• Steel and Composite Structures
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• 제36권1호
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• pp.75-86
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• 2020

The grid structures with welded hollow spherical joint (WHSJ) have gained increasing popularity for use in industrial buildings with suspended cranes, and usually welded with steel tube (ST). The fatigue performance of steel tube-welded hollow spherical joint (ST-WHSJ) is however not yet well characterized, and there is little research on fatigue life prediction methods of ST-WHSJ. In this study, based on previous fatigue tests, three series of specimen fatigue data with different design parameters and stress ratios were compared, and two fatigue failure modes were revealed: failure at the weld toe of the ST and the WHSJ respectively. Then, S-N curves of nominal stress were uniformed. Furthermore, a finite element model (FEM) was validated by static test, and was introduced to assess fatigue behavior with the hot spot stress method (HSSM) and the effective notch stress method (ENSM). Both methods could provide conservative predictions, and these two methods had similar results. However, ENSM, especially when using von Mises stress, had a better fit for the series with a non- positive stress ratio. After including the welding residual stress and mean stress, analyses with the local stress method (LSM) and the critical distance method (CDM, including point method and line method) were carried out. It could be seen that the point method of CDM led to more accurate predictions than LSM, and was recommended for series with positive stress ratios.

• Composites Research
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• 제14권2호
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• pp.50-59
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• 2001

다목적헬리콥터용으로 설계된 복합재 무힌지 로터깃에 대하여 강도저하모델을 활용하여 비행모사 하중스펙트럼에 따라 피로파손 확률분포와 잔여강도 변화거동을 해석하여 피로수명을 예측하였다. 이때 작용하는 피로하중은 실제 헬리콥터 운용상태를 모사하는 무힌지 로터깃의 표준하중스펙트럼인 FELIX 데이터로부터 비행 대 비행 하중스펙트럼을 구성하였고 피로손상이 가장 극심하게 예상되는 깃뿌리 부근의 국부응력스펙트럼은 스킨과 스파의 적층구조해석을 수행함으로써 구하였다.

• Journal of Mechanical Science and Technology
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• 제14권9호
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• pp.935-946
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• 2000

Elastic-plastic stress analysis has been performed to evaluate the fatigue life of an autofrettaged pressure vessel containing cross-bores subjected to pulsating internal pressure of 200 MPa. Finite element analyses were used to calculate the residual and operating stress distributions of the pressure vessel due to the autofrettage process and pulsating internal pressure, respectively. Theoretical stress concentration factors of 3.06, 2.58, and 2.64 were obtained at the cross-bore of the pressure vessel due to internal pressure, 50%, and 100% autofrettage loadings, respectively. Local stresses and local strains determined from the elastic-plastic finite element analysis were employed to calculate the failure location and fatigue life of the pressure vessel with radial cross-bores, incorporating the low-cycle fatigue properties of the pressure vessel steel and fatigue damage parameters. Increase in the amount of overstrain by autofrettage process moved the crack initiation location from the inner radius toward a mid-wall, and extended the crack initiation life. Predicted fatigue life of the fully autofrettaged pressure vessel with cross-bores increased about 50%, compared to the unautofrettaged pressure vessel. At the autofrettage level higher than 50%, the failure location and fatigue life of the pressure vessel were not significantly influenced by the autofrettage level.

• Steel and Composite Structures
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• 제18권3호
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• pp.673-691
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• 2015

In this paper we are particularly focusing on the dynamic crack fatigue life of a 25 m length wind turbine blade. The blade consists of composite materiel (glass/epoxy). This work consisted initially to make a theoretical study, the turbine blade is modeled as a Timoshenko rotating beam and the analytical formulation is obtained. After applying boundary condition and loads, we have studied the stress, strain and displacement in order to determine the critical zone, also show the six first modes shapes to the wind turbine blade. Secondly was addressed to study the crack initiation in critical zone which based to finite element to give the results, then follow the evolution of the displacement, strain, stress and first six naturals frequencies a function as crack growth. In the experimental part the laminate plate specimen with two layers is tested under cyclic load in fully reversible tensile at ratio test (R = 0), the fast fracture occur phenomenon and the fatigue life are presented, the fatigue testing exerted in INSTRON 8801 machine. Finally which allows the knowledge their effect on the fatigue life, this residual change of dynamic behavior parameters can be used to predicted a crack size and diagnostic of blade.

