A smart composite with functional fibers and reinforcement fibers optimally placed with an embroidery machine was created. Fiber orientation affects mechanical properties of composite laminates significantly. Accordingly, if the fibers can be placed along a desired curved path, fiber reinforced plastic (FRP) structures can be designed more lightly and more sophisticatedly. To this end a tailored fiber placement method using the embroidery machine have been studied. To add functions to the FRP structures, shape memory alloy (SMA) wires were placed as functional fibers. First, for a certain purpose the paths of the reinforcement fibers and the SMA wires were simultaneously optimized in analysis. Next, the reinforcement fibers and tubes with the SMA wires were placed on fabrics by using the embroidery machine and this fabric was impregnated with resin by using the vacuum assisted resin transfer molding method. This smart composite was activated by applying voltage to the SMA wires. Fundamental properties of the smart composite were examined and the feasibility of the proposed creation method was shown.
Since shape memory alloy (SMA) actuators can generate large force per unit weight, they are expected as one of the next generation actuators for aircraft. To keep a position of conventional control surfaces or morphing wings with SMA actuators, the SMA actuators must keep being heated, and the heating energy is not small. To save the energy, a new control method proposed for piezoelectric actuators utilizing hysteresis in deformation [Ikeda and Takahashi, Proc. SPIE 8689 (2013), 86890C] is applied to an antagonistic SMA system. By using the control method any position can be an equilibrium point within hysteresis of stress-strain diagrams. To confirm a feasibility of the control method, a fundamental experiment is performed. The SMA wires are heated by applying electric current to the wires. When a pulsed current is applied to the two SMA wires alternately, the equilibrium position changes between two positions alternately, and when a series of pulse whose amplitude increases gradually is applied to one SMA wire, the equilibrium position changes like a staircase. However, just after the pulse the position returns slightly, that is, overshoot takes place. To investigate such a behavior of the system, numerical simulation is also performed. The one-dimensional phase transformation model [Ikeda, Proc. SPIE 5757 (2005), 344-352] is used for a constitutive model of the SMA wires. The simulated result agrees with the experiment qualitatively, including the overshoot. By examining volume fraction of each phase, it is found that the overshoot is caused by that austenite phase transforms into stress-induced martensite phase during the cooling process after the pulse.
To keep a shape of a smart structure with piezoelectric actuators bonded on it, electric voltage must be applied continuously. To reduce the amount of electricity usage, a new control method was proposed and its feasibility was examined in the previous studies [Proc. of SPIE 8689 86890C, Proc. of 29th ISTS 2013-c-40]. In this method hysteretic behavior of piezoelectric actuators in strain-electric field relationship was utilized effectively, which behavior is that some amount of strain remains even at zero voltage once a large voltage is applied. The results showed that displacement of a smart beam with a piezoelectric ceramic actuator bonded remained without applying voltage to the actuators after applying a pulsed voltage. However, the displacement overshot a final position while applying the pulsed voltage. That is generally undesirable. In this paper a suppression method of this overshoot was proposed. To this end another piezoelectric actuator was bonded on the beam opposing the original actuator. The original actuator was a soft type while a hard type piezoelectric actuator was used as the opposing actuator. With help from the two types of actuators, the overshoot could be suppressed while applying the pulsed voltage by controlling the voltage for the opposing actuator adequately, and a desired displacement could be obtained at zero voltage after the pulse.
To keep a shape of a smart structure controlled by piezoelectric actuators attached to it, electric voltage must be also continued to be applied. To reduce amount of electricity usage, a new control method is proposed. In this method strains of the piezoelectric actuators generated by pulses of voltages are kept with zero/less applied voltage by utilizing the hysteresis in strain versus electric field relationship effectively. In this paper to examine feasibility of this control method residual strains of piezoelectric ceramic plates are measured for combinations of amplitude and period of the applied pulse of voltages. Moreover, a cantilever beam on which a piezoelectric ceramic plate is bonded is made as a simple example of applications to the smart structures, and its deformation behavior after a pulse of voltage is observed. The result shows that the present control method is useful from viewpoint of applied energy, although the strain generated by the piezoelectric actuator is less than the conventional control method where the electric voltage is continued to be applied.
