@article{riede_york_furst_mueller_seelecke_2011, title={Elasticity and stress relaxation of a very small vocal fold}, volume={44}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2011.04.024}, abstractNote={Across mammals many vocal sounds are produced by airflow induced vocal fold oscillation. We tested the hypothesis that stress–strain and stress-relaxation behavior of rat vocal folds can be used to predict the fundamental frequency range of the species' vocal repertoire. In a first approximation vocal fold oscillation has been modeled by the string model but it is not known whether this concept equally applies to large and small species. The shorter the vocal fold, the more the ideal string law may underestimate normal mode frequencies. To accommodate the very small size of the tissue specimen, a custom-built miniaturized tensile test apparatus was developed. Tissue properties of 6 male rat vocal folds were measured. Rat vocal folds demonstrated the typical linear stress–strain behavior in the low strain region and an exponential stress response at strains larger than about 40%. Approximating the rat's vocal fold oscillation with the string model suggests that fundamental frequencies up to about 6 kHz can be produced, which agrees with frequencies reported for audible rat vocalization. Individual differences and time-dependent changes in the tissue properties parallel findings in other species, and are interpreted as universal features of the laryngeal sound source.}, number={10}, journal={JOURNAL OF BIOMECHANICS}, author={Riede, Tobias and York, Alexander and Furst, Stephen and Mueller, Rolf and Seelecke, Stefan}, year={2011}, month={Jul}, pages={1936–1940} }
 @article{lynch_brei_chaplya_ounaies_kamlah_seelecke_lucato_weiland_2010, title={Adaptive and active materials: Selected papers from the ASME 2009 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 09) (Oxnard, CA, USA, 21-23 September 2009)}, volume={19}, number={9}, journal={Smart Materials & Structures}, author={Lynch, C. and Brei, D. and Chaplya, P. and Ounaies, Z. and Kamlah, M. and Seelecke, S. and Lucato, S. D. E. and Weiland, L.}, year={2010} }
 @inproceedings{hangekar_furst_seelecke_2010, title={Development of a 6-channel power controller for simultaneous actuation and resistance measurement of SMA wires}, DOI={10.1115/smasis2010-3846}, abstractNote={The use of ‘multifunctional’ Shape Memory Alloy wires as embedded actuators and sensors has been proposed for numerous novel applications. The SMA wires are actuated as a result of the Joule heating induced by passing electric current through it. The resistance of the SMA wire can simultaneously be measured during its actuation enabling it to be used as sensor data that relates to the strain and temperature of the wire. In order to control actuation stroke from the SMA wire, the Joule heating (electric power supplied to the SMA wire) of the wire needs to be controlled. Therefore, a 6-channel power controller device has been developed that simultaneously controls the power supplied to six different SMA wires and measures the resistance of these wires during excitation. This paper continues from the previously presented concept of a multi-channel power controller implementation. The focus of this paper is to discuss the operation, calibration methods and optimization techniques to improve the performance and robustness of the device and to eliminate the issues in multi-channel implementation. Further, this device is implemented in a test setup to study the position control of SMA wire using resistance feedback. Results of these tests can be utilized in practical applications involving SMA wires as embedded actuators and sensors, such as Smart Inhaler system being developed at North Carolina State University.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol 2}, author={Hangekar, R. and Furst, S. and Seelecke, S.}, year={2010}, pages={461–470} }
 @article{furst_hangekar_seelecke_2010, title={Development, Assembly, and Validation of an SMA-Actuated 2-Joint Nozzle and 6-Channel Power Supply for Use in a Smart Inhaler System}, volume={7643}, ISSN={["0277-786X"]}, DOI={10.1117/12.853399}, abstractNote={The Smart Inhaler design concept recently developed at NC State University has the potential to target the delivery of inhaled aerosol medication to specified locations within the lung system. This targeted delivery could help patients with pulmonary ailments by reducing the exposure of healthy lung tissue to potentially harmful medications. However, controlled delivery can only be accomplished if medication is injected at a precise location in an inhaled stream of properly conditioned laminar flow. In particular, the medication must be injected into the inhaled flow using a small nozzle that can be positioned without disturbing the flow. This paper outlines the procedure used to assemble and control a key component of the smart inhaler: a shape memory alloy (SMA) based dual-joint flexible nozzle that exploits the sensing