This PDF file contains the front matter associated with SPIE Proceedings Volume 10165, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Embedded and surface bonded piezoelectric wafers have been widely used for control, energy harvesting, and structural health monitoring applications. The basis for all these applications is the energy transfer between the piezoelectric wafer and the host structure, which takes place through the adhesive bonding layer. The characteristics of the bonding layer are found to have an important impact on the sensing and actuation capabilities of piezoelectric-based applications. In this paper, the high-frequency dynamic response of an elastic beam coupled with a piezoelectric wafer is investigated, including the bonding layer in between. A previously developed three-layer spectral element model, with high-frequency capabilities, is utilized for this purpose. Timoshenko beam and elementary rod theories are adopted to describe axial and lateral deformations in each of the three layers. A parametric study is conducted to evaluate the effects of bonding layer characteristics on the steady-state dynamic response of the coupled system, including frequency response functions and electromechanical impedance. The frequency-dependent nature of bonding layer effects is highlighted and discussed.

Electric antennas are still large structures (approximately 1m for 300 MHz operation), and have so far eluded the miniaturization trend common in the electronics industry. This is due in large part to an impedance mismatch with free space, and an increase in system losses from ohmic heating as antenna dimensions shrink. Recent work has proposed using multiferroic heterostructures to create small energy efficient antennas. This idea was first explored by Rowen’s 1961 paper on electromagnetic (EM) radiation from YIG, and Mindlin’s 1973 paper on radiation from quartz. Since then limited work has looked at EM radiation from adaptive materials, and there are currently no analytical models describing such a device. This presentation provides an analytical model to examine small mechanically powered energy efficient antennas. An analytical framework is provided that couples elastodynamics and electrodynamics using piezoelectric and piezomagnetic constitutive behavior. This approach uses an eigenmode expansion of the undamped longitudinal vibrations in a prismatic rod to describe EM radiation from each harmonic mode. The problem is reduced to examination of damped harmonic oscillators, and EM radiation is shown equivalent to an effective volumetric strain-rate dependent damping. This approach provides the frequency response of a mechanical antenna, and demonstrates important scaling behavior relative to conventional antennas. Resonant analysis leads to simple closed form expressions for antenna efficiency, and leads to a metric directly comparing mechanical and conventional antennas, facilitating both material selection and device design. To summarize, this presentation provides a first look at the strain-mediated control of wireless communications.

Real time measurement of time-correlated ion transport and volumetric changes in electroactive materials is necessary to understand and model mechanoelectrochemistry. Reversible reduction and oxidation of soft electroactive materials such as conducting polymers result in the deformation of the material due to ion transport into and out of the polymer backbone. In cells, ion transport and volumetric expansion are collectively responsible for homeostasis that is essential for life functions and hence, mechanoelectrochemistry of cells is essential to understand cell and developmental biology. The characterization methods required to investigate mechanoelectrochemistry require nanoscale spatial resolution for the imaging of a redox active site in a polymer or a small group of transmembrane proteins in a single cell. Towards this goal, we present an imaging technique using scanning electrochemical microscopy (SECM) hardware with shear-force (SF) feedback for high bandwidth mechanoelectrochemistry characterization. In this proceedings article, we demonstrate this technique referred to as surface-tracked scanning electrochemical microscopy technique (ST-SECM) that is realized by measuring the structural feedback of the glass electrode to position the electrode in 10s of nanometers above the surface of a polypyrrole membrane doped with dodecylbenzenesulfonate (PPy(DBS)). Two ultra-microelectrodes of controlled dimensions (of 20 μm and 30 μm glass diameter) were fabricated using a hydrofluoric acid etching technique and were used to generate a spatially correlated ion storage map of PPy(DBS). We compare the developed technique to a three-dimensional discrete scan over the surface and show that a ST-SECM technique produces a higher resolution and takes approximately 200 fewer minutes as compared to the conventional technique.

The functionality of smart structures and microelectromechanical systems, such as ferroelectric multilayer ac- tuators (MLA), macro-fiber composites, etc., can be essentially influenced by crack formation. In the current research possible cracking patterns in PZT MLAs are numerically modeled by finite element method (FEM). Fully coupled electro-mechanical FE analysis is used to investigate the MLA behavior during poling process and under subsequent in-service electromechanical loading. Ferroelectric user elements are developed for commercial software ABAQUS to mimic micromechanical non-linear bulk material behavior. They allow to simulate realisti- cally the poling process of ferroelectric ceramics as a result of tetragonal domain switching. It is known from the experiments, that cracks mainly originate from an electrode tip and then propagate along the electrode interface. There are as well oblique cracks and cross-cracks observed in MLAs. In many cases the type and direction of emerging cracks depend on cofired, non-cofired or partially cofired model of boundary conditions. Initially, the direction of maximum tangential stresses is studied at different positions along the electrode plane. Then electromechanical cohesive elements (EMCZE) are inserted between the bulk ferroelectric elements perpendicular to the direction of action of the maximum tangential stresses. Damage in the CZE is accumulated in accordance with the traction-separation law. As a result of the simulations different patterns of crack propagation in MLAs with cofired, non-cofired or partially cofired ceramics layers are found and studied. The numerical results co- incide with the experimental observations and lead to a better understanding of the complicated multi-physics processes taking place in smart structures.

We consider global sensitivity analysis (GSA) for correlated parameters in a continuum phase-field model for ferroelectric materials. The model was previously calibrated using density functional theory (DFT) simulations. For single domain ferroelectric lead titanate crystals, GSA is employed to rank the sensitivity of phenomenological parameters governing the Landau energy surface. The sensitivity analysis is based on Sobol’s variance-based decomposition in which the component functions of the high-dimensional representation (HDMR) of the model are computed analytically. For the subset of parameters that are most correlated, high-order component functions and sensitivity indices are found to be significant.

