Advances in Fracture and Failure Prevention

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Authors: Toshimitsu Baba, Kazuhiro Ogawa, Tetsuo Shoji
Abstract: A novel non-destructive inspection (NDI) technique that utilizes high-frequency signal transmission characteristics was developed as a more reliable, faster and cheaper NDI technique. This technique forms a transmission circuit that includes the specimen, and detects the signals generated by any surface breaking-defect. In this research, quantitative measurement of closed fatigue cracks was implemented via a newly developed probe. The greatest advantage of this technique is that there is no significant difference in detection of defects in either paramagnetic materials or in ferromagnetic materials. Therefore, the potential effects of corrosion, ferrite content, or deformation martensite on the measurement signals are minimized, and a better S/N ratio can be expected. This technique can also be used to measure the size of defects in components, including welded components, and its detection sensitivity is less than 1 mm for surface breaking-defects.
Authors: Masumi Saka, Yang Ju, Y. Uchimura, Toru Miyadu
Abstract: A method to estimate crack closure stress on the crack surface was introduced. The crack closure stress was estimated based on the compliance technique, while crack depth was measured by means of the microwave dual frequency technique. The effect of crack closure stress on detection and evaluation of a closed crack in a carbon steel by using the microwave dual frequency technique was discussed in details.
Authors: Hisashi Sato, Yousuke Tsujimoto, Makoto Takahashi, Masaharu Kitamura
Abstract: In the present study, the vibration and ultrasonic measurements have been applied to a high flow rate pump installed in the SSBF in order to develop the monitoring and diagnosis methods. The vibration of the casing of the canned pump is measured by using the laser vibration sensor. The frequency domain analyses have been applied to the measured signals. The measurement results showed the validity of the proposed method to monitor the state of the high flow rate pump.
Authors: Kazushi Yamanaka, K. Aizu, S. Sakai, A. Mizukami, H. Cho
Authors: Hirotaka Sato, Michihiro Kitahara, Tetsuo Shoji
Authors: M. Kitahara, M. Onishi, Kouichi Nakahata, Masayoshi Yamada
Abstract: The Born inverse scattering method is applied to the shape reconstruction of flaws in the concrete materials. To accelerate the inversion process, the algorithm of the fast Fourier transform is introduced in the integration process of the scattering amplitude. The concrete specimens with flaw models are prepared and the scattered waveforms from flaws are acquired in the pulse-echo mode. The shape of flaws is reconstructed by using the measured waveforms and the performance of the inversion method is demonstrated experimentally.
Authors: T. Mihara, Y. Otsuka, H. Cho, Kazushi Yamanaka
Abstract: We developed a laser TOFD (Time of flight diffraction) algorithm which utilizes not only longitudinal wave but also shear wave. This algorithm made it possible to obtain accurate flaw depth without knowing the specimen velocity and probe distance previously. We constructed the laser TOFD system and applied it to estimate the slit depth of aluminum alloy plate. Time of flight of lateral wave, flaw tip diffraction waves and mode converted shear wave at flaw tip were used to estimate the slit depth using new algorithm.
Authors: S. Rangarajan, Douglas Shukert, Yo-ichi Takeda, K. Sakaguchi, Tetsuo Shoji
Authors: Sadahiro Tsurekawa, Tadao Watanabe, N. Tamari
Abstract: Grain boundary engineering (GBE) is rapidly emerging recently as a powerful tool for achieving enhanced properties and performance in polycrystalline metallic materials. The objective of this work is to confirm the potential of GBE for enhancement in properties and performance in ceramic materials such as silicon carbide (SiC). Grain boundary microstructure in SiC could be tailored by doping with different elements (Mg, Al and P) and modifying sintering processing (hot-pressing and spark plasma sintering). FEG-SEM/OIM analyses revealed that both Al doping and SPS increased the frequency of low-energy special boundaries (Σ ≤29 ) and Mg doping enhanced grain growth. It was found that mechanical properties like microhardness depended on the grain boundary character distribution (GBCD) and the grain size. The increment in the frequency of special boundaries could yield increases in the Vickers-microhardness and the fracture stress. Furthermore, intergranular oxidation-induced brittleness in SiC was noticeably improved by increase in the frequency of special boundaries and decrease in the grain size. Thus, we have confirmed that the control of grain boundary microstructure such as grain size, GBCD and grain boundary connectivity is a key for enhancement in bulk properties and performance in ceramic materials.
Authors: Hiroyuki Kokawa, Masahiko Shimada, Zhan Jie Wang, Yutaka S. Sato, M. Michiuchi
Abstract: Optimum parameters in the thermomechanical treatment during grain boundary engineering (GBE) were investigated for improvement of intergranular corrosion resistance of type 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation (EPR) and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice (CSL) boundaries indicated a maximum at the small pre-strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface.

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