and actuating capabilities of thermally activated SMA wires. A novel 6-channel power-supply is used to control input power and measure the resistance across the SMA. Since a practical fabrication process may result in SMA wires with different contact resistances, the power supply employs an initialization procedure to self-calibrate and provide normalized power distribution 6 SMA wires simultaneously. Furthermore, a robust control scheme is used to ensure that a constant current is provided to the wires. In validation tests, a LabVIEW-based video positioning system was used to measure the deflection of the nozzle tip and joint rotation. Results show that the carefully controlled assembly of a stream-lined nozzle can produce a practical smart structure, and joint rotation is predictable and repeatable when power input is also controlled. Future work will assess the use of the SMA-resistance measurement as position feedback and PID position control power as a measurement of the convective cooling that results from the moving airflow.}, journal={ACTIVE AND PASSIVE SMART STRUCTURES AND INTEGRATED SYSTEMS 2010, PTS 1 AND 2}, author={Furst, Stephen J. and Hangekar, Rohan and Seelecke, Stefan}, year={2010} }
 @inproceedings{hodgins_york_seelecke_2010, title={Electro-mechanical analysis of a deap actuator coupled to a negative-rate bias spring mechanism}, DOI={10.1115/smasis2010-3849}, abstractNote={This paper presents the design and analysis of a Negative-rate Bias Spring (NBS) paired with a Dielectric Electro-Active Polymer (DEAP). A NBS is a bi-stable mechanism with a negative slope region between its two stable configurations. The objective of this work is to demonstrate the increased stroke output of a DEAP actuator when biased by such a bistable mechanism. Possible devices that could use this actuation technology are lightweight, miniature pumps and valves. First, the NBS is mechanically tested and its bi-stable behavior is observed along with the negative slope region between the stable configurations. Then the NBS is coupled with a circular DEAP actuator (to provide the bias force) and is experimentally tested under a variety of loading conditions with a focus on the force and stroke capabilities. The stroke output of the device was approximately 1mm for a range of electrical loading rates (0.1Hz, 1Hz, and 10Hz). The measured force and stroke are then correlated to the force vs. displacement data observed during the mechanical characterization experiments. Additionally, the force vs. displacement behavior of the NBS-DEAP is analytically modeled and showed good comparison with the results.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol. 1}, author={Hodgins, M. and York, A. and Seelecke, S.}, year={2010}, pages={315–322} }
 @article{york_dunn_seelecke_2010, title={Experimental characterization of the hysteretic and rate-dependent electromechanical behavior of dielectric electro-active polymer actuators}, volume={19}, ISSN={["0964-1726"]}, DOI={10.1088/0964-1726/19/9/094014}, abstractNote={Dielectric electro-active polymers (DEAPs) can achieve substantial deformation (>300% strain) while sustaining, compared to their ionic counterparts, large forces. This makes them attractive for various actuation and sensing applications such as in light weight and energy efficient valve and pumping systems. Many applications operate DEAP actuators at higher frequencies where rate-dependent effects influence their performance. This motivates the seeking of dynamic characterization of these actuators beyond the quasi-static regime. This paper provides a systematic experimental investigation of the quasi-static and dynamic electromechanical properties of a DEAP actuator. In order to completely characterize the fully coupled behavior, force versus displacement measurements at various constant voltages and force versus voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and rate-dependent material behavior. These experiments provide insight into the electrical dynamics and viscoelastic relaxation inherent in DEAP actuators. This study is intended to provide information, including high frequency performance analysis, useful to anyone designing dynamic actuator systems using DEAPs.}, number={9}, journal={SMART MATERIALS & STRUCTURES}, author={York, A. and Dunn, J. and Seelecke, S.}, year={2010}, month={Sep} }
 @inproceedings{hodgins_seelecke_2010, title={Mechanical behavior of a bi-stable negative-rate bias spring system}, volume={7644}, booktitle={Behavior and mechanics of multifunctional materials and composites 2010}, author={Hodgins, M. and Seelecke, S.}, year={2010} }