• 한국가스학회지
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• 제22권5호
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• pp.62-71
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• 2018

2017년 한국가스안전공사 가스안전연구원의 자체 조사에 따르면, 국내 고압가스배관 중 매설된 배관의 길이는 대략 770km이며, 그 중 84%가 울산과 여수산업단지에 몰려 있다. 특히 20년 이상의 장기 운영 배관이 56%에 달하며, 이는 매설된 고압가스배관의 관리가 시급하다는 것을 시사하고 있다. 매설된 가스배관의 주요 사고 원인으로 미국 PHMSA, 유럽의 EGIG 등에서는 타공사와 외면부식을 지적하고 있으며, 배관 벽두께의 손실에 의한 누출 및 파열 등의 사고로 보고된다. 따라서 배관에 결함이 발생하였을 때, 그 결함이 배관의 잔존수명에 영향을 미치는 바를 평가하는 것이 중요하다. DNV나 ASME 등에서는 배관에 인위결함을 만든 후 수압 파열 실험을 통하여 배관의 잔존강도를 평가했다. 배관의 잔존강도를 운전압력과 연관시키면, 배관이 파열되는 시점의 벽 두께가 계산되며 해당 배관의 부식 성장률만 정확히 알 수 있다면, 배관의 잔존수명을 예측할 수 있다. 본 연구에서는 기존에 결함깊이가 벽두께의 80% 이하에서 적용된 수식을 개선하기 위하여 국내 매설배관의 80%를 차지하는 A53 Grade.B와 A106 Grade.B 배관에 대하여 결함 깊이가 80~90%의 범위에서 실험하였고, 결함과 잔존강도 관계를 표현한 수식을 만들었다.

• 한국자동차공학회논문집
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• 제18권1호
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• pp.139-144
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• 2010

In the automotive electronic industry, the development of vehicle's door wiring harness (W/H) system for new applications is driven continuously for the low-cost and the high strength performance for electronic components. The problem of the fatigue strength estimation for materials and components containing natural defects, inclusions, or inhomogeneities is of great importance both scientifically and industrially. This article gives some insight into the dimensioning process with special focus on the fatigue analysis of wiring harness (W/H) in vehicle's door structures. The results from endurance tests using slim test specimens were compared with the results from FEM for predicted fatigue life. The expectation for the life of components is affected by the microstructural features with complex stress state arising from the combined service loading and residual stresses.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.423-424
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• 2016

Recently, the mass production of Energy storage system (ESS) is actively perform around world. Energy storage system is a technique that stores power to energy storage device to supply energy into grid and load at peak-load. Therefore, the efficient energy management is available by using ESS system. The life of Lithium-ion battery is varied corresponding to the power usage, especially selected depth of discharge (DOD). The lifetime of battery is the one of the most issue of the ESS system because of its stability and reliability. Therefore, lifetime management of battery and power converter of ESS module is required. In this paper, the battery lifetime management method estimating residual power and lifetime of lithium ion battery of ESS system is proposed. Also, total avenue prediction of ESS system is simulated considering the total lifetime of battery.

• 품질경영학회지
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• 제31권2호
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• pp.165-182
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• 2003

The fatigue has been considered to the most important failure mode where optimal design or reliability prediction of the machinery in aircraft, atomic reactors, and structure systems, etc., is required. When the statistical analysis of fatigue life data is performed, some difficulties are present because of the following facts : nonlinear relationship, heteroscedastic data, large scatter in the data, censored data (runouts), and existence of fatigue limit. To find the S-N curve models that characterize fatigue strength better, this research compares existing fatigue curve models developed recently in terms of the residual mean square and the estimate of fatigue limit, etc. for various fatigue data sets.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.469-472
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• 2008

In general, structures in service gradually lose original performance according to time due to initial defects in design and construction, or exposure to unfavorable external conditions such as repeated loading or deteriorating environment, and in extreme cases, may collapse in large disaster. Therefore, in order to maintain the serviceability of structures at optimal level, advanced structure measuring system which can inform optimal time point and method of maintenance is required in addition to accurate prediction of residual life the structure by periodic inspection. To guarantee the safety level of bridge structure and to prevent from disaster, the integration of safety network for bridge structures are needed. Therefore in this study, to enhance the effectiveness of safety network for bridge, the connection methodologies between safety network and pre-installed bridge monitoring system are investigated.

• E2M - 전기 전자와 첨단 소재
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• 제11권11호
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• pp.1-8
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• 1998

This paper presents an arificial neuro-fuzzy technique based prtial discharge (PD) pattern classifier to power system application. This may require a complicated analysis method employ -ing an experts system due to very complex progressing discharge form under exter-nal stress. After referring briefly to the developments of artificical neural network based PD measurements, the paper outlines how the introduction of new emerging technology has resulted in the design of a number of PD diagnostic systems for practical applicaton of residual lifetime prediction. The appropriate PD data base structure and selection of learning data size of PD pattern based on fractal dimentsional and 3-D PD-normalization, extraction of relevant characteristic fea-ture of PD recognition are discussed. Some practical aspects encountered with unknown stress in the neuro-fuzzy techniques based real time PD recognition are also addressed.