• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.343-349
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• 2003

The fuselage-wing intersection suffers from the cyclic bending moment of variable amplitude. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in AFRP/Al laminate of fuselage-wing was investigated in this study. The cyclic bending moment fatigue test in AFRP/Al laminate was performed with five levels of bending moment. The shape and size of the delamination Lone formed along the fatigue crack between aluminum sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging behavior and the delamination zone were studied. As results, fiber failures were not observed in the delamination zone in this study, the fiber bridging modification factor increases and the fatigue crack growth rate decrease and the shape of delamination zone is semi-elliptic with the contour decreasing non-linearly toward the crack tip.

• Journal of Welding and Joining
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• 제5권1호
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• pp.73-80
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• 1987

During PWHT, it is well known that residual stress in weld HAZ is one of the reasons for PWHT embitterment. In case of static loading, it was experimentally found that fracture toughness of weld HAZ was dependant upon PWHT conditions. However, the effects of PWHT on fatigue behavior are not clearly verified. Therefore, in this paper, the effects of heating rate PWHT conditions and residual stress simulated in weld HAZ of Cr-Mo steel on fatigue crack propagation behavior were evaluated by fatigue Testing and SEM observation. The obtained results are summarized as follows; 1. Applied stress($10 Kgf/mm^2$) in weld HAZ during PWHT tneded to decrease fatigue strength and to increase fatigue crack growth rate. 2. Applied stress and slow heating rate of 60.deg. C/hr during PWHT contributed to precipitin of impurity elements as well as carbide, which promoted the fatigue crack growth. 3. Fatigue crack growth rate decreased at the heating rate of 220.deg. C/hr in contrast with 600.deg. C/hr and 60.deg. C/hr.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.125-133
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• 2002

In this study, it was investigated about endurance limit and fatigue behavior of load carrying fillet welded cruciform joints according to welding methods of SMAW, SAW, MIG and FCAW commonly using for welding structures in present. Endurance limit carried omit highly in the order of SMAW, MIG, SAW, FCAW and fatigue crack propagation ratio carried out lowly in the order of SMAW, MIG, FCAW, SAW. By these results, it is needed to use SMAW or MIG welding methods for welding structures with small welding capacity and SAW or FCAW methods for large welding structures after due consideration about economic gains and operation efficiency of welding. Fatigue crack propagation ratio is more effected by strength of welding materials than endurance limit of welding materials according to welding methods.

• 한국안전학회지
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• 제15권3호
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• pp.40-44
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• 2000

The fatigue and tensile test were carried out with Mild steel using the Dump Frame of commercial car. The specimens were heat-treated at $810^{\circ}C$ and $930^{\circ}C$ and worked 4.5, 6.0, 8.0mm thickness in order to look over the mechanical properties and fatigue life by heat treatment and thickness from the tensile test result, the yield strength of the heat treated specimens was increased about 35% more than that of the non-heat treated specimen. The fatigue life of non-heated specimen was decreased 15% but that of heat treated specimens at $870^{\circ}C$ and $930^{\circ}C$ were decreased 16.38% and 13.16% respectably according to increasing the thickness from 4.5 to 8.0mm.

• 한국생산제조학회지
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• 제9권4호
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• pp.48-55
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• 2000

For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimens was joined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm) .As a base test, mechanical properties around weld zone were examined . The results indicated that there were no significant decreases in mechanical properties , but hardness around weld bead was 2.3 times greater than base material . The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimens and base metal was different, and it was increased by 25% when pres-strain was applied. The crack propagation rate was noticeably decreased around weld line and rapidly increased as it passed through weld line. Reviewing the shape of the crack propagation , crack width around weld line was around the weld zone due to retardation of crack growth , but is became narrow passing weld line due to decreased toughness.

