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        Effects of pulsed laser surface remelting on microstructure, hardness and lead-bismuth corrosion behavior of a ferrite/martensitic steel

        Hao Wang,Qian Yuan,Linjiang Chai,Ke Zhao,Ning Guo,Jun Xiao,Xing Yin,Bin Tang,Yuqiong Li,Shaoyu Qiu 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.6

        A typical ferritic/martensitic (F/M) steel sheet was subjected to pulsed laser surface remelting (LSR) andcorrosion test in lead-bismuth eutectic (LBE) at 550 C. There present two modification zones withdistinct microstructures in the LSRed specimen: (1) remelted zone (RZ) consisting of both bulk d-ferritegrains and martensitic plates and (2) heat-affected zone (HAZ) below the RZ, mainly composed ofmartensitic plates and high-density precipitates. Martensitic transformation occurs in both the RZ andthe HAZ with the Kurdjumov-Sachs and Nishiyama-Wassermann orientation relationships followedconcurrently, resulting in scattered orientations and specific misorientation characteristics. Hardnessesof the RZ and the HAZ are 364 ± 7 HV and 451 ± 15 HV, respectively, considerably higher than that of thematrix (267 ± 3 HV). In oxygen-saturated and oxygen-depleted LBE, thicknesses of oxide layers developed on both the as-received and the LSRed specimens increase with prolonging corrosion time (oxidelayers always thinner under the oxygen-depleted condition). The corrosion resistance of the LSRed F/Msteel in oxygen-saturated LBE is improved, which can be attributed to the grain-refinement acceleratedformation of dense FeeCr spinel. In oxygen-depleted LBE, the growth of oxide layers is very low withboth types of specimens showing similar corrosion resistance

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        Acoustic localization of surface defect for low-speed large bearing with averaged generalized inverse beamforming

        Xiang Guo,Xing Wu,Xiaoqin Liu,Linjiang Tang 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.1

        Using microphone array to detect the fault of rotating machinery is an effective method. Compared with the fault diagnosis based on vibration analysis, the advantage of this method is that it does not need the direct contact between the sensor and the machine. In addition, acoustic location can be realized by using microphone array, to accurately identify the sound radiation source on the machine surface. Conventional beamforming (CBF) is widely applied in noise source identification because of its fast speed. In the local reverberation environment, the conventional beamforming is disturbed by the image source, causing inaccurate judgment of the fault location and low imaging resolution. In this paper, an acoustic imaging method of averaged generalized inverse beamforming (AGIB) is proposed. Compared with CBF, generalized inverse beamforming (GIB) possess higher location accuracy. First, the spectral kurtosis (SK) can enhance the impact characteristics of fault signals. According to the center frequency and bandwidth estimated by the spectral kurtosis diagram, the impact information which adopt in beamforming location can be extracted in time domain and frequency domain by spectral kurtosis matched filter. Then the average amplitude and standard deviation of generalized inverse beamforming output at different positions are calculated. Finally, the normalized standard deviation is used for the beamforming output weighting of the central measurement position, so as to enhance the spatially invariant source contribution and effectively attenuate the ghost caused by the local reverberation environment. Through defect location of low-speed large bearing, compared with the averaged conventional beamforming (ACBF), AGIB can not only overcome the influence of local reverberation environment and accurately locate the fault location, but also improve the resolution significantly.

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