Key Engineering Materials Vols. 321-323

Abstract: Detection of hydrogen gas is a crucial task for establishing safety and reliability of fuel cells, a key technology for the environment and our society. However, hydrogen is difficult to detect and various hydrogen sensors have many drawbacks. Here we report a novel hydrogen gas sensor, the ball surface acoustic wave (SAW) sensor, using Pd or PdNi sensitive film. The ball SAW sensor is based on a novel phenomenon, diffraction-free propagation of collimated beam along an equator of sphere. The resultant ultra-multiple roundtrips of SAW makes it possible to achieve highest sensitivity among SAW sensors. Moreover, it enables to use a very thin sensitive film, and consequently the shortest response time (2s) was realized. In terms of the sensing range, it has the widest range of 10 ppm to 100 % among any hydrogen sensors including FET or resistivity sensors. The ball SAW sensor can be applied not only to hydrogen but also to any gasses and possibly to liquids.

Abstract: Distributed Bragg reflector (DBR) porous silicons exhibiting unique reflectivity were successfully obtained by an electrochemical etching of silicon wafer using square wave currents. Optically encoded smart dust which retained optical reflectivity was obtained from DBR porous silicon film in organic solution by using ultra-sono method. The size of optically encoded smart dust was measured by field emission scanning electron micrograph (FESEM) and was about 500 nm to few microns depending on the duration of sonication. Investigation for the optical characteristics of smart dust revealed that smart dust could be useful for application such as chemical sensor for detecting organic vapors.

Abstract:
Destructive accident sometimes takes place though the equivalent stress is rather low in the viewpoint of strength of materials. The propagation of fatigue cracks under multi-axial stress state and cycling load gives the reason. Fatigue fracture has been considered as one of the most commonly encountered industrial problems that lead to the damage of components in engineering products. In general, the machine structure is always under stress concentration or stress cycles. Moreover, the structure material is usually under two axes or multi-axial stresses instead of uniaxial stress state. It is important, therefore, to clarify the propagation behavior and the fatigue failure problem of the crack under the multi-axial stresses and cycling load from the safety reliability and accident prevention measure. In this study, a biaxial fatigue experimental device was developed which can carry out a wide range of fatigue tests under biaxial stresses. The developed experimental device was identified with a biaxial fatigue experiments including static uniaxial and biaxial tensile test by using the aluminum alloy flat plate as specimens. The propagation behavior of fatigue crack for center notched cruciform specimen in the equal biaxial fatigue test was verified.

Abstract: This paper presents the theory, design, and evaluation of a smart device for the enhanced separation of particles mixed in fluid. The smart device takes advantage of the ultrasonic standing wave, which was generated by the operation of a piezoceramic PZT patch installed in the smart device. The details of the device design including the electro-acoustical modelling for separation and PZT transducer are described at first. Based on this design, the separation device was fabricated and evaluated. In the experiments, an optical camera with a zoom lens was used to monitor the position of particles within the separation channel layer in the device. The electric impedance of the PZT patch bonded on the separation device was measured .The device shows a strong levitation and separation force against 50μm diameter particles mixed with water at the separation channel in the device. Experimental results also showed that the device can work at both heavy and light sand particles mixed with water due to the generated standing wave field in the separation channel.

Abstract: In the present work, thermal expansion coefficients of a number of organic coatings were studied by a non-destructive technique (NDT) known as shearography. An organic coating, i.e., epoxy, on a metallic alloy, i.e., carbon steels, was investigated at a temperature range simulating the severe weather temperatures in Kuwait especially between the daylight and the night time temperatures, 20-60 0C. The investigation focused on determining the in-plane displacement of the coating, which amounts to the thermal deformation (strain ) with respect to the applied temperature range. Along with the experimental data, a mathematical relationship was derived describing the thermal deformation of a coated film as a function of temperature. Furthermore, results of shearography indicate that the technique is very useful NDT method not only for determining the thermal expansion coefficients of different coatings, but also the technique can be used as a 2Dmicroscope for monitoring the deformation of the coatings in real-time at a submicroscopic scale.

Abstract:
A novel optical fiber acoustic emission (AE) system with multi-sensing function in single long fiber was developed and utilized for the estimation of AE sources of model steel plate and jointed pipes. Multi-sensing function was achieved by dividing the single sensing fiber into several sensor portions with different resonance frequencies. The resonance frequencies were provided by winding the sensing fiber around the solid rods (sensor holders) with different diameters. The monitoring system with three sensors in a 10 m long fiber was demonstrated to detect three wave packets with different frequencies and correctly estimate the source locations of AEs from artificial (Nelson-Sue) sources on a 0.9 wide x 1.8 m long steel plate. Here the arrival times of AEs for the source location were determined by the continuous wavelet transform. Source locations on the steel plate were determined within a distance error of 53 mm. The system also makes the location of the pipe with damage possible.

Abstract: Speckle interferometry with phase shifting method is used to measure in-plane displacements of a steel plate with a partly through-thickness circular hole and a steel plate with a through-thickness circular hole. The circular hole of steel plate with a partly through-thickness circular hole is cut on the rear side of the plate, so that it is not visible during experiment. The speckle noises of fringe patterns acquired by optical experiment are processed with image processing algorithm of Gaussian blur and the in-plane displacements of the two specimens are obtained by use of the processed fringe patterns. Also the in-plane displacements of the two specimens are calculated by use of ANSYS. The results of optical experiments are quite comparable to those of calculation with ANSYS.

Abstract: A multi-purpose polariscope was developed by applying an electro-mechanical control system to a diffused transmission-type circular polariscope. A conventional polariscope is only good for manual control of optical elements. The new polariscope system was devised to be controlled through two stepping motors and two magnetic clutches. The new polariscope can be used not only for the point-wise measurement using Tardy compensation technique but also for the full-field fringe analysis using conventional and/or phase measuring techniques, if applicable. The distributions of digitally determined unwrapped isoclinics and isochromatics using the digitized images obtained from the developed polariscope were in close agreement to manual measurements.

Abstract: Optical NDE (Nondestructive Evaluation) techniques such as ESPI (Electronic Speckle Pattern Interferometer) and shearography that are non-contact and real-time method are used to detect the defects in material. However, ESPI measurement is affected by disturbance such as rigid body motion, and has difficulty in recognizing the real shape and size of the defect. Shearography also involves several problems like it needs several operator-dependent factors including the amount of shearing and shearing direction for the quantitative analysis of internal defect, and it does not show the exact shape of the defect. In order to overcome these problems and evaluate the internal defect quantitatively in this study, the imaging of the inner defect based on the ESPI technique is proposed. In this method, the external perturbative load such as thermal load is induced to the specimen, and the deformation distribution of the specimen is measured by ESPI. Then the distribution of the shear strain energy is obtained by the strain analysis of the ESPI measurement result. On the edge of the defect, the shear strain energy is concentrated, so we can obtain the outline of the internal defect by following the peak point of the shear strain energy distribution. This method makes it possible to evaluate the size and shape of the defect quantitatively without operator-dependent factors.

Abstract: A new interference-based optical technique called in-plane displacement interferometer (IPDI) is introduced for the detection of in-plane (IP) motion of ultrasonic waves. The IPDI employs a tiny square indentation of about 30 microns in width on the sample surface and a relatively simple optical arrangement for the detection of IP motion of ultrasonics waves. With the IPDI, measurement of IP motions of Lamb waves propagating along a thin brass foil is demonstrated. Dispersion relations for the S0 mode dominated by in-plane motion in the low fd (frequency times thickness) regime is obtained with the IPDI.