The evolution and formation of domain structures in ferroelectric materials is modeled using a continuum phase field approach and compared with density functional theory (DFT) using Bayesian uncertainty analysis. These simulations are carried out on the ferroelectric, lead titanate. Self-consistency between DFT and the continuum approach is advantageous when computing polydomain structures and domain wall dynamics. There is uncertainty in the phenomenological parameters related to the Landau energy, electrostriction, and twinned domain wall energy in single and polydomain ferroelectric crystals. To quantify the model parameter uncertainty associated with the phase field model, Bayesian statistics were used. Specifically, we will focus on estimating the value of the exchange parameters associated with polarization gradients. The phase field model predictions for the 180° domain wall energy are calibrated based upon DFT calculations. Model predictions of domain wall size are found to be on the same order as DFT calculations.

In this paper, we discuss the development of models for PZT bimorph actuators used to power micro-air vehicles including Robobee. Due to the highly dynamic drive regimes required for the actuators, models must quantify the nonlinear, hysteretic, and rate-dependent behavior inherent to PZT. We first employ the homogenized energy model (HEM) framework to model the actuator dynamics. This provides a comprehensive model, which can be inverted and implemented for certain control regimes. We additionally discuss the development of data-driven models and focus on the implementation of a model based on a dynamic mode decomposition (DMD). Finally, we detail attributes of both approaches for uncertainty quantification and real-time control implementation.

Domain engineered rhombohedral relaxor ferroelectric single crystals of PIN-PMN-PT have stable domain structures that increase the piezoelectric constants and reduce dielectric loss, yet modeling the energetics of the domain formation and evolution has proven challenging. In this work a 10th order Landau-Devonshire energy function has been developed that reproduces the dielectric, piezoelectric and ferroelectric properties of PIN-PMN-PT with a composition in the rhombohedral phase near MPB. The coercive field was used to set the saddle points in the energy function governing homogeneous polarization switching. The energy function was implemented in a phase field model to simulate domain wall formation and domain evolution under applied field. The domain wall motion reduces the coercive field in the heterogeneous switching case compared to the homogeneous switching case.

The multiple-shape-memory ionic polymer-metal composite (MSM-IPMC) actuator can demonstrate complex 3D deformation. The MSM-IPMC have two characteristics, which are the electro-mechanical actuation effect and the thermal-mechanical shape memory effect. The bending, twisting, and oscillating motions of the actuator could be controlled simultaneously or separately by means of thermal-mechanical and electro-mechanical transactions. In our study, we theoretically modelled and experimentally investigated the MSM-IPMC. We proposed a new physical principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSMIPMC was developed. It is based on the assumption that the multiple shape memory effect is caused by the thermal stress and each individual Young’s modulus is ‘memorized’ during the previous programming process. As the MSM-IPMC was reheated to each temperature, the corresponding thermal stress was applied on the MSM-IPMC, and the Young’s modulus was recovered, which result in the shape recovery of the MSM-IPMC. To verify the model, a MSM-IPMC sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the experimental results, both results have a good agreement. The current study is beneficial for the better understanding of the underlying physics of MSM-IPMC.

Shape Memory Alloys (SMAs) are drawing much attention from the active materials community due to the solid-solid phase transformation which exhibits large actuation strains at large actuation stress levels. As SMAs become better understood, SMAs may become more commonly utilized as components of a system. Such systems would require SMAs to be attached to other components, often leading to a stress concentration at the attachment point. Therefore it is necessary to develop a more thorough understanding of how stress concentrations affect the failure in SMA actuators. One such stress concentration which is often encountered when attaching structural components together is a hole or notch, which lead to triaxial states of stress around these stress concentrations. In this work, notched cylindrical SMA specimens are investigated to elucidate how the triaxiality of the notches affect the stress profiles and phase transformation behavior. Numerical results indicate that by changing the radius of the notch in cylindrical specimens, the evolution of the phase transformation is directly affected, which also impacts the distribution of stress along the area of minimum cross-sectional area. Experimental results are also presented, providing evidence that phase transformation in the presence of a stress concentration while at sufficient loads may lead to failure of the SMA.

Low-cost iron-based shape memory alloys (SMAs) have great potential for applications in large engineering parts. Their main drawback relates to their higher density compared to Nitinol and Cu-based SMAs, and can be compensated by using porous Fe-SMAs or by lightening the structures through the introduction of engineered cavities. In this manuscript, we simulate the thermomechanical response of a tapered Fe-Mn-Si beam with web openings using a 3D phenomenological model that was previously developed by the authors. The model is implemented in ABAQUS through a user defined material subroutine (UMAT). The results obtained by applying a pressure of 1 MPa and fixing both vertical ending faces show that, at room temperature, the smart beam can recover completely its initial shape. In contrast, a steel beam with the same geometry subjected to identical boundary conditions is found to fail at a much lower load. Even if the deformation of the SMA beam is dominated by plastic deformation as the loading temperature increases, its perfect shape memory effect at room temperature can be used to renovate architectural heritage or to design new smart structures.

Current efforts towards the identification of suitable processing parameters of shape memory alloys (SMAs) that enhance their actuation performance, are based on semi-empirical approaches. This is largely due to a lack of models able to predict the macro-mechanical response of SMAs as function of given composition and the temperature and time of an imposed heat treatment. The present work aims for the development of multi-field Finite Element (FE) based models, for the NiTiHf SMA material system, adequate to address these challenges and able to simulate materials macro-mechanical response including transformation strain, hysteresis and transformation temperatures. Representative Volume Elements (RVEs) with periodic geometry and boundary conditions are used to model materials microstructure. Randomly placed precipitates are considered in the NiTiHF matrix, while eigenstrains corresponding to the lattice mismatch between the precipitates and the matrix are introduced in order to model the residual stress and strain fields. The Hf concentration field is taken into consideration in addition to the displacement field in order to capture the Hf diffusion process through the adoption of Fickian diffusion law. To this end the composition of NiTiHf in the vicinity of the precipitates is computed thus resulting in substantial SMA transformation temperature shifts. The developed framework is validated based on correlations with experimental results.

