Showing papers on "Smart material published in 1991"

Vibration suppression using smart structures

Abstract: The control of structures for vibration suppression is discussed in the context of using smart materials and structures. Here the use of smart structures refers to using embedded piezoelectric devices as both control actuators and sensors. Using embedded sensors and actuators allows great improvements in performance over traditional structures (both passive and active) for vibration suppression. The application of smart structures to three experimental flexible structures is presented. The first is a flexible beam, the second is a flexible beam undergoing slewing motion, the third is a ribbed antenna. A simple model of a piezoelectric actuator/sensor is presented. The equations of motion for each structure is presented. The control issues considered as those associated with multi-input, multi-output control, PID control and LQR control implementation. A modern control analysis illustrates the usefulness of smart structures for vibration suppression.

The Role of Shape Memory Alloys in Smart/Adaptive Structures

Abstract: Adaptive structures, also called Intelligent or smart materials, refers to the various materials systems which automatically or remotely alter their dynamic characteristics or their geometry to meet their Intended performance. By integrating the sensors and actuators into the structural system, typically a composite materials, control of shape, vibration and acoustic behavior an be effected. In addition to active control, passive control of system damping can be achieved in these structures. The sensors employed include piezoelectric ceramics, piezoelectric polymer films, ferroelectrics, and fiber optics. For producing the stress induced changes in dynamic characteristics of a composite the actuators are either embedded within the composite or are surface mounted. In general, the piezoelectric type actuator Is used where small strains at high frequencies are appropriate, while shape memory actuators are used when high forces and strains at lower frequencies are required. Static damping, modulus shift effect on acoustic radiation, and strain energy shift of modal response and acoustic radiation of composite materials with embedded shape memory actuators will be discussed. The constitutive equations for shape memory alloys will be described and how these are used in the design of adaptive composite structures The term smart materials seems to have become a part of the engineering vocabulary with variants such as intelligent materials, and their application in adaptive structures. Smart materials consist of a structural component such as a composite such as fiber reenforced resin, with distributed sensors and actuators and a microprocessor. In response to changing external or internal conditions these materials can change their properties to more effectively perform their function. The external conditions may be environment such as light or heat, loads, vibration or the need to change the geometry or shape of the structure to cope with changing service conditions. Internal conditions may be delamination in a composite, fatigue cracks in a metallic or nonmetallic structure, or other forms of incipient failure. In reviewing papers presented in the past several years at conferences on smart/adaptive structures one would see a dominant number on various aspects of space structures such as mirrors, antennas, robotics booms and satellite docking. In these areas the control of vibration or the precise control of motion are most often the specific subject addressed. Much of the ongoing research is on control theory and the design of algorithms to define the sensor-actuator-microprocessor Integration. Of concern in this paper Is the actuator itself which, in response to commands from the microprocessor, produces strains and forces in the structure to modify Its acoustic or vibratory response or alter Its shape. These actuators are broadly of two types: low to medium force, low strain, high frequency systems, typically a piezoceramic such as PZT, or a high force, high strain, low frequency actuator which is most likely to be a shape memory alloy element.

Tunable transducers as smart materials

Abstract: A solid-state tunable transducer has been developed by incorporating an elastically nonlinear material, silicone rubber, into an electroacoustic transducer made from piezoelectric ceramics. The resonant frequency and mechanical Q of the transducer are tuned mechanically by applying a uniaxial compressive stress to the composite. The resonant frequency is tuned electrically by placing a piezoelectric actuator into the composite and varying the magnitude of the DC bias. >

Optical fiber sensor-based smart materials and structures

Abstract: Embedded or attached optical fiber sensors may be used to measure the physical characteristics of materials, or structures fabricated from those materials, during their entire use lifetimes. First, fibers have been embedded in some materials, such as advanced composites and metals, to allow in-situ process monitoring. For such applications, the fiber and fiber coating must be able to withstand the processing conditions, and the chemical and mechanical interface between the fiber and the matrix is of concern. Polymer, silica and sapphire fiber-based sensors have been used in particular to monitor temperature, strain, resin chemistry, and local material modulus.