• 대한기계학회논문집
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• 제12권4호
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• pp.755-759
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• 1988

Laminated Composites, SS41-Cu-SS41 plates are made by brazing bonding and hot bonding process. Fatigue repeated plane bending tests are carried out and the fracture behavior of Laminated composites, SS41-Cu-SS41 plates are compared with that of homogeneous steel, SS41plates. The following results are obtained; (1) The fatigue life of the brazing bonding plates is higher than those of SS41 plates and hot bonding plates under high stress. (2) The relations between the fatigue crack growth rate, da/dN and stress intensity factor are, da/dN=4.7*10$^{-10}$ $K^{3.20}$, for SS41 da/dN=7.8*10$^{-9}$ $K^{2.43}$, for CAH da/dN=3.6*10$^{-9}$ $K^{2.54}$, for CAB da/dN=1.58*10$^{-9}$ $K^{2.94}$ , for PAH da/dN=1.23*10$^{-9}$ $K^{2.69}$, for PAB

• 한국생산제조학회지
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• 제5권3호
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• pp.31-39
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• 1996

The objective of this study is to investigate the influence of welding residual stresses on the fatigue crack growth behavior of cracks located transverse to the weld bead. For this purpose, G. T. A (Gas Tungsten Arc) welding was performed on hte Al alloy 1100-O plate and the same initial crack is made on HAZ(Heat Affected Zone), weld metal and base meta respectively. Specimens were used CT(Compact Tension) specimens. Initial welding residual stresses were measured by using strai gage sectioning method. All specimens were tested under constant amplitude load with stress ratio R=0.1, It is possible to predict fatigue crack growth behaviors and the fatigue life, using numerical analysis together with distribution of initial residual stress and the values of C and m obtained from $da/dN-{\Delta}K$

• 대한기계학회논문집
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• 제17권1호
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• pp.21-26
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• 1993

본 연구에서는 방전가공면에서의 미시조직의 변화, 잔류응력의 분포등을 주된 연구대상으로 하여, 이들이 피로균열의 발생, 성장거동에 미칠 특이한 영향에 대하여 고찰하고자 한다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1996년도 특별강연 및 춘계학술발표 개요집
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• pp.115-118
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• 1996

1. The crack is inifiated at a toe notch and reptured for the skip and continuous welding. 2. Fatigue life of continuous welding is greater than that of skip welding and fatigue life of 2pad continuous welding appears 1.7 times more than that of pad continuous welding. 3. For the skip and continuous welding, fatigue than that of welding materials appears shorter than that of welding materials because of the effect of plastic strain and compressive residual stresses at the crack tip, which are generated by the over loading. 4. Inter-relationship between da/dN-ΔK and delayed phenomenon increases linearly at the state growth area of heat effect section for the skip and continuous welding.

• 한국안전학회지
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• 제7권2호
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• pp.47-56
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• 1992

The retardation effect of fatigue crack propagation after cyclic overloading seems to be affected by strain hardening exponent. Namely, for the material with high values of n, the delay effect is found to be severe. We proposed a modified crack retardation equation which may apply the retardation of fatigue crack growth after a cyclic overloading, as (da/dN)'$_{cyc}$=($\mu$n＋λ)B $\Delta$ $K^{q}$ /[(1－ $R_{eff}$) $K_{cf}$ －$\Delta$K]. where, $R_{eff}$ is effective stress ratio [＝( $K_{min}$－K, os)/( $K_{max}$－ $K_{res}$)] The constants $\mu$＝－0.5 and λ＝0.6, and the values are found to be identical for materials such as aluminum (A 1060), steel (SS 34), brass ( $B_{s}$ SIB) and stainless steel (SUS 304) used in this investigation. (SUS 304) used in this investigation.ation.n.n.

• 대한조선학회지
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• 제25권1호
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• pp.21-32
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• 1988

An experimental study was carried out to identify the fatigue fracture behavior of steel for merchant ships. The bending and shear loads were applied simultaneously on the specimens to simulate of real load condition for a ship. The effects of the stress intensity factor under mode I with mode II loading condition on the initiation and the propagation of a crack were investigated, with particular emphasis on mode II. When the $K_{II}$ stress intensity factor in mode II was applied under mode I loading condition, the propagation behavior of a crack is to be affected mainly by the anisotropic characteristic of materials.

• 산업기술연구
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• 제11권
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• pp.135-143
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• 1991

The fatigue tension tests were performed by use of the specimens without and with a hole, 1/4 crack and 1/2 crack, made of SS41 and S45C steel round bars. Followings were these results. It was shown that in the base metal and the specimen with a hole the fatigue strength of the high strength steel bars was lower than that of the low strength steel bars under the low stress range. It was shown that the fatigue strength of the specimen with a hole was nearly same as that of the base metal, but the fatigue strength of the specimens with the crack was much lower than that of the base metal. It was shown that the fatigue strength of the specimens with the crack was much lower than that of the other specimens under the high stress range.

• 한국안전학회지
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• 제18권3호
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• pp.46-53
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• 2003

For the tensile tests of the F.E.M., microvoids are created by the boundary separation process at the martensite boundary or neighborhood and at inclusions within the fracture. to grow to the ductile dimple fracture. For the case of the M.E.F., microvoids created at the discontinuities of the martensite phase which exists at the grain boundary of the primary ferrite are grown to coalescence with the cleavage cracks induced at the interior of the ferrite, which as a result show the discontinuous brittle fracture behavior. In spite of their similar tensile strengths, the fatigue limit and the notch sensitivity of the M. E.F. is superior to those of the F.E.M., The M.E.F. is much more insensitive to notch than F.E.M. from the stress concentration factor($\alpha$).

• 한국해양공학회지
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• 제12권1호
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• pp.50-57
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• 1998

The leak before break(LBB) concept is generalized on the design of LNG tanks, pressure vessels and nuclear reactor in that any leakage of containment, in whatever amount, will not result in catastropic failure. For this purpose it is necessary to determine the surface crack shape, the opening displacement and the risk of catastropic brittle fracture when it becomes a through crack. In this study the crack propagation behavior of surface flaws and the crack opening displacement of through cracks under combined membrane and bending stresses were investigated with fatigue tests and fracture toughness test of aluminium alloy A5083-O. And fracture mechanics analysis of the crack opening displacement of through cracks were made in order to develop a new model expressing the behaviors of COD under combined membrane and bending stresses.

• 대한기계학회논문집A
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• 제35권11호
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• pp.1415-1422
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• 2011

운송기계구조물의 제작에 사용되는 판재 알루미늄 합금재료는 일정한 피로응력조건하에서 두께에 따라 균열진전속도의 차이를 보인다. 이러한 두께효과는 판재 알루미늄합금의 주요한 피로파괴특성 중 하나이다. 본 연구에서는 일정한 피로응력조건하에서 실시한 후판 및 박판 Al 2024-T3 합금재료의 피로 시험을 통하여 두께효과를 파악하고, 이를 형상인자인 두께비, $R_t$ 및 하중인자인 두께별 등가유효응력확대비, $U_{i}^{equ}$에 의한 상호관계식, $U_{i}^{equ}=f(R_t)$로 나타내었다. 그리고 두께효과에 의한 후판 대비 박판시험편의 균열진전 지연거동을 ${\Delta}K$ 환산법을 사용하여 정량적으로 분석하였다. 두께효과의 경향을 정량으로 나타내기 위해 두께감소율(DoT)과 응력확대계수범위, ${\Delta}K$의 감소율(DoS) 등의 값을 구하여 이들 상호관계를 규명하였다.