• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.214-221
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• 1999

Spot welding is very important and useful technology in fabriaction of the thin sheet structure such as the automobile, train and air craft, Because fatigue strength of the spot welding point is however considerably lower than base metal due to stress concentration at the nugget edge, reasonable fatigue strength evaluation of spot welded lap joint is very important to estimate the reliability and durability of th spot welded structure and to establish a criterion of ling life fatigue design. For reasonalbe fatigue strength evaluation, it is necessary to estimate the fatigue strength of spot welded lap joints, systematically. So far, many investigators have numerically and experimentally studied on the systematic fatigue strength estimation for various spot welded lap joints, and the methods suggested has been considerably accumulated. By the way, for applying them in practical fatigue design of the thin sheet structure fabricated by spot welding ,it is also necessary to verify their efficiency and reliability on the predicted results, Therefore, in this study, a statistical fatigue strength estimation method for spot welded lap joints was developed by using the Weibull probability distribution function. From the result, it was found that fatigue strength and fatigue life of the spot welded lap joints having various dimension were able to be statically predicted . And also, a reliable criterion for long life fatigue design of the spot welded lap joint could be established.

• Journal of Welding and Joining
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• v.19 no.2
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• pp.215-220
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• 2001

In the T-joint welding, the complete penetration joint which is obtained by groove welding with edge preparation is generally required thor the safety and reliability of structures but this way have the some defects such as increase of working time, consumed welding electrode quantity and large welding deformation. If there is no probrem, in the strength, T-joint welding without edge preparation will be profitably understood in the economical and welding deformation side. In this paper, we performed the finite element analysis to understand the characteristics of welding residual stresses on two models, complete penetration joint have the edge preparation and incomplete penetration joint without edge preparation, respectively. Especially, we observed the relation between welding residual stress distributed on the notch of gap in the root and external force in the incomplete penetration joint without edge preparation.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.88-90
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• 2005

• Steel and Composite Structures
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• v.18 no.1
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• pp.135-148
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• 2015

The cutout hole locating at the place of rib-to-diaphragm welded connection is adopted to minimize the restraint, which is caused by the floor-beam web to rib rotation at the support due to the unsymmetrical loads in orthotropic deck. In practice, an inevitable problem is that there is a large number of welding joint's cracks formed at the edge of cutout hole. In this study, a comparative experiment is carried out with two types of cutout hole, the circular arc transition and the vertical transition. The fatigue life estimation of specimens is investigated with the application of the structural hot spot stress approach by finite element analyses. The results are compared with the ones of the fatigue tests which are carried out on these full-scale specimens. Factors affecting the stress range are also studied.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.644-652
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• 2002

Increasing demands for Electric Resistance Welded pipes of high quality with thick wall require c lose investigations in edge deformation by slitting, strip deformation during break down farming, and difference of circumferential length. In order to obtain good quality of a welding zone, it is necessary to predict the edge shape of the initial strip. The modeling of the multi-pass thick tube roll forming process with rigid plastic finite element method ultra the edge shape prediction of an initial strip with 2nd-degree polynomial regression method are presented. Edge shapes of initial strip have been analyzed by the finite element method and designed by the regression method to satisfy the requirements in target fin pass. It is concluded that the proposed edge design method results in optimal edge shapes sat string the design requirements.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1115-1120
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• 2003

The recent tendency in the automobile industries is toward light weighting vehicle body to improve the problems by environmental pollution as well as improving fuel cost. The effective way to reduce the weight of vehicle body seems to be application of new materials for body structure and such trend is remarkable. Among the various materials for vehicle body, stainless steel sheet (for example, 301L and 304L), TRIP steel and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life design criteria of body structure, it is important and require condition to assess spot weldability of them and fatigue strength of spot welded lap joints which were fabricated under optimized spot welding condition. And, recently, a new issue in the design of the spot welded structure is to predict economically fatigue design criterion without additional fatigue tests. In general, for fatigue design of the spot-welded thin sheet structure, additional fatigue tests according to the welding condition, material, joint type, and fatigue loading condition are generally required. This indicates that much cost and time for it should be consumed. Therefore, in this paper, the maximum stresses at nugget edge of spot weld were calculated through nonlinear finite element analysis first. And next, obtained the ${\Delta}P-N_{f}$ relation through the actual fatigue tests on spot welded lap joints of similar and dissimilar high strength steel sheets. And then, the ${\Delta}P-N_{f}$ relation was rearranged in the ${\Delta}{\sigma}-N_{f}$ relation. From this ${\Delta}{\sigma}-N_{f}$ relation, developed the fatigue design technology for spot welded lap joints of them welded using the optimized welding conditions.

• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.487-494
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• 2000

This paper intends to propose design information with the result or comparing the deformation capacity with different panel stiffness specimens and estimating the plastic deformation capacity, toughness and strength of welded joint connection according to the different scallop types. The test results of the beam to column unit structure are as follow: the non-scalloped and the low stiffness panel specimen have more desirable result values than the scalloped and the high stiffness one in plastic deformation. Comparing the scallop types shows very unlikely tendency as follows, second cracking occurs at the very edge of scallop in the scalloped specimen otherwise cracking occurs bond area of welded beam flange in the non-scalloped one.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.242-249
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• 1999

Spot welding is very important and useful technology in fabrication of an automobile body structure. Because fatigue strength of the spot welding point is however considerably lower than parent metal due to stress concentration at the nugget edge, accurate stress analysis and fatigue stength evaluation of spot welded lap joint are very important to valuate the reliability and durability of automobile body structure and to establish a criterion of long life fatigue design. Many invetigators have studied so far onsystematic fatigue strength evaluation with various methods. It is however necessary to verify their reliability and abailability for practical application to fatigue design of spot welded structure, Thus,in this study, fatigue strength evaluation methods of spot welded lap joint. which are the maximum principal stress method. the fracture and availability with the Weibull probability distribution. From the results, it was found that reliability and availability withe the Weibull probaility distribution. From the results, it was found that reliability and availability of the suggest fatigue strength estimation methods methods were higher than $\Delta$P-$N_f$ relation. However, among them , reliability of the maximum pricipal stress method was the highest.

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.106-113
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• 2004

Recently, a new issue in designing spot welded structures such as automobile and train car bodies is to predict an economical fatigue design criterion. One of the most typical and traditional methods is to use a ΔP-N$\sub$f/ curve. However, since the fatigue data on the ΔP-N$\sub$f/ curve vary according to the welding conditions, materials, geometry of joint and fatigue loading conditions, it is necessary to perform the additional fatigue tests for determining a new fatigue design criterion of spot-welded lap joint having specific dimension and geometry. In this study, the stress distributions around spot welds of various spot welded lap joints such as in-plane bending type (IB type), tension shea. type (TS type) and cross tension type (CT type) were numerically analyzed. Using these results, the ΔP-N$\sub$f/ curves Previously obtained from the fatigue tests for each type were rearranged into the Δ$\sigma$-N$\sub$f/ relations with the maximum stresses at the nugget edge of the spot weld.

• Journal of Welding and Joining
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• v.7 no.1
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• pp.28-35
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• 1989

The fatigue crack growth behavior in GTA butt welded joints of Al-Alloy 5052-H38 was examined using Single Edge Notched(SEN) specimens. It is well known that welding residual stress has marked influence on fatigue crack growth rate in welded structure. In the general area of fatigue crack growth in the presence of residual stress, it is noted that the correction of stress intensity factor (K) to account for residual stress is important for the determination of both stress intensity factor range(.DELTA.K) and stress ratio(R) during a loading cycle. The crack growth rate(da/dN) in welded joints were correlated with the effective stress intensity factor range(.DELTA.Keff) which was estimated by superposition of the respective stress intensity factors for the residual stress field and for the applied stress. However, redistribution of residual stress occurs during crack growth and its effect is not negligible. In this study, fatigue crack growth characteristics of the welded joints were examined by using superposition of redistributed residual stress and discussed in comparison with the results of the initial welding residual stress superposition.