Friction stir spot welding (FSSW) is a solid-state joining process and a rapidly growing dissimilar material welding technology for joining metallic alloys in the automotive industry. Welding tool shape and process conditions must be appropriately controlled to obtain high bonding characteristics. In this study, FSSW is performed on dissimilar materials AA5052-H32 aluminum alloy sheet and SPRC440 steel sheet, and the influence of the shape of joining tool and tool insertion depth during joining is investigated. A new intermetallic compound is produced at the aluminum and steel sheets joint. When the insertion depth of the tool is insufficient, the intermetallic compound between the two sheets did not form uniformly. As the insertion depth increased, the intermetallic compound layer become uniform and continuous. The joint specimen shows higher values of tensile shear load as the diameter and insertion depth of the tool increase. This shows that the uniform formation of the intermetallic compound strengthens the bonding force between the joining specimens and increases the tensile shear load.

In this study, experiments and simulations were performed for fillet joint friction stir welding according to tool shape and welding conditions. Conventional butt friction stir welding has good weldability because heat is generated by friction with the bottom of the tool shoulder. However, in the case of fillet friction stir welding, the frictional heat is not sufficiently generated at the bottom of the tool shoulder due to the shape of the tool and the shape of the joint. Therefore, it is important to sufficiently generate frictional heat by slowing the welding speed as compared to butt welding. In this study, experiments and simulations were carried out on an aluminum battery housing made by friction stir welding an extruded material with a fillet joint. The temperature of the structure was measured using a thermocouple during welding, and the heat source was calculated through correlation analysis. Thermal elasto-plastic analysis of the structure was carried out using the calculated heat source and geometric boundary conditions. It is confirmed that the experimental results and the simulation results are well matched. Based on the results of the study, the deformation of the structure can be calculated through simulation even if the tool shape and welding process conditions change.

The bead geometry according to the welding conditions was analyzed through the laser fillet welding experiment of 9% Ni steel, and the relationship between the shear strength and the five bead geometry measured by selecting the main bead geometry of the fillet weld was analyzed. Among the welding conditions, the welding conditions that directly affect the penetration depth are welding speed and laser power, and the working angle and beam position have a great influence on the formation of leg of vertical and horizontal members. The bead shape, which greatly affects the shear strength, is the horizontal member length, neck thickness, and weld length, and has a proportional relationship with the shear strength. As a result of confirming the relationship between shear strength and bead shape through the derivation of the trend line, it was confirmed that the length of the vertical member, whose R2 value was 0.92, was most closely related to the shear strength.

ACT Column은 기존 CFT 기둥보다 얇은 강판으로도 동일한 구조적 성능을 발휘할 수 있으며, 콘크리트의 구속효과와 강관의 항복 후 좌굴응력의 향상을 기대할 수 있다. ACT Column은 보-기둥 접합부에 외다이아프램을 사용한 접합상세가 적용된다. 그러나 ACT Column 외부에 콘크리트가 피복되는 SRC 타입에서는 외다이아프램을 사용한 접합부의 적용이 난해하다. 그래서 ACT Column의 외부에 수직 스티프너와 수평 스티프너를 사용한 접합상세를 제안하였다. 본 논문에서는 제안상세를 대상으로 단순인장실험을 통해 성능검증을 수행하였다. 실험체는 현장에 사용량이 많은 크기의 ACT Column 으로 2개의 실험체를 제작하였다. 보 플랜지와 보 플랜지의 양측부에 부착된 윙플레이트를 통해 보 플랜지의 단면 내력이 링다이아프램으로 전달되는 명확한 응력전달매커니즘을 나타내었으며, 보 플랜지 전단면이 소성화되어 파괴되었다. 윙플레이트의 크기가 클수록 하중전달량이 증가하였으며, 제안한 접합상세의 강도평가식을 제시하였다.

스폿 용접 접합의 삼차원 모델링을 위하여 강한 불연속이 내장된 유한요소를 사용하였다. 스폿 용접의 기하학적 형상을 유한요소망 대신 요소에 내장된 불연속 면에서의 특수한 응집 법칙을 이용하여 표현하였다. 이를 통하여 기존의 적응적 유 한요소망을 이용하는 접근법과 달리 스폿 용접의 국부적인 형상에 독립적인 유한요소망을 구성할 수 있다. 또한, 스폿 용접 의 형상을 명시적으로 고려하여 모델링함으로써 기존의 점 구속조건을 이용하는 접근법과 달리 망 독립적인 해를 얻을 수 있다.