A constitutive model for rate dependent behavior of ferroelectric materials is developed from a one-dimensional
switching model [Ikeda et al., Proc. SPIE, 7289 (2009), 728905]. The one-dimensional switching model has the
following three features. (i) Several ferroelectric variants can be considered, such as 0-degree, 90-degree, 180-degree,
and initial mixed variants. (ii) Required switching energy is approximated as a sum of two exponential functions of
volume fraction of the variants. (iii) A specimen is assumed to be comprised of grains with infinitesimal size, and
relationship between two grains regarding the required switching energy is unchanged independently of switching
directions. Accordingly, the switching proceeds one-dimensionally. To take into account loading rate effects, a function
of volume fraction rate is added to the required switching energy. That makes energy barrier higher at higher rates. To
verify validity of the present model, electro-mechanical behavior of a thin PZT plate is measured at various loading rates
and simulated using the present model. Result shows the present model can capture the influence of electric loading rate
on responses of electric displacement and strain, such that remnant polarization decreases and coercive field increases
with increasing the loading rate.
KEYWORDS: Microsoft Foundation Class Library, Composites, Actuators, Aerodynamics, Atrial fibrillation, Matrices, Sensors, Ferroelectric materials, Control systems, Structured optical fibers
A novel idea of combining two kinds of electro-mechanical couplings to build Active Flutter Suppression (AFS) strategy
for composite structures is presented. The commercially available MFC and a newly proposed shear actuated fiber
composite (SAFC) are considered. MFC induces normal strains and SAFC can be made to couple the transverse shear
strains. A four noded plate element is employed to build the clamped-free active laminated plate with four MFC and
SAFC each. The stiffness, mass, actuator and sensor matrices are obtained from the electro-mechanical coupling analysis.
The open loop flutter velocity is computed using the linear aerodynamic panel theory (DLM). Further, the structural and
unsteady aerodynamic matrices are represented in state-space form to build the aero-servo-elastic plant. Presently, the
unsteady aerodynamics is approximated using a rational polynomial approach. A Linear Quadratic Gaussian control is
designed to perform the closed loop flutter calculations. The actuation authority is maintained same through applied
control voltage, while evaluating the performance of MFC and SAFC. The results have significantly encouraged the
concept of simultaneously targeting the normal and shear strains of aeroelastically excited modes through electromechanical
couplings to build an efficient active flutter suppression system.
KEYWORDS: Actuators, Microsoft Foundation Class Library, Composites, Vibration control, Matrices, Modeling, Active vibration control, Chemical elements, Structured optical fibers, Smart structures
The use of surface bonded (MFC) and embedded (SAFC) piezoelectric composite actuators is examined through a
numerical study. Modelling schemes are therefore developed by applying the isoparametric finite element approach to
idealize normal strain to electric field and shear strain to electric field relations. A four noded coupled finite element is
developed to compute the electro-mechanical responses of the active plate. A linear quadratic regulator is employed to
perform the active vibration control studies. The system matrices of the smart plate structure are obtained and used in the
state-space control model. Two elastic modes are considered, namely bending and torsion of the active plate. The
emphasis is given to evaluate the performance of two different kinds of flexible piezoelectric actuators in vibration
control application.
A simple constitutive model for temperature dependent behavior of ferroelectric materials is developed. This model is
based on the one-dimensional phase transformation model of shape memory alloys. To model the temperature dependent
behavior of the ferroelectric materials, a paraelectric phase is considered in addition to four ferroelectric variants in a
ferroelectric phase. These ferroelectric variants are connected in series to each other, whereas the paraelectric phase is
connected in parallel to the ferroelectric phase. The internal stress is induced in the material due to this parallel
connection, which increases or decreases the driving energy for the switching depending on the switching direction. As
the temperature increases up to the Curie temperature, the volume fraction of the paraelectric phase is assumed to
increase and the required switching energy is assumed to decrease as observed in experiments. The temperature
dependence of the relationships among the electric field, electric displacement, stress, and strain are simulated and
compared with published experimental data for a soft PZT. The comparison indicates that the present constitutive model
can predict the temperature dependent behavior well. This implies that the proposed model can provide a convenient tool
to understand the physical mechanism of the ferroelectric materials and to design smart structures containing the
ferroelectric materials.
The one-dimensional phase transformation model of shape memory alloys [Ikeda et al., Smart Materials and Structures,
13, 916-925 (2004)] is applied to expressing the major and minor hysteresis loops in ferroelectric materials. An analogy
between the phase transformation in the shape memory alloys and the switching in the ferroelectric materials is involved.
