• 대한기계학회논문집A
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• 제23권11호
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• pp.2078-2086
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• 1999

Fracture behaviors of an interface crack in a ductile layer sandwiched by rigid substrates are analyzed by finite element method. Several fracture mechanisms and the corresponding criteria are examined. And the crack growth behavior and fracture toughness are predicted. As the results, various crack growth procedures such as the crack jump to the other interface on the opposite side, the creation of a new crack far from the initial crack front, and the asymmetric relation of fracture toughness vs. mode mixity ($J_c$-$\Phi$) can be successfully explained.

• 한국정밀공학회지
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• 제6권3호
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• pp.78-89
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• 1989

Applicability of tearing modulus based on J-integral proposed by Paris et al is investigated using compact tension specimens of strutural alloy steel (SCM4). Both general fracture test and instability fracture test are performed. The applied tearing modulus, ( $T_{j}$)app estimated from the real load vs. crack growth curve measured from experiments are compared with that estimated from the limit load vs. crack growth curve. The results are : (1) the $T_{j}$parameter could be applied to predict crack growth instability : (2) The use of ( $T_{j}$)app estimated from the load vs. crack growth curve, proposed in this study could be well predicted crack growth instability instead of that estimated form the limit load vs. crack growth curve.e.

• Journal of Advanced Marine Engineering and Technology
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• 제29권8호
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• pp.855-861
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• 2005

Fracture toughness defined near the initiation of stable crack growth is investigated by R-curve and Direct Current electric Potential Determination(DCPD) under mode I plane strain conditions for CT specimen with 25.4mm thickness of SS400 steel. Fracture toughness. $J_{IC}$lit near crack tip of CT specimen by R-curve is 17.14 $kg_{f}/mm$ and however. its value by DCPD is 22.82 $Rg_{f} mm$ The value of fracture toughness by DCPD is larger than that by R-curve. Therefore, it is suggested that the evaluation of fracture toughness by R-curve is optimum than by DCPD, when considering amount of crack growth about each of fracture toughness.

• 대한기계학회논문집
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• 제18권3호
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• pp.548-554
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• 1994

The high temperature fatigue crack growth behavior of SUS 304 stainless steel at $550^{\circ}C$ and $650^{\circ}C$ was investigated under various kinds of stress ratio and frequency in sinusoidal waveform on the basis of the non-linear fracture mechanics. The result arranging crack growth rate by modified J-integral J' showed influence of stress ratio and frequency. All the data obtained under the test at $550^{\circ}C$ were plotted within data band of da/dN-${\triangle}J_f$ relationship for cycle-dependent crack growth. On the basis of static creep and cycle-dependent data band; both time- and cycle-dependent crack growth behavior was observed under loading conditions at $650^{\circ}C$, but cycle-dependent crack growth behavior predominantly appeared and time-dependent crack growth behaviour was little observed under loading conditions at $550^{\circ}C$. Fractographic examinations for fracture surface indicated that the fracture mode was generally transgranular. The stripes were found on fracture surface and each stripe was accompanied by a crack tip blunting and an abrupt increase in the load-point displacement. The $J'_{an}$ had a validity in case of $650^{\circ}C, but scarcely had it in case of $550^{\circ}C$.

• 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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• 제3권4호
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• pp.133-142
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• 1979

The fracture toughness of a hot rolled 100 mm thick SS41 steel plate was investigated for various crack ratios and thichnesses using the method of J-integral. The experiments were performed on an MTS machine and the crack initiation point was detected by using an electricl impedance method. The J-integral computed at the initiation point of the slow stable crack growth was almost constant within the range of crack ratios tested. The fracture toughness thus obtained was $J_{1c}/=27.0kgf/mm$ for specimens having fracture plane parallel to the rolling direction and 35.5kgf/mm for those perpendicular to the rolling direction. The J- integral computed at maximum load point was found to be unsuitable for fracture toughness determination, becaese of large variation depending on the crack ratio and thickness. It was also found that the slow stable crack growth increases as the thickness and/or crack ration of the specimen decrease.

• 한국기계가공학회지
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• 제2권4호
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• pp.67-72
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, crack growth tests are conducted on spring steel and shot peened specimens. And then the residual stresses and fractographs are examined. The crack growth equation that can describe the whole crack growth behavior is used to evaluate the experiment results. The results show that fatigue crack glows slowly in the shot peened specimen than in the unpeened. And in the case of the 2-step shot peened specimen the initial stress intensity factor range and the fracture toughness is higher than the unpeened specimen due to the compressive residual stress. Fractographs show that the compressive residual stress of the surface suppress the fatigue crack opening and consequently slow crack growth rates.

• 대한기계학회논문집
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• 제14권1호
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• pp.103-111
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• 1990

본 연구에서는 성장하는 균열선단에서 열림변위의 임계증분에 대한 균열성장 조건에 기본을 두고 계산된 파단하중을 실험결과와 비교하여 균열성장저항을 특성 지 을수 있는 새로운 재료상수를 제안한 것이다.

• 한국압력기기공학회 논문집
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• 제11권2호
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• pp.45-50
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• 2015

In many cases, the field fracture mechanism of the thermoplastic pipe is considered as either brittle or environmental fractures. Thus the estimation of the lifetime by modeling slow crack growth considering such fracture mechanisms is required. In comparison of the some conventional and empirical equations to explain the slow crack growth rate such as the Paris' law, the crack layer theory can be used to simulate the crack and process zone growth behaviors precisely, so the lifetime of thermoplastic pipe can also be accurately estimated. In this study, the modified crack layer theory for the stress corrosion cracking (SCC) of high density polyethylene is introduced with detailed algorithm. The oxidation induction time of the HDPE is also considered for the reduction of specific fracture energy during exposed to chemical environments. Furthermore, the parametric study for an important SCC parameter is conducted to understand the slow crack growth behavior of SCC.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.807-810
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• 2001

Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Crystal grain size of the material is about 1000$\mu\textrm{m}$. For this material, the fatigue crack growth mechanism of high manganese steel was clarified from results such as observation of crack growth path and fracture surface. $\Delta$$K_{th}$ is about 8MPa$\surd$m which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low $\Delta$K regsion. The reason of this behavior is crack closure due to fracture surface roughness.