to obtain self-post-tensioned (SPT) concrete. NiTi-based SMAs are promising due to their corrosion resistance and resistance against low frequency/cycle fatigue failure. NiTiNb alloys are a class of SMAs that exhibit a wide temperature hysteresis and transformation temperatures near the service temperatures required for practical application. Here, NiTiNb shape memory alloys are studied to design an optimized SMA that can be activated using hydration heat. The material design and characterization of the SMA tendons are discussed. The temperature increase due to the heat of hydration of four commercially available grouts is investigated. The bond behavior of SMA tendons is evaluated through pullout tests. Digital Image Correlation method is used for monitoring the slippage of the SMA tendons. The feasibility of developing SPT concrete is assessed through experimental studies. The use of SMAs, which possess high fatigue and corrosion resistance, as post-tensioning tendons in concrete members will increase the service life and provide life cycle cost savings for concrete bridges. The replacement of steel tendons with SMA prestressing tendons will prevent corrosion-induced deterioration of tendons in concrete structures. The use of heat of hydration of grout to activate the shape memory effect of SMA tendons will provide self-stressing capability. This will greatly simplify the tendon installation. The need for jacking equipment or electrical source will be eliminated.
Modeling of a Heaving Buoy Wave Energy Converter With Stacked Dielectric Elastomer Generator
Authors: Moretti Giacomo , Fontana Marco , Vertechy Rocco
Published: December 2014

This paper introduces a novel architecture of Wave Energy Converter (WEC) provided with a Dielectric Elastomer (DE) Power Take–Off (PTO) system. The device, named Poly–Buoy, includes a heaving buoy as primary interface, that captures the mechanical energy from waves, and a DE Generator (DEG), made by stacked layers of silicone elastomer, that converts mechanical energy into electricity.

A mathematical model of the Poly–Buoy is proposed, which includes analytical electro–hyperlastic equations for the DEG and a linear model for wave-buoy hydrodynamics.

Procedures for the design and optimization of different layouts and control strategies for the DE–PTO are introduced that specifically consider single–DEG and dual–DEG architectures. A numerical case study is also reported for specific geometrical dimensions of the buoy and specific wave climate data.
Piezoelectric Patch-Based Energy Harvesting on a Heavy Duty Vehicle Panel
Authors: Bayik Bugra , Aghakhani Amirreza , Aridogan Ugur , Basdogan Ipek
Published: December 2014

Vibration-based energy harvesting has drawn significant attention from different engineering disciplines over the last two decades. The studies in this research area have mostly concentrated on cantilevered piezoelectric beam harvesters under base excitations. As an alternative to beam arrangements, patch-based piezoelectric energy harvesters can be integrated on large plate-like structures such as panels of automotive, marine and aerospace applications to extract useful electrical power during their operation. In this paper, electroelastic finite element (FE) simulations of a patch-based piezoelectric energy harvester structurally integrated on a panel of a heavy duty vehicle are presented during different phases of operation. FE model of the panel together with a piezoceramic harvester patch is built using ANSYS software. The FE model takes into account coupled electromechanical dynamics and the fully-conductive electrode layers of the harvester patch. The vibration response of the panel as well as the voltage output of the harvester patch under operating conditions is simulated using the forces obtained from experimental measurements on the heavy duty vehicle. Excitation forces are calculated from operational acceleration measurements using matrix inversion method, which is a force identification technique. Two different operating conditions of the heavy duty vehicle are considered: stationary and moving on a test track while the engine was running. Using the excitation forces in the FE simulations, the electrical power generation of the harvester patch is predicted for a wide range of resistive loads. Electrical power outputs are then presented for short-circuit and open-circuit conditions. The numerical results show that the use of a harvester patch attached on a panel of a heavy duty vehicle generates reasonably well electrical power outputs.
Spectral Analysis and Characterization of a Membrane-Based Artificial Hair Cell Sensor
Authors: Sarlo Rodrigo , Leo Donald , Tarazaga Pablo
Published: December 2014

