• Steel and Composite Structures
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• v.26 no.1
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• pp.103-113
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• 2018

To study the effects of corner braces on fatigue performance of the U-rib and roof weld in steel bridge decks, the fatigue experiment was carried out to compare characteristics of the crack shape with and without corner braces. The improvement of fatigue life and stress variation after setting corner braces were also analysed. Different parameters of corner brace sizes, arrangements, and detail types were considered in the FEM models to obtain stress distribution and variation at the weld. Furthermore, enhancement of the fatigue performance by corner braces was evaluated. The results demonstrated that the corner brace could improve the fatigue life of the U-rib and roof weld, which exerted even no influence on the crack shape. Moreover, stress of the roof weld was decreased and the crack position was transferred from the root weld to U-rib and corner brace weld. It was suggested no weld scallop should be drilled on the corner brace. A transverse rib with lower height which was set between U-ribs was favourable for improvement of fatigue performance.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.157-162
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• 2001

Fretting is a potential degradation mechanism of structural components and equipments exposed to various environments and loading conditions. The fretting degradation, for example, can be observed in equipments of nuclear, fossil as well as petroleum chemical plants exposed to special environments and loading conditions. It is well known that a cast stainless steel(CF8M) used in a primary reactor coolant(RCS) degrades seriously when that material is exposed to temperature range ken $290^{\circ}C{\sim}390^{\circ}C$ for long period. This degradation can be resulted into a catastrophical failure of components. In the present paper, the characteristics of the fretting fatigue are investigated using the artificially aged CF8M specimen. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 1800hr at $430^{\circ}C$ respectively. Through the investigations, the simple fatigue endurance limit of the virgin specimen is not altered from that obtained from the fatigue tests imposed the fretting fatigue. The similar tests are performed using the degraded specimen. The results are not changed from those of the virgin specimen. The significant effects of fretting fatigue imposed on both virgin and degraded specimen on the fatigue strength are not found.

• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.122-129
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• 1988

Recently with the rapid development in marine and shipbuliding industries such as marine structures, ship and chemical plants, there occurs much interest in the study of corrosion fatigue characteristics which was closed up an important role in mechanical design. In this study, the 5086 Al-alloy was tested by use of rotary bending fatigue tester. The retardation effect of overload on the corrosion fatigue crack propagation in sea environment was quantitatively studied. 1) Retardation effect of corrosion fatigue crack propagation is most eminent when overload ratio is 1.52, overload magnitude corresponds to about 77% and 55% of yield strength and tensile strength respectively. 2) After overload ratio 1.52 was used, retardation of corrosion fatigue crack growth rate is largely retarded and quasi-threshold stress intensity factor range($\Delta\textrm{K}_{th}$) appears. 3) According to m of experimental constant, retardation effect of corrosion fatigue crack propagation corresponds to about 25% of constant stress amplitude when overload ratio is 1.52. 4) When overload ratio 1.52 was used, retardation parameter (RP) decreases to about 0.43 and corrosion sensitivity (S)decreses to about 2.1.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.348-352
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• 2004

Recently the steel parts used for automiles and trains are required to be used under higher stress than ever before in need of the weight down. However, threr are a lot of problems with developing such of fatigue strength and fatigue life are mainly focused on by adopting residual stress. And got the following characteristics from crack growth test carried out stress ratio. Fatigue life shows more improvement in the Un-peening material. And Compressive residual stress of surface on the Shot-peening processed operate resistance force of fatigue. So we cam obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is dependent of 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.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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• pp.426-435
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• 2005

The lightness of components required in automobile and machinery industries is requiring high strength of components. Therefore this requirement is accomplished as the process of shot-peening method that the compressive residual stress is made on the metal surface as one of various improvement methods. Special research is, therefore, needed about compressive residual stress on the metal surface in the process of shot-peening method. Therefore, in this paper the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in environmental condition(temperature) and mechanical condition(shot velocity, stress ratio) was investigated with considering fracture mechanics. By using the methods mentioned above, the following conclusions have been drawn. (1) The fatigue crack growth rate(da/dN) of the shot-peened material was lower than that of the un-peened one. In high temperature range. fatigue crack growth rate decreased with increasing temperature range, while fatigue crack growth rate increased by decreasing temperature in low temperature. (2) Fatigue life shows more improvement in the shot-peened material than in the un-peened material. And compressive residual stress of surface on the shot-peen processed operate resistance force of fatigue crack propagation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.596-601
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• 2002

