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음향방출센서를 이용한 선조질강(ESW90)의 압축실험에서의 표면 균열 발생 검출
이정음,이진명,주호선,서영호,김지훈,김상우 한국소성∙가공학회 2020 소성가공 : 한국소성가공학회지 Vol.29 No.1
In the design of the metal forming processes, various types of ductile fracture criteria are used to predict crack initiation and to fabricate metallic products without any defects. However, the quantitative measurement method for determination of crack initiation is insufficient. It is very difficult to detect crack initiation in ductile metals with excellent deformability because no significant load drop is observed due to crack generation. In this study, the applicability of acoustic emission sensors, which are commonly used in facility diagnostics, to measure crack initiation during the metal forming process was analyzed. Cylindrical notch specimens were designed using the finite element method to induce a premature crack on the surface of pre heat-treated steel (ESW90) material. In addition, specimens with various notch angles and heights were prepared and compression tests were carried out. During the compression tests, acoustic emission signal on the dies and images of the surface of the notch specimen were recorded using an optical camera in real time. The experimental results revealed that the acoustic emission sensor can be used to detect crack initiation in ductile metals due to severe plastic deformation
SLM공정에 의해 제조된 316L 스테인레스 스틸 격자구조체의 압축 거동 평가
이진명,이정음,김지훈,김상우 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.4
Lattice structures are multi-functional materials with various advantages such as high specific stiffness, high energy absorption capacity and good thermal management capability. Recently, the development of manufacturing technologies using metal powders has facilitated fabrication of complex products; consequently, interest in lattice structures has grown. In this work, two kinds of lattice structures, pyramidal and tetrahedral, were designed and fabricated via a selective laser melting (SLM) process using stainless steel 316L powder. Scanning electron microscope (SEM) and optical microscope (OM) results revealed that lattice structures with various unit cell sizes and angles of inclination can be manufactured using SLM without the need for additional support structures. However, many unmelted and partially melted particles were observed on the surface of the lattice structures, which caused dimensional errors related to the struts. This research examined the effects of topology and unit cell design parameters on the macroscopic compressive behavior of lattice structures. Compressive characteristics, including elastic modulus, initial peak stress, strain energy absorption and mean stress, were evaluated through uniaxial compression tests. Lattice structures with the same relative density exhibited excellent elastic modulus, initial peak stress, energy absorption and mean stress results at inclination angles of 45–50°. These characteristics showed a tendency to increase with increasing relative density at the same inclination angle. The experimental results suggested these design parameters are the main factors influencing the mechanical characteristics of lattice structures.
박현배 ( Hyun-bae Park ),문성우 ( Seong-woo Moon ),주세정 ( Sejeong Ju ),이정음 ( Jeungeum Lee ),서용석 ( Yong-seok Seo ) 대한지질공학회 2024 지질공학 Vol.34 No.1
우리나라는 1980년까지 광물 지하자원 개발을 활발히 수행하였으나 이후 생산원가 대비 사업성이 크게 줄어들면서 많은 수의 폐광산이 발생되었다. 그 중 대부분은 광산개발 중단 후 오랜 시간이 지나 잔류성 침하가 발생할 가능성이 높은 상태에 있다. 하지만 그 발생 시기와 위치를 정확히 예측하기는 어려움이 있다. 따라서, 본 연구에서는 실제 지반침하가 발생한 사례를 분석하여 연속체 수치해석을 통해 지반침하의 발생 위치나 규모에 대한 예측 가능성을 살펴보고자 한다. 연구지역은 양산단층과 모량단층 사이에 위치하여 이들에 규제받는 ○○광산 지역이며, 이 지역에서는 2005~2009년에 걸쳐 3회의 지반침하가 발생된 바 있다. 지반침하지를 대상으로 시추조사 및 전기비저항 탐사를 수행하여 지층의 분포를 파악하였고, 실내시험을 통해 수치해석 시 적용되는 지반의 물리 · 역학적 특성을 파악하였다. 수치해석 결과 소성영역이 실제 지반침하 범위를 포함하는 형태로 나타나 연속체 해석으로도 채굴적에 의한 침하지 발생 위치 및 규모를 예측하는데 활용할 수 있을 것으로 판단된다. South Korea’s mining industry was actively developed until 1980, but subsequent declining profitability forced many mines to close. Most of the abandoned mines are susceptible to persistent subsidence because of the length of time since mining ceased. Accurate prediction of the locations and times of subsidence is difficult; therefore, this study aims to apply continuum analysis to past cases of subsidence to establish a method of predicting the location and magnitude of future subsidence. The study area is an area of ○○ mining located between the Yangsan fault zone and the Moryang fault zone, in which three subsidence events occurred between 2005 and 2009. Drilling surveys and electrical resistivity surveys were performed at subsidence sites determined the distribution of strata, and through laboratory tests obtained the physico-mechanical properties of the rock. Numerical analysis of the results found that the plastic status area includes the areas of actual subsidence and that continuum analysis can also be used to predict the location and magnitude of subsidence caused by mine goaf.