Key Engineering Materials Vols. 326-328

Abstract: The thermal conductivity of amorphous silicon (a-Si) thin films is determined by using the non-intrusive, in-situ optical transmission measurement. The thermal conductivity of a-Si is a key parameter in understanding the mechanism of the recrystallization of polysilicon (p-Si) during the laser annealing process to fabricate the thin film transistors with uniform characteristics which are used as switches in the active matrix liquid crystal displays. Since it is well known that the physical properties are dependent on the process parameters of the thin film deposition process, the thermal conductivity should be measured. The temperature dependence of the film complex refractive index is determined by spectroscopic ellipsometry. A nanosecond KrF excimer laser at the wavelength of 248 nm is used to raise the temperature of the thin films without melting of the thin film. In-situ transmission signal is obtained during the heating process. The acquired transmission signal is fitted with predictions obtained by coupling conductive heat transfer with multi-layer thin film optics in the optical transmission measurement.

Abstract: Characteristics during the fracture process of a plate-type piezoelectric composite actuator (PCA) using acoustic emission (AE) monitoring were investigated under a bending load. The fracturing of a monolithic PZT ceramic shows typically brittle behavior; furthermore, the AE signal at the maximum load, which corresponds to the final fracture, has a high amplitude and long duration. Analysis of dominant frequency bands by a fast Fourier transform (FFT) in conjunction with AE parametric analysis expressed the characteristic changes of the fracture process in the PCA. For the PCA, a brittle fracture in a PZT ceramic layer induces the local delamination between the PZT ceramic and adjacent fiber composite layers. Based on the AE analysis and damage observations through optical microscopy, the features of AE associated with fracture process can be elucidated for the PCA.

Abstract: The objective of this paper is to investigate the applicability of ultrasonic wave technique to monitor the progress of the thermal shock damage on alumina ceramic. For this purpose, alumina ceramic specimen was heated in the furnace and then was quenched into the water tank. The initiation, growth behaviors of surface micro-cracks as a function of the number of thermal shock cycle have been discussed by taking into account the change of ultrasonic wave velocity and attenuation. The change of both velocity and attenuation of ultrasonic wave showed good relation with the surface crack density changing due to the number of thermal shock cycle. Measuring the change of attenuation gives more effective information to evaluate thermal shock damage than that of velocity nondestructively. The flexural strength was also measured for the thermal shocked specimen. The flexural strength was decreased rapidly at the point of time of observation of microcracks on the surface of specimen, and the flexural strength decline by the crack growth caused thermal shock cycles was slight.

Abstract: Chemical vapor deposit (CVD) diamond coating layer is expected to extend the lifetime of mechanical parts that are used severely abrasive conditions. However, one of the most severe problems is that the delamination between the CVD diamond coating layer and the silicon substrate occurs frequently due to large difference in the material properties. Therefore, the nondestructive evaluation of adhesive property of CVD diamond coating layer is needed. To address such a need, back-scattered Rayleigh surface wave is currently applied. However, the interpretation of the acquired signal is not easy at all. To take care of such a difficulty, we proposed the time trace angular scan (TTAS) plot and the frequency spectrum angular scan (FSAS) plot that can make possible of the systematic interpretation of the back-scattered signals from the diamond coating layer. In this paper, the concept of the TTAS and FSAS plots and the experimental results presented to demonstrate the effectiveness of the proposed approach.

Abstract: Local wall thinning is one of the major causes for the structural fracture of pipes of nuclear power plants. Therefore, assessment of local wall thinning due to corrosion is an important issue in nondestructive evaluation for the integrity of nuclear power plants. In this study, lasergenerated guided waves were used for pipe inspection, where a laser beam illuminated through linear slit array was used as the transmitter and the air-coupled transducer was used as the receiver. Slits was used in order to enhance the mode-selectivity of guided waves, since the space of slits is equal to the wavelength of the generated wave. The air-coupled transducer detected the selected single mode by turning its detection angle that was calculated from the relations between the wave propagation velocity in air and the phase velocity in dispersion curves. Experimental results for a 4- mm thick carbon steel pipe showed that the detection of the specific mode was useful in the distinction of the wall-thinning thickness in the carbon steel pipe.