A fully hydrogel-supported, artificial hair cell (AHC) sensor based on bilayer membrane mechanotransduction is designed with sensitivity and versatility in mind. Thanks to fabrication improvements from previous generations, the sensor demonstrates peak current outputs in the nanoamp range and can clearly measure inputs as high as 2k Hz. Characterization of the AHC response to base excitation and air pulses show that membrane current oscillates with the first three bending modes of the hair. Output magnitudes reflect of vibrations near the base of the hair. A 2 DOF Rayleigh-Ritz approximation of the system dynamics yields estimates of 19 N/m and 0.0011 Nm/rad for the equivalent linear and torsional stiffness of the hair’s hydrogel base, although double modes suggest non-symmetry in the gel’s linear stiffness. The sensor output scales linearly with applied voltage (1.79 pA/V), avoiding a higher-order dependence on electrowetting effects. The free vibration amplitude of the sensor also increases in a linear fashion with applied airflow pressure (18.4 pA/psi). Based on these sensitivity characteristics, an array sensing strategy for these sensors is proposed.
Local Triads of Sensors to Mine Collocated Acceleration for Structural Health Monitoring of an Aluminum Beam With Bolted Joints
Authors: Georgiou Ioannis T.
Published: December 2014

Several aerospace, space, and naval platforms process a core structural system assembled wholly or partially by aluminum alloy elementary structures, such as beams, plates, and cylinders, among others. Aluminum alloys are preferred due to light weight and corrosion resistance. The formed complex aluminum alloy structure is characterized by a number of joints where different structural elements are joined together. Areas with joints are prone to damage. Some joints are made by bolts for assembly and reassembly purposes. A loose bolt can be considered as a man-induced damage in the whole complex structure. This damage can result in a catastrophic failure. The vibration and elastic wave propagation-based monitoring of a critical area bearing bolt joints can offer a reliable monitoring. In this work, we present a basic experimental research effort. We consider an aluminum alloy beam composed of two sunbeams joined by means of two bolts. The bolts are healthy in the sense that they are tight to the level of design recommended force. We use three mono-axial sensors in three dimensional arrangement and mine vibration-wave data in the form of collocated signals. These signals are analyzed by means of the proper orthogonal decomposition transform. The local tri-axial arrangement of mono-axial sensors is used to collect collocated acceleration signals in two local areas. One of the local areas contains the bolted joints. The other local area contains the free end of the structure. This is not considered as a critical area but a boundary accessible area. The POD modal structures of collocated vibration signals are quite different. The behavior is compared to that of structure without bolted joints.
Development and Characterization of Embedded Sensory Particles Using Multi-Scale 3D Digital Image Correlation
Authors: Cornell Stephen R. , Leser William P. , Hochhalter Jacob D. , Newman John A. , Hartl Darren J.
Published: December 2014

A method for detecting fatigue cracks has been explored at NASA Langley Research Center. Microscopic NiTi shape memory alloy (sensory) particles were embedded in a 7050 aluminum alloy matrix to detect the presence of fatigue cracks. Cracks exhibit an elevated stress field near their tip inducing a martensitic phase transformation in nearby sensory particles. Detectable levels of acoustic energy are emitted upon particle phase transformation such that the existence and location of fatigue cracks can be detected. To test this concept, a fatigue crack was grown in a mode-I single-edge notch fatigue crack growth specimen containing sensory particles. As the crack approached the sensory particles, measurements of particle strain, matrix-particle debonding, and phase transformation behavior of the sensory particles were performed. Full-field deformation measurements were performed using a novel multi-scale optical 3D digital image correlation (DIC) system. This information will be used in a finite element-based study to determine optimal sensory material behavior and density.
Experimental Investigation and Numerical Simulation of the Mechanical and Thermal Behavior of a Superelastic Shape Memory Alloy Beam During Bending
Authors: Ullrich Johannes , Schmidt Marvin , Schütze Andreas , Wieczorek André , Frenzel Jan , Eggeler Gunther , Seelecke Stefan
Published: December 2014

Superelastic Shape Memory Alloys (SMA) are typically used in applications where the martensitic phase transformation is exploited for its reversible, large deformation such as medical applications (e.g. stents).

