• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.61-70
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• 1988

In order to consider the concept of the fitness for purpose'in fatigue design of offshore structure, fracture mechanics is applied to evaluate initial or weld defects. Generally, linear elastic fracture mechanics has been applied to tstimate initial fatigue crack propagation rate as well as long fatigue crack propagation rate. But, initial fatigue crack propagation rate in elasto-plastic notch field may not be characterized by application of stress intensity factor range .DELTA. K, because plastic effect due to stress concentration of notch may contribute to initial crack propagation. Therefore, to introduce the plastic effect into fatigue crack driving force, in this studty, the evaluating method of J-integral range .DELTA. J, was developed by willson was modified for application to notch field. In calculation of .DELTA. J obtained from the modified J-integral, stress gradient and crack closure behavior in the notch field were considered. The initial crack propagation rates in the notch fields of mild steels and high tensile strength steels were correlated to .DELTA. J. As the result, it was cleared that the present .DELTA. J is applicable to charachterize the fatigue crack propagation rates in both the elastic and elasto-plastic notch fields.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.187-194
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• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.2
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• pp.42-48
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• 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.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.79-84
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• 2003

A fictitious crack model was used to analyze fatigue crack growth under the influence of residual stress. In the fictitious crack model, crack is represented in terms of the separation of two adjacent interfaces and the constitutive equation between the separation and traction is assumed. The effect of fatigue loading was included in the constitutive equation by considering damage accumulation in the cohesive zone. To investigate the effect of the residual stress on the fatigue crack growth, we calculated the residual stress distribution due to transient heat flux to the specimen by finite element method. Fatigue crack growth was simulated by the fictitious crack model with repeated loading. The mode-I crack growth rates were compared for the cases with and without the compressive residual stress around the crack tip. It was observed that the mode-I crack growth can be suppressed by compressive residual stress.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.856-860
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• 2002

The main objective of this study is to consider the effect of fatigue crack behavior on the variable depth of micro hole defects in SM20C at the symmetric position. The fatigue crack propagation test is performed by rotary bending fatigue test machine. The relationship between crack length(2a), cycles(N) and crack growth rate(da/dN) are investigated in this study. The result from the rotary bending fatigue test under the applied stress at 250MPa turned out that the fatigue life illustrated almost constant when the depth of symmetric micro hole deflects is both part A and B at the hope depth(h) = 0.5mm.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.112-124
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• 1993

It has been reported that fatigue damage sometimes occurred at the stress concentrated and dynamic loaded structural members of bulk carrier. In this paper, studies on fatigue strength of hull structures are reviewed, and the program for evaluating fatigue strength is developed. And the fatigue crack initiation and propagation on the end part of cargo hold frame of bulk carrier were calculated by FEM stress analysis and the fatigue strength evaluation program. These method can be applied not only to the crack initiation life but also to crack propagation life for the hull structural members at the hull design stage and be effective as the guideline to prevent the crack initiation or to estimate the fatigue strength for repairing of the fatigue damaged structures of real ships.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.8
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• pp.80-87
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• 1996

The present paper will give some results of the fatigue behavior of typical axi-symmetric forward extrusion die. The extrusion process is analyzed by rigid-plastic FEM and the deformation analysis of extrusion die is conducted by elasto-plastic FEM. To approach the crack problem LEFM (Linear Elastic Fracture Mechanics) is introduced. Using special element in order to conside the sigularity of stress/ strain in the vicinity of the crack tip, stress intensity factor and the effective stress intensity factor is calculated. Applying proper fatigue crack propagation criterion such as Paris/Erdogan fatigue law and maximum principal criterion to these data, then, the angle and the direction of fatigue crack propagation is simulated. In result, it is proved that the simulated fatigue crack propagates in the zigzag path along the radial direction and fatigue life of the extrusion die is evaluated by using the computed crack growth rate.

• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.20-28
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• 1997

The fatigue crack propagation properties and fatigue life of two kinds of Al body panel for automobile were examined experimentally by using the plate specimen and the single spot welding specimen. The fatigue limit of spot welding specimens was lower than that of a plate specimen. The fatigue limit was similar in two kinds of spot welding specimen. The shape and size of crack propagation were observed and measured on beach mark of fracture surface. The crack propagation of surface crack specimen showed almost same tendency to that of a thick plate as almost semi-elliptical. In spot welding specimen, the fatigue crack occurred in inside surface of nugget area was almost semi-elliptical. The crack growth rate can be explained using equation of stress intensity factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.2091-2099
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• 2001

Fatigue crack growth behavior of inclined cracked Al 6061-T6 thick aluminum plate(6mm) repaired with the bonded composite patch was studied. A 0°inclined crack bonded reinforced composite patch and 15°, 30°, 45°, 60°inclined crack plates were tested. The effect of patch and inclined angle were studied and compared to each other. Also we investigated to the crack propagation direction and debonding behavior during the fatigue crack growth test. In this paper. a study was con(ducted to get an fatigue life, fatigue crack growth ratio and crack growth direction. Finally, the effectiveness of composite patch on inclined cracked plate was investigated. The results demonstrated thats there was a definite variation in fatigue life and fatigue crack growth behavior depending on the inclined crack angle.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.183-190
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• 2015

Fatigue crack growth rate tests were conducted as a function of temperature, dissolved hydrogen (DH) level, and frequency in a simulated PWR environment. Fatigue crack growth rates increased slightly with increasing temperature in air. However, the fatigue crack growth rate did not change with increasing temperature in PWR water conditions. The DH levels did not affect the measured crack growth rate under the given test conditions. At $316^{\circ}C$, oxides were observed on the fatigue crack surface, where the size of the oxide particles was about $0.2{\mu}m$ at 5 ppb. Fatigue crack growth rate increased slightly with decreasing frequency within the frequency range of 0.1 Hz and 10 Hz in PWR water conditions; however, crack growth rate increased considerably at 0.01 Hz. The decrease of the fatigue crack growth rate in PWR water condition is attributed to crack closure resulting from the formation of oxides near the crack tips at a rather fast loading frequency of 10 Hz.