• 비파괴검사학회지
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• 제32권2호
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• pp.162-169
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• 2012

본 논문은 초음파 적외선 열화상과 위상잠금 방법을 이용하여 이종금속용접(STS304 and SA106 Gr. b)된 파이프의 응력부식균열 결함을 검출하였다. 초음파 가진장치는 출력 250 Watt, 주파수 20 kHz이었다. 실험 결과 이종금속용접부의 파이프 내부에 위치한 균열을 적외선 열화상을 이용하여 검출할 수 있었다. 실제 PT검사를 통하여 배관 내부의 균열이 하나가 아닌 일정한 범위 안에 하나 이상의 크랙이 존재하여 열화상 이미지 상에 넓은 범위의 hot spot 이미지를 만들어 냈음을 파악할 수 있었다. 또한 기존 기술로 검출이 용이하지 못한 마이크로 폭의 미세균열을 검출할 수 있었다. 또한, 초음파탐상기술은 $10\;{\mu}m$ 미세크랙의 폭을 갖은 균열을 쉽게 검출하지 못하였다. 그러나 초음파 적외선 열화상 기술은 결함 검출하였다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.331-336
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• 2004

Dissimilar friction welding were produced using 10mm and 11mm diameter solid bar in Inconel ally(IN X-750) to Stainless steel(STS316L) to investigate their mechanical properties. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Virkers hardness surveys of the bond of area and HAZ and macro-structure investigations. The specimens were tested as welded, not heat-treated. The tensile strength of the friction welded steel bars was increased up to $95\%$ of the STS316L base metal under the condition of all heating time. Optimal welding conditions were n=2,000(rpm), $P_1=220(MPa),\;P_2=260(MPa),\;t_1=4(s),\;t_2=4(s)$ when the total upset length is 7(mm).

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.77-82
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• 1999

The compleete joining method for dissimilar hot die punch materials and its real-time evaluation method are not available at present. Brazing method has been used for joining them, but it is known that the welded joint by the brazing has the lower bonding efficiency and reliability than the diffusion welding. The friction wleding with a diffusion mechanism in bonding was applied in this study. So, this work was carried out to determine the optimal friction welding conditions and to analyze mechanical properties of friction welded joints of hot die punch materials (STD61 for the blade part of hot die punch) to alloy steel (SCM440 for the shank park of hot die punch) such as plunger. In addition, acoustic emission test was carried out during friction welding to evaluate the weld quality.

• 비파괴검사학회지
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• 제35권4호
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• pp.268-274
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• 2015

용접 오버레이법은 1980년 초반에 배관 용접부 결함의 임시 보수방법으로 미국발전소에 처음 사용되었다. 원자력발전소의 배관 오버레이 용접부는 초음파검사 기술을 이용하여 주기적으로 검사되어야 한다. 최근 위상배열 초음파 기술 발달로 휴대하기 좋은 소형 장비를 이용할 수 있게 되었다. 현재, 완화기법 및 또는 복잡한 형상의 검사체의 표면검사 조건을 개선하기 위한 선제적인 용접 오버레이 기법 적용이 일반적으로 사용되고 있다. 복합적인 형상(용접 오버레이, 기존 용접부 및 모재)의 적당한 검사를 위해서는 여러 개의 일반 초음파검사용 초점 탐촉자들이 필요하게 된다. 대안으로 위상배열 초음파 탐촉자는 일반 초음파검사 탐촉자와 비교하여 더 좋고 빠른 커버리지를 제공하기 위해 다양한 초점거리에서 여러 검사 각도를 동시에 발생시킬 수 있다. 그래서, 이 기술은 검사 속도 증가, 비용 절감, 방사선 피폭을 줄일 수 있다. 이 논문에서는 현장검사에서 검출된 PAUT 신호에 대한 신호 분석 결과를 설명하였다.

• 한국해양공학회지
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• 제2권2호
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• pp.112-121
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• 1988

A study on friction welding of carbon steel bar (SM45C) to chrome molybedenum steel bar(SCM4) is examined experimentally through tensile test, hardness test, microstructure test and fatigue test. so, this paper deals with optimizing the welding concitions and analyzing various mechanical properties about friction welds of SM45C to SCM4 steel bars. The results obtained are summarized as follows; 1) For friction welded joints of SM45C to SCM4 steel bars, the total upset(U)increases linearly with an increase of heating time ($t_{1}$) till 6s. 2) The determined optimum welding conditions are heating time ($t_{1}$)2s, upsetting time($t_{2}$), 3s, heating pressure($p_{1}$), 4kgf/$mm^{2}$(39.2MPa), upsetting pressure($p_{2}$, 8kgf/mm$^{2}$(78.4MPa) and rotating speed(N), 2, 000rpm when the total upset(U) is 3.4mm, resulting in a computed relationship between the joint tensile strength .sigma.$_{t}$ (kgf/mm$^{2}$and the total upset U(mm); .sigma.$_{t}$ =$0.21U^{3}$ - $3.38U^{2}$ +17.03U + 66.00 3) As the elongation is increased more and more, the fracture position becomes away from weld interface and the fractures are similar to those of SM45C. Fracture is taken place on SM45C side. 4) The weld interface of two dissimilar materials is mixed strongly, and the heat affected zone is about 2.0mm at SM45C while about 2.7 mm at SCM4 side. Therefore, the welded zone and heat affected zone are very narrow, comparing with those of the joints welded by the other welding methods. 5) The fatigue strengths at N=10$^{6}$ cycles of SM45C, SCM4 and friction welded joints are 23kgf/$mm^{2}$, 33kgf/$mm^{2}$(220.5 MPa), and 22.5kgf/$mm^{2}$(220.5MPa) respectively, and fracture at friction welded joint takes place at the side of SM45C. 6) The hardness of the friction weld interface is 3 times higher than that of base metal. 7) Fatigue strength of friction welded joint is higher than that of base metal. 8) Notch sensitivity factor of friction welded joint is lower than that of base metal.

