Archive issue - vol.5 No.1



   No.   Author(s) - Title
Pages

   1.
 

 Asanuma H. and Du H. -- Monitoring of optical transmission loss through optical fiber embedded in SiC fiber reinforced aluminum composite during tensile test
 

7-18
 

   2.
 

 Asaoka T., Kimura K. and Funami K. -- Characteristics of SMA particle dispersed steel matrix composite
 

19-29
 

   3.
 

 Banks H.T. and Smith R.C. -- Hysteresis modeling in smart material systems
 

31-45
 

   4.
 

 Braga A.M.B., DeBarros L.P.F. and Gama A.L. -- Models for the high frequency response of active piezoelectric composite beams
 

47-61
 

   5.
 

 Brennan M.J. -- Actuators for active vibration control - tunable resonant devices
 

63-74
 

   6.
 

 Choi S.B., Kim H.K. and Kim S.C. -- Position and force control of a two-link flexible manipulator with piezoelectric actuators
 

75-88
 

   7.
 

 DeGiorgi V.G. -- Computational evaluation of poling induced stress fields in a piezoelectric ceramic
 

89-100
 

   8.
 

 Friend C.M. and Mattey C.R.D. -- Active vibration control of shape-memory alloy hybrid composites
 

101-111
 

   9.
 

 Fuhr P.L. and Huston D.R. -- A case study of an intelligent civil structure - the Winooski one hydroelectric dam 8 years later
 

113-126
 

   10.
 

 Gabbert U., Berger H., Köppe H. and Cao X. -- On modelling and analysis of piezoelectric smart structures by the finite element method
 

127-142
 

   11.
 

 Henrioulle K., Dehandschutter W. and Sas P. -- Design of a distributed acoustic actuator for active noise control
 

143-155
 

   12.
 

 Clephas B. and Janocha H. -- Extended performance of hybrid actuators
 

157-168
 

   13.
 

 King T. and Xu W. -- The construction and characteristics of a piezoelectric motor using a harmonic drive
 

169-182
 

   14.
 

 Pierce S.G. and Culshaw B. -- Applications of broadband laser-based ultrasound to materials testing
 

183-193
 

   15.
 

 Mezzanotti F. and Salvia M. -- Actuation properties of adaptable hybrid composites with embedded shape memory alloy wires
 

195-206
 

   16.
 

 Scarpa F. and Tomlinson G. -- On static and dynamic design criteria of sandwich plate structures with a negative Poisson's ratio core
 

207-222
 

   17.
 

 Maas J., Schulte T. and Grotstollen H. -- Controlled ultrasonic motor for servo-drive application
 

223-239
 

   18.
 

 Seelecke S. and Papenfuss N. -- A finite element formulation for SMA actuators
 

241-250
 

   19.
 

 Chantalakhana C. and Stanway R. -- Control of plate vibrations using smart technology
 

251-267
 

   20.
 

 Thompson S.P. and Loughlan J. -- The alleviation of post-buckled displacements and non-linear stresses within laminated plates using SMA actuators
 

269-282
 

   21.
 

 Todoroki A. and Suzuki H. -- Health monitoring of internal delamination cracks for graphite/epoxy composites by electric potential method
 

283-294
 

 



1.

MONITORING OF OPTICAL TRANSMISSION LOSS THROUGH OPTICAL
FIBER EMBEDDED IN SiC FIBER REINFORCED ALUMINUM
COMPOSITE DURING TENSILE TEST

H. ASANUMA and H. DU

Department of Mechanical Engineering, Chiba University,
1-33, Yayoicho, Chiba City, 263-8522, JAPAN

     This paper describes a trial of monitoring fracture processes of SiC fiber reinforced aluminum composites with embedded optical fiber. It was embedded in composites reinforced with SiC fiber of different volume fractions by the interphase forming/bonding method using copper insert. These composites were tensile tested with measuring optical transmission loss. The results show that breakage of optical fiber starts at smaller strain than that of SiC fiber. The embedded optical fiber works as an optical path even after severe multiple fractures. Optical transmission loss is dependent on the number of optical fiber breakages. As fracture of SiC fiber enhances that of optical fiber and is reflected on optical transmission loss, fractures of SiC fibers can be detected by monitoring of optical transmission loss. It can also reflect the type of fracture process of the composite, that is, cumulative or non-cumulative.