 @inproceedings{furst_hangekar_seelecke_2010, title={Practical implementation of resistance feedback measurement for position control of a flexible smart inhaler nozzle}, DOI={10.1115/smasis2010-3840}, abstractNote={Many “smart materials” have the capacity to be used simultaneously as both an actuator and sensor. For example, SMA actuator wires can be heated by Joule heating to induce contraction; at the same time, the resistance across the SMA wire can be measured to give the user some indication of the strain in the wire. This multi-functional capability enables the design of applications requiring extremely light-weight and streamlined embedded sensors and actuators. One such “smart structure” application is the flexible nozzle used in the Smart Inhaler system under development at North Carolina State University. The Smart Inhaler allows a doctor to control the locations within the pulmonary system that are medicated by controlling the location at which medication is injected into an inhaled airflow. This can reduce the amount of healthy tissue that is exposed to potentially toxic medications, such as those used to treat lung cancer. However, the practical challenge of injecting medication into a flow without disturbing the flow requires a highly controllable yet non-obstructive nozzle. This paper presents a scheme that correlates the resistance measurement across an SMA actuator wire to the wire strain and the resulting deformation of the flexible nozzle. The relationship between resistance and nozzle deformation is nonlinear and hysteretic; however, the repeatability of the relationship allows the user to calibrate the feedback measurement. This enables the wire to be used as both position sensor and positioning actuator. The results represent the first experiments that exploit the multi-functional capabilities of SMA wires in the context of a practical embedded sensor and actuator application.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol 2}, author={Furst, S. J. and Hangekar, R. and Seelecke, S.}, year={2010}, pages={205–213} }
 @inproceedings{york_seelecke_2010, title={Towards self-sensing of deap actuators: Capacitive sensing experimental analysis}, DOI={10.1115/smasis2010-3847}, abstractNote={Dielectric Electro-Active Polymers (DEAP’s) have become attractive material for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. The materials ability to act as both and actuator and a sensor enable DEAP actuators to have “self-sensing” capabilities. This advancement provides low cost actuator systems that do not require external sensors for feedback control. This paper explores the capacitive sensing capabilities of a DEAP actuator under loading conditions typical for pumping and valve applications. The capacitive sensing capabilities of the actuator are tested using a method similar to that used by Jung et al. [1] which uses the DEAP actuator as a variable capacitor in a high pass filter circuit. This sensing circuit produces a direct voltage output when the actuator is displaced. The sensing response of this system is experimentally investigated under mechanical loading. The sensor is shown to have an effective sensitivity of .041 (V/Vexc) / mm. In addition, the initial results of a dual sensing and actuating system are presented.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol. 1}, author={York, A. and Seelecke, S.}, year={2010}, pages={307–314} }
 @inproceedings{york_hodgins_seelecke_2009, title={Electro-mechanical analysis of a biased dielectric EAP actuator}, DOI={10.1115/smasis2009-1441}, abstractNote={Dielectric Electro-Active Polymers (DEAP’s) can achieve substantial deformation (>300% strain) while, compared to their ionic counterparts, sustaining large forces. This makes them attractive for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. This paper provides a systematic experimental investigation of the quasi-static and dynamic electro-mechanical properties of a commercially available dielectric EAP actuator. In order to completely characterize the fully coupled behavior force vs. displacement measurements at various constant voltages and force vs. voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and rate-dependent material behavior. These experiments provide insight into the viscoelastic and electrostatic behavior inherent in DEAP material. Typical operating conditions of the actuator require it to have a biased force, such as a spring. Experiments are conducted to observe the actuators performance under these conditions. The force and stroke capabilities are investigated while the actuator is loaded with different springs and at a variety of pre-stretch levels. The resulting behavior of the spring loaded actuator is then correlated to the viscoelastic effects observed during the electro-mechanical characterization.}, booktitle={SMASIS 2009, vol 1}, author={York, A. and Hodgins, M. and Seelecke, S.}, year={2009}, pages={289–297} }
