• Journal of the Korean Society for Heat Treatment
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• v.17 no.4
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• pp.254-262
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• 2004

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.113-120
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• 1998

Fatigue crack growth rates(i.e. crack initiation and crack growth of short and long crack) are investigated using commercial plates of high strength Al alloy 7075-T651 for the transverse-longitudinal(T-L) direction in air, water and sea water. Also, the evaluation direct current potential drop(D.C.P.D) method and the fractographical analysis by SEM are carried out. Near threshold region, short crack growth rates were much faster than those of comparable long cracks, and these short crack growth rates actually decrease with increasing crack growth and eventually merge with long crack data. Fatigue crack propagation rates in aggressive media(i.e. sea water) increase noticeably over three times those in air. One of the most significant characters in this phenomenon as a corrosion-fatigue causes an acceleration in crack growth rates. Sea water environment, particularly Cl$^{[-10]}$ solution brings the most detrimental effects to aluminum alloy. The result of fractographical morphology in air, water and sea water by SEM shows obvious dimpled rupture and typical striation in air, but transgranular fracture surface in water and sea water.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.462-469
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• 2005

Single phase bainite structure which is obtained by the conventional austempering treatment reduces the ductility of ductile cast iron. Because of the reduction of ductility it is possible to worsen the fatigue properties. Therefore, semi austempered ductile iron which is treated from ${\alpha}+{\gamma}$ is prepared to investigate the static strength and fatigue properties in comparison with fully austempered ductile iron (is treated from ${\gamma}$). In spite of semi austempered ductile iron shows the $86{\%}$ increase of ductility. Also, semi austempered ductile iron shows the higher fatigue limit and lower fatigue crack growth rate as compared with fully austempered ductile iron. By the fractographical analysis, it is revealed that the ferrite obtained by semi austempering process brings about the plastic deformation(ductile striation) of crack tip and gives the prior path of crack propagation. The relatively low crack growth rate in semi austempered specimen is caused by above fractographical reasons.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.85-99
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• 1998

This paper describes an experimental study to examine collapse causes of the lifting cable due to brittle failure of an fitting anchor under the lifting works. Also, in this study an collapse mechanism that was obtained from stress analysis was compared with an actual collapse procedure. Fractographical analysis as well as chemical component test, tension test and Charpy V-Notch impact test for the fractured steel members were carried out. And then, its results were compared with that of normal steel members. Circumferential surface flaws were developed at internal facets of the fitting anchor before tensile stress occurred. Hence, a higher stress than nominal stress was occurred at flaws by stress concentration at the crack tip. Also, stress intensity factor of members increased by crack size of the potential flaws. Because the stress intensity factor at the crack tip was greater than critical values(fracture toughness), brittle fracture occurred under the lifting works. It is judged that the main collapse of the lifting cable is due to brittle fracture of the fitting anchor.

• Journal of Welding and Joining
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• v.10 no.3
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• pp.26-39
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• 1992

Diffusion bonding of Mo was performed by using the metallic coating of Cu and Cr on the surface to be bonded. Joint characteristics of Mo with or without coating layer were compared in metallurgical and fractograpical aspects. The results showed that the diffusion bonding with coating layer, especially with Cu coating, increased the bending strength of joint. Variation of heating cycle(elevation of temperature for a moment) did not affect significantly the mechanical properties of joint. Fractographical analysis showed that the fracture of joint bonded with Cr coating occurred at the coating layer, while that with Cu coating occurred at the base metal.

• Journal of Yeungnam Medical Science
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• v.7 no.1
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• pp.81-93
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• 1990

The author fractographically analyized the cause of metal failure(the first time this procedure has been used for this metal failure)and also analyized it clinically. In this study, I selected eight cases which have been analyized fractographically. In all these cases, the analysis was done after treatment of metal failure of implants internally fixed to femur shaft fractures at the Department of Orthopedic Surgery, Yeung-Nam University Hospital during the six year period from May 1983 to September 1989. 1. Metal failure occured in five dynamic-compression plates, one Jewett nail, one screw in Rowe plate, and one interlocking nail. 2. The clinical cause of metal failure was deficiency of medial butress in five cases, incorrect position of implant in one case, and incorrect selection of implant in two cases. 3. The time interval between internal fixation and metal failure was four months in one case, between five months to twelve months in six cases, three years in one case. 4. The fractographically analytical cause of metal failure was ; first, impact failure, one case, second, fatigue failure, six cases, machining mark(stress liser), four cases type : low consistent cyclic fatigue failure irregular cyclic fatigue failure third, stress corrosion crack, one case. 5. 316L Stainless Steel has good resistance to corrosion. However, when its peculiar surface film is destroyed by fretting, it shows pitting corrosion. This is, perhaps, the main cause of metal failure. 6. It is possible that mechanical injury occured in implants during the manufacturing of implants or that making a screw hole is the main cause of metal failure.