• 한국산학기술학회논문지
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• 제15권2호
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• pp.646-652
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• 2014

본 논문의 목적은 AZ31 마그네슘합금의 균열성장거동의 경향을 묘사할 수 있는 실험적 피로균열전파모델을 시편두께 조건에서 평가하여 적합한 모델을 제시하는 것이다. 평가에 사용된 실험적 모델은 Paris-Erdogan 모델, Walker 모델, Forman 모델, 수정된 Forman 모델이며, 각 모델의 파라미터를 통계적으로 추정하기 위하여 최우추정법을 사용하였다. 두께조건이 피로균열전파거동 예측에 미치는 영향을 고려하면서 적합한 모델을 평가하기 위해 시편두께의 3가지 조건을 변화시키면서 피로균열전파실험을 수행하여 통계적 균열성장 데이터를 획득하였다. 시편두께 조건에 따라 마그네슘합금의 균열성장거동의 경향을 잘 묘사하는 모델은 Paris-Erdogan 모델과 Walker 모델이며, 모델의 파라미터 중 피로균열성장속도지수는 시편두께가 4.75mm와 6.60mm 조건에서 재료상수가 될 수 있음을 밝혀내었다. 그러나 시편두께가 두꺼운 경우에는 양상에 차이를 보이므로 모델 선정 시 신중한 판단이 요구된다.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.143-150
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• 2003

Experimental research has been carried out to investigate the characteristics of the fatigue crack initiation and propagation behavior of Tailor Welded Blank(TB) sheet used for vehicle body. We used three types of specimens which were machined of the same base metal: one is 1.4mm thick, another is 1.6mm thick, and the third(TB specimen) is laser-welded of two specimens(1.4mm and 1.6mm thick ones). The results of tensile and hardness test indicate that the yield strength of the TB specimen is the highest, and the hardness around welding bead is higher than that of base metal. Fatigue strength and fatigue limit of the TB specimen are much superior to those of the base metal up to $10^6$ cycles. The fatigue crack propagation of the heat-affected zone of the TB specimen is slower than that of the base metal. Welding bead has the fastest crack Propagation in the low stress intensity factor range$(\DeltaK)$ region, but the slowest in the high $\DeltaK$ region. The fatigue propagation characteristic of the TB specimen is relatively stable in comparison with that of the base metal in the high ${\Delta}K$ region around over $28MPa\sqrt{m}$.

• 한국산학기술학회논문지
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• 제6권6호
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• pp.531-535
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• 2005

본 논문은 구멍 또는 이종 재료들로 채워진 구멍들 사이에 전파화는 피로 크랙의 거동을 연구한다. 중앙 크랙의 선단이 구멍의 중심선 가까이에 도달할 때 중앙 크랙은 멈추고 작은 크랙이 구멍이나 다른 이종 재료들로 채워진 구멍 주위로부터 발생하여서 최종 파단에 이르게 된다. 다른 이종 재료들 가까이에서의 중앙 크랙의 역학적 거동들이 또한 조사된다. 이러한 크랙이 진행하여 파괴에 이르는 현상을 컴플라이언스법으로 연구한다.

• International Journal of Railway
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• 제5권2호
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• pp.71-76
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• 2012

Recently, axle load, operating speed and traffic density on railroads have had a tendency to increase and thereby cause additional pressure applied on used track. These operating conditions frequently result in service failure due to wear caused by wheel-rail contact and fatigue damage under cyclic loading. Among rail defects, the transverse crack, which has been the most dangerous type of fatigue damages, is developed from the subsurface crack near the rail running face and grows perpendicular to the rail surface. Therefore, it is necessary to investigate systematically the growth behavior of transverse crack for rail steel under mixed mode. In this study, the fatigue crack growth behavior of the transverse crack in rail steel was experimentally investigated under mixed-mode variable amplitude loadings.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.321-326
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• 1999

In this study, fatigue crack propagation problem of plate under multi-axial loading is mainly considered To analyze this special problem, recently developed technique called EFGM(Element-Free Galerkin Method), one of the Meshfree Methods, and general fatigue crack growth raw herein Paris law are used Using the Implemented scheme, paths of fatigue cracks by constant-amplitude load fluctuation and multiple-crack growth behavior are examined. The failure mechanism of steel plate due to crack propagation is studied. As a result, an algorithm that treats multiple fatigue crack problems is proposed. A numerical example shows that the prediction of growing paths can be achieved successfully and efficiently by proposed algorithm.