In this work, we focus on the mechanical and thermal behavior of a Nickel-Titanium SMA strip in bending mode. One possible application of this mode is to provide a restoring force when used in joints of SMA wire actuator systems making the need for an antagonistic SMA actuator redundant. In these applications mentioned above, typically only the mechanical properties are of interest while the temperature is considered constant, even though the martensitic phase transformation in SMA is a thermo-mechanically coupled process.

As a part of the DFG (German Research Association) Priority Programme SPP1599 “Ferroic Cooling” which aims at advancing the development of solid state cooling devices, we have an equally large interest for the thermal evolution of Nickel-Titanium SMA during deformation and its induced phase transformation.

In this paper we investigate the thermal and the mechanical response of a SMA beam during bending experiments in which the deformation is induced by holding one end of a SMA strip fixed while the other end is subject to a prescribed deflection. Sensors and high speed thermal cameras are used to capture reaction forces, deformations and temperature changes. We compare these experimental results with numerical simulation results obtained from Finite Element simulations where a thermo-mechanically coupled SMA model is implemented into a finite deformation framework.
Smart Disaster Mitigation in Italy: A Brief Overview on the State of the Art
Authors: Felli Ferdinando , Paolozzi Antonio , Vendittozzi Cristian , Paris Claudio
Published: December 2014

Italy is notoriously exposed to several natural hazards, from hydrological to volcanic and, above all, to seismic activity that affects a large part of the national territory. Historically the devastating effects of tsunamis have also been recorded, despite the peninsula is confined in the Mediterranean basin (i.e. Messina earthquake in 1908, and more recent the activity of the undersea volcano “Marsili”). Since Italy is particularly exposed to such hazards, many research institutions are involved in campaigns about monitoring, prevention and mitigation of the effects of such phenomena, with the aim to secure and protect human lives, and secondly, the remarkable cultural heritage.

The present paper will first make a brief excursus on the main Italian research projects aimed at the mitigation of environmental disasters, referring to projects of national and international relevance, being implemented, such as the MOSE (for the containment of the tides and of high water, for the preservation of cultural and artistic heritage of Venice and of the entire ecosystem of the lagoon); the research in earthquake-resistant structures performed for instance by ENEA and finally the COSMO-SkyMed (CSK) program of the Italian Space Agency (ASI), which has among its purposes the environmental monitoring and surveillance applications for the management of exogenous, endogenous and anthropogenic risks.

Furthermore in the paper, it will be described some new ideas concerning the use of smart materials and structures capable of self-monitoring and self-diagnosis of the risk of failure and adapting itself to environmental condition variations, in order to avoid catastrophic effects, thanks to an integrated network of sensors and actuators.
Novel Self-Healing Systems: Expanding and Inhibited Healing Agents
Authors: Rae S. I. , Bond I. P. , Trask R. S. , Wass D. F.
Published: December 2014

A new approach to self-healing systems is presented that aims to overcome the inherent drawbacks of conventional liquid resin based healing systems within composites. Finite embedded systems offer limited healing potential for small volume delaminations and as such cannot effectively heal large damage volumes often associated with shear damaged sandwich panel structures or debonding between skin and core. An expanding polymer based approach aims to overcome such limitations. The mechanical and physical properties of a prepared polyepoxide foam are investigated and how the inclusion of a carbon fibre reinforcement within the foam affects processability and performance. The healing efficiency of different polymer foams to heal damaged structures is also investigated. A secondary investigation is also presented that aimed to overcome the drawbacks associated with the requirement for stoichiometric mixing of two part healing agents, or for healing agent to come into direct contact with a catalyst embedded within the matrix material. Different approaches were taken to develop a self-healing system that once deployed required no additional mixing or stimuli for healing to occur.
Study of Guided Wave Propagation in Honeycomb Sandwich Structures
Authors: Tian Zhenhua , Huang Guoliang , Yu Lingyu
Published: December 2014

