• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 추계학술대회 논문집
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• pp.560-567
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• 1998

The pitch of spot-weld is a important variable in a view of both production cost and strength of car-body. Various renditions for the selection of pitches have been researched and especially in this paper the buckling analysis is carried out for the 2-sheet pannel structures. The optimal pitch is obtained by optimization program and FEM, which can enhance the buckling strength.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1994년도 특별강연 및 춘계학술발표 개요집
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• pp.199-201
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• 1994

• 대한기계학회논문집A
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• 제34권10호
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• pp.1367-1375
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• 2010

본 연구에서는 핫스템핑 소재로 사용되는 보론합금강판 22MnB5의 단일 겹치기 점용접에서 용접부의 강도 향상을 위한 최적화를 수행하였다. 최적화 과정은 다구찌 실험계획법에 의해 행해졌으며 공정변수는 전류, 가압력 및 통전시간으로 선정하였고, 잡음인자로서 핫스템핑 시 소재의 가열온도와 유지시간을 고려하였다. 가열조건에 따라 22MnB5 표면의 알루미늄 도금층과 모재 간의 확산반응에 의해 화합물층 두께에 산포가 발생하였으며 이러한 산포는 너겟의 형성에 영향을 미치는 것을 알 수 있었다. 한편 용접부의 인장전단강도를 목적함수로 하였을 때, 이러한 가열조건에 강건한 최적의 용접 조건은 전류 8kA, 가압력 4kN, 통전시간 18cycle로 선정되었다. 최적 조건의 검증 결과 용접부의 인장전단강도 는 32kN으로서 요구되는 규격인 23kN보다 크게 증가되었다.

• Journal of Welding and Joining
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• 제32권5호
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• pp.44-49
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• 2014

The effect of weldbond hybrid joining process on the mechanical behavior of single lap and L-tensile joints was investigated for the newly developed 1.2GPa grade ultra high strength TRIP(transformation induced plasticity) steel. In the case of single lap shear behavior, the weldbond joint of 1.2GPa TRIP steel showed lower maximum tensile load and elongation than that of the adhesive bonding only. It was considered to be due to the reduction of real adhesion area, which was caused by the degradation of adhesive near the spot weld, and the brittle fracture behavior of the spot weld joint. In the case of L-tensile behavior, however, the maximum tensile load of the weldbond joint of 1.2GPa TRIP steel was dramatically increased and the fracture mode was change to the base metal fracture which is desirable for the spot weld joint. These synergic effect of the weldbond hybrid joining process in 1.2GPa TRIP steel was considered to be due to the stress dissipation around the spot weld joint by the presence of adhesive which resulted in the change of crack propagation path.

• 연구논문집
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• 통권34호
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• pp.59-68
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• 2004

The hot spot stress approach and the notch strain approach are discussed with some results of them. And a stress model that can be applicable to several types of weld joints with single S-N curve of the base material. The stress model uses the geometric characteristics of the stress distribution vicinity of weld joints. The model was applied to five different weld joins(the base material is SM490B). By the representative stress, the experimental fatigue data are plotted very closely to the S-N curve of the base material.

• Journal of Welding and Joining
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• 제24권2호
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• pp.42-47
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• 2006

While it is known that the weld toe grinding method may give 3.4 times of fatigue strength improvement, this improvement may significantly vary according to weld bead shapes and loading modes. Although tremendous interest have been given in improving fatigue strength improvement for ship structures, quantitative results are yet in need. In this context, a series of fatigue tests is carried out for a type of test specimen that are typically found in ship structures. Weld burr grinding is carried out using a electric grinder in order to remove surface defects and improve the weld bead profile. The test results are compared with the same type of test specimen without applying the fatigue improvement technique in order to obtain a quantitative measure of the fatigue strength improvement. On the other hand, both hot spot stress and structural stress methods are employed to compare the effectiveness of the two methods in evaluating the fatigue strength improvement of welded structures.

• Journal of Welding and Joining
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• 제32권1호
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• pp.79-86
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• 2014

The purpose of this study is to determine the proper fillet weld size for the stiffeners on hull bottom plate of crude oil tanker. To achieve it, the effective notch stress and hot spot stress of the fillet weld with leg length specified in the rule were evaluated by using comprehensive FE analyses. Based on the results, the fatigue damages at each location of weld were calculated. Meanwhile the transitional behavior of initial welding distortion in the hull bottom plate under the design conditions was investigated by using a non-linear FEA. Welding distortion and residual stress introduced during fabrication process were considered as initial imperfections. According to FE analysis results, if the fillet leg length satisfies the design criteria of the classification society, the concern on the root failure at the fillet welds in the bottom hull plate during the design life can be negligible. In addition, considering the transitional behavior of the distortion during the service life, the fillet leg length should be minimized.

• 대한기계학회논문집
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• 제17권2호
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• pp.393-406
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• 1993

In resistance spot welding process, size of molten nuggest have been utilized to assess the integrity of the weld quality. However real-time monitoring of the nugget size is an extremely difficult problem. This paper describes the design of an artificial neural networks(ANN) estimator to predict the nugget size for on-line use of weld quality monitoring. The main task of the ANN estimator is to realize the mapping characteristics from the sampled dynamic resistance signal to the actual negget size through training. The structure of the ANN estimator including the number of hidden layers and nodes in a layer is determined by an estimation error analysis. A series of welding experiments are performed to assess the performance of the ANN estimator. The results are quite promissing in that real-time estimation of the invisible nugget size can be achieved by analyzing the dynamic resistance signal without any conventional destructive testing of welds.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.82-88
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• 2002

Simulation systems allow a close inspection of the relation between welding parameters and the resulting weld seam. These systems are very useful in education of weld staff as well as production and planning. In training the influence of variations of parameters can be investigated without the need for real welding experiments. In the design phase requirements of the welding process can be taken into account without several iteration cycles. By estimating a good parameter set for the given welding task the set up phase for a new production cycle can be reduced

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.113-120
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• 2002

The effect of out-of-plane loads on the fatigue strength of welded steel structures is examined through fatigue tests with weldment of two fillet weld joint types. The results of the fatigue tests are compared with those under axial loads, on the basis of the hot spot stress range at the weld toe. From the result of the comparison, a method on how to incorporate the effect of the out-of-plane bending stress is proposed using design S-N curves derived from fatigue tests under the axial load. The proposed method is useful for rational assessment of the fatigue strength of fillet-welded structures, where combined stresses of the in-plane axial stress and the out-of-plane bending stress are induced simultaneously due to the complexity of applied loads and structural geometry.