• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.136-145
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• 2003

The integrity of stiffened panels with stringers in airplane structure is generally enhanced by investigating the fatigue crack propagation behavior in detail and providing the technical methodology to deal with the propagating crack. This paper attempts to clarify the effect of load-ratio on the fatigue crack propagation rate and the fatigue life for the thin aluminum 2024-T3. Both the variable and the constant fatigue loading conditions are considered for the fatigue crack propagation behavior in stiffened panels with stringers.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.2
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• pp.146-151
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• 2001

The effects of slant interface in the hybrid specimen on the dynamic crack propagation behavior have been investigated using dynamic photoelasticity. The dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system is utilized to record the dynamic stress field around the dynamically propagating inclined interface crack tip in the three point bending specimens. The dynamic load is applied by a hammer dropped from 0.08m high without initial velocity. The dynamic crack propagation velocities and dynamic stresses field around the interface crack tips are investigated. Theoretical dynamic isochromatic fringe loops are compared with the experimental reults. It is interesting to note that the crack propagating velocity becomes comparable to the Rayleigh wave speed of the soft material of a specimen when slant angle decreases.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.854-858
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• 2002

In this study, Fatigue crack growth behavior of the laser welded sheet metal due to a single overload was investigated. From Fatigue crack propagation test, it was observed that the retardation of fatigue crack growth has been more effective in the welded specimen than in the base metal. And if the distance between the welded part and the position of overload is too close the retardation of fatigue crack growth at the welded part has been decreased. From FEM analysis, it was observed the retardation has been more effective compressive residual stress than plastic zone.

• Journal of Industrial Technology
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• v.23 no.A
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• pp.3-7
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• 2003

Effect of nitriding on fatigue crack initiation and growth rate has been studied on SNCM. Specimens were nitrided for 15 hr at $860^{\circ}C$. The fatigue limit of nitrided specimens was superior to that of annealed($860^{\circ}C$, 15 hr) specimens. Based on detailed observations of slip band and micro crack initiation, it is concluded that the excellent fatigue limit of nitrided specimens is attributed to improved slip initiation resistance by nitriding. The characteristic of fatigue crack growth rate of nitrided specimens was investigated and compared with those of annealed specimens. It was found that by nitriding the crack growth rate was markedly decreased and the threshold stress intensity factor range was improved. It is concluded that the excellent fatigue limit of nitrided specimens is also attributed to improved fatigue crack growth rate and threshold stress intensity factor range by nitriding.

• Journal of Ocean Engineering and Technology
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• v.14 no.4
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• pp.73-78
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• 2000

Presented are the estimation of the probability distribution of fatigue crack growth life and reliability assessment of structures by simulating material resistance to fatigue crack growth along a crack path. The material resistance is treated as a Weibull stochastic process. A non-Gaussian stochastic fields simulation method proposed by shimozuka, et al is applied with the statistical data obtained experimentally. Test results are obtained for $\delta K$ constant amplitude load in tension with stress ratio of R=0.2 and three specimen thicknesses of 6,12 and 18mm. This simulation method is useful to estimate the probability distribution of fatigue crack growth life and the smallest life.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.47-55
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• 1994

The purpose of the present study is to investigate the effect of specimen thickness on statistical properties of crack growth resistance. In this study, the resistance S$\delta$$_h$(x) to fatigue crack growth was treated as a spatial stochastic process. which varies randomly on the crack surface. The theoretical autocorrelation functions of the resistance to fatigue crack growth considering specimen thickness are discussed for several correlation lengths. The main results obtained are : (1) The theoretical autocorrelation functions of S$\delta$$_h$(x) are almost independent of specimen of specimen thickness except for the origin. (2) The variance increases with decreasing specimen thickness.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.11
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• pp.919-926
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• 2014

In this paper, the effect of material properties on fracture behavior was studied using cohesive zone model and extended finite element method. The rectangular tensile specimen with a central inclined initial crack was modeled by plane stress elements. In the CZM modeling, cohesive elements were inserted between every bulk elements in the predicted crack propagation region before analysis, while in the XFEM the enrichment to the elements was added as needed during analysis. The crack propagation behavior was examined for brittle and ductile materials. For thin specimen configuration, wrinkle deformation was accounted for by geometrically nonlinear post-buckling analysis and the effect of wrinkling on the crack propagation was investigated.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.131-139
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• 2001

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failure occur from cracks subjected to mixed mode loadings. Hence, it is necessary to evaluate the fatigue behavior under mixed mode loading. Under mixed mode loading conditions, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. The mode I and II stress intensity factors of CTS specimen were calculated using elastic finite element method. The propagation behavior of the fatigue crack of the STS304 steeds under mixed mode loading condition was evacuated by using stress intensity factors $K_I$ and $K_II. The MTS criterion and effective stress intensity factor were applied to predict the crack propagation direction and the fatigue crack propagation rate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.704-708
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• 1996

The elastic dynamic crack curving could be obtained by controlling the loading rate, the initial crack-tip blunting to store much energy before crack initiation and the magnitude of reflected wave from finite boundaries. However there is no theoretical and experimental elastic-plastic dynamic curving study. This paper proposes a specimen geometryfor a study of dynamic elastic-plastic crack curving and presents a preliminary result. The specimen has a blunt physical crack tip on a side, and a round notch tip on the other side. From the experiment using this specimen, it is found that the narrow plastic zone ahead of the round notch tip produces the change of load direction and anti-symmetricity of the dynamic isochromatics, and each result causes the crack curving phenomenon. After a certain time, as the elastic-plastic crack gets close to the round notch tip near, the degree of the crack curving get larger. The elastic reack curving propagates more sensitively to the surround of crack tip than the plastic crack curving does. The cynamic elastic-plastic crack curving is found to be proportional to the CTOA(the crack tip opening angle). The dynamic elastic-plastic crack may propagate in the direction perpendicular to the loading. An apparant strip yield zone which is similar to the Dugdale strip yield zone is noted ahead of the physical crack tip.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1216-1221
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• 2003

The specimen materials used in this research is bimaterial. The static photoelastic experiment was applied to them. And then the specimens used in photoelastic experiment were fractured under static load. The static photoelastic hybrid method was introduced and it's validity had been assured. The static photoelastic hybrid method was applied to the Minimum Strain Energy Density Criterion, the Maximum Tangential Stress Criterion and Mode Mixity. Crack propagation criterion by the static photoelastic hybrid method was introduced and it was applied to the above various failure theories. Comparing the experimental initial angle of crack propagation with the theoretical initial angle of crack propagation from the various failure criterions. And then the optimal crack propagation criterion was suggested and it's validity was assured.