This paper addresses a flutter boundary prediction of a smart wing during the process of adaptation in which airplane's safety will easily be endangered. A smart morphing airplane will be more flexible functionally and mechanically than a conventional airplane with a fixed structural configuration. During the process of structural morphing or adaptation, airplane's structure needs to become very flexible, so that the airplane is anticipated to encounter instability in a new manner due to an on-going structural change. Here we will show that the new discrete-time series approach for aeroelastic instability prediction which we proposed for the fixed-wing is useful in predicting the flutter boundary of an adaptive wing, too. A numerical analysis is performed using a two-dimensional wing model in which the structural adaptation changes its natural frequencies and consequently influences its aeroelastic stability although flying at a fixed speed.
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.
We present an analysis on a complicated combined process of martenistic transformation and two-way shape memory effect due to cyclic loadings of stress and heat in order to further develop the constitutive model of an SMA wire which is based on the phase interaction energy function proposed in our previous studies. Stress-induced martenistic transformation is modeled by introducing residual martensite in the transformation process between austenite and detwinned martensite. As for heat-induced two-way shape memory effect, it is assumed that a mixed-state of austenite and residual detweinned martensite changes into another mixed-state of twinned and detwinned martensites during colling of the alloy, whereas a reversal change between the mixed-states occurs during heating. To examine the effectiveness of this analytical model based on the phase interaction energy function, an experiment is performed using a uniform SMA wire. Numerical analysis is carried out to compare with experimental data on the stress-induced martensitic transformation and the heat-induced two-way shape memory effect, which reveal very complicated training effect.
The study to reduce noise and vibration in aircraft cabin through PZT was implemented, using a semi-monocoque structure, 1.5m in diameter and 3.0m long with 2.3mm skin, which stimulates an aircraft body. We utilized PZT of 480 pieces bonded on inner surface of the structure as sensor and actuator. We applied random noise of low frequency range between 0~500Hz to the test model. We tried to reduce the vibration level of structure and internal air due to the external load by controlling the PZTs. Two control methods, gain control and feed-forward control, were tried. We measured internal sound pressure on 150 spots and compared overall values of sound pressure with gain control to them without control and evaluated its reduction capability. The tests showed 4.0dB O.A. reduction at maximum in gain control and 3.5dB O.A. reduction at maximum in feed forward control.
This paper describes a new electromagnetic device for vibration control of a light-weighted deployable/retractable structure which consists of many small units connected with mechanical hinges. A typical example of such a structure is a solar cell paddle of an artificial satellite which is composed of many thin flexible blankets connected in series. Vibration and shape control of the paddle is not easy, because control force and energy do not transmit well between the blankets which are discretely connected by hinges with each other. The new device consists of a permanent magnet glued along an edge of a blanket and an electric current-conducting coil glued along an adjoining edge of another adjacent blanket. Conduction of the electric current in a magnetic field from the magnet generates an electromagnetic force on the coil. By changing the current in the coil, therefore, we may control the vibration and shape of the blankets. To confirm the effectiveness of the new device, constructing a simple paddle model consisting eight hinge- panels, we have carried out a model experiment of vibration and shape control of the paddle. In addition, a numerical simulation of vibration control of the hinge structure is performed to compare with measured data.
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.
Shape memory alloys (SMA) show very complicated thermomechanical behavior due to phase transformations and rearrangements, including large bounding hysteretic stress-strain loops as well as their inner loops. In our previous analyses, incorporating the phase interaction energy function (PIEF) as a dissipation potential with the free energy of the alloy, we proposed a macroscopic model of SMA for the pseudoelasticity and shape memory effect. Analytical bounding loops derived could accurately model experimental results of a wire subjected to cyclic loads up to 1Hz, including the temperature change. In the present paper, to further extend the concept of the PIEF, we propose a microscopic approach by taking into account the pseudoelastic hysteresis in single crystal grains of polycrystalline SMA. In each grain, we assume that the hysteretic behavior is represented by the Preisach model. Again, incorporating the PIEF with the free energy of the grain, and summing up over the whole material, we have derived the stress-strain relationship in which the Cauchy distribution function is used for the probability of the martensitic and the reverse transformation. We will show that the analytical stress-strain model which has been determined using experimental data of a bounding loop can well describe its inner loops.
The active vibration with smart material has potential to realize not only distributed actuator and sensor but also simplified and light weight active control methods. Electro-Rheological Fluid can produce shear force according to voltage of electrical field and respond quickly enough to control structure. In this paper, control methods to achieve effective damping are described. The key points are modeling the smart structure with Electro-Rheological Fluid and control methods for reducing vibration. The nonlinear model is derived to identify physical parameters of Electro- Rheological Fluid. The vibration test results of small specimens show that this analytical model can express electro-rheological effect. The analytical model is made for larger specimen in the same manner. The effects of vibration reduction with Electro-Rheological Fluid on the bema structure are investigated as the vibration control system, where the strength of electrical field for input and minimizing the transmissibility of vibratory loads for objective analytically. As the results of this study, it is revealed that smart structure embedded ERF can achieve the expected damping performance. Some technical issues of control method for applying to any actual structures are discussed.
To realize simplified vibration reduction system, Electro- Rheological Fluid will be used. Since there was no suitable ERF for this study, material specification was created. According to this specification, particle-type ERF was manufactured and tested. To evaluate damping characteristics of laminate with ERF, three kinds of specimens were manufactured and tested. Specimen A, 20mm x 200mm, and B, 20mm x 400 mm, were used to evaluate ERF and acquire basic damping data to establish analytical model. Element specimens, 40mm x 500mm, were tested as small part of the actual structure to evaluate performance of the smart structure concept. From technical point of view, this smart structure concept has the ability to reduce vibration well but there are some technical issues to be resolved for applying to actual structures. The specification for applicable ERF and manufacturing method for smart structures are discussed.