This paper demonstrates the feasibility of forming multi-functional graphene based surfaces capable of thermal heating for de-icing applications. Developmental ink layers are deposited onto composite laminate skin surfaces and used to melt the ice-skin interface by Joule heating while simultaneously developing a thermal strain in the skin structure to develop a shear stress to debond the ice-skin interface. The electrical properties, microstructure, processing parameters, heat transfer and electro-thermal response of the electrically conductive developmental ink layers are examined along with the change in shape of the composite structure with temperature. Initial de-icing tests are demonstrated. Application sectors for the multifunctional skins include exposed instrumentation housings, structural members exposed to extreme environments, such as wind turbines, and transport (aerospace). The opportunity to limit the extent of ice build-up on structures has broad application opportunities to provide light -weight structures with reduced material costs and fuel saving for mobile applications and improved performance for instrumentation.

Traditional electrochemical characterization microscopy methods based on charge measurement do not provide nanometer spatial resolution. The recently developed electrochemical scanning microscopy (ESM) which is based on atomic force microscopy (AFM) provides nanoscale measurements, however, the electrochemical measurements consist of other effects such as electromechanical and electrostatic effects. We developed a scanning thermo-ionic microscopy (STIM) to probe local electrochemical activities at the nanoscale regime. The microscopy mechanism is based on imaging the Vegard strain induced by thermally driven stress and temperature oscillation. The Vegard strain linearly correlates with material lattice constant and can be used as a measure of ionic species concentration. Through theoretical analysis and experimental validation, we have demonstrated that second and fourth harmonic components of the AFM deflection signal contains information about species concentration. It is demonstrated that the second harmonic response predominantly correlates with the local thermal expansion information, while the fourth harmonic one is characteristic of local transport activities that is presented only in ionic systems. All our measurements are resonance enhanced and since the tip-sample resonance varies during scanning, four lock-in units and a PID controller are integrated with the AFM to track the resonance frequency. The technique has been applied to probe Sm-doped nanocrystalline Ceria and LiFePO4, both of which exhibit higher STIM amplitude near grain boundaries as expected. The STIM is an innovative tool to study local electrochemistry with high sensitivity and spatial resolution for a wide range of systems, without any electrical cross-talk which makes it suitable to be applied in operando.

Materials and structures with auxetic and negative linear compressibility are of great potential to be used in many applications because of their uncommon mechanical deformation features. However, their design and manufacture are less studied as compared to other mechanical properties. The aim of this research is to explore several new approaches relating to the design and fabrication of cellular materials and structures with these two uncommon features. For most cellular materials and structures, these uncommon properties only exist for a limited geometric range. To begin with, the geometric limit of the microstructure of a 2D elastomer-based auxetic material was identified numerically through large deformation analysis. Within the geometric limits, a tuning method was developed further to control their mechanical properties with prescribed performance constraints. A metallic auxetic metamaterial was used as an example of the developed tuning approach, and its effectiveness was validated by experimental results with specimens manufactured using 3D printing technique.To reduce the manufacturing cost using 3D printing, a composite approach was proposed to manufacture these metamaterials. Several new cellular composite structures with negative linear compressibility composite structures were used as examples to demonstrate the effectiveness of the design approach. The test samples were manufactured using the traditional composite method with low cost. These investigations mentioned above have clearly demonstrated the feasibility of designing and manufacturing of mechanical metamaterials using the presented approaches and laid the foundation for the expansion of their potential applications.

Metamaterials with unit-cell integrated with piezoelectric transducer circuits exhibit interesting bang gap behaviors that can be used for wave/vibration manipulation. This research assesses the uncertainty effect to typical piezoelectric metamaterial, where uncertainties in geometry/configuration and circuitry elements are taken into consideration. Monte Carlo-based uncertainty analysis based on finite element discretization and order-reduced modeling is performed. Results show that band gap behavior is not sensitive to configuration uncertainty but is considerably affected by circuitry parameter uncertainty.

The self-folding of polystyrene sheet can be realized by the localized thermal absorption in narrow area, and it is easily achieved by light and black-colored line pattern printing. Lighting to polystyrene sheet provides thermal energy stored in infrared ray to black-colored area except transparent area, then the polystyrene sheet near black-colored area becomes glass transition state. The extreme thermal contraction deformation at black area results in folding deformation of polystyrene sheet. In this paper, various self-folding structure u sing the light-absorption folding technique of polystyrene sheet can be designed and manufactured . For prediction of light-activated folding behavior of polystyrene sheet, the cohesive line element is employed . In the cohesive line element, the additional nodes are defined at folded line, and the discontinued folding angles can be identified and be analyzed from finite element analysis .

Evaluation of sensing for electrical conductive composites has been implemented using electrical conductive nano materials such as graphene, CNT and carbon fiber. Electrical resistance (ER) measurement for nondestructive evaluation (NDE) was developed using self-sensing composites because method of damage sensing and crack prediction of composites under external load is possible to use at aerospace, heavy industry, and automobile. In this research, diverse damage sensing from mechanical impact and thermal aging for electrical conductive composites was investigated by using ER method. To have the test, electrical conductive materials such as graphene, CNT and carbon fiber and matrixes such as epoxy and vinyl ester were used for damage sensing and finding optimum materials for improving the bonding force. Two and three dimensional ER mapping was used to sense and predict damages from tensile, compressive, impact and drilling force. The differences in ER from different force were compared to explore their usage for real time monitoring and sensing of damages. Enhance optimum materials and conditions from diverse force were confirmed by ER method.

For more than 4000 years, paper has been mainly used for the purpose of recording information. With the recent advance in the field of flexible electronics and wearable devices, paper is being investigated as an environmentally friendly alternative to the traditional petrochemical-based polymeric materials. In this work, carbon nanotubes (CNTs) were employed as fillers to produce electrically conductive papers using a typical papermaking process. Lignin was utilized as a renewable dispersant to prepare aqueous suspensions of CNTs and softwood fibers, which served as precursors for sheet fabrication (60 g/m2). CNTs were functionalized to increase the presence of hydroxyl groups and further improve the interfacial strength between CNTs and cellulose fibers through hydrogen bonding. Both tensile strength and breaking length of the papers increased by more than 10% with volume resistivities in the range of 1,600 Ω.cm for CNT loadings as low as 2.5 wt%. The multifunctional sensing behavior of the composite papers to aqueous solutions and tensile strain was thoroughly studied. Results show that the relative electrical resistance significantly increased under water and returned almost to their initial levels after drying, with fast and reproducible signals over multiple immersion/drying cycles. The piezoresistive behavior of the composites increased linearly at low strains followed by an exponential growth at larger strains, and exhibits higher sensitivity than conventional strain gauges. These novel CNT-cellulose composite papers have outstanding multifunctional properties and are promising to be employed for the design of various smart materials, which can revolutionize the way electronic devices are manufactured and used.