 @article{yang_seelecke_2009, title={FE analysis of SMA-based bio-inspired bone-joint system}, volume={18}, ISSN={["0964-1726"]}, DOI={10.1088/0964-1726/18/10/104020}, abstractNote={This paper presents the finite element (FE) analysis of a bio-inspired bone–joint system. Motivated by the BATMAV project, which aims at the development of a micro-air-vehicle platform that implements bat-like flapping flight capabilities, we study the actuation of a typical elbow joint, using shape memory alloy (SMA) in a dual manner. Micro-scale martensitic SMA wires are used as ‘metal muscles’ to actuate a system of humerus, elbow joint and radius, in concert with austenitic wires, which operate as flexible joints due to their superelastic character. For the FE analysis, the humerus and radius are modeled as standard elastic beams, while the elbow joint and muscle wires use the Achenbach–Muller–Seelecke SMA model as beams and cable elements, respectively. The particular focus of the paper is on the implementation of the above SMA model in COMSOL.}, number={10}, journal={SMART MATERIALS & STRUCTURES}, author={Yang, S. and Seelecke, S.}, year={2009}, month={Oct} }
 @inproceedings{furst_bumgarner_seelecke_2009, title={Quantification of the effectiveness of various conductive and non-conductive epoxies as an attachment method for small SMA wires}, DOI={10.1115/smasis2009-1450}, abstractNote={The discovery of thermoelastic behavior in shape memory alloys (SMA) such as Nitinol enabled the conceptualization of many applications where actuators and sensors are embedded into a structural component. These so called “adaptive structures” can be extremely compact and energy efficient. SMA wires show characteristics similar to that of muscle fibers, and thus enable replication of an animal’s musculoskeletal system. Also, SMA wires are extremely attractive in the biomedical field where compact robotic elements can reduce the invasiveness of some surgical procedures. Unfortunately, widespread implementation of adaptive structures actuated by small SMA-wires in industry has been hindered by two significant challenges. First, SMA wires exhibit hysteretic behavior during heating and cooling that can be difficult to model without substantial computation. Second, attaching a small (∼50–100 μm diameter) SMA wire is extremely difficult because standard methods such as crimping are infeasible. The goal of this study is to quantify the effectiveness of using adhesives to hold a small SMA wire. A wide range of commercially available adhesives are tested under the conditions relevant to an application where SMA-wires are embedded directly within a structure. Epoxies are tested so that the adhesive will bond to both plastic and metallic elements. The experimental setup is designed to test the failure shear stress between an SMA wire and adhesive. A wire is encapsulated in a small drop of adhesive. Then the area of the wire that is exposed to the adhesive is measured under a microscope and the wire is pulled as a load cell measures the tensile load. The force that causes failure of the bond is recorded and used to calculate the failure shear stress between the adhesive and wire. The effects of using wires with different surface temperatures, and handling procedures (i.e. washing with acetone and handling with latex gloves) are also tested. Measurements under each set of parameters are repeated and quantitative results are obtained.}, booktitle={SMASIS 2009, vol 2}, author={Furst, S. J. and Bumgarner, D. and Seelecke, S.}, year={2009}, pages={409–418} }
 @article{heintze_seelecke_2008, title={A coupled thermomechanical model for shape memory alloys - From single crystal to polycrystal}, volume={481}, journal={Materials Science & Engineering. A, Structural Materials: Properties, Microstructure and Processing}, author={Heintze, O. and Seelecke, S.}, year={2008}, pages={389–394} }
 @article{morrison_seelecke_krevet_kohl_2008, title={A free energy model for magneto-mechanically coupled NiMnGa single crystals}, volume={158}, ISSN={["1951-6401"]}, DOI={10.1140/epjst/e2008-00678-x}, journal={EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS}, author={Morrison, P. and Seelecke, S. and Krevet, B. and Kohl, M.}, year={2008}, month={May}, pages={213–220} }
 @article{kleinstreuer_li_basciano_seelecke_farber_2008, title={Computational mechanics of Nitinol stent grafts}, volume={41}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2008.05.032}, abstractNote={A finite element analysis of tubular, diamond-shaped stent grafts under representative cyclic loading conditions for abdominal aortic aneurysm (AAA) repair is presented. Commercial software was employed to study the mechanical behavior and fatigue performance of different materials found in commercially available stent-graft systems. Specifically, the effects of crimping, deployment, and cyclic pressure loading on stent-graft fatigue life, radial force, and wall compliances were simulated and analyzed for two types of realistic but different Nitinol materials (NITI-1 and NITI-2) and grafts (expanded polytetrafluoroethylene-ePTFE and polyethylene therephthalate-PET). The results show that NITI-1 stent has a better crimping performance than NITI-2. Under representative cyclic pressure loading, both NITI-1 and NITI-2 sealing stents are located in the safe zone of the fatigue-life diagram; however, the fatigue resistance of an NITI-1 stent is better than that of an NITI-2 stent. It was found that the two types of sealing stents do not damage a healthy neck artery. In the aneurysm section, the NITI-1&ePTFE, NITI-1&PET, and NITI-2&PET combinations were free of fatigue fracture when subjected to conditions of radial stress between 50 and 150mmHg. In contrast, the safety factor for the NITI-2&ePFTE combination was only 0.67, which is not acceptable for proper AAA stent-graft design. In summary, a Nitinol stent with PET graft may greatly improve fatigue life, while its compliance is much lower than the NITI-ePTFE combination.}, number={11}, journal={JOURNAL OF BIOMECHANICS}, author={Kleinstreuer, C. and Li, Z. and Basciano, C. A. and Seelecke, S. and Farber, M. A.}, year={2008}, month={Aug}, pages={2370–2378} }
