• 한국안전학회지
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• 제21권4호
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• pp.19-24
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• 2006

Fatigue crack propagation tests for the brake disc cast iron were conducted for investigating fatigue crack propagation rate(da/dN), crack propagation path and fracture toughness($K_c$) of the material. The threshold stress intensity factor range, ${\Delta}K_{th}$, was found to be about $6MPa{\sqrt{m}}$ at the stress ratio of R = 0.1. Also, fracture toughness value was determined to be $24.7MPa{\sqrt{m}}$. Irregular fatigue fracture surfaces were observed, indicating that fatigue crack growth occurred at the interface between randomly scattered flak graphite and ferrite, where the interfacial strength was relatively weak.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.599-608
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• 2002

Finite element analysis for the stress intensity factor (SIF) at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels is developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior at the inclined crack. In order to investigate the crack growth direction, maximum tangential stress (MTS) criterion are used. Also, this paper is to study the performance of the effective bonded composite patch repair of a plate containing an inclined central through-crack. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stress intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter including; composite patch thickness and stiffener distance. We report the results of finite element analysis on the stiffener locations and crack slant angles and discuss them in this paper. The research on cracked structure subjected to mixed mode loading is accomplished and concludes that more work using a different approaches is necessary. The authors hope the present study will aid those who are responsible for the repair of damaged aircraft structures and also provide general repair guidelines.

• 한국세라믹학회지
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• 제33권2호
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• pp.203-213
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• 1996

In this study the subcritical crack growth behavior in an Al2O3-SiCw composite has been investigated using in situ fracture technique of applied moment double cantilever beam (AMDCB) specimens indside an SEM. This technique allows the detailed observation of whisker and grain bridging in the crack wake region. The experimental results indicated that the KI-a curve was deviated from the conventional powder law form and that the existed a region where the rate of microcrack growth was decreased with increasing the externally applied stress intensity factor. This behavior could be explained by arising crack growth resistance i.e. R-curve behavior which was associated with crack shielding due to whisker and grain bridging. The R-curve was also analyzed from the KI-a curve data in order to quantify the bridging effect in the Al2O3-SiCw composite.

• 한국해양공학회지
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• 제9권2호
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• pp.112-122
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• 1995

In this work, prediction of fatigue life and fatigue crack growth are studied. 4th order polynominal function is presented to describe the crack growth behaviors from artifical pit of SM45C steel. Crack growth curves obtained from 4th order polyminal growth equations are in good agreement with experimental data The crack growth behaviors at arbitrary stress levels and investigated by the concept of elastic-plastic fracture mechanics using ${\Delta}J$. Fatigue life prediction are carried out by numerical integral method. Prediction lives obtained by proposed method in this study, is in good agreement with the experimental ones. Life prediction results calculated by using of ${\Delta}J$ better than those of ${\Delta}K$.

• 한국해양공학회지
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• 제9권1호
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• pp.111-119
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• 1995

The elastic-plastic fracture toughness($J_{IC}$) and fracture resistance (J-R curve) of SA508-3 alloy steel used for nuclear reactor pressure vessel are investigated by using CT-type specimens. Fracture toughness tests are conducted by unloading compliance method and multiple specimen method at room temperature, -2$0^{\circ}C$ and 20$0^{\circ}C$. The apparent negative crack growth phenomenon which usually arises in partial unloading compliance test is well known. The negative crack growth phenomenon in determining J sub(IC) or J-R cure from partial unloading compliance experiments may be eliminated by the offset technique. In this study, the evaluation of $J_{IC}$ multiple specimen method recommended by the JSME gives the most reliable results by using half-size CT(similar-type) specimens.