Development of multifunctional materials with power storage and structural capabilities poses many challenges, of which the formulation of a solid polymer electrolyte (SPE) with adhesive like properties may be the greatest. This is due to the targeted properties of the SPE, i.e. high ionic mobility combined with high mechanical strength and good adherence to multiple substrates, which are all mostly divergent. To date, gel electrolytes have been used to prove the feasibility of power storage flexible materials. However, mechanically, these materials do not exhibit notable properties. This presentation will discuss the development process and electrochemical and mechanical properties of a PEG based SPE and highlight the remaining challenges to be surmounted for the successful development of a true structural composite material with power storage capabilities.

This study presents the analysis and electrochemical tests of a new conductive and high energy density air-cathode made of a thin film of aligned carbon fiber as oxygen diffusion layer and a carbon nanotubes buckypaper as oxygen reduction reaction and oxygen evolution reaction bifunctional catalyst for electrically rechargeable zinc-air batteries with high strength and flexibility.

Electrothermal actuators (ETAs) are novel active materials that can generate different kinds of motions by thermal expansion induced from Joule heating. The degree of expansion, which influences the deformation and response force, is determined by the coefficient of thermal expansion (CTE) of the material. In order for the material to be activated, it is necessary to create conductive network for Joule heating to take place. As a result, one of the most common methods for creating ETAs is to insert high electrical and thermal conductive filler into the matrix, which allows for fast and uniform heat distribution though out the material, thus initiate the actuation. In this study, we present the characterization results of newly developed ETA composites that has ultra-low activation voltage requirement (9V). To create the novel ETA composites, polydimethylsiloxane (PDMS) is coated to conductive networks which are constructed from high electrical conductive fillers such as carbon nanotubes. The actuation performance of the novel ETA composites is characterized in terms of the conductive network distribution, CTE, heat capacity, change in thermal gradient, and its actuation behaviour.

The main objective of the present study was to investigate the effect of nanoclay reinforcement on time-dependent volumetric shrinkage of three epoxy resins during polymerization and associated change of mechanical properties of the resulting composite materials. The materials used in this work were two part epoxies from Applied Poleramics Inc., namely, ER3/EH103, ER10/EH103, and DR5/EH103. Conventional methods which utilize 1D and 2D strains measurement are highly dependent on boundary conditions and can be used only for approximation of volumetric measurements. In order to measure the volume directly and monitor time-dependent shrinkage during the polymerization process, the Accupyc II 1340 gas pycnometer with Peltier controller was used. The materials were cured in-situ in the pycnometer chamber at 49 °C for 4 h followed by a post cure of 4 h at 65 °C. Time-dependent shrinkage of individual resins was monitored through continuous volumetric measurements during the entire curing cycle. On the other hand, the tensile specimens were cured in the conventional oven using the same curing cycle. Experimental results showed that depending on the epoxy and nanoclay concentration, variation in time-dependent shrinkage was observed relative to pristine epoxies. Besides, inclusion of nanoclay has shown considerable change in mechanical properties of the composite material. Although such observations were expected, detailed quantification on the volumetric shrinkage with a new technique and its effect on structural components made of such resin are not well documented. Overall, the study lays the groundwork for understanding shrinkage induced effects on strengths of resin/adhesive dominant structural components.

The increasing demands of human-machine integration require stretchable electronic devices. Percolating networks of carbon nanotubes (CNTs) have potential to work as stretchable electrodes and semiconductors, since CNTs can reorient and slide under large deformation. In this work, we investigate the effect of cyclic loadings on the resistance and morphology of stretchable CNT electrodes, by combining experiment, coarse grained molecular static (CGMS) simulation, and analytical modeling. Experimentally, a CNT electrode spray-coated on the surface of a stretchable substrate is subject to cyclic stretches with the maximal strain sequentially increasing. The resistance of the electrode in both stretching and transverse directions increases during the loading, while it remains almost a constant during the unloading, forming a hysteresis between the loading and unloading. To understand the strain-dependent and hysteretic resistance of stretchable CNT electrodes, we have developed a CGMS method to simulate the morphological change of CNT networks under cyclic loadings. Then we calculate the evolution of the resistance for different CNT configurations, by modeling a network of nanotube resistances and contact resistances. We find that during stretching, the CNTs reorient to the stretching direction. As the strain increases, the nanotubes slide between each other, and the resistance of the network increases. During the unloading, the CNTs buckle due to the compression, and the resistance of the network remains almost a constant. Based on this understanding, we have further developed an analytical model to describe the evolution of the resistance of CNT electrodes under arbitrary loadings. This combined approach enables us to design stretchable CNT devices with optimized properties.

Viscoelastic materials are widely used to control vibrations. However, their mechanical properties are known to be frequency and temperature-dependent. Thus, in a narrow frequency bandwidth, there is an optimal temperature that corresponds to a maximum loss factor and it is tricky to get a high damping level over a wide frequency range. Furthermore, an optimal temperature for a maximum structural damping leads to a poor static stiffness because the peak of the loss factor is obtained during the glass transition when the storage modulus is decreasing. Additionally, in industrial applications, the requirements might change according to the system life-cycle. For instance, the stabilization functions that are used for optronics applications require high stiffness for positioning steps, and high damping for filtering functions. To achieve this goal, engineers usually use several viscoelastic materials with functionally graded damping properties. This allows obtaining a high loss factor over a wide frequency range. This solution is however not adaptive. In order to be able to adjust the properties in real time, we suggest in this paper to use a single material which properties are functionally graded thanks to a non-homogeneous temperature field over the structure. A composite structure has been numerically designed integrating a viscoelastic core and a heat control device. The optimal temperature field has been obtained based on the static and dynamic elastic strain energy densities that reflects the compromise between structural damping over a wide frequency band and high static rigidity.

