• 한국생산제조학회지
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• 제19권1호
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• pp.26-32
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• 2010

SM45C steel rods using generally for machine components were selected and welded by butt-GMA welding method for this study. And then they were studied about characteristics of fatigue behavior and fracture surfaces by rotary bending test. Fatigue strength in weld zone present highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. The region of infinite life by Haigh diagram present highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. Fatigue cracks in unnotched specimens of base metal and weld zone introduce simultaneously from extensive out-side of circumferential cross-section and propagate to the other side indicating beach markings and dimples according to consolidation of fatigue cracks. Fatigue cracks in all of notched specimens introduce simultaneously in out-side of circumferential cross-section by high stresses and propagate to center of it indicating beach markings.

• Journal of Welding and Joining
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• 제29권2호
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• pp.46-55
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• 2011

This paper deals with the crack propagation life assessment of T-joint welded structure where typical fatigue cracks have been frequently initiated when the marine vessels experience the storm load. Welding residual stresses are calculated to investigate its effects on the fatigue life. Thereafter the residual stress distribution was applied to the AFGROW life prediction program, which incorporated the loading, the welding residual stress, and the geometric shape of the structure. The fatigue tests of the T-joint welded specimen under storm loading show the beach mark clearly generated on the fractured section of the weldment. The crack propagation life estimated based on the beach mark is compared with that of AFGROW to validate the life prediction. Based on the results, the evaluation method of the remaining fatigue life for T-joint fillet weldment of marine vessel's cargo hold with random load or storm load was established.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.65-73
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• 2004

Fatigue crack growth from surface defects is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LPG/LNG fuel tank and other various structures. This paper attempts to analysis some practical or general problems such as the estimation of crack growth life to penetrate the plate thickness, based on fatigue crack growth a single surface flaw and the interaction of multiple flaws. An experiment on the coalescence of multiple undercuts was carried out under cyclic tension condition as a attempt to the analysis of multiple crack problems. It is noted that the fracture strength is characterized by the analogy to that in a single crack growth.

• 대한기계학회논문집
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• 제7권4호
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• pp.425-433
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• 1983

Fatigue tests by axial loading (R=0.1) were carried out to investigate fatigue crack growth properties of small surface cracks in mild steel at room temperature, 250.deg. C and 400.deg. C, by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present tests are determined as a function of the stress intensity factor range, so that the applicability of liner fracture mechanics to the fatigue crack growth of surface cracks at elevated temperatures is investigated and discussed in comparison with the data of type 304 stainless steel at room temperature and elevated temperature. The obtained results are as follows: 1) Relations of both surface fatigue crack length and its depth to cycle ratio fall within a narrow scatter band in spite of different stress levels. 2) The .DELTA. .sigma. .root. .pi. a-da/dN relation of surface fatigue crack growth at room temperature is independent of the stress level and can be plotted as a straight line at log-log diagram, but the relation at 400.deg. C depends partly on the stress level. 3) Relations of the fatigue crack growth into depth d(2b)/dN and is stress intensity factor range .DELTA. $K_{I}$, accounted for the aspect ratio variation, fall within a narrow scatter band for wide range of the applied stress levels. And .DELTA. $K_{I}$E-d(2b)/dN relations of mild steel at different stress level coincide relatively well with the data of type 304 stainless steel. 4) The value of aspect ratio obtained by a beach mark method and a temper coloring method approaches about 0.9 in common with crack growth and it is independent of stress level and temperatures. 5) The equi-crack length curve is parallel to S-N$_{f}$ curve at elevated temperatures.s.s.s.

• 한국강구조학회 논문집
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• 제10권3호통권36호
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• pp.423-435
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• 1998

본 연구에서는 기존의 강교에서 흔하게 발견되고 있는 맞대기 용접부의 용입불량으로 인한 부재의 피로강도 저하도를 정량적으로 평가하고자 하였다. 이를 위하여 강교량의 재료로 널리 사용되고 있는 SWS490강으로 제작된 완전용입 및 용입깊이가 서로 다른 불완전용입 맞대기 용접시험편을 대상으로 일정진폭하중시험을 수행하여 S-N선도를 산출하고 이를 비교 검토하였으며, 파괴역학적 방법을 이용하여 불완전용입 용접재의 피로수명을 계산하였다. 본 연구의 결과로서, 완전용입 용접재의 경우 AASHTO의 피로강도등급선도와의 비교에서 피로한도값은 A등급보다 높은 값을 보였고, S-N선도의 기울기는 5.57로 매우 높게 나타났다. 불완전용입 용접재의 경우 불완전용입깊이 D가 증가함에 따라 피로강도가 감소하는데, D=14.7mm인 경우 AASHTO의 E'등급보다 낮게 나타난다. 불완전용입 용접재의 파손거동에서 피로균열은 내부 용접루트 선단부에서 a/c가 매우 작은 반타원형 표면균열의 형태로 발생하고, 시험체의 두께방향으로 진전하여 최종파손을 유발한다. 파괴역학적 방법을 이용한 불완전용입 용접재의 피로수명을 평가하기 위하여 3차원 반타원형 균열형상에 대한 응력확대계수 K를 유한요소해석으로 구하였다. 여기서 얻어진 K값과 실험으로 얻어진 Paris식의 상수를 이용하여 불완전용입 용접재의 피로수명을 계산하여 비교하였다. 그리고 실제 불완전용입 맞대기용접부의 파손으로 붕괴사고가 발생한 성수대교의 수직재에 본 연구결과를 적용하여 피로수명을 계산해 보았다.