Tadashige Ikeda

Constitutive model of shape memory alloys for unidirectional loading considering inner hysteresis loops

A specimen-based macroscopic constitutive model of shape memory alloys for unidirectional loading, which is simple yet accurate and has a physical background, was derived from a grain-based microscopic model. To consider the inner hysteresis loops of a stress?strain?temperature relationship, a new inner loop model called the shift and skip model was proposed. This model is based on microscopic aspects and includes the memory effect of deformation history. Stress?strain relationships were simulated for some representative strain cycles. Numerical results showed that the proposed simple model could capture corresponding experimental results accurately enough to be applied for smart structural design. Comparison with major specimen-based macroscopic models was also discussed, under a unifying approach based on the driving energy and required transformation energy pair.

Thermo-mechanical behavior associated with pseudoelastic transformation of shape memory alloys

We have performed a simulation analysis of the pseudoelastic behavior of a NiTi shape memory alloy wire placed in air, subjected to tensile cyclic loads over a range of low strain rates. Thermomechanical interactions, such as energy dissipation, latent heat and heat transfer, are accounted for in a one-dimensional thermomechanical model based on the phase interaction energy function which was introduced in our previous analyses. The interaction energy function was numerically determined so as to make an analytical constitutive relationship fit available experimental stress-strain curves. Numerical results show that the loading strain rate is influential on changes in the stress-strain characteristics and the temperature of the wire. Good agreement between experiment and analysis was obtained, and the effectiveness of the thermomechanical model proposed here has been confirmed.

Active vibration control of smart plates with partially debonded multilayered PZT actuators

The influence of actuator damage on the performance of closed loop vibration control is numerically evaluated. Debonding is considered a damage mode and finite element procedures are subsequently developed to introduce its effect on system matrices, namely elastic and electro-elastic stiffness. A simple modelling scheme for multiple debonding is proposed, which can also idealize multiple delamination in the host laminate. Debonding in actuators in general has reduced their load carrying appreciably as well as vibration control characteristics. Therefore, incorporating such a damage mode in the control design as an uncertainty parameter would help to realize a damage-tolerant active vibration control system. It is interesting to note that debonding in actuators has influenced both active damping and active stiffening effects.

A numerical analysis of phonation using a two-dimensional flexible channel model of the vocal folds.

A two-dimensional flexible channel model of the vocal folds coupled with an unsteady one-dimensional flow model is presented for an analysis of the mechanism of phonation. The vocal fold is approximated by springs and dampers distributed in the main flow direction that are enveloped with an elastic cover. In order to approximate three-dimensional collision of the vocal folds using the two-dimensional model, threshold values for the glottal width are introduced. The numerical results show that the collision plays an important role in speech sound, especially for higher resonant frequency components, because it causes the source sound to include high-frequency components.

Electromagnetic forces for a new vibration control system: experimental verification

In our previous work we proposed a new concept of the control system in which vibrations of a partially magnetized thin beam are actively suppressed using electromagnetic forces induced by an electric current conducted through the beam. In this experimental study we will demonstrate the effectiveness of the electromagnetic force which plays a major role in our new vibration control system. As a partially magnetized beam is not available at the present moment, a magnetic field generated by a permanent magnet is used to control the motion of a thin elastic beam on which an electric current is conducted through an electric wire glued onto the beams surface across its breadth. The objective of the present study is to examine if an actually induced electromagnetic force acting on the electric wire is effective in suppressing the beams vibrations. A feedforward control analysis of the corresponding experiment is performed to confirm experimental results.

Vibration Control System Using Electromagnetic Forces

This paper presents the concept of a new vibration control system in which motions 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. Analytical evaluation of the induced electromagnetic forces acting both on the electric current applied and on the magnetized segments are derived from an electromagnetic consideration. To examine the feasibility of the proposed vibration control system, we have formulated a simple regulator problem in which the disturbed motion of the thin alloy beam caused by an impulsive force is suppressed.

A One-Dimensional Unsteady Separable and Reattachable Flow Model for Collapsible Tube-Flow Analysis

Taking into account both flow separation and reattachment observed in available experimental results on flows in a quasi-two-dimensional channel, we present a one-dimensional unsteady flow model, which is applicable to a flow in a collapsible tube. The flow model has been derived from the two-dimensional Navier-Stokes equations by introducing the concept of a dividing streamline, which divides a separated flow into a jet and a dead-water zone. We also present a criterion for the determination of a separation point. Numerical results show that the locations of the predicted separation points agree well with the experimental data. The predicted static pressure of the separated flow is almost constant downstream of the separation point and increases quickly just before the reattachment point as observed in the experiment. Finally, using the present flow model and the separation criterion, we examine the oscillatory behavior of an unsteady flow in a symmetric channel whose walls move sinusoidally.

Micromechanical modeling of polycrystalline shape-memory alloys including thermo-mechanical coupling

The main objective of this paper is to derive a simple, engineering model for a NiTi-based shape memory alloy (SMA) that can be used as a first-step, inexpensive computational tool in designing components including SMAs. The model is based on a Reuss approximation in which the stress in every grain is considered the same. A random and a simple texture distribution for the grain orientations as well as a normal distribution for the transformation force are used in the calculations so that a round shape of stress–strain curve and transformation start and finish temperatures can be considered. A new algorithm based on minimizing the energy at each transformation step is provided that is simple, fast and accurate. Thermo-mechanical coupling is taken into account, therefore various strain-rate regimes can be modeled. Both superelastic and shape memory effect (SME) are analyzed. The model can also replicate complex behavior encountered in real materials such as small strain–amplitude hysteresis cycles, ratio of lateral to longitudinal strain during transformation and asymmetric behavior in tension compared with compression, while keeping the number of modeling parameters small. Numerical simulations show excellent agreement with available experimental results by applying the adequate grain orientation and the transformation force distribution.

Concept and Electro-elastic Modeling of Shear Actuated Fiber Composite using Micro-mechanics Approach

A Shear Actuated Fiber Composite (SAFC) concept is developed that may find application in structural actuation and health monitoring tasks. The fabrication aspects of SAFC are briefly discussed. A uniform field model is employed to study electro-elastic behavior of the SAFC. The composite actuator is modeled as a general laminate having seven layers, and the effective properties are evaluated further using shear deformation lamination theory. The geometric parameters such as fiber volume fraction, fiber thickness, and fiber orientation are considered, and their influence on the characteristics of SAFC is analyzed. It is observed that a higher fiber thickness may provide better shear actuation capability for the SAFC actuator; but conformability requirements bring a constraint on fiber thickness that needs to be optimized. A fiber volume content of 85—95% appears to provide a design envelope for the SAFC actuator. SAFC has shown a promising feature of simultaneously coupling both transverse shear strains, if the poled PZT fibers are oriented directionally. Therefore, SAFC can be used as a torsional actuator for developing electro-elastically tailored smart laminated or sandwich structures. It is also expected that the SAFC actuator may provide a better solution for active aeroelastic control applications, where torsion mode is critical.

Analytical Study on Training Effect of Pseudoelastic Transformation of Shape Memory Alloys in Cyclic Loading

With increasing number of loading cycles, stress-strain hysteresis loops of pseudoelasticity of a shape memory alloy vary continuously in experiments. To account for such characteristic variance observed during phase transformations, the effect of residual martensite is taken into account in a thermomechanical model based on the phase interaction energy function which we proposed in our previous studies. A functional form of volume fraction of the residual martensite which monotonically increases with increasing loading cycle has been determined using experimental stress-strain loops. It is shown that a simple function of the volume fraction of the residual martensite may model complicated behavior of the transformations in the cyclic loading.