Key words:

smart materials, health monitoring, fiber reinforced metals, optical fiber, fracture process.

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2.

CHARACTERISTICS OF SMA PARTICLE DISPERSED
STEEL MATRIX COMPOSITE

T. ASAOKA and K. KIMURA

Department of Mechanical Engineering, Tokyo Denki University,
Hatoyama, Hiki-Gun, Saitama 350-03, JAPAN

K. FUNAMI
Dept. of Mechanical Engineering, Chiba Institute of Technology,
Narashino, Chiba 275, JAPAN

     Crack arrest effect on the propagation of cracks in steels, by using stress induced transformation and following volume change of dispersed SMA particles, has been studied. To realize the effect, Ti-Ni SMA particle dispersed Cr-Mo steel was fabricated by powder metallurgy method. The dissolution of Ti from Ti-Ni particle and the formation of Ti compound layer at the matrix-particle interface has been observed in the fabricated materials. These phenomena seemed to introduce the change in transformation temperatures of dispersed particles and to affect the crack propagation. Results of fracture toughness test suggested the stress release mechanism due to the debonding of matrix-particle interface near the crack tip.

Key words:

crack arrest effect, shape memory alloy, Ti-Ni, steel matrix composite.

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3.

HYSTERESIS MODELING IN SMART MATERIAL SYSTEMS

H.T. BANKS and R.C. SMITH

Center for Research in Scientific Computation,
North Carolina State University,
Raleigh, NC 27695-8205, USA

    In this paper, we discuss several techniques for modeling hysteresis in smart material systems. The physical mechanisms leading to hysteresis vary greatly among materials and applications. This leads to a variety of models ranging from purely phenomenological models for systems in which the physics is not well understood to characterizations which incorporate significant physical properties of the system. We provide an overview of such approaches with examples drawn from current smart material applications.

Key words:

hysteresis, nonlinear systems, smart material systems, internal variables.

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4.

MODELS FOR THE HIGH FREQUENCY RESPONSE OF ACTIVE
PIEZOELECTRIC COMPOSITE BEAMS

A.M.B. BRAGA and L.P.F. DE BARROS

Department of Mechanical Engineering,
Pontifícia Universidade Católica do Rio de Janeiro,
PUC-Rio, 22453-900, Rio de Janeiro, BRAZIL
e-mail: abraga@mec.puc-rio.br

A.L. GAMA
Department of Mechanical Engineering,
Universidade Federal Fluminense,
UFF, Rua Passo da Pátria 156, 24210-000, Niterói, BRAZIL

     The problem addressed in this paper is that of modeling composite beams excited by distributed piezoelectric actuators. A model based on Reddy's layerwise laminate theory is proposed. Through comparisons with exact wave-dispersion analytical results, it is shown that the model may provide an accurate description of the active beam's response in the high-frequency (short-wavelength) range.

Key words:

smart structures, composite structures, piezoelectric materials, wave propagation, vibrations.

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5.

ACTUATORS FOR ACTIVE VIBRATION CONTROL -
TUNABLE RESONANT DEVICES

M.J. BRENNAN

Institute of Sound and Vibration Research,
University of Southampton,
Southampton, Hampshire, SO17 1BJ, U.K.

     This paper is concerned with the control of vibration using a smart structure. Such a structure requires actuators and sensors coupled with a controller, but only actuators are discussed here. Because the limiting factor in the active control of vibration is often the actuator, the work described in this paper discusses the use of resonant devices to generate the required secondary force. The control of such a device is much simpler than a fully active system as it simply involves tuning the device so that it operates most effectively at the unwanted disturbance frequency. A major issue is how to design a tunable device, and four ways of achieving this with a simple beam and attached masses are described and compared in this paper.

Key words:

vibration control, vibration absorbers, adaptive-passive control.

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6.

