Papers by Keyword: Smart Structure

Abstract: The objective of this work was the development of a processing methodology for embedding NiTi fibers into a polymer-based composite plate. A carbon fiber reinforced polymer (CFRP) prepreg and NiTi thin wires were used. A uniaxial hot press was prepared to be used in the composite processing. Two prototypes were fabricated to provide fiber alignment and fixation fixture. A CFRP composite plate without fiber and another with NiTi fibers were processed. Micrometers and a universal materials testing machine were used to measure the plate thickness and Young's modulus. It was possible to develop a processing methodology for embedding NiTi fibers into a polymer-based composite plate. The CFRP plate without fiber presented almost no variation in plate thickness and Young's modulus measurement thus enabling the CFRP manufacture by the hot uniaxial press. The fiber fixation fixture developed was able to produce CFRP-NiTi fiber hybrid composites with different number of fibers embedded, the spacing distance between fibers was at least 1 mm and the fiber alignment was achieved.

Abstract: Optical fiber sensors have a number of advantages over conventional electronic sensors such as light weight, small diameter and immunity to electromagnetic interference. Despite all the advantages of optical sensors, one must recognize that optical fibers are foreign entities to the host structure, therefore will induce stress concentration in the vicinity of the embedded sensor. As an optical sensor is embedded between plies, a lenticular resin pocket exists in the composite plies. The resin pocket acts as a crack-like region, and can form the site of the initiation of the delamination under mechanical loads. In this investigation, the geometry of the lenticular resin pocket around the optical sensor is derived basing on the principal of minimum potential energy. It shows that the geometry of the resin pocket is dependent on the stiffness of the plies, the stacking sequence, the diameter of the optical fiber and the curing pressure. The stress distributions in the resin pocket and in the laminated composites are obtained by using the finite element method. The numerical results demonstrate that the stress increases rapidly in the vicinity of the optical fiber sensor, causing a high stress concentration factor. The high stress field may produce delamination and fracture in the composite.

Abstract: The purpose of this paper is to investigate the optimal placement of piezoelectric actuator for active vibration control of smart structure. The structures can be described in the modal space based on the independent modal space control method and dynamic equations derived from finite element model. The modal damping ratios are derived from modal equations and an optimal target is given by maximizing the modal damping ratios. Accumulation method is adopted to the optimization calculation. Simulations are carried out for active vibration control of a conical shell with distributed piezoelectric actuators. Control effects proved the validity of the optimal method above by compared with the non-optimal results. The optimal method in this paper gives a useful guide for quantity optimization of actuators to piezoelectric structures.

Abstract: This paper deals with nonlinear finite element analysis of smart structures with integrated piezoelectric layers. Two geometrically nonlinear finite plate elements incorporating piezoelectric layers are applied based either on first- or third-order transverse shear deformation theory. Nonlinear strain-displacement relations are used that are valid for small strains and moderate rotations. Numerical tests are performed for the time histories of the tip displacement and sensor output voltage of a thin beam with a piezoelectric patch bonded to the surface.

Abstract: This paper presents the laboratory validation of a prototype optic-fiber instrumented structural element. The element is a reduced-scale reinforced concrete beam, of dimensions 3.8×0.3×0.5m that can be pre-stressed by an internal Dywidag bar. The sensing technology is based on a multiplexed version of the SOFO strain sensor, prepared in the form of a 3-field smart composite bar; in-line multiplexing is obtained by separating each measurement field through broadband FBGs. The experiment aims to identify the response of the sensors to differing damage conditions artificially produced in the element, including cracking and loss of prestressing. A numerical algo-rithm, based on Bayesian logic, is applied to real-time diagnosis: by processing the sensor meas-urements and prior information, the method assigns a posterior probability to each assumed damage scenario, as well as the updated probability distributions for each relevant structural parameter. With respect to classical damage detection approaches, the merit of those based on Bayesian logic is to provide not only information on the damage, but also the degree of confidence in this informa-tion. The paper discusses the ability of the system to identify the differing damage conditions. The reported test clearly shows that an occurrence such as a loss of prestressing can be recognized early with a high degree of reliability based on the strain data acquired.