The one-dimensional phase transformation model has the following two features. (i) A specimen is assumed to be
comprised of grains with infinitesimal sizes, and the order of the energy required for the transformation of the grains is
unchanged independently of the transformation directions. Accordingly, the phase transformation occurs onedimensionally.
(ii) The required transformation energy is approximated as a sum of two exponential functions of phase
volume fraction. To express the ferroelectric behavior, four phases (variants) are considered, namely, the 0° variant, 90°
variant, 180° variant, and initial mixed variant. Electro-mechanical behavior of a ferroelectric material is simulated
numerically. The result shows the model can approximately duplicate the electro-mechanical behavior observed in the
ferroelectric material.
Deformation of a cantilever beam having thin piezoelectric actuators partially debonded and buckling is analyzed by
using a linear mathematical model based on the Timoshenko beam theory. Effects of location and size of the debonding
are investigated for passive and active extension and bending. The buckling of the actuators is considered by applying a
constant force equal to the buckling load at the boundary between the debonded and the bonded regions. When the
actuators are debonded at their edges, only the bonded regions contribute to the deformation of the beam but the
debonded regions do not contribute at all. When the actuators are debonded in the middle, both the ends of which are
keeping bonded, their performances are almost the same as those for perfectly bonded actuators irrespective of the
location and size of the debonded region before the debonded region buckles. However, after it buckles, the performance
deteriorates depending on the distance from the clamp and the size of the debonded region.
A Smart Vortex Generator (SVG) concept has been proposed, where the SVG is autonomously transformed between an
upright vortex-generating position in take-off and landing and a flat drag-reducing position in a cruise. This SVG is
made of a Shape Memory Alloy (SMA), which is in the austenite phase and memorizes the upright position at high
temperatures of the take-off and landing. At low temperatures during ascent the SVG is transformed into a martensite
phase, and it lies flat against a base structure due to external or/and internal forces. In this paper, we examine whether
the SVG can be transformed into the drag-reducing position by an aerodynamic force. To this end, numerical
simulations are carried out with a simple line element model. The aerodynamic force applied on the SVG is calculated
by a commercial CFD program. Result reveals that this SVG can be transformed from the upright vortex-generating
position into the drag-reducing position by just an airplane climbing, and vice versa, if the SMA applied to the SVG has
the two-way shape memory effect. If the SMA has the one-way shape memory effect, it is necessary to reduce the
stiffness of the SVG or/and use a counter spring.
The one-dimensional phase transformation model proposed by the author was applied to an analysis of bi-axial tensiletorsional
pseudoelastic deformation behavior of a shape memory alloy (SMA) tube. In the one-dimensional phase model,
virtual grains are sorted in order of energy required for transformation and the order of these grains is assumed to be
unchanged irrespective of phases before and after the transformation. Accordingly, the transformation always takes
place in the same order. Here a torsional stress induced martensitic phase was considered in addition to an austenitic
phase and a tensile stress induced martensitic phase. Tensile and torsional stress-strain hysteresis loops for a
pseudoelastic SMA thin tube were simulated. The simulated loops were in quantitatively good agreement with available
experimental data for a pure tensile and a pure torsional strain loading. For combined loadings, the simulated loops
qualitatively agreed with the experimental data.
A simple yet accurate model of shape memory alloys (SMAs) is proposed, which can consider asymmetric tension-compression ferroelastic behavior. Features of this model are (1) energy-based transformation criterion, (2) partial transformation rule based on the micromechanical viewpoint, (3) required transformation energy in the form of a sum of two exponential functions in terms of phase volume fraction, and (4) energy balance equation including thermoelastic effect and dissipated energy due to interaction between the phases. In this ferroelastic model, three phases are considered, namely, an austenitic phase, a tensile stress induced martensitic phase, and a compressive stress induced martensitic phase. The tension-compression asymmetry is expressed by using different required transformation energy functions in different transformation directions and by using different intrinsic strains and Young's moduli in different phases. Stress-strain hysteresis loops for a SMA bar under tensile-compressive cyclic loading are simulated. The obtained result shows that the proposed model can well capture the asymmetric stress-strain loops for tension and compression, minor loops, and effects of temperature and strain rate. This indicates that this model would be a useful tool for understanding the mechanism of SMA behavior and designing smart structures with SMA elements.