POSITION AND FORCE CONTROL
OF A TWO-LINK FLEXIBLE MANIPULATOR
WITH PIEZOELECTRIC ACTUATORS

S.B. CHOI and H.K. KIM

Smart Structures and Systems Laboratory,
Department of Mechanical Engineering,
Inha University, Incheon 402-751, KOREA

S.C. KIM
Department of Mechanical Design Engineering,
Inha Technical Junior College, Incheon 402-752, KOREA

     This paper presents a new control strategy for the position and force control of flexible manipulators. The governing equation of motion of a two-link flexible manipulator which features piezoceramic actuators bonded on each flexible link is derived via Hamilton’s principle. The control torques of the motors to command desired position and force are determined by a sliding mode controller (SMC) on the basis of the rigid-mode dynamics. In the controller formulation, the sliding mode controller with perturbation estimation (SMCPE) is adopted to determine appropriate control gains. The SMCPE is then incorporated with the fuzzy technique to mitigate inherent chattering problem while maintaining the robust stability of the system. A set of fuzzy parameters and control rules are obtained from estimated perturbation. During the commanded motion, undesirable oscillation is actively suppressed by applying feedback control voltages to the piezoceramic actuators. These feedback voltages are also determined by the SMCPE. Consequently, accurate position and force control of a two-link flexible manipulator are achieved.

Key words:

flexible manipulator, piezoelectric actuator, fuzzy-SMCPE.

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7.

COMPUTATIONAL EVALUATION OF POLING INDUCED STRESS FIELDS
IN A PIEZOELECTRIC CERAMIC

V.G. DEGIORGI

Code 6350, Multifunctional Materials Branch,
Naval Research Laboratory
Washington, DC 20375, USA

     Poling, the process of applying an electric field to activate and orient a material's piezoelectric response in a preferred direction, is an essential step in the manufacture of ferroelectric ceramics for use in smart devices. In this work finite element techniques are used to calculate electric field and stress. Poling, the process of applying an electric field to activate and orient a material's piezoelectric levels resulting from the poling process. The effects of electrode spacing, material condition and the strength and sequencing of applied fields during poling are examined using computational experiments. The material section evaluated is a thin panel of PZT-5A ceramic.

Key words:

smart materials, piezoelectric materials, finite element, poling.

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8.

ACTIVE VIBRATION CONTROL OF SHAPE-MEMORY
ALLOY HYBRID COMPOSITES

C.M. FRIEND and C.R.D. MATTEY

Cranfield University, Shrivenham,
Swindon, SN6 8LA, U.K.

     This paper investigates experimentally and analytically the effect of Active Strain Energy Tuning (ASET) on low actuator fraction Shape-Memory Alloy (SMA) hybrid composite laminates. It shows that in these materials ASET results in reductions in resonance frequencies during actuation, in contrast to the behaviour observed in higher actuator fraction laminates. A simple analytical model is presented to interpret the results. This shows that in general terms there is no difference in the mechanism of frequency shifts in low and high actuator fraction materials. The reductions in natural frequency observed in low actuator fraction laminates occur simply because the force developed by the actuators is too small to overcome matrix thermal stresses; in contrast to the control authority available in composites containing higher actuator fractions.

Key words:

shape-memory alloys, smart structures, vibration control.

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9.

A CASE STUDY OF AN INTELLIGENT CIVIL STRUCTURE -
THE WINOOSKI ONE HYDROELECTRIC DAM 8 YEARS LATER

P.L. FUHR and D.R. HUSTON

University of Vermont College of Engineering,
Burlington, Vermont 05405, USA

     The Winooski One hydroelectric dam in Winooski Vermont, built in 1992, represented the world's first high performance civil structure into which were embedded various fiber optic sensors. While the goal was to have these sensors provide measurements not previsouly attainable, given the large levels of electromagnetic interference present within such a power generation facility, in some respects the larger issue has been the overall survivability of fiber optic sensors which have been embedded into a reinforced concrete structure. Details regarding sensor choices, sensor placement, installation details, measurements, and the benefits to the dam owners are presented.

Key words:

civil structures, fiber optic sensors, in-situ monitoring, smart structures.

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10.

ON MODELLING AND ANALYSIS OF PIEZOELECTRIC SMART
STRUCTURES BY THE FINITE ELEMENT METHOD

U. GABBERT, H. BERGER, H. KÖPPE and X. CAO

Institut für Mechanik, Otto-von-Guericke-Universität Magdeburg,
Universitäts-platz 2, D-39106 Magdeburg, GERMANY

     In the paper, a general purpose finite element software for the simulation of piezoelectric material systems and controlled smart structures is presented. The equations of coupled electromechanical problems are given in a weak form, which are used for the development of 1D, 2D, 3D as well as multilayered composite shell elements. The smart structures finite element code includes static and dynamic analysis, where also controlled problems can be simulated. To demonstrate the capability of the simulation tool some test examples are reviewed.