In this study, the mechanical characteristics with micro structure were analyzed on the butt joint of AZ60 magnesium material extruded by GMAW and GTAW processes. As the result of tensile test, the fracture in the welding joint area happened at both processes and seemed to be brittle fracture. The yield strength of GMAW was 84.29% and GTAW was 60.43% as compared with base metal. The yield strength of GMAW was higher 23.86% than that of GTAW. The result of decreased micro hardness was indicated at both processes. The value of minimum micro hardness in FZ at GMAW was Hv 46.7 and GTAW was Hv 43.6 as compared with base metal. The value of minimum micro hardness at GMAW process was higher 5.64 % than that at GTAW process. The size of grain boundary at GMAW process in HAZ is smaller than that at GTAW process. GMAW process is more superior than GTAW process from the productivity and quality in case of automatic welding for magnesium alloy such as the automobile seat frame.

Two steel-frame joint specimens with welding joint parts were constructed and evaluated. Two types of displacement load, monotonic and cyclic, were used to evaluate the steel-frame joint specimens. According to the experimental results, the maximum moment of the cyclic test results was 80% smaller than that of the monotonic test results. Local buckling was observed in the compression area of the H-beam flange. A finite element analysis model based on the experimental results was proposed to analyze the steel-frame joint specimens. The numerical results predicted the experimental behavior of the steel-frame joint specimens well. Therefore, it is possible to use the proposed finite element analysis model to evaluate middle- and low-rise steel-frame buildings constructed in South Korea.

Abstract: In this study, finite element analysis modeling is proposed to evaluate middle- and low-rise steel-frame buildings constructed in South Korea. Two steel-frame joint specimens with welding joint parts were constructed and evaluated. Two types of displacement load, monotonic and cyclic, were used to evaluate the steel-frame joint specimens. According to the experimental results, the maximum moment of the cyclic test results was 80% smaller than that of the monotonic test results. Local buckling was observed in the compression area of the H-beam flange. A finite element analysis model based on the experimental results was proposed to analyze the steel-frame joint specimens. The numerical results predicted the experimental behavior of the steel-frame joint specimens well. Therefore, it is possible to use the proposed finite element analysis model to evaluate middle- and low-rise steel-frame buildings constructed in South Korea.

This study presents an experimental study of the structural behavior for steel plate-concrete column-to-steel girder connections. Experiments were carried out to investigate the moment-rotation characteristics, failure behavior and ultimate moment capacity of these connections. The results of this experimental study involving three welded moment-resisting connections subjected to cyclic loading are presented. The specimens were fabricated at full scale to evaluate their hysteretic behavior. A description of the test specimens, the details of the joint, the test system and the testing methods are described. The test results showed that the structural behavior of these composite connections was influenced by the connection details.

Recently, applied areas of nonferrous materials have been expanded in terms of efficiency of materials used and cost reduction. And, in accordance with compactness and accuracy of parts, the need of joining of dissimilar materials is raised. Accordingly, this study aimed at finding out the optimal welding current value(6.3～6.5kA) considering tensile strength, fracture test and welding residue after joining with various welding conditions by means of copper pipe(Φ7.0 × t0.5) and aluminium pipe(Φ7.0 × t0.7) using an eutectic diffusion bonding machine.

The spot weldability of dissimilar metal joints between stainless steels (AISI316) and interstitial free (IF) steels were investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensileshear strength, hardness, and microstructure. The fracture surface was investigated by using a Scanning Electron Microscopy (SEM). The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the STS316 sheet was larger due to the higher bulk-resistance. The microstructure of the fusion zone was fully martensite. In order to evaluate the microstructure further, dilution of stainless steels were calculated and imposed onto the Schaeffler diagram. The predicted microstructure from the Schaeffler diagram was martensite. In order to confirm the predicted microstructure, XRD measurements were carried out. The results showed that that initial weld nugget was composed of austenite and martensite.