This paper studies the guided waves in honeycomb sandwich structures and explores the ability of guided waves for the debonding damage detection. Both the finite element (FE) simulations and laser vibrometry experiments are used. A three-dimensional (3D) FE model is built to simulate the guided waves in a honeycomb sandwich plate. The simulation results show the guided waves in the structure depend on the wave frequency. At low frequencies, the global guided waves propagate in the entire sandwich, while leaky guided waves dominate in the skin panel at high frequencies. To further understand the guided wave propagation fundamentals, laser vibrometry experiments are performed. The waveforms, time-space wavefields, and frequency-wavenumber spectra obtained from the experiments are used to unveil the wave propagation features. The experimental results confirm the leaky guided waves. Moreover, the experimental results show the complex wave interactions induced by the honeycomb core. When the debonding between the skin and honeycomb core presents, the guided wave amplitude increases, and the wave interaction with the honeycomb core reduces.
Crack-Curing of Concrete Beams Using Cold-Drawn SMA Reinforcing Fibers
Authors: Choi Eunsoo , Kim Dong Joo , Chung Young-Soo , Jung Chungsung
Published: December 2014

This study used NiTi shape memory alloy (SMA) wires of 1.0 mm diameter to manufacture reinforcing fibers for cement composite. The wires were elongated by a cold drawing method which also reduced the diameter to 0.965 mm. This study prepared two types of SMA fibers such as straight and dog-bone-shaped. For bending tests, three concrete beams with a dimension of 40 mm × 400 mm × 200 mm (B×H×L) were prepared for each type of specimen. Three points bending tests were conducted. After cracking, the beams were heated at the bottom by fire frame and, then, the recovery stress in the SMA fibers developed. This stress closed the cracks, and the widths of cracks were measured. The SMA fibers, in particular don-bone shaped, were effective to close cracks and will be used for crack-curing of concrete beams.
Enhancement of Bone Implants by Substituting Nitinol for Titanium (Ti-6Al-4V): A Modeling Comparison
Authors: Moghaddam Narges Shayesteh , Elahinia Mohammad , Miller Michael , Dean David
Published: December 2014

Mandibular segmental defect reconstruction is most often necessitated by tumor resection, trauma, infection, or osteoradionecrosis. The standard of care treatment for mandibular segmental defect repair involves using metallic plates to immobilize fibula grafts, which replace the resected portion of mandible. Surgical grade 5 titanium (Ti-6Al-4V) is commonly used to fabricate the fixture plate due to its low density, high strength, and high biocompatibility. One of the potential problems with mandibular reconstruction is stress shielding caused by a stiffness mismatch between the Titanium fixation plate and the remaining mandible bone and the bone grafts. A highly stiff fixture carries a large portion of the load (e.g., muscle loading and bite force), therefore the surrounding mandible would undergo reduced stress. As a result the area receiving less strain would remodel and may undergo significant resorption. This process may continue until the implant fails. To avoid stress shielding it is ideal to use fixtures with stiffness similar to that of the surrounding bone. Although Ti-6Al-4V has a lower stiffness (110 GPa) than other common materials (e.g., stainless steel, tantalum), it is still much stiffer than the cancellous (1.5–4.5 GPa) and cortical portions of the mandible (17.6–31.2 GPa). As a solution, we offer a nitinol in order to reduce stiffness of the fixation hardware to the level of mandible. To this end, we performed a finite element analysis to look at strain distribution in a human mandible in three different cases: I) healthy mandible, II) resected mandible treated with a Ti-6Al-4V bone plate, III) resected mandible treated with a nitinol bone plate. In order to predict the implant’s success, it is useful to simulate the stress-strain trajectories through the treated mandible. This work covers a modeling approach to confirm superiority of nitinol for mandibular reconstruction. Our results show that the stress-strain trajectories of the mandibular reconstruction using nitinol fixation is closer to normal than if grade 5 surgical titanium fixation is used.
An Investigation of Effective Process Parameters on Phase Transformation Temperature of Nitinol Manufactured by Selective Laser Melting
Authors: Andani Mohsen Taheri , Haberland Christoph , Walker Jason , Elahinia Mohammad
Published: December 2014

