• 대한조선학회논문집
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• 제60권2호
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• pp.65-75
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• 2023

Ships operated at sea for a long time are subjected to various kinds of loads, which may cause various types of damage. Such damages will eventually reduce the strength of hull structures. Therefore, it is necessary to estimate and evaluate the residual strength and remaining fatigue life of aging ships in order to secure structural safety, establish a reasonable maintenance plan, and make a judgment of life extension. For this purpose, the corrosion damage and local denting damage should be measured, fatigue damage estimation should be performed, and material properties of aged steel should be identified. For this study, in order to investigate the mechanical properties of aged steel, steel plates were obtained from a naval ship that reached the end of her life span. The specimens were manufactured from the obtained steel plates, and static and dynamic tensile tests, fatigue tests, and metallographic tests were performed. The mechanical properties obtained from the aged steel plates were compared with those of new steel plates to quantify the aging effect on the mechanical properties of marine steel materials.

• KIEAE Journal
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• 제7권6호
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• pp.119-126
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• 2007

In the field of composite structures, the use of carbon tube for the confinement of concrete has been arisen since 1990's. However, experimental and analytical studies were limited to those of reinforced concrete and concrete filled steel tube. The carbon tube provides excellent confinement capabilities for concrete cores, enhancing compressive strength and ductility of concrete significantly. The carbon tube has high tensile strength, light weight, corrosion immunity and high fatigue strength properties. Since carbon fiber is an anisotropic material, carbon tube could be optimized by adjusting the fiber orientation, thickness and the number of different layers. In this study, both experimental and analytical studies of axial and lateral behavior of full-scale CFCT (Concrete Filled Carbon Tube) columns subjected to monotonic axial load were carried out using Drucker-Prager theory. And, based on comparison results between experiment results and analytical results, k factor estimation was proposed for effective analysis.

• 한국정밀공학회지
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• 제16권12호
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• pp.143-151
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• 1999

The shape of surface micro-crack is very irregular due to nonhomogeneous microstructure but is very important in respect to qualitative estimation of fatigue life. Fractal geomety can quantify the shape of surface mciro-crack. Fractal dimension is measured for surface micro-cracks with coast line and box counting method and estimates cycle ration in Al 2024-T3. The average fractal dimension $D_{favg}$ of surface micro-cracks has 3-parameter weibull distribution and location parameter is nearly constant but shape parameter decreases as cycle ration increases. The fractal dimension by coast line method is measured for individual surface micro-crack but the fractal dimension by box countin method is measured for all the surface micro-cracks under sampling area. Therefore, This paper shows fractal dimension $D_{fb}$ can predict cycle ratio $N/N_f$ more convenient than fractal dimension $D_{favg}$.

• 대한조선학회논문집
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• 제48권3호
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• pp.238-245
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• 2011

Welding inevitably introduces the residual stresses which affect the fatigue strength of the joint structure. The mitigation of fatigue strength depends on the residual stress magnitude and distribution. Stress relief analyses are of practical interest for all cyclic loaded welded structures, such as ships and offshore structures. In order to estimate the effects of relaxation of residual stresses in the welded structure, this paper presents a finite element analysis procedure and experimental results for the welded structure. Cruciform specimens joint by MAG welding have been tested to measure the released stress. Relieved welding residual stresses obtained by finite element analysis are compared with those measured by experiment.

• 한국산학기술학회논문지
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• 제14권1호
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• pp.13-19
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• 2013

국내 승용차용 삼원촉매의 경우 열적 내구성을 만족시키지 못하고 조기 파손되는 사례가 증가하고 있다. 이것은 차량의 배기가스 정화장치의 신뢰성에 치명적 손상을 유발시키므로 삼원촉매의 내구성 평가 모델을 파악할 필요가 있다. 따라서 본 연구에서는 세라믹 모노리스 담체에서 발생되는 열응력을 구한 뒤 강도저하계수모델과 파손확률을 기초로 삼원촉매의 열적 내구성을 평가하였다.

• 대한기계학회논문집
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• 제9권5호
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• pp.564-571
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• 1985

본 논문에서는 미시조직인자를 변화시킨 마르텐사이트-페라이트 복합조직강을 준비하여 균열선단 및 안정영역의 파괴양상과 파괴저항과의 관계를 검토하였다.

• Steel and Composite Structures
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• 제39권4호
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• pp.353-366
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• 2021

Cored moment resisting stub column (CMSC) was previously developed by the features of adopting a core segment which remains mostly elastic and reduced column section (RCS) details around the ends to from a stable hysteretic behavior with large post-yield stiffness and considerable ductility. Several full-scale CMSC components with various length proportions of the RCSs with respect to overall lengths have been experimentally investigated through both far-field and near-fault cyclic loadings followed by fatigue tests. Test results verified that the proposed CMSC provided very ductile hysteretic responses with no strength degradation even beyond the occurrence of the local buckling at the side-segments. The effect of RCS lengths on the seismic performance of the CMSC was verified to relate with the levels of the deformation concentration at the member ends, the local buckling behavior and overall ductility. Estimation equations were established to notionally calculate the first-yield and ultimate strengths of the CMSC and validated by the measured responses. A numerical model of the CMSC was developed to accurately capture the hysteretic performance of the specimens, and was adopted to clarify the effect of the surrounding frame and to perform a parametric study to develop the estimation of the elastic stiffness.