We are carried out the tests for the sound and vibration control of the CFRP square panel. 500Hz bandwidth noise through two speakers is applied to the CFRP panel. Our objects are to improve the structural damping of the panel and attenuate the sound power radiated from the panel using piezoelectric sensors and actuators. The dimensions of the CFRP plate are 600.0 mm x 600.0mm in area and 1.8mmt in thickness. Eighteen piezoelectric elements (40.0 x 20.0 x 0.3mmt) are bonded on the surface of the panel by epoxy adhesive. The panel is driven using some piezoelectric elements as actuators. The vibration of the panel is monitored using piezoelectric elements as sensors. We can get the strain of the panel from the voltage induced by piezoelectric elements. The signals are sent to digital signal processor (DSP) through filters and the control signal are sent to the power amplifiers. The amplified signals drive the piezoelectric actuators. The vibration and the radiated sound power of the panel are suppressed. We try to apply two methods for the control which are the gain control and the reduced LQG control. In the case of the gain control, the strain is reduced as much as 10-20 dB at some resonant peaks and the radiated sound pressure level as much as 1-15 dB. The radiated sound power is reduced by 1.59dB in the 0-500Hz frequency range. In the case of the LQG control, the strain is reduced as much as 7-10dB at some resonant peaks and the radiated sound pressure level as much as 1-7dB. The radiated sound power is reduced by 0.7dB in the 0-500Hz frequency range.
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.
Introducing an interaction energy in the free energy function, the first two of the present authors proposed a 1D pseudoelastic model of shape memory alloys. The model has been demonstrated to represent qualitatively well some complicated experimental data on stress-strain-temperature relationships. To study the effect of large hysteresis due to pseudoelasticity of the alloys on their vibrational behavior, we carry out numerical simulations of vibration of a simple mass-spring system connected with a prestrained shape memory alloy wire whose constitutive equation is expressed by the present authors' pseudoelastic model.
This paper presents an overview on the smart structures research and development activities in Japan which were reported after 1992 to some time in 1996, including a brief description of the recent situation in the smart structures research circle. Mention will be made of investigations on the vibration, shape and motion controls of space structures, vibration suppression of substructural elements and smart reinforced composites, shape memory alloys, design approaches, etc., focussing on their new aspects and ideas.
By introducing an interaction energy function, the first two of the present authors proposed a one-dimensional pseudoelastic theory of shape memory alloys, which has been demonstrated to model complicated experimental results and Tanaka's transformation kinetics qualitatively well. To study the stress-strain-temperature relationship, we further develop the pseudoelastic theory by introducing temperature-dependent terms in the free energy function proposed by Ranieki and Bruhns. In addition, the effect of temperature is included in the interaction energy. For computational analysis, material parameters are estimated from data measured by Tobushi and his coworkers in their experiments. Numerical results show that predictions by the present theory agree with some essential feature of their experimental results.
We have presented a concept of a new vibration control system in which a motion of an Al-Fe alloy thin beam plate with magnetized segments can be suppressed or activated through electromagnetic forces induced by an applied electric current. To further exploit the proposed vibration control, in this paper we evaluate the effect of the self-inductance of the electric circuit of the control system, because the change in the electric current in a magnetic field induces the counterelectromotive force to oppose the change in current. Numerical evaluation shows that the self-induction of the circuit of the system is influential to control of sound, but little influence is given to suppression of vibration of a thin plate. To examine the feasibility of the proposed vibration control system, we treat a simple regulator problem in which the disturbed motion of a thin alloy cantilevered beam late caused by an impulsive force is suppressed.
The paper presents a short overview of the 1997 Smart Structures and Integrated Systems Conference program from the perspective of an overview of the technologies contributing to this field, their interrelationships, and selected key areas in which development is needed to further their application. Four specific technology areas are addressed; integrated systems applications, vibration and acoustic control, actuation technologies for smart structures, and health monitoring, damage detection and damage mitigation. The states of the art in each of these four areas, as exemplified by contributions to this conference, are examined and evaluated with respect to technical maturity and application challenges. Conclusions are drawn from this examination which indicate several, interrelated technical areas in which future concentration of study and development would significantly benefit the evolution of smart structures and other integrated smart systems.
This paper presents an extension of the authors' previous analyses on the one-dimensional pseudoelastic theory of shape memory alloys (SMA), in which an interaction energy has been introduced to represent the energy dissipation during the phase transformation. From the equilibrium condition of the two-phase state, we show that the partial derivative of the interaction energy with respect to the phase fraction represents the thermodynamic driving force for the phase transformation. Two functions for the interaction energy are derived from the assumptions about the driving force of the equilibrium transformation. Using this interaction energy, we also examine the stability of equilibrium state and the formation of subloops due to incomplete transformations. Analytical predictions by the proposed theory agree well qualitatively with available experimental observations.
The objective of this study is to provide experimental data on bending oscillation of a deploying or retrieving beam cantilevered by a clamping device with three pairs of rollers and springs, and to formulate a finite element analysis for treating the corresponding oscillation of the axially moving beam by using beam elements of varying length. The equation of motion of the beam derived is numerically solved with the aid of the modified Newmark method, the so-called (alpha) -method, to simulate the transitional motion of the beam measured experimentally.
This paper describes computer simulation analyses onapplication of a fuzzy logic and a neural network control to trackingand rendezvous of a moving target for docking by an adaptive spacestructure in order to examine the effectiveness and feasibility ofboth the controls. The example simulations have shown that theapplication of the fuzzy control/neural networks is very effectivein the tracking/rendezvous problem.