Friction welding of particulate reinforced aluminum composites was performed and the following conclusions were drawn from the study of interfacial bonding characteristics and the relationship between experimental parameters of friction welding and interfacial bond strength. Highest bonded joint efficiency (HBJE) approaching was obtained from the post-brake timing, indicating that the bonding strength of the joint is close to that of the base material. For the pre-brake timing, HBJE was . Most region of the bonded interface obtained from post-brake timing exhibited similar microstructure with the matrix or with very thin, fine-grained layer. This was attributed to the fact that the fine-grained layer forming at the bonding interface was drawn out circumferentially in this process. Joint efficiency of post-brake timing was always higher than that of pre-brake timing regardless of rotation speed employed. In order to guarantee the performance of friction welded joint similar to the efficiency of matrix, it is necessary to push out the fine-grained layer forming at the bonding interface circumferentially. As a result, microstructure of the bonded joint similar to that of the matrix with very thin, fine-grained layer can be obtained.

본 연구에서는 1994년 미국 노스리지 지진 이전에 건설된 기존 철골 건물의 용접형 철골 박스기둥과 보 접합부의 내진성능을 반복재하 실험에 의해 평가하였다. 실험결과에 의하면 노스리지 지진 이전 접합상세를 갖는 박스기둥과 보 접합부에서도 H-형강 기둥과 보 접합부 실험결과와 유사하게 취성파단이 발생하였다. 하지만, 박스기둥과 보 접합부에서의 플랜지 응력전달 경로가 H-형강 기둥과 보 접합부에서의 것과 상당한 차이가 있고 또한 박스기둥의 형상에 따라 균열 전파의 형태가 다를 수 있다는 것이 밝혀졌다. 따라서 용접형 철골 박스기둥과 보 접합부의 내진성능을 향상시키기 위해서는 H-형강 기둥과 보 접합부에 대한 기존 연구결과를 그대로 적용하기보다는 박스기둥에 적합한 접합부의 보강상세 개발이 요구된다.

용접 철골 모멘트접합부는 일반적으로 평면유지의 가정을 전제한 초등휨이론에 의해 설계되어 왔다. 그러나 1994년 노스리지 지진 이후 보-기둥 접합부의 설계에 초등휨이론을 적용하는 것은 타당치 않음이 몇몇 연구자에 의해 제기된 바가 있다. 본 연구에서는 필자의 최근 해석 및 실험연구를 주 근거로 하여 다양한 형식의 접합부의 응력전달 메커니즘을 재평가하고, 거의 모든 용접 모멘트접합부의 설계에 초등휨이론을 적용하는 것이 부적절함을 보이고자 하였다. 보의 웨브, 수평헌치의 웨브, 리브 등과 같은 수직 플레이트 접합요소는 모두 스트럿 작용에 의해 응력을 전달하는 유사성이 있음을 해석적, 실험적으로 확인하였다. 또한 최근 가장 큰 주목을 받고 있는 고연성 RBS 접합부의 전단력 응력전달 메커니즘은 PN형식 접합부의 그것과 크게 다르지 않음을 확인하였다. 아울러 접합부 설계에 유용하게 활용될 수 있는 단순화된 해석적 응력전달 모형을 소개하였다.

용접접합부 균열의 파괴역학적 해석을 위해서는 용접중에 발생하는 잔류응력해석과 파괴해석이 병행되어야 한다. 잔류응력이 존재하면 J-적분은 더 이상 적분경고에 관계없이 인정한 값을 갖는 특성을 잃어버리게 된다. 또한 균질한 재료와는 달리 이종재료 계면균열에서는 균열선난에서 Mode I과 Mode II의 파괴거동이 동시에 발생한다. 그러므로 이종강재 용접접합부 균열의 J-적분 해석을 위해서는 이종강재 용접시 발생하는 잔류응력이 존재하는 경우에도 적분경로에 관계없이 일정한 값을 갖는 새로운 J-적분식이 도입되어야 한다. 따라서 본 연구에서는 기존의 J-적분을 수정하여, 이종강재 용접시 발생하는 잔류응력이 존재하는 경우에 경로 독립성을 유지하는 J-적분을 고찰하고, 이를 이용하여 잔류응력과 외력이 동시에 작용하는 균열선단에서의 J-적분을 해석할 수 있는 프로그램을 개발하였다. 자체개발한 탄소성 해석프로그램을 이용하여 이종강재 용접시 잔류응력과 외력에 대한 응력분포를 계산하였으며, 이를 이용하여 잔류응력과 외력의 복합하중에 대한 J-적분을 계산하였다.

