• Journal of Mechanical Science and Technology
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• v.14 no.5
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• pp.530-536
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• 2000

In this paper, the influence of several factors such as hardness, internal defect and non-propagating crack on fatigue limits was investigated with three kinds of ductile iron specimens. From the experimental results the fatigue limits were examined in relation with hardness and tensile strength in case of high strength specimens under austempering treatment; in consequence the marked improvement of fatigue limits were not showed. The maximum defect size was an important factor to predict and to evaluate the fatigue limits of ductile irons. And, the quantitative relationship between the fatigue limits$({\sigma}_w)$ and the maximum defect sizes $(\sqrt{area}_{max})$ was expressed as ${\sigma}_w^n{\cdot}{\sqrt{area}}_{max}=C_2$. Also, it was possible to explain the difference for the fatigue limits in three ductile irons by introduction of the non-propagating crack rates.

• Journal of the Korean Society of Safety
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• v.23 no.3
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• pp.12-16
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• 2008

For industrial centrifuges, the state of their welding areas, even with a naked-eye observation, offers potential safety problems such as inconsistent bead formation. STS304, which is used mainly in centrifuges, is made of metal alloys with chrome and nickel as the main ingredients, offering excellent corrosion resistance, thermal resistance, and high strength, and thus allowing it to be used for diverse purposes. This paper conducted tensile and fatigue tests of STS304 to improve the safety of centrifuges. In the findings, for the static behavior of the STS304 material, welded specimens increased their yield and tensile strength compared with the base test specimens, but decreased their elongation ratio. Also, the data dispersion phenomenon of welded specimens remarkably increased.

• Journal of Advanced Marine Engineering and Technology
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• v.17 no.2
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• pp.52-59
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• 1993

This study is investigated of tensile and fatigue strength for advanced composite materials under hygrothermal environment. The materials used are two types of Carbon/Epoxy reinforced composite materials i.e., 13$0^{\circ}C$ cure-type composite T-1/347, and 18$0^{\circ}C$ cure-type MM-1/982X. These are composed by cross-ply laminates. Test condition is the distilled water of 8$0^{\circ}C$. The separate absorption contents estimated by the Fick's diffusion rule are similar to the experiment results. The tensile strength of T-1/347 wet specimens more increased than that of dry ones, but that of MM-1/982X decreased. The fatigue strengthes of both T-1/347 and MM-1/982X wet specimen more decreased than those of dry specimens.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.390-395
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• 2003

This study examined the effects of the testing temperature on the mechanical properties of the stainless steels (STS301CSP-3/4H and STS301CSP-H) for flat spring. Hardness test and fatigue test were performed at room temperature (2$0^{\circ}C$ Tensile testandcreeptestwere performed attemperature range 2$0^{\circ}C$~10$0^{\circ}C$. The micro-victors hardness values of STS301CSP-3/4H and STS301CSP-H were HV=443 and HV=488. respectively. The Elastic modulus, tensile strength, yield strength and strain of these materials were decreased with increasing testing temperature. respectively. The maximum creep strain for 100hr atcreep temperature (10$0^{\circ}C$~20$0^{\circ}C$ and creep stress (Tensile strength$\times$50%) of these materials were 0.53％~0.58%. The fatigue limit of STS301CSP-3/4H and STS301CSP-H were 64.5Kgf/mm$^2$ and 67.4Kgf/mm$^2$, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.95-96
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• 2006

This study examined the effects of the tempering temperatures($360-420^{\circ}C$) on the mechanical properties of the carbon tool steel (SK4M) for flat spring. Hardness test, tensile test and fatigue test were performed at room temperature($20^{\circ}C$). The tensile strength and yield strength of $390^{\circ}C\;and\;420^{\circ}C$ tempered SK5M were 0.93-0.97 times and 0.81-0.87 times those of $360^{\circ}C$ tempered SK5M, respectively. The fatigue limit of $360-420^{\circ}C$ tempered SK5M were 35-40% of tensile strength of $360-420^{\circ}C$ tempered SK5M, respectively.

