Key Engineering Materials Vols. 326-328

Abstract: New system (load cell) for measuring a contacting force in a high temperature and pressure water condition (i.e. 320
, 15 MPa) has been developed. The primary purpose is to apply it to the experiments of a nuclear fuel fretting wear, which occurs on the contacts between the fuel rods and the spacer grid spring/dimples due to a flow-induced vibration of the rods. A bi-axial load cell of a cylindrical shape is specially designed. Strain gages for a special use in a high temperature condition were attached on to the sensitive region of it to accommodate the bi-axial loading condition in fretting. The full scale of this load cell is ±50 N in axial force and ±50 N in bending force, respectively. In order to increase the sensitivity and to compensate for an ambient temperature effect, the load cell consists of two Wheatstone full bridge arrangements. The calibration results of the load cell show that the coupling effects of each force were almost negligible. This paper mainly presents the experimental techniques used during the development of the new load cell system. The techniques are characterized by a design optimization of a jig of a cylindrical type, the application of a metallic sealant for a waterproofing, a free welding fabrication process and a temperature compensation circuit. Details on the development procedure, calibration method and application results are also given in this paper.

Abstract: In this paper we present the design and prototype of a six-legged walking robot which uses Lightweight Piezoceramic Composite curved Actuator (LIPCA) as its actuator. LIPCA consists of multiple layers of glass/epoxy and carbon/epoxy that encapsulate a unimorph piezoelectric ceramic actuator. It uses lightweight fiber-reinforced plastic layers, and it is a lighter structure and generates a higher force and a larger displacement than other conventional piezo-composite type actuators. Like most six-legged walking insects including cockroaches, our robot uses the alternating tripod gait where the front and rear legs on the same side move together with the middle leg on the other side for its locomotion. Two LIPCA strips in different phases are used for actuating each tripod so that only one tripod may touch the ground ensuring static stability while walking. All the experiments with the prototype show that LIPCA can be used as an alternative actuator for small and light mobile robots.

Abstract: The efficiency of fish swimming dynamics has motivated researchers to develop fish-like robots. As a beginning step, a fish-like robot (boat) is built to simulate the fish swimming dynamics. By using data collected from inertial sensors, a suitable mathematical model explaining fish turning dynamics is obtained through system identification method. The identified model matches well with the experimental results and thus can be used for the design of controllers.

Abstract: This paper presents a mechanical design of biomimetic fish robot using the Lightweight Piezo-Composite Actuator (LIPCA). We have designed a mechanism for converting actuation of the LIPCA into caudal fin movement. The linkage mechanism consists of rack-pinion and four-bar linkage systems. Two kinds of caudal fins are fabricated such that the shapes resemble subcarangiform and ostraciiform caudal fin shape, respectively, and then attached to the linkage system. The swimming test using 300 Vpp input with 1 Hz to 3 Hz frequency was conducted to investigate the effect of tail beat frequency and shape of caudal fin on the swimming speed. The maximum swimming speed was reached when the device was operated at its natural swimming frequency. At the natural swimming frequency of 1.016 Hz, maximum swimming speeds were 1.267 cm/s and 1.041 cm/s for ostraciiform and subcarangiform caudal fin, respectively. The Strouhal numbers, which are a measure of thrust efficiency, were also calculated in order to examine thrust performance of the present biomimetic fish robot.

Abstract: This paper experimentally investigates the power generation property of carbon nanotubes in an aqueous environment. Carbon nanotube based films are investigated in this paper as a new method for power generation based on ionic conductivity of the fluid. It is demonstrated that a carbon nanotube film that is bonded onto a structure vibrating with an electrolyte on the surface produces an alternating current without a net fluid flow. The power produced is smaller than for a piezoelectric material of the same size, but the CNT power generator is lightweight and has no moving parts, and does not require the structure to be immersed in an electrolyte. There are various possible applications for nanotube power generators.

Abstract: Structural health monitoring (SHM) is becoming a popular topic. Carbon fiber reinforced concrete (CFRC) is an intrinsically smart material that can sense strain. The resistivity increases reversibly under tension and decreases under compression. A new skin-like sensor —cement-based smart layer had been put forward, which can serve as whole field strain sensor. The smart layer is satisfactorily consistent with concrete structure. The smart layer is a thin carbon fiber mat cementbased composite material layer with finite electrodes. It can cover the surface of concrete structure, and provide on-line reliable information about the deformation of whole concrete structure. The static characteristics of the new-type sensor had been researched. Its gage factor is 20-25 under tension and 25-30 under compression within the elastic deformation range. Furthermore the smart layer has satisfactory linearity and repeatability. In this paper, the sensor characteristics of the bare carbon fiber mat have been reached. The resistivity of carbon fiber mat has good agreement with strain under uniaxial tension. The gage factor can be up to 375, and the sensor limit can be up to 10000 microstrain. The strain and the fractional change in electrical resistance .R/R0 are totally reversible and reproducible under cyclic loading and amplitude-variable cyclic tensile loading.

Abstract: In this study, specially used in fluidic jetting apparatus, the electrical properties of piezoelectric ceramics were investigated by the resonance method and from its vibratory motion point of view. The piezoelectric ceramics were a rectangular bar type bulk and estimated by their piezoelectric constants, for example, electromechanical coupling factor, piezoelectric strain constant and so on. The measured values were compared with the displacement by the Laser Doppler Vibrometer analysis and with the droplet properties.

Abstract: This paper experimentally investigates the hysteretic behaviors of yield stress in electrorheological (ER) and magnetorheological (MR) materials which are known as smart materials. As a first step, the PMA-based ER material is prepared by dispersing the chemically synthesized polymethylaniline (PMA) particles into non-conducting oil. For the MR material, commercially available one (Lord MRF-132LD) is chosen for the test. Using the rheometer, the torque resulting from the shear stress of the ER/MR materials is measured, and then the yield stress is calculated from the measured torque. In order to describe the hysteretic behavior of the fielddependent yield stress, a nonlinear hysteresis model of the ER/MR materials is formulated between input (field) and output (yield stress). Subsequently, the Preisach model is identified using experimental first order descending (FOD) curves of yield stress in discrete manner. The effectiveness of the identified hysteresis model is verified in time domain by comparing the predicted field-dependent yield stress with the measured one.

Abstract: The optimum design for bow structure of high tensile steel yacht belongs to the nonlinear constrained optimization problem. The determination of scantlings for the bow structure is a very important matter out of whole structural design process of a yacht. The optimum design results are produced with the use of Real-coded Micro-Genetic Algorithm including evaluation LR small craft guideline, so that they can satisfy the allowable stress criterion. In this study, the minimum weight design of bow structure on the HTS yacht was carried out based on the finite element analysis. An analysis model is a bow structure of HTS yacht with structural scantling derived from the minimum weight optimization. The weight of bow structure and the main dimensions of structural members are chosen as an objective function and design variable, respectively. Optimization results were compared with a pre-existing design. From the FE analysis results, bow structure with high tensile steel (AH40) designed by using RμGA has a volume efficiency of 19% than the design of the actual mild yacht.

Abstract: To test the temperature stress and deformation of the major platform in Nanjing Olympic Sports Center, 8 shrinkage members and 3 creep members were poured on the worksite for comparison analysis. With finite elements analysis, gliding rubber supporters were used on all the pillar tops. The floor stress would be in a constant compressive stress with pre-stress and post-cast-span. This method makes the appearance and developments of structure cracks under effective control. Under temperature changes, the buildings were ensured not to have damageable cracks. This project was passed with super quality.