• 한국정밀공학회지
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• 제16권1호통권94호
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• pp.227-237
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• 1999

As the interface bonding phenomenon between the matrix and the reinforcements has a large effect on the mechanical properties of MMCs, a sugestion of the strength analysis technique considering the residual stress and the interface bonding phenomenon is very important for the design of pans and the estimation of fatigue behavior. In this paper the three dimensional finite element anaysis is performed during the elasto-plastic deformation of the particulate reinforced metal matrix composites. It was analyzed with the volume fractions in view of microscale. Bonding strength. interface separation and matrix void growth between the matrix and the reinforcements will be predicted on deformation under tensile loading. An interface seperation is estimated by the fracture criterion which is a critical value of generalized plastic work per unit volume. The shape of the reinforcement is assumed to be a perfect sphere. And the type of the reinforcement distribution is assumed as FCC array. The thermal residual stress in MMCs is induced by the heat treatment. It is included at the simulation as an initial residual stress. The element birth and death method of the ANSYS program is used for the estimation of the interface bonding strength, void generation and propagation. It is assumed that the fracture in the matrix region begin to occur under the external loading when the plastic work per unit volume is equal to the critical value. The fracture strain will be defined. The experimental data of the extruded $SiC_p$>/606l Al composites are compared with the theoretical results.

• International Journal of Automotive Technology
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• 제5권1호
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• pp.55-59
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• 2004

Spot welding is a very important and useful technology in fabrication of thin sheet structures such as the parts in an automobile. However, because the fatigue strength of the spot welding point is considerably lower than that of the base metal due to stress concentration at the nugget edge, the nugget size must be estimated to evaluate a reasonable fatigue strength at a spot welded lap joint. So far, many investigators have experimentally studied the estimation of fatigue strengths of various spot weldments by using a destructive method. However, these destructive methods poses problems so testing of weldments by these methods are difficult. Furthermore, these methods cannot be applied to a real product, and are time and cost consuming, as well. Therefore, there has been a strong, continual demand for the development of a nondestructive method for estimating nugget size. In this study, the effective nugget size in spot weldments have been analyzed by using thermoelastic stress analysis adopting infrared thermography. Using the results of the temperature distribution obtained by analysis of the infared stress due to adiabatic heat expansion under sinusoidal wave stresses, the effective nugget size in spot welded specimens were estimated. To examine the evaluated effective nugget size in spot weldments, it was compared with the results of microstructure observation from a 5％ Nital etching test.

• 대한토목학회논문집
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• 제8권2호
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• pp.109-116
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• 1988

구조(構造)의 강도(强度)와 하중(荷重)은 시간(時間)이 경과함에 따라 변하며 확률과정(確率過程)이 된다. 이들의 상호관련성(相互關聯性)으로부터 신뢰도(信賴度)의 추정(推定)이 가능하다. 따라서 안정성(安定性)을 확보(確保)하기 위한 안전(安全)의 여유를 고려하는 경우 허용응력(許用應力)은 신뢰성(信賴性)에 근거한 안전율(安全率)로부터 구하는 것이 합리적(合理的)이다. 본(本) 연구(硏究)에서는 장기적(長期的)으로 피로하중(疲勞荷重)을 받는 철도(鐵道)레일을 대상(對象)으로 해서 신뢰성(信賴性)의 지표(指標)인 파괴확률(破壞確率)을 구하는 방법(方法)을 적용(適用)해 보았다. 신뢰도(信賴度)의 추정(推定)에 있어서 모수(母數)의 추정(推定)이 어려운 경우 파괴확률(破壞確率)의 수치계산(數値計算)은 의미가 없다. 이와 같은 문제점을 극복하기 위하여 상대적(相對的)인 신뢰성(信賴性)을 구하는 관용설계법(慣用設計法)이 제안(提案)되었다. 본(本) 연구(硏究)에서는 Cornell의 관용설계법(慣用設計法)을 적용(適用)하였다. 불확정요소(不確定要素)로서는 강도(强度)와 하중(荷重)의 변동계수(變動係數)를 사용하였고 이들의 파괴확률(破壞確率)에 대한 영향과 신뢰성(信賴性)에 근접(根接)한 안전율(安全率)을 검토하였다. 본(本) 연구(硏究)의 결과는 다음과 같다. 신뢰성(信賴性)에 있어서 용접재(鎔接材)는 강도변동(强度變動)의 영향을 크게 받고 모재(母材)는 하중변동(荷重變動)의 영향을 크게 받았다. 신뢰도(信賴度)에 근접(根接)한 안전율(安全率)로 구한 허용응력범위(許用應力範圍)는 안전측(安全側)에 있음을 확인(確認)하였다.