• 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.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.396-398
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• 2005

At present, fatigue design of welded structures is primarily based on nominal stress or hot spot stress approach with a series of classified weld S-N curves. However, these methods are known to possess drawbacks, such as difficulty associated with defining proper nominal stress and the finite element sue sensitivity etc. Recently, a mesh-size insensitive structural stress definition is proposed by Battelle that gives a stress state at weld toe with relatively large mesh size. The structural stress definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of weld toe. As an experimental validation of the structural stress method in obtaining the fatigue strength of weldments, a series of experiment is carried out for various sizes of weldments. Based on the result from this study, it is expected to develop a more precise fatigue strength evaluation technique and to save time period required in the fatigue design of ship and offshore structures.

• Structural Engineering and Mechanics
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• 제19권3호
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• pp.261-279
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• 2005

The hot spot stress approach is usually adopted in the fatigue design and analysis of tubular welded joints. To apply the hot spot stress approach for fatigue evaluation of long span suspension bridges, the FEM is used to determine the hot spot stress of critical fatigue location. Using the local finite element models of the Tsing Ma Bridge, typical joints are developed and the stress concentration factors are determined. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. A comparison is made between the nominal stress approach and the hot spot stress approach for fatigue life evaluation of the Tsing Ma Bridge. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.

• 한국강구조학회 논문집
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• 제11권4호통권41호
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• pp.397-407
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• 1999

본 연구는 공칭응력 및 변동응력을 이용한 현수교 횡프레임의 피로안전성 평가를 위하여 수행되었으며, 본 논문에서는 해석모델의 모형화 방법 및 공칭응력을 이용한 피로안전성 평가를 주요 내용으로 다루었다. 본 연구의 목적에 부합되는 해석모형을 도출 하고자 해석모형의 지지조건에 따른 영향, 평면해석과 입체해석간의 구조해석 결과의 차이 및 모형화되는 횡프레임 수의 영향에 대해서 검토하였다. DB-24하중을 피로조사하중으로 이용하였으며, 단일트럭하중에 의한 발생응력을 조합하여 실교통류 흐름의 효과를 고려하였다. 피로검토대상 구조상세에 대해 산출된 공칭응력을 국내 및 국외의 피로등급과 비교하고 그 결과에 대해 고찰하였다.

• 대한조선학회논문집
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• 제42권2호
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• pp.129-135
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• 2005

At present, fatigue design of welded structures is primarily based on a nominal stress or hot spot stress approach with a series of classified weld S-N curves. Although well accepted by major industries, the nominal stress based fatigue design approach is cumbersome in terms of securing a series of S-N curves corresponding to each class of joint types and loading modes. The hot spot stress based fatigue design has a difficulty of finding a proper stress through the global model, the midium size model, and the detail model of ship structure. Also, it is difficult to link proper displacements within three different mesh size models. Recently, the structural stress is proposed as a mesh-size insensitive structural stress definition that gives a stress state at weld toe with relatively large mesh size. However, this method requires an experimental validation in obtaining the fatigue strength of weldments. Therefore, in this study, a series of experiment is performed for various sizes of weldments.

• 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.

• 한국해양공학회지
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• 제35권2호
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• pp.161-171
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• 2021

For the fatigue design of offshore structures, it is essential to understand and use the S-N curves specified in various industry standards and codes. This study compared the characteristics of the S-N curves for five major codes. The codes reviewed in this paper were DNV Classification Rules (DNV GL, 2016), ABS Classification Rules (ABS, 2003), British Standards (BSI, 2015), International Welding Association Standards (IIW, 2008), and European Standards (BSI, 2005). Types of stress, such as nominal stress, hot-spot stress, and effective notch stress, were analyzed according to the code. The basic shape of the S-N curve for each code was analyzed. A review of the survival probability of the basic design S-N curve for each code was performed. Finally, the impact on the conservatism of the design was analyzed by comparing the S-N curves of three grades D, E, and F by the five codes. The results presented in this paper are considered to be a good guideline for the fatigue design of offshore structures because the S-N curves of the five most-used codes were analyzed in depth.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.267-269
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• 2004

현재 구조물의 피로설계에는 주로 공칭응력(Nominal Stress) 및 핫스팟 응력(Hot Spot Stress, HSS)이 사용되고 있다. 공칭응력을 바탕으로 구조물에 대한 피로설계를 할 경우에는 각 부재에 사용되는 각각의 용접부 형상에 대한 피로시험을 따로 수행하여 피로수명 곡선을 구해야 하는 번거로움이 있다. (중략)

• 한국구조물진단유지관리공학회 논문집
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• 제15권5호
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• pp.101-112
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• 2011

본 논문은 중간부 부착파괴된 CFRP 보강 RC 보의 휨강도 산정을 다루고 있다. CFRP 보강 RC 보의 중간부 부착파괴의 영향을 고려하기 위해 강도감소계수를 제안하였다. 제안된 계수는 CFRP의 유효응력(또는 유효변형률)과 극한응력(또는 극한변형률)비로 정의 되는 유효변률 모델을 이용하여 실험데이터로부터 유도하였다. 휨강도 산정식은 강도감소계수를 변수로 하여 함수를 구성하였다. 제안된 강도감소계수의 유효성, 정확성 및 타당성을 입증하기 위해서 각국의 설계기준 및 연구자들에 의해 제안된 계수 값과 실험값을 본 연구결과와 비교 및 검증했다. 본 논문에서 제시하는 해석 결과는 제안된 강도감소계수가 중간부 부착파괴된 CFRP 보강 RC 보의 휨강도를 매우 효율적으로 평가할 수 있음을 나타낸다.

• 한국안전학회지
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• 제6권1호
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• pp.5-13
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• 1991

Fail-safe design of machine elements or structural members is very aim of the whole mankind. Fracture occurs generally from cracks that exist originally or produced from flaws. The most important job we have to do is to make stopping or decreasing the crack growth rate. For fail-safe design variable thickness plates have been used as structural members in practical engineering services. In this paper, optimum design of CT type plate with varlng thickness is studied with the theoritical analysis. The theoritical analysis was based on the stress concentration and nominal stress analysis. From the study, the optimum design curve was determined for use of designing of such structures using the computer analysis program of optimum design.