• 한국산학기술학회논문지
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• 제12권2호
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• pp.594-599
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• 2011

본 논문은 마그네슘합금 AZ31의 피로파손수명의 확률론적 특성과 신뢰성에 미치는 경계조건의 영향을 평가하였다. 경계조건으로 시편두께와 응력비 그리고 최대피로하중을 적용하였으며, 각 경계조건별로 세부 실험조건에 대한 피로균열전파실험을 수행하여 피로파손수명에 대한 통계 데이터를 획득하였다. 마그네슘합금의 피로파손수명의 통계적 해석을 위하여 3-모수 와이블분포를 사용하였다. 시편두께가 두꺼울수록, 응력비가 클수록, 그리고 최대피로하중이 작을수록 통계적 피로파손수명이 길게 나타났다. 반면에 시편두께가 얇을수록, 응력비가 작을수록, 그리고 최대피로하중이 클수록 신뢰성이 급격히 감소하였다.

• Journal of Welding and Joining
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• 제28권6호
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• pp.45-50
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• 2010

Most of joining processes for machine and steel structure are performed by butt and fillet welding. The mechanical properties and fatigue strength of their welding zone can be effected largely by the differential of generated heat and changes of grain size according to thickness of material and number of passes in welding process. In this study, it was investigated about characteristics of fatigue failure according to thickness of material and number of passes in cruciform fillet weld zone as the basic study for safe and economic design of welding structures. Fracture modes in cruciform fillet weld zone are classified into toe failure and root failure according to non-penetrated depth. It can be accomplished economic design of welding structures considering fatigue strength when the penetrated depth in fillet weld zone is controled properly.

• 콘크리트학회논문집
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• 제11권6호
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• pp.113-119
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• 1999

Fatigue failure is a phenomenon such that structures under cyclic service load is failed by sudden brittle manner. Therefore, in order to obtain structures safety against the fatigue failure during their service lifes, fatigue characteristics should be considered for design and analysis of the structures. As stress range of prestressed (PS) tendons, which governs fatigus characteristic of prestressed concrete (PSC) structures, increases with increased use of partial prestressig, it is more necessary to consider fatigue characteristics of PS tendons. In this paper, direct-tension fatigue experiments with special specimen-setting devices are carried out to obtain fatigue characteristics of domestic low relaxation PS strands having different diameters and PS strands connected with coupler. Then, allowable stress range of fatigue for PSC beams using low relaxation strands are presented for the fatigue examination of prestressed concrete beams applied cyclic loading.

• Journal of Welding and Joining
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• 제29권4호
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• pp.67-72
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• 2011

The proportion of the welding in the production process of machinery, buildings and marine structures is increasing and the joining are mainly conducted by butt and fillet weld. In the case of fillet weld, the shape of structures is complicated depending on the constraint on the geometry of the structures, therefore, the full penetration is mostly difficult. Accordingly, it is necessary to establish safe and economical criteria of design of the structures through the strength based on the penetration state of the fillet weld. Patterns of fatigue failure in cruciform fillet weld jont appear in the form of the root, toe and mixed failure. In the case of toe and mixed failure, the fatigue strength is higher than root failure. Therefore, we have to make the enough depth of penetration or perform the welding work through improving the fatigue strength of cruciform joints in welded structures. So it is necessary to optimize the penetrated depth in the range of the possible mixed failure and find the way in the cost-effective design to lessen the amount of the welding work.

• 대한토목학회논문집
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• 제7권2호
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• pp.9-20
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• 1987

아스팔트포장(鋪裝) 공용성(供用性)을 저하(低下)시키는 하나의 원인(原因)으로 피로균열파괴(疲勞龜裂破壞)를 들 수 있다. 본(本) 연구(硏究)에서는 아스팔트혼합물(混合物)의 피로파괴(疲勞破壞)에 미치는 재료특성(材料特性)의 영향(影響)에 대해서 검토(檢討)를 하고 밀입도(密粒度)아스팔트 콘크리트에 대한 반복(反覆)휨변형율제어어시험(變形率制御試驗)을 하여 피로파괴포락선(疲勞破壞包絡線)을 구(求)했다. 다음에 탄성이론(彈性理論)의 결과(結果)와 피로파괴포락선(疲勞破壞包絡線)으로부터 온도(溫度) 아스팔트층(層)두께 하층(下層)의 탄성계수(彈性係數)와 피로파괴회수(疲勞破壞回數)의 관계를 고찰(考察)했다.

