• 대한기계학회논문집A
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• 제28권9호
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• pp.1328-1336
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt-welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.108-113
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• 2004

According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt~welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.298-303
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• 1998

Most of mechanical structures are combined of substructures such as beam and/or plates. There are few system with unibody structures but are not a few systems with united body structures. Generally the dynamic analysis of whole structures is perform ed under alternating load. However, the analysis of each joint area is more important than others for zero severity. This paper presents the results of analysis of concentration stress in bolt jointed structure with variable preload. At frist, a static vibration test was performed to find out a nominal stress of bolt joint ed plates from the relationship between natural frequency and nominal stress. Then a concentration stress was computed at contact point between bolt and plate in the structure. It is believed that the proposed method has promising implications for safer design with fatigue quality index of stress concentration factor and has merit for cost down and saving time at the beginning of vehicle development.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.249-251
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• 2004

According to our fatigue tests carried out at 20 ㎐, R=0.1 on transversely butt-welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short hie range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.305-313
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• 2010

HDPE smooth and textured GMs were cut into dumbbell shape and notched where depth of the notch produced a ligament thickness of 90% to 10% of the nominal thickness of the specimen at 10% interval. Yield stress and elongation were measured of those samples and plotted on Graph. Yield stress and elongation at yield point decreases gradually as the notch depth is increased. Both installations damaged and notched GMs were used to understand stress crack behavior. Intact sample were notched in such a manner that the depth of notch produced a ligament thickness of 80% of the nominal thickness of the specimen. Installation damaged samples were not notched. Stress Crack Resistance behavior was observed using NCTL Test at $50{\pm}1^{\circ}C$ at different yield stresses immerging with pH 4 and pH 12 buffer solutions. Significant difference was observed in both cases.

• 터널과지하공간
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• 제30권6호
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• pp.551-558
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• 2020

기존 시험법은 암석시편의 절리면 직접전단시험시 겉보기 면적의 변화를 고려해야 한다고 명시하고 있다. 본 기술보고는 암석코어 시편의 절리면 직접전단시험시 겉보기 면적 계산방법을 제시하였다. 암석코어 시편의 초기 절리면을 타원으로 가정하고, 타원의 중첩면적 감소를 계산하는 수식을 정리하였다. 전단변위와 겉보기 면적을 정규화하면 타원형상에 관계없이 일정한 변화 비율을 가지는 것을 확인하였다. 암석코어 시편 전단시험을 위한 정규화 실험상수를 제안하여 일반화된 계산방법을 제안하였다. 그 방법을 실제 전단시험의 데이터에 적용하여 결과 변화값을 확인하고, 정확도에 대해 간략히 토의하였다.

• 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.

• 콘크리트학회논문집
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• 제14권1호
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• pp.24-32
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• 2002

전단문제에서는 일부 설계기준(AASHTO 1994)에 이미 수정압축장이론이 도입되었다. 그리고 현행 콘크리트 설계기준에는 콘크리트의 전단강도가 철근의 전단강도와 합하여 공칭전단강도를 계산하고 있다. 그러나 최근에 개정된 콘크리트설계기준에는 콘크리트의 비틀림강도가 공칭비틀림강도 계산에서 누락되었다. 콘크리트의 인장응력은 비록 크기가 작으나 균열후에 균열사이의 콘크리트에 존재한다. 그러나 휨과 비틀림문제에서는 균열 후 콘크리트의 인장강성은 생략되고 있다. 역학적으로 콘크리트보의 비틀림거동은 전단거동과 매우 유사하다. 그러므로 균열 후 콘크리트의 비틀림강도를 철근콘크리트 보의 공칭비틀림강도의 계산에 포함시켜야 한다. 본 논문에서는 콘크리트의 평균주인장응력이 이루는 콘크리트의 비틀림강도를 횡방향 비틀림철근의 비틀림강도와 함께 공칭비틀림강도를 구성함을 밝혔으며, 이의 타당성을 검증하기 위해 개정 전후의 ACI 의 설계기준에 의한 공칭비틀림강도와 함께 실험값과 비교하였다. 그 결과 본 논문이 제안한 모델에 의한 공칭비틀림강도가 가장 좋은 결과를 보였다.

• Composites Research
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• 제31권5호
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• pp.177-185
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• 2018

섬유금속적층판은 금속과 섬유 강화 복합소재를 함께 적층한 하이브리드 재료 중 하나다. 섬유금속적층판은 계면의 접착층이 파괴되는 층간분리 현상이 발생할 수 있기 때문에 계면의 접착층에 대한 한계응력과 에너지 해방률을 실험적으로 도출해야만 한다. 하지만, 온도에 따른 에너지 해방률을 실험적으로 도출하는 과정에서 측정 장비의 사용 온도에 대한 제약을 받는다. 따라서, 본 연구에서는 Levenberg-Marquardt 기법을 기반한 역해석 기법을 사용하여 접착층에 대한 모드 I 한계응력과 에너지 해방률에 대한 예측 가능성을 확인하는 것이 목표다. 먼저, 한계응력은 접착층의 인장강도와 같다고 가정하였으며, 에너지 해방률은 DCB 시험(double cantilever beam test)을 수행하여 정의하였다. 또한, 유한요소법 기반 모델을 적용하여 한계응력과 에너지 해방률을 수치해석적으로 예측할 수 있는 지 확인하였다. 그 후, Levenberg-Marquardt 기법을 유한요소법 기반 모델에 적용하여 모드 I 한계응력과 에너지 해방률을 수치해석적으로 예측하였다. 아울러, 본 연구에서 사용한 역해석 기법의 수렴성을 확보하기 위하여 두 가지 경우의 초기 매개변수에 대한 역해석을 추가적으로 수행하였다. 결과적으로, 본 연구에서 사용한 역해석 기법은 모드 I 한계응력과 에너지 해방률을 효과적으로 예측할 수 있음을 보였다.

• 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.