• Journal of Welding and Joining
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• 제24권1호
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• pp.71-76
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• 2006

In this study, the microstructure and mechanical properties of spot friction stir welded A 5052 alloy were investigated. Especially, the effect of insertion depth of welding tool on microstructural changes and mechanical properties was investigated in order to obtain the optimum spot friction stir welding condition. The lap shear load of spot friction stir welded A 5052 alloy plates showed lower value at the shallowest insertion depth and increased with tool insertion depth. At 1.6mm, the maximum value of 3.35 kN was obtained, and then dropped to lower load when the insertion depth was deeper. Spot friction stir welded joints showed shear fracture mode at shallower insertion depths and fracture mode changed to plug fracture mode as the insertion depth was deeper.

• 대한기계학회논문집A
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• 제24권3호
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• pp.743-751
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• 2000

Because welding residual stress is formidable result in electric resistance spot welding process, and it detrimentally affect to fatigue crack initiation and growth at nugget edge of spot welded la p joints, it should be considered in fatigue analysis. Thus, accurate prediction of residual stress is very important. In this study, nonlinear finite element analysis on welding residual stress generated in process of the spot welding was conducted, and their results were compared with experimental data measured by X-ray diffraction method. By using their results, the maximum principal stress considered welding residual stress at nugget edge of the spot welded lap joint subjected to tension-shear load was calculated by superposition method. And, the $\Delta$P- $N_f$ relations obtained through fatigue, tests on the IB-type spot welded lap joints was systematically rearranged with the maximum principal stress considered welding residual stress. From the results, it was found th2at fatigue strength of the IB-type spot welded lap joints could be systematically and more reasonably rearranged by the maximum principal stress($\sigma$1max-res considered welding residual stress at nugget edge of the spot welding point.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1997년도 추계학술대회 논문집
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• pp.127-131
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• 1997

In systematic and orderly estimation of fatigue strength of the spot welded lap joints, because the influence of residual stress of fatigue crach initiation and growth is not negligible, there need to estimate fatigue strength considered residual stress at near spot weld part of the lap joints. Therefore, in this thesis, peformed stress distribution and residual stress analysis at near the spot weld part by F.E.M and X-ray diffraction method, and obtained the maximum principal stress considered residual stress at nugget edge by superposing residual stress at nugget edge by superposing their results. From the results obtained above, we could find that fatigue strength of the IB-type spot welded lap joints was rearranged by the maximum principal stress considered residual stress at nugget edge and was entirely low about 13 percents compare with that neglected residual stress.

• 마이크로전자및패키징학회지
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• 제6권3호
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• pp.45-50
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• 1999

동(CU)은 전기전자부품에 널리 사용되어 왔는데, 특히 점 저항용접된 동은 콘덴서나 저항의 리드부분에 사용되고 있다. 그러나 일반적으로 동은 전기 저항이 낮아 저항용접이 어렵다. 본 연구에서는 동의 점 용접성을 개선하기 위하여, 상대적으로 전기 저항이 높은 Sn-37%Pb 솔더를 동 표면에 도금하였다. 실험변수로, 가 압력은 100kgf에서 200kgf, 용접시간은 20ms에서 50ms, 용접전류는 100A에서 2500A까지 변화시켰다. 실험결과, 솔더 도금된 동박판은 용접전류 400~2200A, 가압력 100~200kgf, 용접시간 20~50ms범위에서 저항용접이 가능하였다. 점 용접부의 인장전단 강도는 임계 전류값까지는 용접전류가 증가함에 따라 증가하고, 임계 전류값 이후부터는 용접전류에 따라 인장전단 강도가 감소하였다.

• International Journal of Automotive Technology
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• 제7권3호
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• pp.353-360
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• 2006

The nominal structural stress calculation method proposed by Radaj has included some problems as follows: (a) How the value of the diameter D is decided in the method; (b) It is not possible to estimate nominal structural stress of the spot welded joints with the balanced sheet in-plane load that no general loads are obtained by FE shell analysis. In this paper, the new method for calculating nominal structural stress was proposed to solve above-mentioned problems. The proposed method calculates the nominal structural stress through the circular plate theory in theory of elasticity. This theoretical analysis uses not only general loads but also nodal displacements around spot welding provided by FE shell analysis as boundary condition. Fatigue test data of various spot-welded joints could be arranged in a narrow bandwidth on S-N chart using the nominal structural stresses calculated by proposed method. The fatigue life prediction method using the proposed method for calculating nominal structural stress is useful for the prior evaluation technique that can predict the fatigue life of spot welding by CAE.

• Journal of Mechanical Science and Technology
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• 제14권11호
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• pp.1187-1197
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• 2000

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2002년도 춘계공동학술발표회요약집
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• pp.212.2-212
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• 2002

• 한국기계가공학회지
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• 제6권1호
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• pp.20-26
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• 2007

In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.

• 대한기계학회논문집A
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• 제29권11호
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• pp.1488-1493
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• 2005

In this study, fatigue tests to obtain S-N curves and FE analyses to obtain structural stress concentration factors were conducted for the two types of cruciform fillet welded joints, that is, load-carrying and non load-carrying types. Then we changed the obtained S-N curve of load carrying joint to that based on hot spot stress. As a result, the S-N curve of load carrying joint based on hot-spot stress was almost exactly coincided with that of non load-carrying joint based on nominal stress. So we have conducted that the fatigue strength of a welded joint with different geometry from the non stress distribution along the expected crack path.

• 한국생산제조학회지
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• 제6권4호
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• pp.27-33
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• 1997

Spot welding has been used in the sheet metal jointing processes because of its high productivity and convenience. In this study, effects of welding conditions on the fatigue life and prediction methods of fatigue life of spot welded joint have been studded . Fatigue life was estimated by stress index parameter considering multiaxial stresses. Fatigue tests were conducted with the tensile-shear specimens using SPCC. Fatigue life of spot welded joint was influenced by welding currents and was predicted exactly with taking into account StageIII.