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.

     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.

    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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.

     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.