Key words:

smart structures, piezoelectric materials, finite element analysis.

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11.

DESIGN OF A DISTRIBUTED ACOUSTIC ACTUATOR
FOR ACTIVE NOISE CONTROL

K. HENRIOULLE, W. DEHANDSCHUTTER and P. SAS

Katholieke Universiteit Leuven, Department of Mechanical Engineering
Division of Production Engineering, Machine Design and Automation
Celestijnenlaan 300B, B-3001 Heverlee, BELGIUM
e-mail:
Kris.Henrioulle@mech.kuleuven.ac.be

     A distributed acoustic actuator for active noise control is designed and simulated. The distributed actuator consists of a piezoelectric PVDF film, which covers the entire surface of a passive carrier structure. The piezo elements are driven in anti-phase, resulting in a bending motion of the actuator. An analytical model for the acoustic actuator is derived, relating the actuator's displacement to the applied voltage, taking into account the influence of the piezoelectric film on the actuator's stiffness. The model is used to optimise the specifications for the piezoelectric film and the carrier structure, resulting in the highest sound power output a frequency range from 30-500 Hz. An analytical model for the behaviour of a double panel partition with a distributed acoustic actuator integrated in the cavity is derived. An active control system increases the sound power transmitted through the double panel partition. Simulation results show that a substantial increase in transmission loss can be achieved in a frequency region from 30 to 500 Hz with this configuration.

Key words:

piezoelectric actuator, PVDF, active noise control.

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12.

EXTENDED PERFORMANCE OF HYBRID ACTUATORS

B. CLEPHAS and H. JANOCHA

Laboratory for Process Automation (LPA),
University of Saarland,
66041 Saarbrücken, GERMANY

     A hybrid actuator basically consists of a piezoelectric and a magnetostrictive transducer oscillating in their resonant frequency. So the reactive energy is exchanged between both transducers, which leads to a high efficiency and a compact mechanical and electrical construction. Driven in its natural frequency, however, the strain-time characteristic of the hybrid actuator is always nearly sinusoidal; this restricts possible applications and therefore an extended performance was investigated by driving the actuator with signals different from a sinusoidal form. This contribution briefly reviews the basics of hybrid actuators and the oscillatory application in a linear motor. Then a hybrid relay is introduced as an example for quasi static operation. Based upon different drives enhanced strain-time characteristics of a hybrid stack actuator are theoretically and numerically predicted and verified by measurements. Finally, a method of detecting the external mechanical load by measuring the resonance frequency will be explained. This could be applied to the linear motor, which can be enabled to identify its load without an additional sensor.

Key words:

piezoelectric actuator, magnetostrictive actuator, linear motor, injection valve, switching amplifier.

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13.

THE CONSTRUCTION AND CHARACTERISTICS OF
A PIEZOELECTRIC MOTOR USING A HARMONIC DRIVE

T. KING

Mechatronics Research Group,
School of Textile Industries,
The University of Leeds, Leeds LS2 9JT UK

W. XU
The University of Surrey, UK

     The construction and characteristics of a newly developed piezomotor are presented. The motor uses a harmonic drive principle, coupled with flexure hinged mechanical displacement amplifiers, to yield a form of positive drive stepping motor suitable for use in open loop speed and position control applications. Comparison with previous harmonic piezomotors and other piezomotors shows a useful performance improvement has been achieved.

Key words:

piezoelectric, stack actuator, multilayer actuator, harmonic drive, flexure hinge, motor.

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14.

APPLICATIONS OF BROADBAND LASER-BASED
ULTRASOUND TO MATERIALS TESTING

S.G. PIERCE and B. CULSHAW

University of Strathclyde, Optoelectronics Division,
Department of Electronic & Electrical Engineering,
204 George St, Glasgow G1 1XW, U.K.

     We discuss the role of broadband Lamb wave propagation for materials testing applications in metal and composite material plates. Using a high powered pulsed laser-acoustic source it was possible to initiate broadband acoustic pulses in the samples. The pulses were detected by non-contact, broadband optical receivers. Temporal and spatial sampling of the ultrasonic wavefield allowed simultaneous measurements of several separate Lamb wave modes. A recent development of the technique is described whereby a low power CW laser diode was used to generate Lamb waves in a steel sample at a significantly reduced peak power compared to the pulsed laser source. Digital modulation of the injection current to the diode coupled with correlation detection allowed observation of the low amplitude ultrasound propagating in the sample.

