• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.137-146
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• 2011

In the fabrication of steel bridges, blast cleaning prior to painting is carried out on the steel members to clean the forged surface and to increase the adhesive property of the applied painting systems. The effect of blast cleaning on the fatigue strength improvement of the weld joints, however, is not clear. In this study, Almen strips and steel specimens were blast-treated, conforming to ten types of blast-cleaning conditions deducted from the blast-cleaning conditions of seven steel structure fabrication companies. The arc height, roughness, hardness, and compressive residual stress were measured before and after the implementation of the ten blast-cleaning methods, and the relationship between the blast conditions and the measured values was studied. The geometry of the weld toe and the compressive residual stress near the weld toe were also measured before and after the blast cleaning of the butt-welded joints, and fatigue tests were carried out on the butt weld joints. The test results showed that blast cleaning significantly increases the fatigue strength and limit.

• Journal of Navigation and Port Research
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• v.26 no.4
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• pp.435-440
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• 2002

The quantitative assessment of the effect of the residual stress on fracture behavior was executed by some experiment and numerical analysis. First of all, artificial residual stresses were imposed on CT(Compact Tension) specimens by local heating using gas torch, and an appropriate distribution of residual stresses was obtained by thermal elastic-plastic FE analysis. To certify the result of the FE analysis, an experimental measurement was performed in accordance with ASTM standard. Fracture toughness test was executed on the several types of specimens. The first type was the specimen without residual stresses, and the others had different peak value of compressive residual stress at crack front via controlling the heat flux. All the test results were presented on th J resistance(JR) curves and discussed to verify the effect of compressive residual stresses on fracture behavior.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.333-338
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• 2013

The compressive residual stress and fatigue behavior of shot peened alloy 600 under a high-temperature environment is investigated in this study. Alloy 600 is used in the main parts of nuclear power plants, and the compressive residual stress induced by the shot peening process is considered to prevent SCC (stress corrosion cracking). To obtain practical results, the fatigue characteristics and compressive residual stress are evaluated under the actual operating temperature of a domestic nuclear power plant, as well as a high-temperature environment. The experimental results show that the peening effects are valid at a high temperature lower than approximately $538^{\circ}C$, which is the threshold temperature. The fatigue life was maintained at temperatures lower than $538^{\circ}C$, and the compressive residual stress at $538^{\circ}C$ was 68.2% of that at room temperature. The present results are expected to be used to obtain basic safety and reliability data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.609-615
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• 2012

In LSP (laser shock peening) treatment, the laser source geometries when the laser beam strikes the metal target area are diverse. The laser spot geometry affects the residual stress field beneath the treated surface of the metallic materials, which determines the characteristics of the pressure pulse. In this paper, detailed finite-element (FE) simulations on laser shock peening have been conducted in order to predict the magnitude and of the residual stresses and the depth affected in Inconel alloy 600 steel. The residual stress results are compared for circular, rectangular, and elliptical laser spot geometries. It is found that a circular spot can produce the maximum compressive residual stresses near the surface but generates tensile residual stresses at the center of the laser spot. In the depth direction, an elliptical laser spot produces the maximum compressive residual stresses. Circular and elliptical spots plastically affect the alloy to higher depths than a rectangular spot.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.110-117
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• 1997

Alloy 690 제1열 시제 전열관을 U 굽힘 가공할 시 전열관에 도입된 표면 잔류응력 및 굽힘 단면에서 치수변화 (벽두께, 진원도)를 위치별로 측정하여 평가하였다. 외측호(extrados)의 표면 잔류응력은 $\psi$=0$^{\circ}$에서 축 방향 응력이 -319 MPa (압축)로 가장 높았으며, 내측호(intrados)는 $\psi$=0$^{\circ}$, 160$^{\circ}$ 위치인 천이영역 부관에서 응력 변화가 크게 되는 경향을 보였다 측면(flank)은 인장 잔류응력으로 $\psi$=90$^{\circ}$(apex)에서 최대 190 MPa 로 축방향 응력으로 나타났다. 잔류응력치는 벽두께 보다는 진원도 변화와 일치되어 나타났으며, 시제 전열관의 벽두께 및 진원도는 ASTM의 치수 허용치 내에 포함되는 것으로 평가되었다. 잔류응력 측정은 스트레인 게이지를 이용한 구멍뚫기 방법 (Hole-Drilling Method)을 사용하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.46-51
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• 2002

Cold expansion of fastener holes is a mechanical process widely used in the aerospace industry. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses on the hole surface. The residual stress profile depends on the parameters of cold expansion, which are expanding rate, inserting direction of mandrel, material properties dtc. Despite its importance to aerospace industiries, little attention has been devoted to the accurate modeling of the process. In this paper, three-dimensional finite element simulations have been conducted for the cold expansion in an aluminium plate in order to predict the magnitude and distribution of the residual stress. To prove the results of FE analysis, the residual strain was measured by strain gage in cold expansion test. Maximum compressive residual stress could be increase about 7 percentage using the 2-step cold expansion method.