Abstract: Statistical damage detection in a structure operating under different temperatures via vibration testing is addressed by means of a stochastic global model based approach. The approach relies upon novel global models of the Functionally Pooled (FP) form, which are capable of describing the dynamics under any temperature, and statistical decision making. In its present form the approach utilizes response (output–only) vibration data, although excitation–response data may be also used. Its effectiveness is confirmed via a large number of experiments performed on a smart composite beam under different temperatures within the [¡20; +20]oC range.

Abstract: The attenuation of structure vibration is very slow when flexible strucure is stirred external force. It seriously affected the life of flexible structure. Smart structures used piezoelectric ceramics as actuators are an effective manner to solve the problem. This paper uses Fiber Bragg Grating (FBG) as sensors and piezoelectric ceramics as actuators to study the active vibration control for the resonance of the smart beam. Two groups of piezoelectric ceramics will be used for vibration exciter and vibration abatement, respectively. The fiber smart beam is excited to a sharp vibration nearby the particular resonance frequency by controlling the frequency of the vibration excitation. The vibration signal is measured by the FBG sensors and the close loop feedback control is fulfilled by the vibration abatement group, and the vibration amplitude of the fiber smart beam is abated. The experiment results show that the resonance amplitude of the beam is obviously abated by adjusting the frequency, amplitude and phase of the vibration abatement circuit.

Abstract: Most animals and insects use opposing muscles, called flexors and extensors, to articulate the joints of their limbs. However, some spiders do not have extensors in some of their joints and use, instead, a simple and efficient miniaturized hydraulic system to extend their limbs. An actuator inspired by the hydraulic system of spiders, which can be embedded on adaptive structures, is investigated in robot-like configurations in this paper. Its design and characteristics are discussed and the effects of the geometrical parameters on its performance are investigated.

Abstract: Structural Health Monitoring (SHM) is an important and growing field in civil engineering. The goal of SHM techniques is to identify, quantify and locate damage in structures. In light of the aging infrastructure and recent failures of important bridges, long-term monitoring techniques are being increasing investigated and adopted. In addition to SHM, structural control (SC) is increasingly adopted in modern structures around the world. In the past two decades a number of SC techniques, including, passive, semi-active, and active control methods have been developed and adopted in civil engineering–particularly, in infrastructure such as important tall buildings, critical facilities, and long span bridges. Both SHM and SC technology face significant challenges due to the size and scale of civil engineering structures. In response of these challenges researchers in the U.S.A and around the world have developed new and innovative techniques.This paper summarizes some of the ongoing research in the U.S.A. in the area of monitoring, damage detection and control in civil engineering structures.

Abstract: Piezoceramics are considered as key functional material in micro systems and smart structure technology. Showing superior mechanical, dielectric, pyroelectric, ferroelectric and piezoelectric properties they introduce improved functionality, e.g. sensing, actuation, energy harvesting, health monitoring or shape control. Various applications such as micro integrated valves, drives, voltage converter, piezoelectric, pyroelectric and ultrasound sensors are expected. Another field of application concerns active structures in space, automotive or machine building industry. Progress was achieved by combining flexible board and piezo technology which opens up a new class of reliable ready to use actuator and sensor modules. Tailored design and packaging are seen as key factors for progress in custom applications. Load carrying structures with embedded actuators, sensors and electronics, which are usually pre-integrated in modules, offer the opportunity for noise reduction, vibration and shape control and health monitoring. The present paper summarizes the potential of advanced, microsystems compatible piezotechnology for active structures and systems. The focus will be given to PZT film and fibre processing and the integration in silicon wafer, ceramic multilayer and polymer matrix architectures. Finally, forward-looking applications are highlighted.