• 한국기계가공학회지
• /
• 제4권2호
• /
• pp.43-49
• /
• 2005

The purpose of a fatigue crack arrest design is to prevent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flanges, crack arrest is possible; arrest occurring when the fatigue crack reaches the second element. In the present work, a numerical analysis was carried out to estimate the effect of shape parameters on fatigue crack growth and arrest behavior of integrally stiffened panels. Based on these results, a set of fatigue crack arrest design chart is presented as "non-dimensional arrest load - thickness ratio" relationship.

• 한국기계가공학회지
• /
• 제5권2호
• /
• pp.42-48
• /
• 2006

In order to assess the validity of fatigue crack arrest design charts obtained from our previous numerical approach to fatigue crack arrest condition, an extensive fatigue crack growth/arrest test was performed using CT-type integrally stiffened panels. The results are presented as fatigue crack growth rate and non-dimensional crack length relationship, and these are compared with numerically simulated crack growth rates. The measured values of da/dN at the moment of fatigue crack arrest occurred in stiffened panels are good agreement with those numerically simulated crack growth rates.

• 한국기계가공학회지
• /
• 제4권2호
• /
• pp.50-56
• /
• 2005

To demonstrate the feasibility of utilizing FCAD chart proposed in our previous work, series of crack growth/arrest behavior in the integrally stiffened panels were simulated by numerical method using upper mentioned FCAD charts and a new crack growth rate equation. It is concluded that proposed family of FCAD curves, in the form of non-dimensional arrest load ranges, are reliable indicators of fatigue crack growth/arrest behavior of integrally stiffened panels considered here.

• 한국재료학회지
• /
• 제10권4호
• /
• pp.305-311
• /
• 2000

샤피 V-노치 충격 하중-변위 곡선으로부터 얻은 균열정지하중을 이용하여 원자로압력용기강의 균열정지파괴인성($K_{Ia}$)을 예측할 수 있는 방법을 모색하고 그 타당성을 고찰하였다. 샤피충격 하중-변위 곡선으로부터 얻은 균열정지하중값의 변화는 특성온도로 보정된 지수함수의 형태로 잘 표현될 수 있었다. 특성온도 $T_{Pa=2kN}$은 실험적인 무연성천이온도($T_{NDT}$) 및 $T_{41\;J}$과 높은 상관성을 나타냈으며, 원자로압력용기강의 균열정지파괴인성을 표현하는 새로운 특성온도로 사용할 수 있을 것으로 판단되었다. 또한 균열정지하중값의 변화는 파면으로부터 측정된 안정균열길이의 변화와 매우 높은 상관성을 나타내었다. 따라서 무딘 노치를 갖는 시편에 대한 계장화샤피충격시험을 통하여 균열정지하중 및 안정균열길이를 측정하믈써 비교적 정확하게 원자로압력용기강에 대한 하한값의 파괴인성치($K_{Ia}$)를 평가하는 것이 가능한 것으로 판단되었다.

• 한국안전학회지
• /
• 제6권4호
• /
• pp.45-52
• /
• 1991

The purpose of a fatigue crack arrest desing is to prvent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flangers, crack arrest is possible; arrest occuring when the fatigue crack reaches the second element. In the present work, the possibility of crack arrest and the design criterion of fatigue crack arrest in the variable thickness plates are examined numericaiiy by using fatigue crack arrest thresthod $\Delta$K$_{th}$of SA-508 reactor vessel steel and stress intensity factor which was obtained in the previous work as a result of 3-dimensional finite element analysis for CT type variable thickness plates having discontinuous interface.e.

• 한국기계가공학회지
• /
• 제20권7호
• /
• pp.8-14
• /
• 2021

Even welds that have passed non-destructive testing in the case of brittle crack arrest steel materials will actually have very fine weld defects. Based on studies showing that these defects adversely affect the structure if subjected to a certain period of load, the following conclusions were obtained by conducting CTOD tests on welding joints of high-strength BCA materials, structures comprising the upper decks of a large container vessel. First of all, the fatigue pre-cracking in the weld metal and heat affected areas was tested and the behavior was identified. Both parts of the welding joint are allowable range for the class regulations. In addition, CTOD results showed that the CTOD value in the heat affected area was more than 0.5 times higher than in the weld metal area.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1996년도 춘계학술대회 논문집
• /
• pp.697-703
• /
• 1996

Fatigue strength of high strengthsteels are variable with many different surface treatment. It is well known that residual compressive stress retard fatigue crack growth rate(or arrest crack). High strngth steels are manufactured by following process. Heat treatment, shot peening and chromium plating process. High strength steel(HRC40 or above) which are subjected to fatigue load and dynamic load, chromium plated parts shall be peened in accordance with requirements and baked after plating. The purpose of this paper is to compare and discuss the influence of surface treatment and hydrogen embrittlement on fatigue strength of high strength steel. Therefore, fatigue test was performed to investigate influence of surface treatment. The results shows that shot peening is very effect method in creasing fatigue life and after plating, baking process is essential to prevent hydogen failure. In this paper, the experimental investigation is made to clarify the influence of shot peening conditions and baking process on fatigue strength of high strength steel.

• 대한기계학회논문집A
• /
• 제23권11호
• /
• pp.1886-1895
• /
• 1999

The delamination behavior of multidirectional carbon-fiber/epoxy composite laminates under 10NA intermediate and high rates of test, up to rate of about 11.4m s has been investigated using the double cantilever beam specimens. The mode I loading under rates above l.0m/s showed considerable dynamic effects on the load-time curves and thus higher values of the average crack velocity than that expected from a simple proportional relationship with the test rate. The modified beam analysis utilizing only the opening displacement and crack length exhibited an effective means for evaluating the dynamic fracture energy $G_{IC}$. Based on the assumption of constant flexural modulus, values of $G_{IC}$ at the crack initiation and arrest were decreased with an increase of the test rate up to 5.7m/s, but the maximum $G_{IC}$ was increased at 11.4m/s.

• Composites Research
• /
• 제12권5호
• /
• pp.40-53
• /
• 1999

저속시험 및 약 11.4m/s까지의 고속시험을 받는 다방향 탄소섬유/에폭시 복합적층판의 층간파괴거동에 대해 양외팔보(DCB)시험편을 이용하여 연구했다. 모드I의 하중을 1.0m/s이상으로 가한 결과 하중-시간곡선에 동적효과가 발생하여, 시험속도에 비례하는 단순관게식으로 예상되는 것보다 더 큰 균열속도가 나타났다. 시험편 개구변위와 균열길이만을 사용하는 수정된 선형보해석식은 동적인 층간파괴에너지$G_{IC}$를 평가하기 위해 유효했다. 또한 굽힘탕선계수의 실측값은 시험속도의 증가에 다라 증가했는데, 이를 $G_{IC}$의 평가시에 고려했다. 시험속도가 1.0m/s까지 증가할 때, 균열개시 및 정지시의 $G_{IC}$값은 변화가 없었으나, 11.4m/s의 속도에서 최대 GIC값은 섬유가교효과의 증대로 크게 증가했다. 또한 초기균열길이가 길수록 고속시의 최대GIC값은 저하했다.