Key Engineering Materials Vols. 321-323

Abstract: Composite pressure tanks are rapidly expanding in their range of use. However, for high pressure flammable or toxic gases, there is less confidence about their reliability. In this study, fiber Bragg grating (FBG) sensors embedded into a composite pressure tank monitored strain and detected damage. The sensor heads and fiber optic lines were protected with an acrylate recoating, adhesive films, PVC tubes and Teflon
film to survive under the harsh environment of the filament winding process. During the quasi-static loading test, the internal strain was measured with embedded FBG sensor arrays. In order to detect damage occurred during the test, impacts were applied on three different positions in each side by an impact hammer. The difference between damaged and undamaged sides in impact response was analyzed. An interrogation system using a wavelength-swept fiber laser (WSFL) was used for measuring strain, and an erbium-doped fiber amplifier (EDFA) laser source with a tunable Fabry-Perot filter was used for measuring impact response.

Abstract: The thermomechanical behavior of SMA thin film actuator and their application are investigated. The numerical algorithm of the 2-D SMA thermomechanical constitutive equation is developed using user material (UMAT) subroutine written by FORTRAN. For the numerical results of SMA thin film, the ABAQUS finite element program has been utilized with UMAT subroutine of the numerical algorithm of SMA. The application of SMA thin film for the membrane pump actuator is demonstrated.

Abstract: Smart structures needs lots of sensor installation to sense their status and also the external environmental change. Wireless technique can give a good solution to install sensors without heavy cables. So, in this work, a wireless device was developed to transmit static strain and elastic wave propagation of structures. The specification of this device was as follows: 2.4 GHz of transmitted frequency, 8 channels, 57,600 bps of the transmitted speed, and 10 mW of the transmitted power. In order to confirm the wireless device’s feasibility, a beam test was performed with five optical fiber strain sensors and two piezo-ceramic sensors with the wireless instrumentation.

Abstract: To explore the structural strength of CFRP shape memory alloy composites, it is necessary to evaluate the interface bonding strength. Jang and Kishi experimentally investigated the adhesive strength between NiTi fibers and CFRP composite [1]. In this paper, the interface de-decohesion behavior was simulated by three-dimensional cohesive zone method. The values of related numerical parameters were chosen to fit the experimental result.

Abstract: This paper presents a theoretical and experimental study of a non-collocated pair of piezopolymer PVDF sensor and piezoceramic PZT actuator, which are bonded on a cantilever beam, in order to suppress unwanted vibration at the tip of the beam. The PZT actuator patch was bonded near the clamped part and the PVDF sensor, which was triangularly shaped, was bonded on the other part of the beam. This is because the triangular PVDF sensor is known that it can detect the tip velocity of a cantilever beam. Because the arrangement of the sensor and actuator pair is not collocated and overlapped each other, the pair can avoid so called "in-plane coupling", which can be found at a matched piezoelectric sensor and actuator pair and restricts the stability and performance of direct velocity feedback control. The test beam is made of aluminum with the dimension of 200 × 20 × 2 mm. Before control, the sensor-actuator frequency response function is confirmed to have a nice phase response without accumulation in a reasonable frequency range of up to 5000 Hz. The feedback control attenuates the magnitude of the first two resonances in the error spectrum of about 6 -7 dB.

Abstract: This paper presents concept, analysis and experiment of a novel sensor which is based on biologically inspired approach for acoustic emission (AE) detection. It is known that a conventional AE sensor consists of a matching layer, piezoelectric transducer, backing layer, supporting electric circuit and casing. The conventional AE sensors have been widely used to detect defects in various structures and they have designed as either broadband or resonant type. However, the novel sensor described in this paper utilizes the concept of hearing organs in animals with the help of micro electro-mechanical systems (MEMS) technology. The basic design with theoretical investigation including finite element analysis showed the core hearing element such as a hair cell could be implemented with the piezoeletric material. Also it is found that the dimensional variety and proper distribution of such elements inside the sensor are critical parameters to the detectability of AE signals from structures. Both the broadband and resonant type AE sensors with relevant electric circuits could be implemented with this novel sensor concept.

Abstract: The IPMC, one of new sensing and actuating materials is known for the fast and flexible bending actuation upon electric fields. In this paper, we investigated the dynamic deformation characteristics of the novel IPMC according to several fabrication methods. First we studied the effect of the surface modification of metallic electrodes on the large deformation. Present results show that the sandblasting method can give more reliable and large deflections than the sandpapering method under the same control voltage because the platinum electrode can be infiltrated into the ionic-polymer by the sandblasting method. Second, the IPMC with Li+ counter ions shows more large deformation than that with any other counter ions. Also, present results show the dynamic hysteresis according to driving voltages.

Abstract: Smart structures are to be possessed many functions to sense the external effects, such as seismic loads, temperature, and impact by some explosion, influenced on the safety of structures. This work was focused on the development of a sensing function of smart structures to get the temperature distribution on structures to detect fire occurrences. A fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor system was developed to detect the fire occurrence by measuring the temperature distribution of a building’s exterior surfaces. This fiber optic sensor system was constructed with a laser diode and two electro-optic modulators, which made this system faster than systems using only one electro-optic modulator. The temperature distributed on an optical fiber can be measured by this fiber optic BOTDA sensor. An optical fiber, 1400 m in length, was installed on the surface of a building. Using real-time processing of the sensor system, we were able to monitor temperature distribution on the building’s surfaces, and changes in temperature distribution were also measured accurately with this fiber optic sensor.

Abstract: In this paper a method for safety and condition assessment of bridge components based on long-term monitoring data and reliability analysis is proposed with the target to provide quantitative information to bridge managers for decision making on optimizing and prioritizing bridge inspection and maintenance. In the proposed method, the probability density function (PDF) of the load effect is obtained directly from continuous strain measurement, while the PDF of the resistance is determined using the material strength and its variation coefficient prescribed in provisions or obtained by material tests, and further revised with the damage identification results. Then the safety indices of structural components are estimated using the first-order reliability method (FORM), which can be readily used to decide bridge inspection/maintenance strategy because the correspondence between the safety index and the required maintenance action has been established. This method can incorporate the identified structural damage in a probabilistic manner into the safety index evaluation. Case studies of two truss bridge structures have been provided to illustrate the proposed method.

Abstract: A method for probabilistic fatigue life assessment of steel bridges by using long-term monitoring data is proposed and applied for fatigue reliability analysis of the suspension Tsing Ma Bridge. In this method, the daily number of cycles for each stress range is obtained from the measured stress history and its probability distribution is estimated based on statistical analysis of long-term measurement data. The statistics obtained for all concerned stress ranges is combined with the S−N relationships stipulated in specifications to conduct a probabilistic assessment of fatigue life with the use of the Palmgren-Miner rule, from which the mean value and standard deviation of the fatigue life as well as the failure probability and reliability index versus fatigue life are obtained. The proposed method is illustrated by using 80-day strain measurement data from the suspension Tsing Ma Bridge which is instrumented with a long-term structural health monitoring system.