Takehito Fukuda

Fuzzy control of vibration of a smart CFRP laminated beam

In the present study, the fuzzy control of vibration is investigated for a hybrid smart composite beam actuated by piezoceramics and electro-rheological fluids (ERFs) actuators. A carbon fiber reinforced plastics cantilevered beam containing ERF with bonded piezoceramics is vibrated under forced sinusoidal external excitation. A fuzzy model of the controlled element containing two actuators is formed because the application of a linear control theory to the vibration control is difficult due to intense nonlinearity in the ERF actuator. The parameters of the fuzzy model are identified by using a hybrid neuro-fuzzy system. The fuzzy controller for vibration suppression of the composite beam designed is based on the fuzzy model by using modern control theory. The effect of the vibration control system with a fuzzy controller is verified by simulation and experiment.

Strain monitoring of braided composites by using embedded fiber-optic strain sensors

Recently, fiber optic strain sensors have been applied to internal strain and damage monitoring of composites because of their small size, light weight and flexibility. Braided fiber reinforced plastics (FRP) are compatible with fiber optic sensors because optical fibers can be integrated directly and easily into fabrics. In the present paper, the strain monitoring of braided glass fiber reinforced plastics (GFRP) was conducted by using embedded fiber Bragg grating (FBG) and extrinsic Fabry–Perot interferometric (EFPI) sensors during the cure process, tensile tests and fatigue tests. From the experimental results of cure monitoring, it was found that both sensors can be used only for monitoring of thermal residual strain during cooling process. From the results of tensile tests, it was found that both sensors could measure strain correctly until damage initiation of braided GFRP. It also appeared that FBG sensors could monitor damage to FRP by observing the reflected spectral shape. From the fatigue tests, it appeared that the strain measured by embedded FBG sensors was affected by fatigue damage. Therefore, it is concluded that internal strain monitoring of braided FRP using fiber optic strain sensors is very useful for cure and health monitoring.

Flexural - torsion coupling vibration control of fiber composite cantilevered beam by using piezoceramic actuators

In the experiment two piezoceramic actuators are prepared. One is adhered to the beam along the structural axis for controlling the flexural vibration mode of the beam, where it is called ACT1. Another is attached perpendicular to the principal axis of elasticity (PAE) of the beam for controlling the torsional vibration mode of the beam; where it is called ACT2. In the static test a cantilevered composite beam having an eccentric mass at the free end is prepared and the direction of the PAE is found based on the definition of the PAE, and natural frequencies of flexural and torsional vibration are obtained by the experiment. The vibrational behavior of the beam is examined by forced vibration tests under sinusoidal excitation having a natural frequency of the first flexural or torsional mode when ACT1 and/or ACT2 are operated. Equations of motion with two degrees of freedom are derived using laminated plate theory and the equilibrium of forces and moments. The experimental result is substantiated by simulation using the equations of motion and control theory.

Smart autoclave processing of thermoset resin matrix composites based on temperature and internal strain monitoring

Cure cycle optimization and process control for autoclave cure of thermoset resin matrix composites based on temperature and internal strain monitoring were studied. Cure of thermoset resin is usually an exothermic reaction, which causes temperature increase of composites during cure. Slowing down the temperature ramp rate is effective in lowering the peak temperature. However, the slower is the ramp rate, the longer the cure time becomes. Therefore, it is desirable to control the ramp rate in order to depress the peak temperature with prolongation of cure time minimized. Besides that, precise determination of cure completion is also required in order to minimize cure time. The procedure for smart processing described above was developed and tried on laminate of carbon fiber/epoxy resin prepreg. In this procedure, temperature ramp rate is controlled so that the peak temperature predicted by Springers thermochemical model is kept below an allowable value. Cure completion is determined by a cure rate equation and internal strain monitoring with embedded EFPI optical fiber sensors. The internal strain is correlated with specific volume change of the matrix resin caused by cure shrinkage and thermal expansion/contraction. The authors found that the cure shrinkage terminates at a certain degree of cure, and EFPI sensors can detect this point. Although the degree of cure can be calculated by integrating the cure rate equation along temperature history, errors may be accumulated. Therefore, the degree of cure is corrected and integration of cure rate equation is restarted at the cure shrinkage termination point detected by EFPI sensors. Thus, cure completion is determined precisely. This smart autoclave processing procedure was able to depress the peak temperature and determine the end of cure.

