http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
용탕단조법으로 제조된 AZ91-X (Y, Nd, Sr) 합금의 미세파괴기구
이승혁,이성학,김도향 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.5
A study was made of the effects of alloying elements on the microstructure and microfracture mechanism of squeeze cast AZ91-X(X=Y, Sr, Nd) magnesium alloys. Particular emphasis was placed on the role of Y and Nd, which are important alloying elements in magnesium alloys fabricated by rapid solidified process. Microstructural observation, in situ fracture test, and fractographic observation were conducted on the alloys to clarify the microfracture process. Microstructural analyses indicated that the grain refinement could be achieved by small addition of alloying elements, although Mg_(17)Al_(12) phases were still present along grain boundary. From in situ observation of the AZ-Sr alloy, coarse needle-shaped particles and Mg_17)Al_(12) phases located along grain boundary provided easily intergranular fracture sites under low stress intensity factor levels, resulting in the drop in toughness. In the AZ-Y and the AZ-Nd alloys, on the other hand, a number of planar slip bands and twinnings were well developed inside grains, thereby leading to the enhancement of overall mechanical properties. These findings indicated that small addition of Y or Nd was very effective in improving mechanical properties on the basis of the well-developed twinnings and slip bands.
무인기 탐지를 위한 멀티모드 레이다 신호처리 프로세서 설계
이승혁,정용철,정윤호 한국항행학회 2019 韓國航行學會論文誌 Vol.23 No.2
Radar systems are divided into the pulse Doppler (PD) radar and the frequency modulated continuous wave (FMCW) radar depending on the transmission waveform. In particular, the PD radar is advantageous for long-range target detection, and the FMCW radar is suitable for short-range target detection. In this paper, we present design and implementation results for a multi-mode radar signal processor (RSP) that can support both PD and FMCW radar systems to detect unmanned aerial vehicles (UAVs) at short distances as well as long distances. The proposed radar signal processor can be implemented based on Altera Cyclone-IV FPGA with 19,623 logic elements, 9,759 registers, and 25,190,400 memory bits. The logic elements and registers of the proposed radar signal processor are reduced by approximately 43% and 30%, respectively, compared to the sum of logic elements and registers of the conventional PD radar and FMCW radar signal processor. 레이다 시스템은 송신 파형에 따라 크게 PD (pulse Doppler) 레이다와 FMCW (frequency modulated continuous wave) 레이다로 구분되며, 송수신 특성에 따라 PD 레이다는 장거리 표적 검출에 유리한 반면, FMCW 레이다는 단거리 표적 검출에 적합한 특성을 갖는다. 이에 본 논문에서는 중/장거리 뿐 아니라 단거리 무인기 탐지를 위해 PD 레이다 시스템과 FMCW 레이다 시스템을 모두 지원가능한 멀티모드 레이다 신호처리 프로세서 (RSP; radar signal processor)를 제안한다. 제안된 레이다 신호처리 프로세서는 Verilog-HDL을 이용하여 RTL 설계 후, Altera Cyclone-IV FPGA를 이용하여 구현 및 검증 되었다. 구현 결과, 총 19,623개의 logic elements, 9,759개의 register, 그리고 25,190,400의 memory bit로 구현 가능함을 확인하였으며, 기존의 PD 레이다와 FMCW 레이다 신호처리 프로세서를 개별 구현한 경우에 비해 logic elements와 register 요구량이 약 43%와 39% 감소됨을 확인하였다.