• 한국강구조학회 논문집
• /
• 제17권6호통권79호
• /
• pp.727-736
• /
• 2005

본 연구에서는 사장교의 적절한 초기평형상태 결정을 위하여 최소자승법을 이용한 케이블 장력 결정 방법을 제시하였다. 본 방법은 거더의 케이블 지지점을 지점으로 한 연속보로부터의 처짐 및 모멘트 등을 목표치로 하고 케이블을 포함한 사장교 전체계 해석으로부터 구해진 응답과의 차이를 오차로 정의하여 거더 및 주탑의 오차를 최소화하는 방법이다. 특히, 주탑 모멘트, 거더 모멘트, 그리고 처짐의 보정 정도를 가중행렬을 도입하여 선택적으로 조절할 수 있으며, 여러 가지 사장교 형식에 대한 수치예제 및 기존 연구와의 비교를 통하여 본 방법의 효율성 및 타당성을 검증하였다.

• 한국정밀공학회지
• /
• 제20권7호
• /
• pp.44-55
• /
• 2003

The Nd:YAG laser process is known to have high speed and deep penetration capability to become one of the most advanced welding technologies. This paper describes the machining characteristics of SM45C carbon steel welding by use of an Nd:YAG laser. In spite of its good mechanical characteristics, SM45C carbon steel has a high carbon contents and suffers a limitation in the industrial application due to the poor welding properties. The major process parameters studied in the present laser welding experiment were position of focus, travel speed and laser power. Optical microscope and SEM were used to investigate the microstructures of the welded zone. The experimental results showed that penetration depth of the welding process increases with laser power. Both the microstructural investigation and the theoretical calculations indicated that materials undergoes a very high heating and cooling cycle during welding process. It was also found that the austenite nucleation takes place at the initial stage and the completion temperature of austenite transformation is much higher than in the case of the arc welding.

• 한국정밀공학회지
• /
• 제29권4호
• /
• pp.395-408
• /
• 2012

An experimental investigation with 2.8kW Nd:YAG laser system was carried out to study the effects of different laser process parameters on the microstructure and hardness of STD11. The optical lens with the elliptical profile are designed to obtain a wide surface hardening area with uniform hardness. The Laser beam is allowed to scan on the surface of the work piece varying the power (1600, 1800 and 1900kW) and traverse speed (200, 400, 600, 800 and 1000mm/min) at three different F-numbers of lens. After laser surface treatment three zones, In the microstructure have been observed : melted zone(decarburization), heat affected zone(martensite), and the substrate.

• Journal of Welding and Joining
• /
• 제34권1호
• /
• pp.75-81
• /
• 2016

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and $800{\mu}m$ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

• 한국구조물진단유지관리공학회 논문집
• /
• 제9권1호
• /
• pp.259-269
• /
• 2005

본 연구에서는 철근콘크리트 연속보의 이산최적설계를 수행하기 위해서 유전알고리즘을 적용하였다. 콘크리트, 거푸집, 주철근 및 스터럽의 경비를 포함한 경비 최소화를 목적함수로 하였고, 제약조건으로는 휨강도와 전단강도, 처짐, 균열, 철근간격, 피복두께, 철근비 상 하한치 및 단면형상에 대한 기하학적 제약조건과 더불어 주철근의 정착을 고려하였다. 보의 폭과 유효깊이, 철근량을 설계변수로 취하였으며, 설계변수 값은 실무에서 사용되는 단면치수와 철근량을 데이터베이스화한 이산집합으로부터 선택되도록 하였다. GA의 신뢰성을 검증하기 위해서 이산변수로 철근콘크리트보에 대한 최적설계를 수행한 기존 문헌과 그 결과값을 비교 검토하였으며, GA의 적용성 및 효율성을 보이기 위하여 국내 구조설계기준을 만족하는 3경간 및 5경간 철근콘크리트보에 대해 이산최적설계를 수행하였다.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
• /
• pp.184-191
• /
• 2000

In this research, a numerical model is developed for analysis of buried pipelines considering longitudinal permanent ground deformation(PGD) due to liquefaction induced lateral spreading. Buried pipelines and surrounding soil are medeled as continuous pipelines using the beam elements and a series of elasto-plastic springs uniformly distributed along the pipelines, respectively. Idealized various PGD patte군 based on the observation of PGD are used as a loading configuration and the length of the lateral spread zone is considered as a loading parameter. Numerical results are verified with other research results and efficient applicability of developed procedure is shown. Analyses are performed by varying different parameters such as PGD pattern, pipe diameter and pipe thickness. Results show that response of buried pipelines are more affected by pipe thickness than pipe diameter. Finally, the critical length of the lateral spread zone and the critical magnitude of PGD which cause yielding, local buckling or tension failure are proposed for the steel pipe which are normally used in Korea.

• 한국방재학회:학술대회논문집
• /
• 한국방재학회 2007년도 정기총회 및 학술발표대회
• /
• pp.49-52
• /
• 2007

Terrestrial Laser Scanning(TLS) was developed at the mid-to-late 1990s. This technique enables to perform reconnaissance surveying of regions or structures hard to access. Besides, TLS has been extended its application gradually such as preservation of historical remains, underground surveys, slopes, glaciers monitoring and so on. However, though the technique has a lot of advantages, an application for structural health and safety monitoring is a beginning stage and it need much research. Therefore in this study, as a groundwork, the estimation model on stress of structures using TLS and Finite Element Method(FEM) applied by the Digital Elevation Model(DEM) technique of geoinformatics is proposed. For the verification of this model, experiments were performed with a continuous steel beam subjected to point loads and outputs were compared with those of electrical strain sensors.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 1993년도 특별강연 및 춘계학술발표 개요집
• /
• pp.120-124
• /
• 1993

The Charpy V impact test on subsize was performed on narrow laser welds of low carbon steel sheets, joined by using a continuous wave 3kW CO$_2$ laser. Under certain conditions, a bimodal fracture behaviour has been experienced in Charpy V impact test of narrow laser beam welds. Deviation of the fracture path from the fusion zone into the base metal was dominated at high test temperature. It can be seen that the deviation always occurred after ductile initiation. If the deviation occurs on a small testing specimen, the same trend would happen on the actual laser welded structure. Fracture will then propagate through the base material even if the weld metal has low toughness.

• 비파괴검사학회지
• /
• 제33권4호
• /
• pp.317-322
• /
• 2013

This paper presents a new laser lock-in thermography (LLT) technique for nondestructive evaluation. LLT utilizes a modulated continuous wave laser beam as a heat source to obtain high fidelity thermal wave images even at the presence of background heat disturbances. The thermal waves propagating along the surface and through-the-thickness directions of a structure are visualized using newly developed laser lock-in amplitude and phase images, enhancing the detectability of surface and subsurface defects. The LLT technique is numerically investigated and experimentally validated using thermal images obtained from a steel specimen with low emissivity.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2004년도 추계학술대회 논문집
• /
• pp.250-256
• /
• 2004

For many years and primarily for economical reasons, Dissimilar Metal Welds have been used as transition joints in a variety of equipment and applications. But Dissimilar Metal Welds have several fabrication and metallurgical drawbacks that can often lead to in-service failures. In this paper, the laser weldability of STS304 stainless steel and SM45C at dissimilar metal welds using a continuous wave Nd:YAG laser are experimentally investigated. An experimental study was conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser were tested.