Tuned sloshing damper using electro-rheological fluid

A tuned sloshing damper (TSD) utilizing an electro-rheological (ER) fluid as a sloshing liquid (ER-TSD) is proposed. The sloshing frequency of the TSD depends on the sloshing stroke length of the liquid contained in the tank. In this paper, the ER-TSD is used in the form of a rectangular tank with electrodes. The ER-TSD sloshing frequency can be controlled by applying an electric field to the ER fluid. We have studied the vibrations of a structure which had two natural frequencies. The forced and free vibration tests were carried out with and without the ER-TSD. By controlling the electric field, the ER-TSD can suppress the vibrations of the structure even when the natural frequency of the structure changes. The free vibration responses of the structure with the ER-TSD were analytically obtained by using a tuned mass damper model based on the Housner theory. The simulated results appeared to be in reasonable agreement with experiments.

Optimum vibration control of CFRP sandwich beam using electro-rheological fluids and piezoceramic actuators

In the present study, the vibration control of a hybrid smart composite beam actuated by both electro-rheological fluids (ERFs) and piezoceramic actuators is investigated. A carbon fiber reinforced plastics beam, including interleaved ERF and bonded piezoceramics, is prepared and tested under sinusoidal external excitations. Four kinds of feedback control strategies for both ERF and piezoceramic actuators are adopted in order to suppress the deflection at the free end of the cantilevered composite beam. The optimum combination of these control strategies for two types of actuators is discussed when the two actuators operate simultaneously.

Report on a simultaneous ion viscosity, strain and impedance measurement technique using a novel integrated dielectric, optical fiber and piezoelectric sensing element for the online characterization of smart structures

This paper reports on a simultaneous ion viscosity, strain and impedance (SISI) system in order to measure the physical and chemical properties of composites during their curing process. The SISI system uses an integrated multi-sensing element, entitled DOP, that is comprised of dielectric (D), optical fiber (O) and piezoelectric (P) sensors. This system was used to measure several data simultaneously in real time and in situ. The results clearly show that there is a direct relationship between the ion viscosity, impedance and strain changes during the curing process. It was found that dielectric sensor is very sensitive to physical and chemical changes of the composite both in the heating and cross-linking periods. The piezoelectric proved to be a useful element during the heating period with a very sensitive and surprising behavior during the cooling period. The optical fiber also demonstrated a very striking profile in strain variations during cooling.

Controller design for vibration of a smart CFRP composite beam based on the fuzzy model

In the present study, vibration control is investigated for a smart carbon fibre reinforced plastics (CFRP) composite beam actuated by piezoceramics (PZT) and electro-rheological fluid (ERF) actuators. A fuzzy model of the controlled element containing two actuators is formed because the application of linear control theory to the vibration control is very different due to the intensive nonlinearity in the ERF actuator. The fuzzy model is identified based on the result of system identification test by using a hybrid neuro-fuzzy system. A controller for guaranteeing bounded input-bounded output (BIBO) stability of the vibration control system of the composite beam is designed by solving linear matrix inequalities (LMI) obtained based on Lyapunovs stability theory. The effect of vibration control system is verified by simulation and experiment.

Fiber optic strain monitoring of textile GFRP during RTM molding and fatigue tests by using embedded FBG sensors

This paper describes cure and health monitoring of glass fiber reinforced plastics (GFRP) textile composites both during a resin transfer molding (RTM) process and in loading tests. Carbon fiber reinforced plastics (CFRP) textile composites also were used for a comparative study. Fiber Bragg grating (FBG) fiber optic sensors were embedded in FRP to monitor internal strain. From the results of cure monitoring, it was found that the embedded FBG sensors were useful to know when cured resin constrained fibers. It also appeared that specimens were subjected to friction stress resulted from difference of coefficient of thermal expansion between FRP and a stainless steel mold in cooling process of RTM molding. After the molding, tensile and fatigue tests were conducted. The results of tensile tests showed that output of the embedded FBG sensors agreed well that of surface-bonded strain gauges despite deterioration of reflected spectra form the sensors. From the results of fatigue tests, the FBG sensors showed good status until 100,000 cycles when specimens had no damage. From these results, it can be concluded that embedded FBG sensors have good capability of monitoring internal strain in textile FRP both during RTM process and in service.

Pattern recognition application in classification of intelligent composites during smart manufacturing using a C4.5 machine learning program

The development of an on line computer based classification system for the real time classification of different composites is addressed in this study. Different parameters were collected simultaneously when embeded sensors (dielectric, optical fiber, and piezoelectric sensors) were used within two different composite matrices during the curing process. The measurements were used by an algorithm software as a logged data file, resulting in to inducing a decision tree. Later, a systematic software is designed based on the rules derived from this decision tree, to recognise the type of composites used in the experiment together with recognition of their physical and mechanical characteristics. This is a new approach to data acquisition in intelligent materials produced by smart manufacturing system.