Structure and Control Laboratory, Structural Mechanics Research Group 
Department of Aerospace Engineering, Nagoya University  
Furo-cho, Chikusa-ku, Nagoya 
Research Topics in Ikeda Lab.
We have studied about new aerospace structural systems, especially, smart composite materials and structural systems. We observe phenomena occurring on materials, structures, and related thermos-fluid-servo interactive system, propose mathematical models, veify the models, analize the phenomena using the proposed models, propose applications of the phenomena, designe and realize the applications, and evaluate their performance numerically and experimentally.
Oridinal strutures support loads and keep their configuration. Smart structure have functions of sensors and actuators in addition, and they change their configuration and/or their properties in response to variation of the surrounding or internal conditions.

Shape-memory alloy (SMA) is one of the smart materials, which have unique properties of (i) large recoverable strains, (ii) large stress generation, (iii) large hysteresis loops in the stress-strain relationship, and (iv) variable electrical resistance as well as (v) a Young’s modulus which is sufficient for them to be used for structural members. SMA elements can be used as structural members with the functions of actuator, damper, and/or sensor due to their unique properties. They are attractive in the aerospace engineering industry, which demands low weight and a high level of reliability, because the number of parts and complexity of a system can be redyced. For this reason, the potential applications of SMAs, for both the replacement of existing systems and the development of new devices, has been a major areas of research in the field of aerospace engineering ever since they were discovered.

The unique properties are based on phase transformation and that makes the deformation behavior be complicated depending on not only loads but also temperature as well as their history. To understand mechanism of such a deformation behavior and to design a product using SMA optimally, simple yet reasonably accurate constitutive models are necessary. To this end we have proposed One-dimensional Phase Transformation Model where crystrals in SMA are assumed to transform one-dimensionally. We have confirmed that this model can quantitatively capture the stress-strain-temperature relationship under multiaxial stress condition and its rate dependence. This model for SMA has been applied to analysis of deformation behavior of ferroelectric materials.

As an application of SMA, we have proposed Smart Vortex Generator. Vortex Generators are devices designed to delay or prevent flow separation by generating vortexes and mixing a flow. Some of them (VGs) are necessary only in takeoff and landing phases, because a flow on the surface of wing separates, when the main wings are at a large angle of attack to the flow and flaps are deflected by a large angle. However, this type of VGs has an adverse effect in a steady cruise phase because they generate drag due to the vortexes. To slove the problem, we have proposed a smart vortex generator made of SMA It takes upright vortex-generating position in the takeoff and landing phases to prevent flow separation by generating vortexes, whereas in a steady cruise phase it takes a flat drag reducing position to reduce drag, without any energy supply, by using functions of SMA and approx. 70K difference in ambient temperature between the ground and the cruise altitude.

Mechanical properties of composite laminates significantly depend on the fiber orientation. When the fiber orientation changes by just a few degrees, the strength and stiffness varies significantly. Accordingly, if the fibers can be placed along desired orientations for a certain stress field in an application, the composite can be designed more optimally for some purposes. To this end Tailored Fiber Placement (TFP) has been studied, where an embroidery machine is used to place the fibers so as to be suitable for the Vacuum Assisted Resin Transfer Molding (VaRTM) processing composites at low cost. Availability of this method has been verified by examining properties of laminate plates with optimized fiber paths for a bending-torsion loading or for controlling eigenfrequencies.

A new molding method for carbon fiber reinforced thermoplastics (CFRTP) is also developed to process low cost, high stiffness and strength as well as recyclable composites. In the method an In-situ Molding Technique without prepregs and autoclaves is explored. Efforts are made to understand the physical processes such as thermal conduction in materials, bonding, and impregnation of resin into fibers, and the molding processes of CFRTP are examined.

(3) Fluid-Structure Interaction Problem and Analysis of Voice Generation
Biological compliant tubes conveying fluid show very interesting static and dynamic behavior. In particular, their dynamic charactereistics have turned out to be much more complex than was thought at an early strage of study. The phenomenon of coupling between the deformation of the collapsible tube and the static pressure of its internal fow represents a typical eample of complicated nonlinear dynamic systems. When subjected to even slight external static pressure, the compliant circular tubes are easily collapsed to a three-dimensional configulation, so that the flow in the tube is separated and reattached downstream, and the velocity distribution also becomes three dimensional along the collapsed segment. To understand the complicated behavior of the tube-flow problem, we presented an Unsteady One-dimensiona Separable and Reattachable Flow Model in which the comncept of a dividing streamline was introduced so that the effect of both the flow separation and the reatcchment on the static pressure distribution can be included in the model. Validity of the model was shown by flow visualization and pressure measurement of a channel flow with a vibrating throat.

This model was applied to analysis of voice generation. Source sound of the voice is generated by selfexcited oscillation of the vocal folds, and it becomes voice by resonating in the vocal tract and radiating from the mouth to the atmosphere. It is important to understand the mechanism of phonation, since that may also become a breakthrough in increasing qualities of synthesized voice, and contribute to the development of artificial larynxes and medical examination technique against voice disorders. We proposed a new vocal fold flow model in which the vocal fold was approximated by a two-dimensional flexible channel composed of distributed springs and damping elements enveloped by a massive cover and the glottal flow was given by the unsteady one-dimensional separable and reattachable flow model. By using this model the effects of lung pressure, stiffness of vocal fold, and transient time of the lung pressure on the sound pressure were examined. The numerical result showed that the calculated speech sound waveforms were in qualitatively good agreement with those measured.
 (4) UAVs
The following unmanned aerial vehicles (UAVs) were built for students competitions. They were awarded a prize in the competitions. The students show their potential much more for such competitions than their reserach.
 Ring wing type airplane (2008)
 Flying wing type airplane (2007)
Airplane using Magnus effect (2008) Airplane with a vector thruster (2014)
 Aircraft which participated to Students Competition in Indoor UAV.