Different failure mechanisms determine strength and fracture toughness of particle composites as, for example particle debonding and ductile matrix fracture. In real composites the particles are not homogeneously distributed. This leads to different levels of particle interaction under loading and consequently to higher stress concentrations in the matrix and at the particle/matrix interface for closer particles. This local inhomogeneity is modelled and the effect on stress-strain behaviour is discussed. On the other hand the variation of stresses in front of a crack also effects the stress concentration as a function of crack distance in the periphery of the local inhomogeneously distributed particles. This variation is considered for the modelling of fracture toughness of such composites. The influence of the pair distribution function on dissipation energies and on fracture toughness as a function of particle volume fraction is discussed.

The purpose of our study is to investigate the influence of fiber breakages of recycled carbon fibers at pelletizing on a tensile strength of its composite. The recycled carbon fibers used in this study were obtained by extracting from a wasted Prepreg by pyrolysis method in a muffle furnace under air condition at 600 deg-C for 30, 60 and 90min, respectively. Recycled carbon fibers were compounded with PP resin by twin extruder machine where the conditions of the barrel temperature and screw rotation were changed, respectively. A specific mechanical energy for extruding unit mass of compound was introduced, in order to discuss the changes of residual fiber lengths in pellets. It was confirmed that the tensile strength was decreased since flaws on the carbon fiber were induced due to the oxidization process.The measured data of residual mean fiber length in pellets were expressed by a single master curve after the experimental data were shifted according to the SME. The shift factor on the SME was driven by relating with a probability of fiber breakage when the strength of carbon fiber was changed. The other master curve was applied to predict the strength of molded composite where a mechanical model proposed for calculating the strength of composites with chopped fibers was referred. The estimated strengths in this study well agreed with experimental data. It was possible to estimate of the change of tensile strengths of recycled carbon fibers reinforced composites accompanying with the change of strengths of single fibers at recycling process.

The large diffusion of structural parts made of carbon fibres reinforced polymers (CFRP) in the aerospace and automotive sectors has highlighted the importance of developing hybrid multifunctional materials characterised by improved mechanical properties and coupled with non-structural features. Indeed, while due to their high specific strength and light weight, composite systems are characterised by very high mechanical properties in the in-plane direction, their intrinsic layered structure makes them very susceptible to low-velocity impacts resulting in Barely Visible Impact Damage (BVID) that can lead to the critical failure of primarily structures. Based on these premises, the development of a multifunctional hybrid system can overcome this drawback by tackling this issue from two different points of view, enhancing the total reliability of light-weight composite parts in order to improve fuel efficiency and optimise the footprint of new generation aero-structures. Indeed, by including an additional metallic phase within the structure of a traditional laminate it is possible to develop a smart multifunctional system in which the hybrid phase acts simultaneously as a reinforcement to enhance the out-of-plane properties of the material and as an intelligent embedded sensor system able to communicate information about the health status of the part and detect impact events or critical loads. This work is focused on the design, manufacturing and testing of a hybrid CFRP (H-CFRP) in which the hybridisation is obtained by including an array of Shape Memory Alloys (SMA) or Copper wires within the laminate. The electrical properties of the hybrid network is exploited to design a smart sensing system which can be interrogated to monitor the load distribution on the part and detect critical solicitations in critical points. The low-power system, controlled by an Arduino microcontroller, is able to monitor the integrity status of the part using each wire as a linear probe to scan complex structures at a certain frequency, measuring the local change in the electrical resistance from which it is possible to build a map of the stress distribution. The position of the metallic network along the laminate’s thickness was determined by analysing the response of different configurations of hybrid samples subjected to Low Velocity Impacts (LVI) in order to optimise the design of the H-CFRP and enhance the energy absorption. Using the same Arduinocontrolled Multiplex the smart wires array was exploited as heat source to scan the sample inner structure and monitoring the variation of the superficial apparent thermal variation with an Infra-Red (IR) Camera, a simulated delaminated area was detected.

This paper details the development of compliant textured surfaces based on fibrous composites that possess enhanced hydrophobic surface wetting properties. The fibrous composites consist of various micro-fiber phases reinforcing a compliant elastomeric matrix. The fiber phase is textured such that it is aligned transversally and protruding out of the elastomer surface. This is achieved by mechanically cutting and rearranging a longitudinally aligned molded composite – a process that takes advantage of the fiber debonding and pullout phenomenon. The textured surface brought about by the aligned and protruded fibers is apparent in both the surface morphology and metrology of the composites. Contact angle wetting studies indicate that the fiber protrusions enhances the hydrophobicity of the surface. A maximum contact angle of 110° is observed with a carbon fiber content of 16vol%, representing a 32% improvement in the surface hydrophobicity over unreinforced TPU (84°). The textured fiber composites in this study represent a facile method to enhance the multi-functionality of composites, by imparting hydrophobic behavior, without the need for any additional surface coating or post-process texturing.

Bistable laminated composites are candidates for morphing structures as they are capable of large deflections without actuation and can exhibit drastic shape change when actuated. The coupled stable shapes of traditional thermally-cured fiber-reinforced polymeric laminates are the result of a globally-prestressed matrix and hence cannot be tailored independently. In this paper, we address this limitation by presenting an equivalent laminated composite in which mechanical prestress is applied to the matrix of selected laminae to achieve bistability; shapes are tailored individually by changing the magnitude of prestress in each lamina. The application of mechanical prestress is associated with an irreversible non-zero stress state which when combined with smart materials with controllable stress-states results in multifunctional morphing composites. The proposed bistable composite consists of a core that is sandwiched between two prestressed fiber-reinforced elastomers and is actuated by shape memory alloy wires. Composite mechanics is modeled analytically by incorporating the material and geometric nonlinearities of prestressed elastomers and the 1-D constitutive behavior of a shape memory alloy (SMA). The experimentally-validated model of the passive composite has an accuracy of 94%. A sensitivity study is conducted that shows the effects of prestress and SMA properties on composite curvature and serves as a guide for the design of active bistable composites. Simulations with the chosen parameter set resulted in the exact compensation of the nonlinear effects of applied stress and phase transformation kinetics to yield a linear response of composite curvature to Martensitic volume fraction.