It’s well accepted that the thermo-mechanical properties of Nitinol (NiTi) are strongly affected by the material processing. Additive manufacturing has been recently considered as an interesting technique to develop Nitinol devices with sophisticated geometries, which are impossible or very difficult to be produced through typical manufacturing procedures. In the present work, the effect of energy input on the phase transformation temperatures, as the most critical thermal parameters of the shape memory material, of Nitinol parts manufactured by selective laser melting is investigated and discussed.
Vibration Characteristics of Magnetic Nano Fluids-Filled Flexible Cantilevers Under Varied Magnetic Fields
Authors: Masoumi Masoud , Wang Ya
Published: December 2014

In this paper, the influence of an external magnetic field on the vibration responses and damping ratios of a vascular beam filled with three different magnetic nanofluids are investigated. First, the equation of motion of a fluid-filled beam is derived based on the published works and some amendments are made to simultaneously include the damping ensuing from the surrounding air and also the effects of viscosity of the fluid inside the vascular channel. Then, the effects of an external magnetic field on the viscosity of the fluid is studied and incorporated into the equation of motion of the beam. Finally, based on three magnetic nanofluid samples, simulations are conducted to represent the changes in frequency response functions and damping ratios of the vascular channel beam. The maximum increase observed in the viscosity of the magnetic nanofluid samples under the influence of magnetic field with the intensity of 1 Tesla was 16%, while the reduction in the vibration amplitude found 12.7% and 33.8% for the first and second vibration mode under the influence of the maximum magnetic field intensity of 0.3 Tesla. Moreover, the maximum decrement of the damping ratio was 1.1% under the same magnetic field. However, it seems that the higher values for vibration reduction can be achieved by using the magnetic nanofluid with higher magnetic particle concentrations and viscosities.
Effects of Sensor Geometry on the Stress-Averaged Output of PVDF Sensors in Tires
Authors: Headings Leon M. , Park Jungkyu , Dapino Marcelo J.
Published: December 2014

Polyvinylidene fluoride (PVDF) sensors are attractive for use in tires due to their high sensitivity, fast response time, low cost, and ability to operate without power supplies or signal amplification. Based on sensor design, placement, and signal processing techniques, they may be used to determine tire parameters such as tire revolutions, footprint size, and cornering and traction conditions. PVDF sensors generate a voltage output that is related to the average stress acting on the sensor. For non-uniform distributions of stress over the sensor area, there can be a significant difference between the stress at a point and the average sensor stress calculated from the measured voltage. Understanding the effects of sensor geometry on sensor output is important for designing sensors for specific applications, such as tires. This paper presents analytical and numerical models for PVDF voltage output that are developed from the linear piezoelectric constitutive equations, with the average sensor stress modeled using a convolution of the stress input and the PVDF electrode shape. Parametric studies on rectangular, stepped, and triangular sensor shapes show the effects of sensor geometry on voltage output for PVDF sensors under sinusoidal and tire stress inputs.
Efficient Response Monitoring of Flexible Structures
Authors: Chierichetti Maria , Rahneshin Vahid
Published: December 2014