• 한국도로학회:학술대회논문집
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• 한국도로학회 2008년도 추계학술대회 논문집
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• pp.93-102
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• 2008

An energy based crack growth model is developed in this study to simulate the propagation of top-down cracking in asphalt pavements. A viscoelastic fracture mechanics approach, generalized J integral, is employed to model the crack growth of asphalt concrete. Laboratory fatigue crack propagation tests for three different asphalt mixtures are performed at various load levels, frequencies and temperatures. Disk-shaped specimens with a proper loading fixture and crack growth monitoring system are selected for the tests. It is observed from the tests that the crack propagation model based on the generalized J integral is independent of load levels and frequencies, while the traditional Paris' law model based on stress intensity factor is dependent of loading frequencies. However, both models are unable to take care of the temperature dependence of the mixtures. The fatigue crack propagation model proposed in this study has a good agreement between experimental and predicted crack growth lives, which implies that the energy based J integral could be a better parameter to describe fatigue crack propagation of viscoelastic materials such as asphalt mixtures.

• 항공우주시스템공학회지
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• 제17권2호
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• pp.1-8
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• 2023

회전익 항공기의 동력전달축은 경량화를 위하여 중공축을 적용하였으며 선형탄성 파괴역학을 이용해 균열 전파 거동을 예측할 수 있다. 본 논문에서는 유한요소해석을 통하여 원주방향 관통형 균열을 가지는 중공축의 균열성장수명을 예측하였다. 비틀림을 부여하고 균열을 고려한 요소를 형성하여 2차원 유한요소모델을 생성하였다. 초기 균열 길이를 정의하고 균열 길이를 증가시켜 유한요소해석을 수행해 균열 선단의 응력확대계수를 도출하였다. 응력확대계수가 중공축을 구성하는 재료의 파괴인성을 초과하기 직전의 길이를 한계 균열 길이로 정의한다. 응력확대계수 핸드북을 통해 응력확대계수를 계산하여 한계 균열 길이를 도출하고 균열성장속도식을 수치적분하여 각각의 균열성장수명을 비교해 제안한 유한요소해석 기법을 검증하였다.

• 한국기계가공학회지
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• 제3권4호
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• pp.88-94
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• 2004

High manganese steel was maintained stability of Non-Magnetics performance. Fatigue tests were carried out under constant stress amplitude, using a non-magnetic high manganese steel. The fatigue crack growth mechanism of the high manganese steel was clarified from results such as observation of crack growth path and fracture surface. The result of getting this study was shown as following: 1) Remarkably ${\Delta}Kth$ of the high manganese steel is big with about 3 times of the general steel product. 2) In the low ${\Delta}K$ value region, da/dN is dependent on Kmax, and in the high ${\Delta}K$ value region, it is dependent on ${\Delta}Keff$. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. 3) It seems to ease the stress concentration of crack tip crack growth behavior in the ${\Delta}Kth$ vicinity by the generation of the secondary crack.

• 한국해양공학회지
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• 제6권1호
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• pp.105-112
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• 1992

The main purpose of this study is to derive a law of fatigue crack growth rate in the region of elastic or elasto-plastic fracture mechanics at elevated temperatures through the application of dimensional analysis. An equation of elasto-plastic fatigue crack growth rate at elevated temperatures appeared a new Arrhenius type equation containing J-integral range and absolute temperature. The elastic or elasto-plastic crack growth rate equation shows a fairly good agreement with the experimental results for Cr-Mo-V rotor steel and Hastelloy-X alloy in the comparatively wide temperature ranges.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.101-107
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• 1996

In this study, the wedge splitting test (WST) specimens with various strength levels were tested to investigate the fatigue crack growth behavior of concrete. Selected test variables were concrete compressive strength with 2 levels (28 MPa, 60 MPa, 100 MPa) and maximum fatigue loading with 2 levels (75%, 85%). Fatigue testing was preceded by fracture energy test and the crack growth was measured by means of the compliance calibration method, 60 WST specimens were cast for the fatigue test, and 6 companion cylinders ($\phi$100${\times}$ 200 mm) for each batch. In fatigue test, the frequency of loading cycle was 1 Hz, and the minimum fatigue loading level was 5~10 % of ultimate monotonic loading. On the basis of the experimental results, a fracture mechanics-based empirical relationships for fatigue crack growth rate (da/dN-$\Delta$KI relationships) were presented. In addition, the effect of initial notch depth on the fracture energy and the validity of compliance calibration technique for the WST were shown.