Key words:

laser-ultrasound, Lamb waves, non-destructive testing.

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15.

ACTUATION PROPERTIES OF ADAPTABLE HYBRID COMPOSITES
WITH EMBEDDED SHAPE MEMORY ALLOY WIRES

F. MEZZANOTTI and M. SALVIA

Ecole Centrale de Lyon,
Laboratoire Ingéniérie et Fonctionnalisation des surfaces,
UMR CNRS 5621, BP 163, 69131 Ecully Cedex, FRANCE

     Adaptable hybrid composites are materials in which actuators are embedded into polymer matrix composites. Shape memory alloys (SMA) are among the potential candidates for actuators embedded in such composite smart structures. After plotting Clausius-Clapeyron diagrams for three structural states, thin wires ('fi'=120 micrometers) of Nickel-Titanium-Copper (nitinol) were incorporated parallel with the reinforcing fibres into a glass-epoxy unidirectional laminate during lay-up. Then the whole structure was subjected to different curing procedures. The interfacial shear strength between the matrix and the nitinol wires in various structural states was determined by micromechanical tests involving the interface directly: the pull-out and microdebond tests. The clamped-free (cantilever) beam method was used to evaluate the effect of actuation by heating the nitinol wires embedded into the composite. The comparison between the different composites points out to the leading role of the interfacial shear strength. The influence of the training conditions before embedding and the occurrence of a self-trained two way shape memory effect, can also be noted.

Key words:

fibre reinforced polymer (FRP), shape memory alloy (SMA), pull out test, self-trained TWSME, shape controlled beam.

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16.

ON STATIC AND DYNAMIC DESIGN CRITERIA OF SANDWICH PLATE
STRUCTURES WITH A NEGATIVE POISSON'S RATIO CORE

F. SCARPA and G. TOMLINSON

Dynamics Research Group, Department of Mechanical Engineering,
The University, Sheffield, S1 3JD, UK

     In this paper the static and dynamic performances of sandwich structures with in-plane negative Poisson's ratio core are investigated from an analytical point of view. The cellular material theory is applied to calculate the orthotropic mechanical properties of re-entrant cell honeycomb cores, which shows negative Poisson's ratio values. This special geometrical layout of the cells allows higher out-of-plane shear modulus, compared to the one of regular honeycombs. The laminate orthotropic plate theory with shear correction factors is applied in order to describe the static and dynamic behaviour of symmetric sandwich plates with different core to sheet thickness ratios. Comparisons are made with analogous structures with regular honeycomb. The maximum deflections due to uniform pressure and buckling loads are enhanced, while the natural frequencies show a slight enhancing for some parameters of the cells.

Key words:

Poisson's ratio, auxetic, honeycombs, sandwich panels.

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17.

CONTROLLED ULTRASONIC MOTOR FOR
SERVO-DRIVE APPLICATION

J. MAAS

Daimler Chrysler Research and Technology
Actuators and Mechatronics (FT2/LA)
Goldsteinstrasse 235, 60528 Frankfurt, GERMANY
e-mail:
juergen.maas@daimlerchrysler.com
(formerly in after-mentioned Institute)

T. SCHULTE and H. GROTSTOLLEN
Institute for Power Electronics and Electrical Drives, FB-14 LEA,
University of Paderborn, Pohlweg 47-49,
33098 Paderborn, GERMANY
e-mail: schulte@lea.uni-paderborn.de

     This papers deals with an advanced speed control scheme for inverter-fed travelling wave ultrasonic motors. It is implemented as an additional outer control loop of an underlaid voltage and travelling bending wave vector controller and verified by measurements on a prototype drive. The novel speed control uses an inverse contact model by a neural network, trained by measured values of speed and torque, in order to compensate the nonlinear torque generation of the motor. Since the reference values of the bending wave control are calculated from the desired torque value by the neural network, first, an open loop control of the drive's torque is feasible and then common speed control schemes, well performing in common electrical drives, can be applied. Thus, the so equipped ultrasonic motor-drive meets the requirements for applications in the field of servo-drives, e.g. robotics.

Key words:

piezo motors, speed control, neural network.

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18.