A simple yet accurate specimen-based macroscopic constitutive model of shape memory alloys (SMA) was derived from a grain-based micromechanical model, to understand the complicated thermo-mechanical behavior of SMA and to design structural elements with SMA components optimally. This model was composed of a phase transformation energy criterion, a strain equation, and a heat and energy flow equation. New features are that (1) a partial transformation cycle model was proposed, which is called the shift-skip model, and that (2) required energy for phase transformation was found to be well approximated by a sum of two exponential functions in terms of martensite volume fraction. In the shift-skip model, the energy required for the partial transformation was obtained by shifting and skipping the energy required for the complete transformation, based on a microscopic transformation rule. Comparison of the calculated stress-strain loops for the complete and partial transformation cycles with experimental data and with other often used models was carried out. Result showed that the proposed model could capture the measured stress-strain loops well and much better than the other models.
To understand the complicated thermodynamical behaviors of shape memory alloys (SMA) and to optimally design structures with SMA components, a simple yet micromechanical model of SMA was proposed based on Reuss assumption, namely, an assumption of uniform stress state in every grain. Since interaction between grains doesn't exist in Reuss assumption, we considered a specific distribution for phase interaction energy and also hardening due to the grain interaction.
Choosing adequate distributions for both grain orientation and phase interaction energy, the model could describe the round shape around yielding stresses and the inner loops on a stress-strain hysteresis relationship and the temperature differences between transformation start and finish. They were in quantitative agreement with available experimental data for wires. Moreover, a heat balance equation was combined with the constitutive equation to take into account the effect of temperature change of the material. This combined model could capture quantitatively a temperature variation of about 20K in one cycle due to self heating and cooling as well as the effect of strain rate on stress-strain hysteresis loops. Finally, by reducing this proposed model to a model for unidirectional loading we showed that the proposed model became our previously developed macromechanical 1D model. Thus we could bridge the gap between a grain-based micromechanical model and a specimen-based macromechanical 1D model.
In our previous studies, we first introduced the phase interaction energy function as a dissipation potential for the phase transformation of pseudoelasticity between austenite and martensite of shape memory alloy wires. Next, to treat both shape memory effect between twinned and detwinned martensites and the pseudoelasticity in a unified manner, we developed the phase interaction energy function and performed a thermomechanical analysis of the wire based on the developed phase interaction energy function. In the present study, the phase interaction energy function is further extended to include the effect of phase rearrangement and transformations associated with twinned and detwinned rhombohedral phases.
The hysteresis type of material specific damping capacity (SDC) of a unidirectional hybrid fibre reinforced smart composite has been studied in the present work using a multi-cell method.To do this, as a first step, we reviewed various micromechanics modelling for the mechanical properties in general and material damping in particular in order to compare the theoretical capabilities and limitations of the existing analytical models. A new refined unit cell featuring a more realistic fibre-matrix domain has then been proposed for the present modelling. SDC equations corresponding to all the six directions were derived using the strain energy concept within the framework of mechanics of material approach. The generality of the present model in terms of the range of fibre volume ratio, different combinations of fibre-matrix systems etc., has been verified by comparing the present results with the literature including available experimental results. An important merit of the present theory that has to be emphasized over other available theories is the accurate prediction of the transverse and shear directions SDC for composites having a high fibre/matrix modulus ratio. Further, the scope of the present model to the practical applications of a typical shape memory alloy hybrid composite has also been demonstrated through numerical simulations.
The hysteresis between transformation to martensite and austenite in a SMA is discussed here as an intrinsic material property to be used to enhance damping. Initially the SMA constitutive modeling is described on a thermomechanical basis before considering the coupling of the SMA with a host structure targeting in the long term to a composite. The different parameters influencing damping with regard to the applied loads is discussed and conclusions are drawn with regard to how these parameters have to be set such that damping of a SMA-composite can be optimized.
Introducing the phase interaction energy between austenite and detwinned martensite, the presented authors studied pseudoelastic transformations of shape memory alloys and have analytically shown that the transformation is a thermomechanical process along a stable equilibrium path, as observed in experiments. To further exploit the phase interaction energy, here we present a unified approach for treating both shape memory effect and pseudoelasticity, taking into account another state of phase, i.e., twinned martensite. Analytical models formulated using experimental data will be compared with experimental constitutive relationships. A god curve-fitting to complicated experimental stress-strain curves is also presented through a higher-order polynomial representation of the interaction energy function.
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