Recently the construction of residential building faces many difficulties due to the shortage of building materials and works. Simplifying the stage of processing and assembling reinforcing rods and increasing the efficiency of them in reinforced concrete construction can be used to settle the difficulties. In the respect, structural wire-fabric is utilized. The purpose of this study, instead of deformed steel bars, to examine the utilization of slab joint, which is accompanied with a large deformation in the structure subjected to seismic loads, to suggest reinforcing method which is efficient, easily constructible and structurally safe. The results are as follows ; 1. The ductility capacity of slab reinforced by welded wire fabric was less than with deformed bar in discontinuous slab joint. To enhance the ductility capacity, deformed bar should be used with welded wire fabric for the longitudinal reinforcement. 2. It is avoid to use loop welded wire fabric as the longitudinal reinforcement in wall, because the strength and ductility capacity showed lower value than that with deformed bar. 3. Using welded wire fabric in wall structures, it need deformed bar reinforcement with sufficient anchorage length.

Recently the construction of residential building faces many difficulties due to the shortage of building materials and works. Simplifying the stage of processing and assembling reinforcing rods and increasing the efficiency of them in reinforced concrete construction can be used to settle the difficulties. In the respect, structural wire-fabric is utilized. The purpose of this study, instead of deformed steel bars, to examine the utilization of slab joint, which is accompanied with a large deformation in the structure subjected to seismic loads, to suggest reinforcing method which is efficient, easily constructible and structurally safe. The results are as follows ; 1. The ductility capacity of continuous slab joints reinforced by welded wire fabric is less than that with deformed bar. But continuous slab joint is reinforced by deformed bar for the longitudinal reinforcement, it is increase strength and ductility capacity. 2. It is recommended that simple cut jointing of welded wire fabric should be avoided in wall-wall joints.

최근에 용접 수평헌치로 보강된 내진 철골 모멘트 적합부의 응력 전달모형 및 설계법이 Lee-Uang에 의해 새로이 제안된 바가 있다. 본 연구에서는 반복재하 실물대 실험을 통하여 이 설계방안의 타당성을 실험적으로 확인하고 응력집중에서 기인하는 헌치단부의 균열을 방지할 수 있는 효과적인 상세도 제안하고자 하였다. Lee-Uang의 방안에 의해 설계된 3개의 시험체는 모두 설계의도에 부합되게, 헌치단부의 외측에서 형성된 소성힌지에서 0.04 radian에 달하는 뛰어난 소성회전능력을 발휘하였다. 도한 헌치단부에 구배를 주고 처공하거나 또는 보 웨브 스티프너를 헌치의 웨브로 부분적으로 또는 완전히 연장하는 상세에 의해 헌치단부의 균열발생을 효과적으로 방지할 수 있음을 실험적으로 입증하였다. 아울러 해석적으로 예견되었던 헌치 웨브의 스트럿 거동도 스트레인 계측을 통하여 실험적으로 입증하였다.

본 연구에서는 용접 수평헌치로 보강된 철골 모멘트 접합부의 내진설계법을 제시하고자 한다. 최근의 실험결과에 의하면 보의 하부를 수평헌치로 용접하는 방안은 취약한 내진성능이 드러나 기존 철골 모멘트 접합부의 내진보강이나 내진성능이 뛰어난 건물의 구축에 매우 효과적임을 알 수 있다. 용점 삼각헌치로 보강된 접합부의 설계법은 최근에 미국의 연구자들에 의해 제시된 바가 있다. 그러나 이 설계법은 응력 전달 메커니즘이 상이한 수평헌티 접합부의 설계에는 적용될수 없다. 본 논문에서는 우선 수평헌치와 보의 상호작용 및 변형의 적합 조건을 고려하여 도출된 단순화된 해석적 응력전달 모형을 간략히 기술한다. 이를 기초로 수평헌치 접합부의 단계별 내진 설계절차를 제안한다. 아울러 헌티단부의 응력집중을 줄이는데 매우 효과적인 디테일도 제시하고자 한다.