• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.3
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• pp.197-203
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• 1982

The fatigue crack propagation behavior or non-heat-treatment and thermally aged type 304 stainless steel was investigated on the basis of linear elastic fracture mechanics. This Study was concentrated on the relations between the crack propagation rate and the stress intensity factor range. The following results are obtained : The precision measurement and observation of fatigue crack propagation behavior is studied with moire grating. The effect of thermally aged type 304 stainless steel is investigated under small load. In the equation da/dN=c(.DELTA. k)/SUP m/, factor m of thermally aged steel is a little higher than non-heat-treatmented steel and its limit is m=1.35-4.2.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.1
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• pp.30-36
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• 1998

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environments and in the air. These experiments were done to investigate the corrosion fatigue crack propagation behavior, the variation of aspect ratio for part through crack and electro-chemical characteristics of the metal. The main results obtained are as follows ; 1. Comparing the same surface crack length with the crack depth, the crack depth toward the thickness of specimen in air propagated faster than that in corrosion environment. 2. The aspect variation of the half elliptical crack can be estimated as following equation; b/a=i-jb/t where a : surface crack length, b : crack depth, t : specimen thickness, i,j : experimental constants but the slope j is decreased as specific resistance decreases. 3. As the specific resistance of corrosion environment decrease or the corrosion fatigue crack propagates, the corrosion potential become less noble.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.74-82
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• 1987

This study has been made to investigate into the behavior of fatigue limit, of fatigue crack initiation, and of fatigue crack propagation under the condition of rotating bending stress; specifically on the independency of stress field as well as the crack behavior of surface micro hole defect, which is made artificially through the specimen. The results obtained can be summarized as followa; 1) For the single micro hole defect, initiation of fatigue crack is occurred at both tips of microhole defect simultaneosly along the slip which are produced in the range of maximum principal stress arround micro hole defect independent of the size of micro hole defect. 2) For the neighbored deuble micro hole defects with equal size, in the range ($\frac{L}{r}$)ratio $\gtrsim$ 3 defined as the size of micro hole defect(2r) to the distance between the centers of micro hole defects (2L), the crack behavior of the micro hole defects is same as single one. However, for the range of $\frac{L}{r}$<3, the interference effect becomes significant as the ratio approaches to 1.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.5
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• pp.842-849
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• 1997

The aim of this study is an investigation of the interaction of two micro hole defects affecting fatigue crack initation life and propagation behavior. The locatio of two micro hole defects was considered as an angle of alignment and the distance between the centers of two micro hole defects. The fatigue cracking behavior is experimented under bending. When micro defects are located close to each other, the fatigue crack initiation lives are varied with their relative locations. In the experiments, the area of local plastic strain strongly played a role in the fatigue crack initiation lives. Therefore we introduce a parameter which contains the plastic deformation area at stress concentrations and propose a fatigue crack initiation life prediction curve. In addition, the directions and propagation rates of fatigue cracks initiated at two micro hole defects are studied experimentally.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.279-286
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• 1998

Fatigue crack propagation behavior for variable load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum 7075-T651 and 5052-H32 alloys. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was ap;ied to check the crack closure and cracked area.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.74-83
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• 2001

After the concept of fracture mechanics was applied to fatigue crack propagation by Paris. Paris' law is widely used to predict fatigue crack growth behavior. Since Elber proposed the effective stress intensity factor(SIF) and showed a good agreement with experimental results using the proposed SIF, emphasis in crack propagation studies has been placed on measuring the effective stress range ratio. This paper proposes a numerical model to simulate the crack closure and propagation behaviour under various loading spectrum. The validity of the proposed model is checked by comparing with the Toyosada numerical solutions on the crack propagation behaviour. Important insights developed are summarized.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.188-197
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• 1986

With respect to structural carbon steel(SM 22C), it was studied how the overstress or the understress has effects on fatigue inside crack propagation curve of a two level stress. Obtained results are summarized as follows. (1) The overstress or the understress, at a slip band occurrence stage, does not change the inside crack propagation curve because the crack closure and opening phenomena do not happen. (2) The overstress, at a crack propagation stage, does not change the inside crack propagation curve because the crack closure of overstress in compressive state is nearly same that of base stress in compressive state. (3) The understress, at a crack propagation stage, give rise to an acceleration of crack growth because the crack closure of understree in compressive state is more open than that of base stress in compressive state and the phenomenon is the essential increase of the actual applied stress of the specimen.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2004-2010
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• 2003

Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference. between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.943-951
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• 1999

The welded structure unnecessarily remains residual stress due to the very high heating of local region and lastly cooling. The residual stress sometimes causes fracture initiation of welded structures. In this paper, distribution and magnitude of tensile and compressive residual stresses in the TIG(Tungsten Inert Gas) welded aluminum alloy such as Al5083-H112 are measured by using the hole-drilling method. Furthermore, the effects of residual stresses in the TIG welded aluminum CCT(Center Crack Tension) and SEN(Single Edge Notched) Specimens on the fatigue crack propagation behavior are analyzed. The fatigue cracks initiated at residual stresses region are influnced by tensile and compressive residual stresses. However, the effects are found to be released fast for both cases according to the cyclic loads and extension of crack length.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.553-559
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• 1998

This thesis studied to evaluate the fatigue behavior and propagation of rail steel under welding line. Test of crack growth was performed by all member of rail under constant amplitude loading at the structures laboratory in Hongik University. The effect of the following parameters with initiated crack length on the bottom edge of rail were studied. Here, fracture mechanics mode is opening mode. and Testing Material is KS50N Rail. From analysis and experimented result on the three Point bending in the lab, This paper presented a effect of crack growth , shape and remaining service life. Further more, according to the variable crack length, variable section and the ratio of section the fatigue behavior and propagation were studied.