 @article{krevet_kohl_morrison_seelecke_2008, title={Magnetization- and strain-dependent free energy model for FEM simulation of magnetic shape memory alloys}, volume={158}, ISSN={["1951-6355"]}, DOI={10.1140/epjst/e2008-00677-y}, journal={EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS}, author={Krevet, B. and Kohl, M. and Morrison, P. and Seelecke, S.}, year={2008}, month={May}, pages={205–211} }
 @article{davis_turner_seelecke_2008, title={Measurement and prediction of the thermomechanical response of shape memory alloy hybrid composite beams}, volume={19}, ISSN={["1045-389X"]}, DOI={10.1177/1045389X06073172}, abstractNote={ An experimental and numerical investigation into the static and dynamic responses of shape memory alloy hybrid composite (SMAHC) beams is performed to provide quantitative validation of a recently commercialized numerical analysis/design tool for SMAHC structures. The SMAHC beam specimens consist of a composite matrix with embedded pre-strained SMA actuators, which act against the mechanical boundaries of the structure when thermally activated to adaptively stiffen the structure. Numerical results are produced from the numerical model as implemented into the commercial finite element code ABAQUS. A rigorous experimental investigation is undertaken to acquire high fidelity measurements including infrared thermography and projection moiré interferometry for full-field temperature and displacement measurements, respectively. High fidelity numerical results are also obtained from the numerical model and include measured parameters, such as geometric imperfection and thermal load. Excellent agreement is achieved between the predicted and measured results of the static and dynamic thermomechanical response, thereby providing quantitative validation of the numerical tool. }, number={2}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Davis, Brian and Turner, Travis L. and Seelecke, Stefan}, year={2008}, month={Feb}, pages={129–143} }
 @article{kim_seelecke_2007, title={A rate-dependent three-dimensional free energy model for ferroelectric single crystals}, volume={44}, ISSN={["1879-2146"]}, DOI={10.1016/j.ijsolstr.2006.06.007}, abstractNote={The one-dimensional free energy model for ferroelectric materials developed by Smith et al. [Smith, R.C., Seelecke, S., Ounaies, Z., 2002. A free energy model for piezoceramic materials. In: 9th SPIE Conference on Smart Structures and Materials, San Diego, USA, pp. 17–22; Smith, R.C., Seelecke, S., Ounaies, Z., Smith, J., 2003. A free energy model for hysteresis in ferroelectric materials. J. Intell. Mater. Syst. Struct. 14, 719–739; Smith, R.C., Seelecke, S., Dapino, M.J., Ounaies, Z., 2005. A unified framework for modeling hysteresis in ferroic materials. J. Mech. Phys. Solids 54, 46–85] is generalized to three space dimensions including both polarization and strain. In the resulting nine-dimensional energy function, six free energy potentials representing the six distinct types of tetragonal variants of perovskite lattice structures are given as quadratic functions of polarization vector and strain tensor. Energy barrier expressions as functions of thermodynamic driving forces are obtained through a generalization of the one-dimensional equations derived from the model of Smith et al. This approach presents an alternative to the cumbersome determination of higher-dimensional saddle points and is attractive for a computationally efficient implementation. The energy barrier expressions are combined with evolution equations for the variant fractions based on the theory of thermally activated processes and thus allow for a natural treatment of rate-dependent effects. The predictions of the model are compared with recent measurements on BaTiO3 single crystals by Burcsu et al. [Burcsu, E., Ravichandran, G., Bhattacharya, K., 2004. Large electrostrictive actuation of barium titanate single crystals. J. Mech. Phys. 52, 823–846]. The effects of applied stress and 90°- and 180°-switching processes are discussed in detail.}, number={3-4}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Kim, Sang-Joo and Seelecke, Stefan}, year={2007}, month={Feb}, pages={1196–1209} }