The definition of an accurate model to represent the dynamic behavior of a flexible system has a significant impact on the understanding of its current health. However, due to lack of information on the physical properties as well as complexity of applied loads, accurate modeling is not usually a simple task, and inaccuracies in predicting the response of the flexible structure arise. In this work, a combined experimental and numerical approach, called Extended Load Confluence Algorithm (ELCA), is presented to improve the accuracy in the estimate of the dynamic response using an iterative approach that corrects the initial model. The objective is to accurately estimate the displacements, strains, and accelerations of the entire body. The full-field dynamic response is reconstructed from a limited set of experimental data, with little knowledge about the applied loads. ELCA estimates the state of the structure by defining fictitious applied forces that depend on the error of the estimate. The proposed algorithm is based on an initial numerical model for the prediction of the system s behavior. This model is updated based on a modal expansion of the response in the frequency domain. The algorithm starts with an initial guess of the applied loads and updates them in few iterations in order to match the numerical dynamic response with the experimental measurements at the sensors locations. Numerical and experimental analyses will show the feasibility of the proposed approach. It will be shown that a few sensors are sufficient to represent the overall behavior of the system and ELCA converges in a few iterations.
Microvascular Composites for Thermal Management
Authors: Fetfatsidis Konstantine A. , Dropkin Amanda , Dahlstrand Paul , Hansen Christopher , Poillucci Richard , Olson Brad
Published: December 2014

Manned and unmanned aircraft are commonly manufactured from lightweight composite materials, replacing heavier metallic aircraft materials. Here, we describe a collaborative industrial-academic effort to develop novel microvascular composites that offer thermal and structural multifunctionality via embedded micro-capillary array-based heat exchangers for thermal management embedded within aerospace-grade carbon prepreg material. The current research establishes a route to create prepreg materials suitable for heat exchanger network manufacture by automated fiber placement processes. Potential network geometries are investigated with analytical fluid models to predict flow characteristics and heat distribution for pre-defined heat exchanger configurations within a carbon composite panel. Based on these predictions, two geometries are fabricated for thermal management experiments. The mechanical effect of the embedded microvascular networks on the panel structural properties is also investigated analytically.
Experimental Investigations on Viscoelastic Properties of a Shape Memory Polymer
Authors: Butaud Pauline , Ouisse Morvan , Placet Vincent , Foltête Emmanuel
Published: December 2014

The shape memory polymers (SMPs) are polymeric smart materials which have the remarkable ability to recover their primary shape from a temporary one under an external stimulus. The study deals with the synthesis and the thermo-mechanical characterization of a thermally-actuated SMP, the tBA/PEGDMA, with a special focus on viscoelastic properties. The mechanical characterization is performed using three kinds of tests: quasi-static tensile tests, dynamic mechanical analysis (DMA) and modal tests. The first one allows the identification of the Youngs modulus and the Poisson’s ratio at ambient temperature. Modal analyses are done for various temperature values, and resonance frequencies are measured. In order to validate the time-temperature equivalence on this SMP, a DMA is performed under harmonic loading for different temperatures and a master curve highlights a complementarity of the results. Finally a suitable model for the viscoelastic behavior of the SMP is identified.
Dynamic Characteristics Analysis of a Silicon Pressure Sensor Using Network Methods
Authors: Hessinger Markus , Werthschützky Roland
Published: December 2014

This paper presents a method to describe electromechanical systems with an equivalent network description for an early investigation of the dynamical behavior during the design process. The procedure using equivalent circuits modeling for system description is outlined with an example of characterizing a silicon pressure sensor for a first analysis of its transmission behavior. Therefore, the sensor is separated into acoustic and mechanical systems of the casing and electromechanical systems of the silicon element. Friction, compliance and mass of the diaphragm for the pressure application are modeled in the mechanical domain using the equivalent electrical symbols of resistance, inductance and capacity. The pressure transmission with a filling fluid in a canal is modeled using acoustic parameters. The solution of the transfer function enables an analysis of the amplitude frequency response between the acoustic, mechanical and electric systems of the sensor. A first comparison between simulation and measurement results shows a correlation in the pressure transfer function of the silicon sensor.
Modelling of Piezoceramic Patches for Actuator Placement Strategies
Authors: Rose Michael
Published: December 2014