• 대한조선학회논문집
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• 제33권4호
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• pp.133-141
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• 1996

하중 전달형 필릿 용접 이음부에서 피로파괴는 용접투우부와 용접루트부로 부터 발생된 피로균열 발생 및 전파의 특성에 지배된다. 또한 그 피로균열의 특성은 필릿의 형상과 응력범위에 따라 큰 영향을 받는다. 본 연구의 목적은 하중 전달형 십자형 필릿 용접 이음부에서 피로하중 작용시 용접토우부에서 파괴하기 이한 용접부의 임계다리길이와 응력범위등을 검토하는 것이다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.269-273
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• 1998

The failure of material structures or mechanical system is considered as a direct or indirect result of fatigue. In the design of mechanical structure for estimating of reliability, the prediction of failure life is the most important failure mode to be considered. However, because of a complicated behavior of fatigue in mechanical structure, the analysis of fatigue is in need of much researches on life prediction. This document presents a prediction of fatigue life of the SAPH45 steel, which is extensively for vehicle frame. The method using lethargy coefficient and stress distribution factor at pediction of fatigue life based on the consideration of the failure characteristics from the tensile test should be provided in this study.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.60-64
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• 2001

In this paper, the tension-compression fatigue test method and the fatigue life characteristics of carbon fabric/epoxy laminate coupon are presented. To avoid the buckling during the compression, a proper design for the test coupons is essential. The critical buckling loads for the coupons are calculated by assuming the coupons as columns under two types of fixed conditions. The first is that both ends of each coupon are perfectly clamped, the second is that both ends of each coupon are simply supported. The strain-load curves are obtained by compressing the representative coupons, on each surface of which a strain gage is attached. The buckling loads obtained from the tests are all between the two calculated critical buckling loads. All the coupons are broken by the compression during the fatigue tests. It is estimated to be the reason that the fatigue load causes delamination before the eventual failure of each coupon, and sequentially the micro-buckling in the delaminated region drives each coupon into fatigue failure during the compression. The S-N curve, the fatigue life characteristics of carbon fabric/epoxy is obtained.

• 한국정밀공학회지
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• 제17권1호
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• pp.61-67
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• 2000

Gears are the most commonly used parts in automotive and industrial applications. One of most common modes of gear failures is tooth breakage, which is usually produced by the bending fatigue failure. It is important to manufacture the gears which can withstand the applied stresses in view of safety and economic requirement. This paper deals with bending fatigue strength for cold forged bevel gear. Especially, to compare fatigue characteristics for manufacturing processes difference, bending fatigue tests of bevel gears made by three different processes respectively. Results indicate that the fatigue strength of bevel gear is improved by cold forging process. Intergranular fracture is found on fatigue fracture surface, and dimples are observed on final fracture surface. The fatigue failure cannot be considered as a deterministic quantity, but must be characterized statistically. This study proposes a method to estimate bending fatigue lift of the bevel gear using the probability-load-life and Weibull analysis.

• 한국가스학회지
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• 제16권3호
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• pp.29-34
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• 2012

모든 구조물의 붕괴 사고로부터 인명과 재산의 손실을 방지하기 위하여 안전 설계 및 안전사용 방법을 찾는 것은 필요하며 피로해석으로부터 피로균열의 초기수명 및 전파수명과 함께 전 피로수명을 평가하는 것은 매우 중요하다. 본 연구의 목적은 교량, 선박, 가스 저장 시설을 포함하여 완전 용입이 어렵고 최종 파괴될 때까지 피로 수명 비를 계산하기 어려운 미 용입 십자형 필릿 용접 구조물에서 잘 나타나는 피로균열이 루트 부로부터 발생할 때 초기수명과 전파수명을 파악하는 것이다. 그 결과 피로파괴에 대한 각 피로수명 비는 재료 두께에 따라 5% 범위의 차이가 있으나 전반적으로 초기수명 비는 34~39% 범위이고 전파수명 비는 61~66%범위로 나타났다.