Abstract: Elastic properties of high tension bolt are evaluated non-destructively by measuring acoustic longitudinal and shear wave velocities using mode-converted ultrasound. Mode-converted longitudinal and shear waves along bolt are captured to calculate acoustic wave velocities and determine elastic constants such as Young’s modulus and Bulk modulus based on acoustoelasticity. Ray analysis to select a specific mode conversion from longitudinal mode to shear mode is carried out and discussed with experimental results. From experiment results of maximum 5% of measurement error, it is shown that the proposed mode-converted ultrasonic technique is very effective and sensitive enough to characterize mechanical modulus of high-tension bolts quantitatively.

Abstract: One of the serious problems that make the flaw identification in a multi-layered thick composite panel more difficult is the interference effect of the upper layer. To take care of such a problem, here we propose an image enhancement approach that can get rid of such an interference effect to ultrasonic C-scan images by a normalization of the acquired signals by a reference signals, and demonstrate its performance in the experiments. Specifically, three specimens with artificial flaws are prepared and ultrasonic C-scan images are acquired experimentally to eliminate the undesired interference effect. Great successes are observed in the present study demonstrating the high potential of the proposed algorithm as a practical image enhancement tool in many practical situations.

Abstract: In recent society, the lap joint that is one of the joint techniques in the industrial society is used for the purpose of joint with the material and the material or the material and the metal and dissimilar materials. We are given the favor in the daily life for the merchandise, the tool and the other goods. The studies of concerning of the lap joint such as the analysis of the surface for the adhesive and the adherent are reported. There is much report about the FEM, but the experimental analysis is not much. Especially, the thermal stress analysis of the lap joint is reported a few. These are almost about the FEM methods, but the report of the thermal analysis is few. The authors think that the experimental analysis is not enough about the study of the thermal analysis and tried to experiment the stress of the adherent. Therefore the authors tried to analyze using the photoelasticity methods. The authors made for the device to analyze the under same temperature of around the circumstance. This new device keeps the temperature constantly; the adhesive and the adherent are keeping in this device. This was observed the variation of the stress under constant temperature. It was obtained the result that the stress of the adhesive joint was influenced about the heat.

Abstract: Understanding chondrocyte behavior inside complex, three-dimensional environments with controlled patterning of geometrical factors would provide significant insights into the basic biology of tissue regenerations. One of the fundamental limitations in studying such behavior has been the inability to fabricate controlled 3D structures. To overcome this problem, we have developed a three-dimensional microfabrication system. This system allows fabrication of predesigned internal architectures and pore size by stacking up the photopolymerized materials. Photopolymer SL5180 was used as the 3D microfabricated scaffolds. The results demonstrate that controllable and reproducible inner-architecture can be fabricated. Chondrocytes from human nasal septum were cultured in 3D scaffolds for cell adhesion behavior. Such 3D scaffolds might provide effective key factors to study cell behavior in complex environments and could eventually lead to optimum design of scaffolds in various tissue regenerations such as cartilage, bone, etc. in a near future.

Abstract: Scaffold technology is integral in advancing tissue engineering and one of the tissues of interest here is the tendon/ligament. Advancement in the tissue engineering of tendon/ligament has become very much a materials engineering problem than ever, with the selection of appropriate biomaterial and scaffold architecture. Such is the key to successful tendon/ligament tissue regeneration construct. Popular materials used in recent years include various poly (l-lactic) biomaterials and collagen. However, shortcomings of these materials, in terms of poor mechanical strength or short degradation period, are yet overcome. Bombyx mori silk, though used in biomedical sutures for decades due to its excellent mechanical properties, has been overlooked for applications in ligament tissue engineering, only until recently. This is largely due to previous misconceptions in its biocompatibility and biodegradability characteristics. This paper describes the use of a silk-based scaffold with knitted architecture and investigates its strengths as compared to previous PLGA-based knitted scaffolds. An electrospun nanofiber surface on knitted microfiber architecture is adopted and it is found to have better composite-material integrity, in vitro degradation resistance, and encourages cell adhesion and proliferation.