NanoSonic has designed and produced a multifunctional material having low air permeability, cryogenic flexibility, and self-healing capabilities as a candidate bladder for expandable vehicles and habitats deployed during space missions. This innovative self-healing mechanism is accomplished rheologically, rather than chemically, which allows for immediate self-sealing under reduced pressure encountered during space explorations. Investigations were conducted in collaboration with NASA Johnson Space Center (JSC), Colorado State University (CSU) and the NASA Space Radiation Laboratory (NSRL). These initial studies were designed to evaluate tolerance to damage from exposure to ionizing radiations that simulated heavy ion components of Galactic Cosmic Rays (GCR) and high doses from solar protons. Results verified that these composites maintain durability using tests for air permeability, self-sealing following puncture, and sustained mechanical strength with minimal loss in elasticity upon cryogenic flexure.

Additive Manufacturing (AM) is an emerging field with rapid growth. Fused Deposition Modeling (FDM), as an AM method, is becoming increasingly popular. With the ability to create parts from a wide range of thermoplastics, it is necessary to understand the effects of FDM process on the printed part’s mechanical properties for a given material. This paper investigates the mechanical properties of 3D printed TPU parts created by a typical low cost desk-top FDM machine. TPU was first extruded into filament suitable for FDM and printed into samples for tensile tests according to the ASTM 3039 standard. The effects of raster orientation, nozzle temperature, and air gap on the mechanical properties were investigated. The compression-molded samples were used as the baseline. While the printed samples had an overall lower ultimate tensile strength (UTS) compared to the molded samples, the printed samples with a negative air gap showed nearly isotropic material properties, irrespective of raster orientation and nozzle temperature. For samples with a positive air gap, raster orientation had a large influence on the overall UTS. Nozzle temperature did not have much effect on the UTS. When compared to rigid thermoplastics TPU has a much lower glass transition temperature (Tg) at -40° C. This allows for much better interlayer bonding between print lines as TPU is above T_g for the entire printing process.

Additive manufacturing refers to a new technology in which physical parts are directly produced from a computer model by incremental addition of the constituent materials. Fused deposition modeling (FDM) is one of the most common types of additive manufacture processes. The ultimate mechanical performance of FDM printed parts is a function of the interlayer bond quality. Current literature however focuses only on the phenomenological evolution of standard mechanical properties (such as tensile and bending) as a function of printing conditions. Such studies do not provide direct information about the interlayer adhesion and in-practice failure characteristics. In this work, a fracturemechanics- based methodology was used to characterize the fracture resistance of FDM 3D printed Acrylonitrile Butadiene Styrene (ABS) samples as a function of nozzle and bed temperatures. Double cantilever beam (DCB) specimens was printed in such pattern that the applied load exerted only tensile opening stresses at the crack front. This facilitated the measurement of crack growth under pure mode-I condition. A finite element model was then used to obtain the J-integral strain energy release rate values, as a measure of the fracture resistance. Since the crack propagated at the interlayer in all the cases, the fracture resistance was a direct indication of the interlayer adhesion. The results revealed that the critical crack growth load, the actual fracture surface area (governed by printed mesostructure) and the apparent fracture resistance all increased when the nozzle or bed temperature was increased; the nozzle temperature showed a much stronger effect. The layer-to-layer adhesion, as reflected by the interlayer fracture resistance, did not show monotonous increase with the temperatures and appeared to level off at higher temperatures, indicating that complete interlayer fusion was achieved. This work provides insight into and characterizes the relationships between the 3D printing conditions, the resultant mesostructure, the apparent fracture resistance and the interlayer adhesion in FDM 3D printed materials.

This study demonstrates how to judiciously use two different external fields to engineer a polymer- based composite that responds to both electric and magnetic fields. Specifically, we demonstrate the electric and magnetic alignment of M-type Barium Hexaferrite (BF) in polydimithylsiloxane (PDMS) to obtain a multifunctional composite whose electrical and magnetic properties depend on the orientation of the BF. First, the BFs are electrically aligned in the polymer matrices by applying an AC electric field. From optical microscopy (OM) imaging, the optimal electrical alignment conditions are determined, and those parameters are used to fabricate the composites. After the composite is electrically aligned and partially cured, magnetic field is then applied. Under the magnetic field, BFs are further aligned in-plane and out-of-plane along their magnetic c-axis within the chains that formed during electrical aligning. Following complete cure, the microstructures from the OM image show parallel chain formation. Vibrating Sample Magnetometry (VSM) and XRD results confirm BFs are crystallographically aligned along their magnetic c-axis. The textured BF-PDMS composites are found to have anisotropic magnetic and dielectric properties. The possibility of electrical alignment of magnetic particles will open up new doors to manipulate and design particle-modified polymers for different applications.

Hypervelocity impacts generate shockwaves causing catastrophic damage and failure of surrounding material and structures. Adaptive materials have been previously studied to mitigate shockwaves by providing diagnostics tools, wave steering, and dissipating mechanical energy. Numerous ferroelectric studies have been conducted, with less focus on ferromagnets, or magnetoelasticity. This presentation explores the response of magnetoelastic Galfenol (Fe81.6Ga18.4) to high strain-rate, high stress amplitude loading. Experimentally, 2 GPa rarefacted shockwaves are generated in Galfenol using a Nd:YAG laser. Magnetization changes are recorded using inductive coils along the sample length and interferometry is used to infer the stress amplitude at the specimen’s back surface. The experimental results highlight how the shockwave evolves as it travels, including the onset of lateral release waves. Magnetic field control of the mechanical wave speed by 20% is observed, accompanied by large control of the measured magnetization changes. These changes highlight the coupled magnetoelastic nature of the effect. Furthermore, it is observed that the magnetization more strongly couples to lateral release waves than the incident compressive pulse. Last, magnetization changes are seen to precede the propagating mechanical wave, indicating dipolar coupling can transfer energy ahead of the mechanical wave front. A numerical model has been developed to provide further insight into the experimental study. This model fully couples elastodynamics with magnetostatics using a nonlinear magnetoelastic constitutive behavior. The nonlinear model captures the main findings of the experimental study, including wave evolution, and strong magnetoelastic coupling to the release waves.