 @article{ball_smith_kim_seelecke_2007, title={A stress-dependent hysteresis model for ferroelectric materials}, volume={18}, ISSN={["1530-8138"]}, DOI={10.1177/1045389X07070937}, abstractNote={ This article addresses the development of a homogenized energy model which characterizes the ferroelastic switching mechanisms inherent to ferroelectric materials in a manner suitable for subsequent transducer and control design. In the first step of the development, we construct Helmholtz and Gibbs energy relations which quantify the potential and electrostatic energy associated with 90 and 180 dipole orientations. Equilibrium relations appropriate for homogeneous materials in the absence or presence of thermal relaxation are respectively determined by minimizing the Gibbs energy or balancing the Gibbs and relative thermal energies using Boltzmann principles. In the final step of the development, stochastic homogenization techniques are employed to construct macroscopic models suitable for nonhomogeneous, polycrystalline compounds. Attributes and limitations of the characterization framework are illustrated through comparison with experimental PLZT data. }, number={1}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Ball, Brian L. and Smith, Ralph C. and Kim, Sang-Joo and Seelecke, Stefan}, year={2007}, month={Jan}, pages={69–88} }
 @article{smith_seelecke_dapino_ounaies_2006, title={A unified framework for modeling hysteresis in ferroic materials}, volume={54}, ISSN={["1873-4782"]}, DOI={10.1016/j.jmps.2005.08.006}, abstractNote={This paper addresses the development of a unified framework for quantifying hysteresis and constitutive nonlinearities inherent to ferroelectric, ferromagnetic and ferroelastic materials. Because the mechanisms which produce hysteresis vary substantially at the microscopic level, it is more natural to initiate model development at the mesoscopic, or lattice, level where the materials share common energy properties along with analogous domain structures. In the first step of the model development, Helmholtz and Gibbs energy relations are combined with Boltzmann theory to construct mesoscopic models which quantify the local average polarization, magnetization and strains in ferroelectric, ferromagnetic and ferroelastic materials. In the second step of the development, stochastic homogenization techniques are invoked to construct unified macroscopic models for nonhomogeneous, polycrystalline compounds exhibiting nonuniform effective fields. The combination of energy analysis and homogenization techniques produces low-order models in which a number of parameters can be correlated with physical attributes of measured data. Furthermore, the development of a unified modeling framework applicable to a broad range of ferroic compounds facilitates material characterization, transducer development, and model-based control design. Attributes of the models are illustrated through comparison with piezoceramic, magnetostrictive and shape memory alloy data and prediction of material behavior.}, number={1}, journal={JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS}, author={Smith, RC and Seelecke, S and Dapino, M and Ounaies, Z}, year={2006}, month={Jan}, pages={46–85} }
 @article{seelecke_kim_ball_smith_2005, title={A rate-dependent two-dimensional free energy model for ferroelectric single crystals}, volume={17}, ISSN={["1432-0959"]}, DOI={10.1007/s00161-005-0207-7}, abstractNote={The one-dimensional free energy model for ferroelectric materials developed by Smith et al. [29–31] is generalized to two dimensions. The two-dimensional free energy potential proposed in this paper consists of four energy wells that correspond to four variants of the material. The wells are separated by four saddle points, representing the barriers for 90°-switching processes, and a local maximum, across which 180°-switching processes take place. The free energy potential is combined with evolution equations for the variant fractions based on the theory of thermally activated processes. The model is compared to recent measurements on BaTiO3 single crystals by Burcsu et al. [8], and predicitions are made concerning the response to the application of in-plane multi-axial electric fields at various frequencies and loading directions. The kinetics of the 90°- and 180°-switching processes are discussed in detail.}, number={4}, journal={CONTINUUM MECHANICS AND THERMODYNAMICS}, author={Seelecke, S and Kim, SJ and Ball, BL and Smith, RC}, year={2005}, month={Dec}, pages={337–350} }
