• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.634-644
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• 2000

Fatigue crack growth and life is estimated by various fracture mechanical parameters but affected by load, material and environment. Fatigue character of component without surface notch cannot be e valuated by above-mentioned parameters due to microstructure of in-service material. Single fracture mechanical parameter or nondestructive parameter cannot predict fatigue damage in arbitrary boundary condition but multiple fracture mechanical parameters or nondestructive parameters can Fatigue crack growth modelling with three point representation scheme uses this merit but has limit on real-time monitoring. Therefore, this study shows fatigue damage model using backpropagatior. neural networks on the basis of X-ray half breadth ratio B/$B_o$ fractal dimension $D_f$ and fracture mechanical parameters can predict fatigue crack growth rate da/dN and cycle ratioN/$N_f$ at the same time within engineering estimated mean error(5%).

• 연구논문집
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• s.32
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• pp.55-64
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• 2002

Performance demonstration with real flawed specimens has been strongly required for nondestructive evaluation of safety class components in nuclear power plant. Specimen has been designed to produce mechanical fatigue flaw with tension stress and fatigue flaw has been produced to control stress and cycle, for suitable roughness. Notch condition is considered for control of fracture mode. After seal welding for fracture surface, final welding was performed to complete flaw specimen with GTAW(Gas Tungsten Arc welding) and FCAW(Flux Cored Arc Welding). It was demonstrated flaw size of flawed specimen by radiographic. testing and ultrasonic testing.

• Transactions of Materials Processing
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• v.10 no.3
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• pp.179-184
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• 2001

The influence of the fatigue crack propagation by shot peening was studied in this paper. Fatigue tests were carried out on the unpeened and shot peened CT specimens. The changes of mechanical properties, residual stress, fatigue fracture surface etc. by shot peening were investigated. The mechanical properties, residual stress, fatigue surface etc. by shot peening were investigated. The mechanical peened specimen improved in fatigue life up to 14% by shot peening. The reason of increase in the fatigue life was closely related with the compressive residual stress, which was 519.7MPa on surface. Another reason was the constraint on crack opening on surface region, it is due to the decrease in slope of crack propagation direction.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.281-287
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• 2002

Nowadays, many components used in machinery industry is required lightness and high strength. Therefore, the effects of compressive residual stress by shot-peening which is method to improve fatigue lift of spring steel (JISG SUP-9), which used in suspension of automobile, on fatigue crack growth characteristics was investigated with considering fracture mechanics. So, we can obtain followings 1. The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is dependent on Paris equation. 2. Although the maximum compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maximum compressive residual stress is formed in surface. 3. The threshold stress intensity factor range is increased with increasing compressive residual stress. 4. In fracture surface of fatigue crack growth it is investigated that compressive residual stress remarkably retards fatigue crack growth.

• International Journal of Railway
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• v.5 no.3
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• pp.129-134
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• 2012

Contact fatigue damages on the rail surface, such as head checks and squats are a growing problem. The fatigue cracks forming on the contact surface grow according to load and lubricating conditions and may end up breaking the rail. Rail fracture can be avoided by preventing the cracks from reaching the critical length. Therefore, the crack growth rate needs to be estimated precisely according to the conditions of the track and load to develop a maintenance plan against rail damages. Therefore, it is important to understand the mechanism of cracks initiation and growth on a rail due to repetitive rolling contact. In this study, we have investigated the crack growth behavior on the rail surface by using the twin-disc tests and the finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.21-26
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• 1993

A study on the fatigue fracture at electro discharge machined(E.D.M) surface has been made with special emphases on the microstructure variation and the residual stress distribution at the E.D.H heat affected zone. Results obtained are summarized as follows. (1) E.D.M brings about a variation of microstructure in heat affected zone, structures of molten, quenching, tempering are formed in order of formation from E.D.M surface. (2) Residual stress generated by E.D.M reduces the fatigue strength of the material through the influencing fatigue crack initiation and growth. (3) Magnitude of the residual stress existed in a microscopic area is approximately estimated by a COD measurement method which was originally suggested by authors.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.8
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• pp.28-34
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• 2010

Railway wheel and axle is the most critical components in railway system. A wheel and axle failure can cause a derailment with its attendant loss of life and property. The service conditions of railway vehicles have become severe in recent years due to a general increase in operating speeds. Therefore, more precise evaluate of wheelset strength and safety has been desired. Fracture mechanics characteristics such as dynamic fracture toughness, fatigue threshold and charpy impact energy with respect to the tread, plate, disc hole of wheel and the surface of press fitted axle are evaluated. This paper describes the difference of fracture toughness, fatigue crack growth and fatigue threshold at the locations of wheel and axle. The results show that the dynamic fracture toughness, $K_{ID}$, is obviously lower than static fracture toughness, $K_{IC}$ and the fracture mechanics characteristics are difference to the location of wheel tread and hole.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1062-1067
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• 2003

In this study, corrosion fatigue characteristics of CF8M and CF8A steel were investigated on the simulated PWR condition(Temp.:$316^{\circ}C$, Pres.: 15:MPa). To make the simulated PWR condition. the special test machine consisted of INSTRON, Autoclave, LOOP and Measurement system was developed. As ${\Delta}K$ is ranged from 11 to $20MPa{\sqrt{m}}$, Crack growth rate of PWR condition is faster than air condition. Above $20MPa{\sqrt{m}}$, the crack growth rate of PWR and air condition is similar. Corrosion fatigue characteristics regardless of the ferrite contents($10{\sim}25wt.%$) is not different. After the test, the fracture surface of specimens was examined. It was difficult to verify the fracture modes such as striation, intergranular crack and cleavage and so on. As the ferrite content of CF8M is increased, the more particles covered fracture surface were peeled.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.4
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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.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.11
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• pp.69-76
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• 1997

The rotating bending fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely sued in thermal power plant turbines, at various temperatures such as room temperature, 300 .deg. C, 425 .deg. C and 550 .deg. C. The characteristics of fatigue crack propagation were examined and analyzed by using fracture mechanics parameter. The plastic replica method was also applied in order to measure the crack length on the basis of serial observation of fatigue crack propagation behavior on the defected specimen surface. The fatigue crack propagation behavior of Cr-Mo-V steel was investigated within the frame work of elastic-plastic fracture mechanics. The propagation law of fatigue crack is obtained uniquely by using the term .sigma. $^{n}$ sub a/where .sigma. $_{a}$ is the service stress, a is the crack length and n is a constant. The values of constant n are nearly equal to 2.48, 2.60 and 8.61 at room temperature, 300 .deg. C and 425 .deg. C.