A FINITE ELEMENT FORMULATION FOR SMA ACTUATORS

S. SEELECKE and N. PAPENFUSS

Technical University of Berlin, Institute of Thermodynamics,
Sekr. HF2, Straße des 17. Juni 135, D-10623 Berlin, GERMANY
e-mail:
seelecke@thermodynamik.tu-berlin.de
e-mail: nopi@thermodynamik.tu-berlin.de

     An efficient design of control strategies for smart structures is based on a reliable simulation of the structural behavior. Due to its general applicability, the finite element method has become the most widely used simulation tool, and it is thus desirable to implement constitutive models for actuators into such a frame. The paper presents a finite element formulation for a shape memory wire based on an extended version of the Müller-Achenbach model. Its potential is illustrated by simulating the behavior of an adaptive beam which is actuated by several electrically heated SMA wires.

Key words:

shape memory alloys, model, SMA, finite elements, actuators, smart structures.

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19.

CONTROL OF PLATE VIBRATIONS USING SMART TECHNOLOGY

C. CHANTALAKHANA and R. STANWAY

Department of Mechanical Engineering, University of Sheffield,
Mappin Street, Sheffield, S1 3JD,
UNITED KINGDOM

     In this paper, the authors describe progress on the development of a hybrid (active/passive) scheme for use in adaptive structures. An aluminium plate is employed as the demonstrator. The technique is based upon the use of a finite element model of the plate, extended to include passive control in the form of viscoelastic and constraining layers. Experimental results are presented to demonstrate the validity of the finite element model of the plate. Onto this framework is superimposed an active control scheme, formulated in modal state space. Emphasis is placed upon model reduction to obtain a low-order controller and to minimise the spillover effects which are induced when such controllers are implemented. Through a series of numerical experiments, it is shown how the presence of passive control introduces damping to improve robustness of modal control strategies. The paper concludes with a discussion of issues which remain to be resolved.

Key words:

finite element modelling, smart technology, plate vibrations, modal control.

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20.

THE ALLEVIATION OF POST-BUCKLED DISPLACEMENTS AND
NON-LINEAR STRESSES WITHIN LAMINATED
PLATES USING SMA ACTUATORS

S.P. THOMPSON and J. LOUGHLAN

Structures & Materials Technology Group,Cranfield College of Aeronautics,
Cranfield University, Bedford, MK43 0AL, UNITED KINGDOM

     Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of various laminated plate structures. An extensive experimental and numerical programme has been conducted, of which, results will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy plates is outlined. Such specimens feature 0.4 mm diameter shape memory alloy wires located within tubing at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminates. Structural finite element analysis has been employed to determine the hybrid plates adaptive response while under the influence of the uniaxial compressive load, in excess of its critical buckling value. It is shown that, utilizing the considerable control authority generated, even for a small actuator volume fraction, the out-of-plane displacement of the post-buckled laminates can be significantly reduced. Such displacement alleviation allows for the load redistribution away from the specimens unloaded edges. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.

Key words:

shape memory alloys, carbon/epoxy plates, post-buckling, FEA.

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21.

HEALTH MONITORING OF INTERNAL DELAMINATION
CRACKS FOR GRAPHITE/EPOXY COMPOSITES BY
ELECTRIC POTENTIAL METHOD

A. TODOROKI

Department of Mechano-aerospace Engineering
Tokyo Institute of Technology
2-12-1, Ohokayama, Meguro-ku, Tokyo 152, JAPAN
E-mail:
atodorok@ginza.mes.titech.ac.jp

H. SUZUKI
Graduate student of Tokyo Institute of Technology
JAPAN

     Detection of delamination cracks in laminated composite structures is significant to improve reliability of these structures. For the detection of delamination cracks, real-time delamination monitoring is required. The composite laminates reinforced with graphite fiber can use the reinforcement graphite fiber itself as sensors for an electric potential method. The adoption of graphite fiber as sensors does not cause the strength reduction of smart structures induced by imbedding sensors into the structures. It was proved experimentally by the authors in their previous paper that the edge delamination crack was detected by using graphite/epoxy composites. In the present study, therefore, analytical investigations were conducted to investigate the effectiveness of the method for delamination cracks for detection of internal delamination cracks. As a result, this method was shown to be attractive for detection of internal delamination cracks, and the crack size, position and stacking sequences have a large impact on the change of electric resistance.

Key words:

electric potential method, composites, delamination, structural health monitoring.

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