• Journal of Welding and Joining
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• 제31권2호
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• pp.16-20
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• 2013

Titanium and its alloys have been widely using in the various field of industry application due to high corrosion resistant properties and mechanical properties. Titanium is highly reactive in the high temperature state and the formation of titanium oxide and porosities in the nuggets of fusion welding will results in the degradation of the mechanical properties. For this reason the studies of friction stir welding for titanium have been investigated recently. The FSW zones of titanium were classified by the weld nugget (WN), the linear transition boundary (TB) and the heat affected zone (HAZ). The WN along with titanium parent was characterized by the presence of twins and dislocations. The average grain size and hardness of WN has been changed according to heat input. The grain refinement resulted from the FSW increased the hardness in the stir zone. Sound dissimilar joints between SUS 304 and CP-Ti were achieved using an advancing speed of 50 mm/min and rotation speeds in the range of 700-1100 rpm. Aluminum 1060 and titanium alloy Ti-6Al-4V plates were lap joined by friction stir welding, hence the ultimate tensile shear strength of joint reached 100% of Al 1060. Mg alloy and Ti were successfully butt joined by inserting a probe into the Mg alloy plate with slightly offsetting. But Ti-Al intermetallic compound layers formed at the interface of these joints.

• 대한기계학회논문집A
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• 제24권2호
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• pp.438-448
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• 2000

Mechanical press joining technique has been used in sheet metal joining processes because of its simple process and possibility of joining dissimiliar metals, such as steel and aluminum. The static and cyclic behavior of single overlap AI-alloy and steel(SPCC) joints has been investigate. Relationships were developed to estimate the strength of the joint taking into consideration base metal strength properties and the geometry of the joint. Fatigue test results have shown that fatigue resistance of the SPCC mechanical press joints is almost equal to that of the spot weld at the life of $10^6$ cycles. Also, the dissimilar material jointed specimen with upper SPCC plate and button diameter corresponding to the nugget diameter of the spot welded specimen has almost same strength as the same material jointed specimen and as the spot welded specimen.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.101-108
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• 2000

In this paper, the real-time prediction of high temperature creep life was carried out for the friction welded joints of dissimilar heat resisting steels(SUH3-SUH35). Various life prediction methods such as LMP(Larson-Miller Parameter) and ISM(initial strain method) were applied : The creep behaviors of those steels and the welds under static load were examined by ISM combined with LMP at 500, 600 and $700^{\circ}C$, and the relationship between these two methods was investigated. A real-time creep life( $t_{r}$ , hr) prediction equation by initial strain($\varepsilon$$_{0}$ , %) under any creep stress ($\sigma$, MPa) at any high temperature(T, K) was developed as follows : $t_{r}$ =$\alpha$$\varepsilon$$_{0}$ $^{\beta}$$\sigma$$^{1}$ where, (equation omitted) for SUH3-SUH35 friction weld of =16mm and =20mm, respectively.

• 한국정밀공학회지
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• 제19권5호
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• pp.43-50
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• 2002

Friction welding has many merits such as energy efficiency, simple processing, etc butt difficult to obtain good weld at the welded interface and heat affected zone. To date, the continuum mechanics and fracture mechanics are utilized to analyse stresses at the interface and propagation of cracks. In this study. STS304 and SM15C are selected because they can be differentiated distinctively from metallic point of view and crack can be observed easily. It is ovserved during friction welding that STS304, rotary part is hatter than SH15C, fixed part. The last fracture occurs around the center because the surface of fatigue fracture has smooth regions, due to the separation phenomenon in plastic flows layers and striation dimple pattern.

• 동력기계공학회지
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• 제4권4호
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• pp.54-58
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• 2000

The complete joining method for dissimilar hot die punch materials and its real-time evaluation method are not available at present. Brazing method has been used for joining them, but it is known that the welded joint by the brazing has the lower bonding efficiency and reliability than the diffusion welding. The friction welding with a diffusion mechanism in bonding was applied in this study. So, this work was carried out to determine the optimal friction welding conditions and to analyze mechanical properties of friction welded joints of hot die punch materials (STD61 for the blade part of hot die punch) to alloy steel (SCM440 for the shank part of hot die punch) such as plunger. In addition, acoustic emission test was carried out during friction welding to evaluate the weld quality.