• The Korean Journal of Rheology
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• v.9 no.1
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• pp.16-26
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• 1997

사출 성형된 제품에서 발생하는 잔류응력은 최종 제춤의 기하학적 정밀도와 기계적 성질 및 열적 성질에 영향을 미친다. 사출성형된 제품의 잔류응력을 예측하기 위해서는 먼 저 열 및 유동장의 해석을 수행하여야 하고이를 위해서는 사출 성형의 세단계. 즉 충전, 보 압, 냉각을 모두고려해야한다. 검사체적 방법에 기초한 혼합 유한요소/유한차분방법을 사용 하는 수치 해석적 기법에 의하여 충전과정가 후충전 과정의 유동장 해서을 수행하였다. 일 반화된 헬레쇼 유동을 가정하였고 보압과 냉각과정시의 고본자의 압축성을 고려하였다. 점 도의 전단 변형률의 크기와 온도에 대한 의존성은 개선된 크로스 모델을 사용하여 나타내었 다. Tait에 의해 제안된 상태방정식은 고분자의 온도, 압력, 부피의 상호관계를 묘사하는 좋 은 방법을 제공하였다. 유동해석을 통하여 전 공정에 걸쳐서 온도와 압\ulcorner장의 변화에 대한 데이터를 얻었고 제품의 고체 응력해석의 입력 데이터로 사용하였다. 유한요소응력해석에는 평면 응력요소를 사용하였다. 다양한 형태의 금형에 대해서 공정 변수들을 달리하여 유동장 의 해석과 잔류응력의 계산을 수행하였다. 이로부터 공정조건과 유동장의 관계를 밝히고 최 종 제춤의 잔류 응력에의 영향을 고찰하였다.

• Korean Journal of Materials Research
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• v.6 no.12
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• pp.1162-1169
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• 1996

rf 플라즈마 화학증착을 이용하여 증착된 hydrogenated DLC막의 잔류응력 거동에 대해 조사하였다. 합성된 DLC막의 압축 잔류응력은 이온 에너지뿐만 아니라 이온/원자 유입량 비에 의해 영향을 받는 것으로 조사되었다. 잔류응력의 최대치는 이온/원자 유입량비가 증가할수록 낮은 이온 에너지 구간에서 일어나며 그 값은 증가하였다. 이온 에너지에 따른 DLC막의 결합 구조의 변형을 Raman 스펙트럼을 이용하여 분석하였다. DLC막의 잔류응력은 sp3결합의 net working이 최대가 되는 점에서 최대치를 보이며, 이는 sp3 net working에 의한 부피팽창 요인에 기인하는 것으로 생각된다. DLC막 내의 유입되는 수소는 잔류응력의 직접적인 원인으로 작용하지 않는 것으로 분석되었다.

• Korean Journal of Materials Research
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• v.3 no.1
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• pp.58-64
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• 1993

The degree of work hardening in the subsurface zones varied with the experimental conditions under the rolling contact fatigue wear test of high carbon Cr-Ti alloy steel was evaluated by the distribution of residual stresses. Surface residual stresses before the test did not affect the wear property. Surface residual stresses after the test decreased by the increase of contact stress and running. velocity. but the maximum compressive residual stress and its depth of saturation in the subsurface zone increased. The relationship between these experimental results and the distribution of the theoritical shear stress was also discussed.

• Journal of the Society of Disaster Information
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• v.11 no.1
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• pp.1-8
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• 2015

This paper presents finite element (FE) analyses to clarify the effects of external pressure on the residual stresses in a girth-welded steel pipe. At first, FE simulation of the girth welding process is carried out to obtain the weld-induced residual stresses employing sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Then, 3-D elastic-plastic FE analyses incorporating the residual stresses and plastic strains obtained from the preceding FE simulation are performed to investigate the residual stress behavior in the girth-welded pipe under external pressure. The FE analysis results show that the hoop compressive stresses induced by the external pressure significantly alter the hoop residual stresses in the course of the mechanical loading.