 @article{smith_seelecke_ounaies_smith_2003, title={A Free Energy Model for Hysteresis in Ferroelectric Materials}, volume={14}, ISSN={1045-389X 1530-8138}, url={http://dx.doi.org/10.1177/1045389x03038841}, DOI={10.1177/1045389X03038841}, abstractNote={ This paper provides a theory for quantifying the hysteresis and constitutive nonlinearities inherent to piezoceramic compounds through a combination of free energy analysis and stochastic homogenization techniques. In the first step of the model development, Helmholtz and Gibbs free energy relations are constructed at the lattice or domain level to quantify the relation between the field and polarization in homogeneous, single crystal compounds which exhibit uniform effective fields. The effects of material nonhomogeneities, polycrystallinity, and variable effective fields are subsequently incorporated through the assumption that certain physical parameters, including the local coercive and effective fields, are randomly distributed and hence manifestations of stochastic density functions associated with the material. Stochastic homogenization in this manner provides low-order macroscopic models with effective parameters that can be correlated with physical properties of the data. This facilitates the identification of parameters for model construction, model updating to accommodate changing operating conditions, and control design utilizing model-based inverse compensators. Attributes of the model, including the guaranteed closure of biased minor loops in quasistatic drive regimes, are illustrated through examples. }, number={11}, journal={Journal of Intelligent Material Systems and Structures}, publisher={SAGE Publications}, author={Smith, Ralph C. and Seelecke, Stefan and Ounaies, Zoubeida and Smith, Joshua}, year={2003}, month={Nov}, pages={719–739} }
 @article{smith_dapino_seelecke_2003, title={Free energy model for hysteresis in magnetostrictive transducers}, volume={93}, ISSN={["1089-7550"]}, DOI={10.1063/1.1524312}, abstractNote={This article addresses the development of a free energy model for magnetostrictive transducers operating in hysteretic and nonlinear regimes. Such models are required both for material and system characterization and for model-based control design. The model is constructed in two steps. In the first, Helmholtz and Gibbs free energy relations are constructed for homogeneous materials with constant internal fields. In the second step, the effects of material nonhomogeneities and nonconstant effective fields are incorporated through the construction of appropriate stochastic distributions. Properties of the model are illustrated through comparison and prediction of data collected from a typical Terfenol-D transducer.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Smith, RC and Dapino, MJ and Seelecke, S}, year={2003}, month={Jan}, pages={458–466} }
 @article{vortmann_schnerr_seelecke_2003, title={Thermodynamic modeling and simulation of cavitating nozzle flow}, volume={24}, ISSN={["0142-727X"]}, DOI={10.1016/S0142-727X(03)00003-1}, abstractNote={Numerical simulations of cavitating flows are frequently performed by applying simple law of state-cavitation models. Here, the phase transition criterion is usually defined by assuming that cavitation occurs, if the pressure drops below the equilibrium vapor pressure. Since this simple modeling should be improved, an advanced method is developed, which takes phase non-equilibrium effects into account. The inclusion of non-equilibrium effects is important for future simulations of high-speed flows in very small-scale injector nozzles. Related to the van der Waals theory, the new approach is based on postulating Gibbs free energy for the phase mixture. This leads to a rate equation for quality. The two-phase flow is treated numerically by combining the rate equation with a volume-of-fluid algorithm. Unsteady calculations of cavitating flow in a converging–diverging passage and in a channel with a triangular obstacle show cyclically developing cavitation zones. The capability of this model to predict typical effects of cavitation, e.g. the formation of a re-entrant jet, is studied. Simulation of cavitating flow in the channel with a triangular obstacle is compared with the experiment and with numerical investigations of other authors.}, number={5}, journal={INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW}, author={Vortmann, C and Schnerr, GH and Seelecke, S}, year={2003}, month={Oct}, pages={774–783} }
 @article{seelecke_2002, title={Modeling the dynamic behavior of shape memory alloys}, volume={37}, ISSN={["0020-7462"]}, DOI={10.1016/S0020-7462(02)00030-6}, abstractNote={The paper studies the single degree of freedom vibration of a rigid mass suspended by a thin-walled shape memory alloy tube under torsional loading. The behavior is analyzed for the cases of quasiplasticity (low temperatures) and pseudoelasticity (high temperatures) on the basis of an improved version of the Müller–Achenbach model. To illustrate the strong hysteresis-induced damping capacity and the non-linear vibration characteristics, both, free and forced vibrations are considered in the first part of the paper. This is done on the basis of an isothermal version of the model, while the second part of the paper focuses on the effect of non-constant temperature caused by the rate-dependent release and absorption of latent heats.}, number={8}, journal={INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS}, author={Seelecke, S}, year={2002}, month={Dec}, pages={1363–1374} }