Piezoceramic Patches are commonly used as actuator devices in smart structures if the induced forces are sufficient for the application. To model these devices in a structural dynamics simulation, a finite element model can be augmented by active layers. This needs a suitable element meshing, taking care of the actual shapes and positions of the active patches in use. If many different setups have to be evaluated, which is naturally the case for placement strategies for suitable actuator positions, this approach is quite cumbersome. To ease and speed up the augmentation of fixed finite element models with piezoceramic patches, so called modal correction methods have been successfully used in this context. These approximative methods avoid the remeshing and the reassembling of the underlying finite element model by adapting the modal description of the structural model with the mass, stiffness and electrical coupling effects of the applied patches. In this paper different aspects of this modelling approach are discussed especially for a tool chain to optimize patch locations in an ASAC simulation environment.
Fast and Globally Convergent Nonlinear System Model for 3D Magnetostrictive Systems
Authors: Tari Hafez , Dapino Marcelo J.
Published: December 2014

A globally convergent and fully coupled magnetomechanical model for 3D magnetostrictive systems is presented. In magnetostrictive actuators, magnetic field and stress inputs generate magnetic flux density and strain. We refer to models that follow this scheme as direct models (no relation to the direct magnetomechanical effect). In certain design and control situations, inverse models are necessary in which the magnetic field and stress are found from specified magnetic flux density and strains. This inversion typically involves an iterative procedure, which may be prone to convergence issues. An inverse model approach is proposed for arbitrary magnetostrictive materials. The inversion requirement is a continuous and second order differentiable direct model for any chosen magnetostrictive material. The approach is globally convergent, which makes it ideal for use in finite element frameworks. The premise of the proposed iterative system model is to constitute a recursive correction formula based on second order approximations of a novel scalar error function which allows to achieve a faster convergence rate. A continuation approach is then used to achieve global convergence for arbitrary input parameters. To illustrate, Galfenol is chosen as the magnetostrictive material, and analytical derivations of the Jacobian and Hessian matrices are presented. Finally, the computational efficiency of the proposed approach is shown to compare favorably against existing models.
Model Calibration for Beam Models in the Presence of Model Discrepancy
Authors: Lewis Allison L. , McMahan Jerry A. , Smith Ralph C.
Published: December 2014

Piezoelectric, magnetic and shape memory alloy (SMA) materials offer unique capabilities for energy harvesting and reduced energy requirements in aerospace, aeronautic, automotive, industrial and biomedical applications. However, all of these materials exhibit creep, rate-dependent hysteresis, and constitutive nonlinearities that must be incorporated in models and model-based control designs to achieve their full potential. Furthermore, models and control designs must be constructed in a manner that incorporates parameter and model uncertainties and permits predictions with quantified uncertainties. In this presentation, we compare the Euler-Bernoulli and Timoshenko beam models for a cantilever beam with an applied PZT patch to illustrate parameter estimation in the presence of model discrepancy.
Modeling of ion drift in 4H-SiC-based chemical MOSFET sensors
Authors: Erlbacher Tobias , Schwarzmann Holger , Bauer Anton J. , Döhler Gottfried H. , Schreivogel Martin , Lutz Theresa , Guillén Francesco H. , Graf Jürgen , Fix Richard , Frey Lothar
Published: December 2014

The effect of mobile ions on electrical performance in ion-sensitive metal–oxide–semiconductor field effect transistor fabricated on 4H silicon carbide for the application as chemical fluid and gas sensors in harsh environments was investigated. The drift and diffusion of these mobile ions in the dielectric gate stack were identified as the source for a change in the sensor signal. The movement of the ions and the resulting electrical properties were successfully modeled using a novel drift–diffusion model implemented in tcad simulation software. The diffusion coefficient and activation energy for drift and diffusion of sodium through an amorphous silicon nitride layer were estimated from these simulations.