Polyimide-based azobenzene polymer networks have demonstrated superior photomechanical performance over more conventional azobenzene-doped pendent and cross-linked polyacrylate networks. These materials exhibit larger yield stress and glass transition temperatures and thus provide robustness for active control of adaptive structures directly with polarized, visible light. Here we develop a constitutive modeling framework and experimentally quantify both the photomechanical and theromechanical coupling in these materials. Whereas photochemical reactions clearly lead to deformation, as indicated by a rotation of a linear polarized light source, temperature and viscoelasticity can also influence deformation and complicate interpretation of the photostrictive constitutive behavior. The rate dependent deformation induced by these two effects is quantified experimentally through photomechanical stress measurements and infrared camera measurements. The results are compared to a model that includes both rate dependent deformation as a function of the optically active azobenzene molecules, coupling to the polymer network viscoelasticity, and thermal expansion. Bayesian statistics is utilized to elucidate the differences in thermomechanical and photomechanical deformation and the influence of viscoelasticity on light induced shape memory effects.

As traditional electric motors scale down, the available power density rapidly decreases. For a motor occupying a volume of 1 micron cubed, the available power density is roughly six orders of magnitude lower than a 1 millimeter cubed motor. Strain-mediated multiferroic heterostructures have recently been proposed to create high power density, micron scale, magnetic motors. These motors leverage magnetoelastic anisotropy to rotate the magnetic moment of a small disk, and use dipolar forces to couple rotors or beads to the stray magnetic field. A key challenge to the creation of these motors is to deterministically control magnetization rotations without the need for complex fabrication or control schemes. This presentation demonstrates how controlling the relative orientation of magnetic exchange bias and magnetoelastic anisotropies can be used to deterministically control motor rotations over a broad frequency range. A Stoner-Wohlfarth magnetic macrospin model is created that couples a single domain magnetic disc to a [011] cut PMN-PT substrate. This model accounts for magnetoelastic, shape, and exchange anisotropy energies. The exchange anisotropy is rotated relative to the biaxial strain created by the PMN-PT substrate. Results demonstrate precessional magnetization dynamics deterministically controlled with an oscillating voltage on the PMN-PT substrate. This approach enables 360 degree rotations over a broad frequency range. The frequency response is provided up through ferromagnetic resonance, and power density calculations are made with comparison to existing micromechanical motors.

In this study, a triple-shape memory polystyrene based polymer (SMPS) is synthesized, which mainly consists of styrene, vinyl compound, and cross-linking agent (bifunctional monomer). Benzoperoxide is used as the reaction initiator, the polymerization temperature is 75 oC, and the reaction time is 24 h. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results demonstrate that the crosslinked styrene based polymer possess two well-separated transition temperatures, which are subsequently used for the fixing/recovery of two temporary shapes. Furthermore, the versatile triple-shape memory functionality is demonstrated, and the result shows that the material has an excellent triple-shape memory effect. Based on the unique advantages, the SMPS material can be potentially used in sensors and actuators.

As smart polymers, shape memory polymers (SMPs) are able to change shape and structure when exposed to an external stimulus, including heating, electrical and magnetic fields, water, light etc. This feature leads to potential for SMPs in many applications such as aerospace, smart textiles, robotics, automobile and biomedical engineering. SMPs can be produced to different forms and structures from nanoscale to macrolevel, including fibers, membranes, particles and foams. SMP foams have been developed due to the light weight, large deformation, etc. However, the fabrication method is too complected and the actuation speed is slow. Herein, to solve these problems, we fabricate a class of shape memory polycaprolactone foams and their composites by microwave, which can also be triggered by microwave. The merits of these foams include fast fabrication (less than 60 s), uniform pores, large compression deformation (80%) and quick shape recovery speed with in 100 s. This approach of using microwave to synthesize shape memory polymer foams in microwave oven would enable the synthesis of a wide variety of novel shape-memory foams. Moreover, microwave actuated shape memory foams can provide higher recovery speed for remote control in various applications.

In this paper, the high temperature polyimide-based shape memory polymers were exposed to simulated vacuum thermal cycling environments from −170 °C to +170 °C up to 600 hours for an accelerated irradiation. The effects of vacuum thermal cycling on optical transmittance, stretchable shape memory effects, thermomechanical and thermal properties were evaluated. Even if they experienced 600 hours of vacuum thermal cycling irradiation, the glass transition temperatures (T_g), optical transmittance, thermal stability, and the shape memory effects had no significant changes. The results are quite instructive in selecting and evaluating material for aerospace structures. polyimide-based shape memory polymers also shows great potential application in large-area space flexible electronics.

Power transformer is the one of the largely important as well as one of the costly elements in the electricity grid. Any malfunction of this element may affect the reliability of the entire network and could have considerable economic impact on the system. For several reasons, overloading of power transformers beyond their rating has been reported frequently. The primary issue leading to the failure of transformer is contamination of transformer oil by the working components due to prolonged high temperature exposure. Transformer oil temperature can be utilized as a primary parameter in monitoring the life of the transformer. At present, electrical approach are vulnerable to electromagnetic interference and are limited by sensors lifetime. Other non-contact techniques are ineffective due to difficulties in processing the output signal. In this work a CuAlNi/Polyimide shape memory alloy composite has been applied to act as a temperature sensor in mineral oils. The composite film has been developed through thermal evaporation which exhibited two-way displacement without and post-processing and training. The developed films are employed in a custom made oil rig and the suitability of using it as a circuit breaker in temperature sensing application has been probed. The circuit breaker can be triggered by measuring the displacement of the bimorph using laser displacement sensor. The measurement is of noncontact type and the temperature can be monitored at regular intervals. For comparison a procure Nickel-Titanium spring with transformation temperature less than 100 °C is also used for the studies. The results show that the developed bimorphs has good sensitivity of 0.2 mm/°C and the output displacement is significant. Further the effect of contamination in the mineral oils is also probed by adding known amounts of impurities and the ageing effect has been studied. A higher resolution measuring system using interferometry has been proposed.