• Korean Journal of Metals and Materials
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• v.47 no.7
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• pp.391-396
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• 2009

Tensile, low cycle fatigue, and fatigue crack growth rate tests were conducted at RT and $300^{\circ}C$ for type 304 stainless steel. Tensile was tested under displacement control and low cycle fatigue was tested under strain control. Fatigue crack growth rate test was conducted under load control and crack was measured by DCPD method. Yield strength and elongation decreased at $300^{\circ}C$. Dynamic strain aging was not detected at $300^{\circ}C$. Low cycle fatigue life increased but fatigue strength decreased at $300^{\circ}C$. Fatigue crack growth rate increased at $300^{\circ}C$. Dislocation structures were mixed with cell and planar and did not change with temperature. Grain size did not change but plastic strain increased at $300^{\circ}C$. Strain induced martensite after low cycle fatigue test increased at RT but decreased at $300^{\circ}C$. It was concluded that the increase of low cycle fatigue life at $300^{\circ}C$ was due to the decrease of strain induced martensite at which crack was initiated.

• Transactions of Materials Processing
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• v.21 no.6
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• pp.354-359
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• 2012

Effects of a nitriding treatment on the tensile and high cycle fatigue properties were investigated by conducting ion-nitriding and gas nitro-caburizing treatments on the spheroidized SCr430B medium-carbon steel and performing tensile and tension-tension high cycle fatigue tests. The nitrided samples showed much lower strength and ductility compared to those in the initial as-spheroidized state and premature fracture occurred at the hardened layers. The micro-voids in the compound layer caused fatigue crack initiation. Thus, the removal of the compound layer with micro-voids remarkably improved the fatigue resistance to even beyond that of the as-spheroidized sample.

• Journal of Welding and Joining
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• v.23 no.1
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• pp.35-40
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• 2005

In this paper, static and fatigue load tests for the specimens, components and carbody were carried out to investigate the strength of welded joints in aluminum rolling stock. Tensile test results showed that the static strength of welded joint for the heat-treated alloy is reduced significantly and fatigue strength data are scattered by the welding imperfections. Component and whole carbody fatigue test results showed agreements with the design fatigue strength standards for specimens of the same joint detail. Test results revealed that full penetration welding and strict management of welding procedure are crucial for securing the strength of welded joint in aluminum carbody.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.5
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• pp.42-50
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• 1991

According as the members and inner and outer plates of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. Therefore, it has been increasingly required to improve the fatigue strength of the spot welded structures. As one of the improving methods for such problem, the author had previously proposed the method of alleviating stress concentration at nugget edge of the spot weld part and improving its fatigue strength [1]. But, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic estimation method of them. In this report, by considering nugget edge of the spot weld part of the spot welded lap joint subjected to tensile load to the ligament crack, fatigue strength of various spot welded lap joints was estimated with the stress intensity factor (S.I.F.) K which is fracture mechanical parameter. It is known that evaluation of fatigue strength of the spot welded lap joint by the stress intensity factor (S.I.F.) K is more effective than the maximum stress $(\sigma_{ymax}$) at edge of the spot weld part on the center line of width of the plate.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.193-197
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• 2005

Influences of microstructure on high-cycle fatigue (HCF) limit of high carbon $(>0.7wt.\;\%)$ steel filaments used for tires have been investigated. A series of the fatigue tests was carried out depending on carbon content by using Hunter-type tester at a frequency of 60 Hz at a tension/compression stress of 900 to 1500 MPa. Microstructural changes of the filaments were identified in the lateral direction by using transmission electron microscopy (TEM). It was found that the mechanical properties, such as fatigue limit and tensile strength, were improved with increasing carbon content, which was mainly attributed to decreased lamellar spacing and cementite thickness. However, the fatigue ratio, which is defined as the ratio of the fatigue limit to the tensile strength, was reduced in a higher carbon range of 0.8 to $0.9\;wt.\%$, while the fatigue ratio was nearly constant in a lower carbon range of 0.7 to $0.8\;wt.\%$. Overall mechanical properties of the filaments, depending on carbon content, have been discussed in terms of the microstructural parameter change of lamellar spacing and cementite thickness. In addition, the variation of cementite morphology on the fatigue crack propagation of high carbon $(0.9wt.\;\%)$ filaments will be discussed.