Soft electro-elastic materials are an emergent class of materials with electromechanical coupling: electric field induced actuation, strain or pressure sensing, and mechanical energy harvesting. Anisotropic electro-elastic materials consist of an isotropic matrix embedded with oriented fibers or particles that are either electro-passive or active. Here, a new soft electroactive polymer composite consisting of contractile dielectric elastomer fibers is proposed. A series of computational simulations that capture the coupled electromechanical response and account for finite deformations is conducted. The simulations explore the feasibility of enabling novel deformation modes currently unattainable by their isotropic counterparts. In previous work, we proposed a constitutive formulation for isotropic dielectric elastomers under hyperelastic conditions. The model has been shown to be robust under generalized 3D loading, finite deformations, and large electric fields. More recently, constitutive models have been developed for isotropic dielectric elastomers assuming viscoelastic behavior. In this paper, the active fiber network is treated as viscoelastic, and a new anisotropic constitutive model is proposed based on current models of physiological muscle. The model is implemented into the commercial finite element code by employing a user-defined subroutine. The FEM formulation is verified by comparing analytical solutions for uniaxial, biaxial, and simple shear tests. In the new composite, we consider the effect of spatially distributed electric fields and for the first time investigate multi-dimensional electric field activation. Distributed activation via spatially distributed fibers in a pressure-loaded membrane configured for pump-like actuation is demonstrated. We utilize our computational capability to design and optimize complex dielectric elastomer actuator composites configured for electro-hydrostatic coupling.

This paper considers the comparison and evaluation of Superficial-Rockwell (HRT) hardness tests using the steel and tungsten carbide ball indenters. There are differences observed in Superficial-Rockwell HRT hardness scale tests by using 1.588 mm (1/16") diameter steel and tungsten carbide ball indenters. The modeling was made with HRT hardness reference blocks and widespread soft thinner gage material (copper, aluminum, steel) with different thickness. In the simulation determined that the tungsten carbide indenter balls have the advantage of being less likely to flatten with repeated use and the use of hard metal ball indenters may have different measurement results than tests using steel ball indenters. The simulation of indentation process is performed by the finite element method in the Academic version of ANSYS software product, which is available for free use on the website The simulation results are confirmed by experimental studies. For further analysis of the results of comparisons it is interesting to conduct researches for micro- Vickers and Berkovich hardness scales. Furthermore, the practical application of the obtained results allows to evaluate the quality abradable surfaces in the design of structural components with small clearances. The obtained results are important for evaluation of the results of international comparisons of the national standards. This work was performed as part of preparation the Draft A COOMET.M.H-S3 - Supplementary comparison of regional metrological organization for Superficial-Rockwell Hardness scales.

A finite element model of scarf repaired laminates in tension is built in this paper. The ultimate strengths of the repaired structures are calculated with progressive damage analysis method. The predicted results agreeing well with the experimental results which means the model is effective. The failure model of these structures is adhesive failure which is obtained by analyzing the failure process of these structures. The effects of scarf ratio and scarf depth on the ultimate strength are analyzed which indicates that the ultimate strength can be improved by both decreasing scarf ratio and decreasing scarf depth .The results of this study can provide some references for the design of scarf repaired composite laminates.

A plastic deformation of the metal significantly changes its internal structure and greatly influences many mechanical, physical and chemical properties. In the plastic deformation process increases the electrical resistance, changes the magnetic properties and decreases the thermal conductivity and the workability of the metal. But this influence is especially evident in the measurement of the hardness of the deformable body, which is connected directly to an increase in the yield strength of the material, i.e. the hardening. Hardness measurements were made on samples of whole over the entire length. After the experimental study by rupturing samples were carried out repeated measurements of hardness over the entire length. Modeling the process of rupturing samples was carried out by finite element method (FEM) in Academical version of ANSYS. The phenomenological link between the calculated and experimental values of hardness and stress state of the sample were determined. The obtained results are important for evaluation of the results of international comparisons of the national standards of hardness. As the perspective directions for the practical application of the results proposed evaluation and prediction of hardness standard measures the hardness of the first rank in their manufacture. The predictions of the FEM models were compared with experimental data, and the accuracy of these predictions was quite satisfactory.

Dental composite resins are the main direct tooth restorative materials. The recent research and development on dental composite resins focused on developing materials with adequate strength, high wear resistance and low shrinkage. Polymerization shrinkage and its accompanied stress may destroy the interfacial bonds between composite and tooth and lead to recurrent caries. In this paper, novel light-curable composite resins with calcium phosphate silicate cement (CPSC) added to the filler phase were formulated. CPSC was synthesized with tricalcium silicate (C₃S) and calcium phosphate monobasic (CPM). C₃S hydrates to produce calcium silicate hydrate (C-S-H) gel and calcium hydroxide (CH) which accompanied volume expansion. CPM reacts with the CH to precipitate hydroxyapatite (HAP) in situ within C-SH which can largely remove CH. Microstructures of composite resins were characterized by SEM and XRD. Chemicalphysical properties were evaluated include volume change, flexural strength, hardness and elastic modulus. The results showed that shrinkage of dental composite resins with CPSC added to the filler phase could be compensated and reduced effectively.

Deformation characteristic of CFRP bi-stable composites according to negative initial curvature is discussed, and twisted shape bi-stability of CFRP composites is introduced. Initial curvature of composites has effect on final curvature of bistable composites. Positive initial curvature tailor final curvature linearly. However, some negative initial curvature induces twisted shape bi-stability. CFRP laminated composites have three different final state (i.e. conventional shape bistability, mono-stability, and twisted shape bi-stability) according to initial curvature. Twisted shape bi-stable composites have different curvature changing characteristic from conventional shape bi-stable composites. In order to analysis effect of initial curvature, analytical model that include force and moment equilibrium is proposed. FE simulation results and analytical results are compared to verify the proposed analytical model. It is verified that some range of negative initial curvature induce losing of bi-stability or twisted shape bi-stability by analytical model. Final state shape of three different state is analyzed by FE simulation and analytical model. Final states shape from two different analyses are well matched each other in three different state.