Rotary bending fatigue tests were carried out to investigate the fatigue characteristics of high performance ductile cast iron experienced super rapid induction treatment. The influence of super rapid induction treatment on fatigue limit was experimentally examined with the special focus on the variation of surface microstructure and the fatigue crack initiation and propagation through fractography. Main results obtained are as follows. By super rapid induction treatment in FCD500, the martensite structure obtained through conventional heat treatment was confirmed on the specimen surface. The fatigue crack initiation in the hardened surface layer was restricted by the martensite structure and compressive residual stress. Thus, it could be interpreted that the initiation stress would be increased by improved structure in the surface. The fatigue crack propagation in the hardened layer was retarded by the presence of the globular shape martensite around the graphite nodule and compressive residual stress and the crack propagation behavior has zigzag pattern in the hardened surface layer.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.541-549
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• 2007

This work describes an investigation into the feasibility of using an acoustic emission (AE) technique to evaluate the integrity of a composite actuator with a PZT ceramic under electromechanical cyclic loading. AE characteristics have been analyzed in terms of the behavior of the AE count rate and signal waveform in association with the performance degradation of the composite actuator during the cyclic tests. The results showed that the fatigue cracking of the composite actuator with a PZT ceramic occurred only in the PZT ceramic layer, and that the performance degradation caused by the fatigue damage varied immensely depending on the existence of a protecting composite bottom layer. We confirmed the correlations between the fatigue damage mechanisms and AE signal types for the actuators that exhibited multiple modes of fatigue damage; transgranular micro damage, intergranular fatigue cracking, and breakdown by a short circuiting were related to a burst type signal showing a shortly rising and slowly decaying waveform with a comparably low voltage, a continuous type signal showing a gradual rising and slowly decaying waveform with a very high voltage and a burst and continuous type signal with a high voltage, respectively. Results from the present work showed that the evolution of fatigue damage in the composite actuator with a PZT ceramic can be nondestructively identified via in situ AE monitoring and microscopic observations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.1
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• pp.35-40
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• 2019

The objective of this paper is to identify the fatigue properties of carbon-fiber composite which is widely applied for the development of aircraft structures and obtain data for full-scale fatigue test. The durability and damage tolerance evaluation of composite structures is achieved by fatigue tests and parameters such as fatigue life factor and load enhancement factor. The specimens are made with carbon-fiber/epoxy UD tape and fabric prepreg. Fatigue tests are performed with several stress ratios and lay-up patterns. The Weibull shape parameters are analyzed by Sendeckyj model and individual fatigue lives with Weibull distribution. And the fatigue life factor and load enhancement factor considering reliability are evaluated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.543-554
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• 2016

This study examined the fatigue and its association with job stress among male workers engaged in small-scale manufacturing industries. The study subjects were 553 male workers under 50 members of manufacturing industries. The study survey was a structured questionnaire of the Korean Occupational Stress Scale (KOSS) and Multidimensional Fatigue Scale (MFS) during April, 2015. The data were analyzed using the SPSS ver 21.0 program. The results showed that the high risk fatigue group was significantly higher in the high risk group of job stress than in the normal group of job stress. Fatigue was positively correlated with job stress. The odds ratio of the high risk fatigue group were increased significantly in the high risk group of job stress than in the normal group of job stress. The factors of influence with explanatory powers of 27.7% on fatigue included age, marital status, educational level, subject health status, sleeping time, drinking coffee, job tenure, shift work, visiting out-patient department, sense of satisfaction in job life, and job stress. Fatigue was associated with the sociodemographic characteristics, health behavior related characteristics, job-related characteristics, and job stress.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.12
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• pp.1346-1350
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• 2012

Contact wire is one of the most important components supplying electricity to railroad cars. At the beginning of the research on contact wire, wear problem caused by friction between contact wire and pantograph was considered even more important issue for the failure of contact wire. However, since several fatigue fractures were reported from Shinkansen in Japan, fatigue fracture has become another important issue for the failure of contact wire. Despite of its importance, standard of the fatigue test of contact wire has not been established yet. Thus, fatigue characteristics of contact wire is very difficult issue to evaluate quantitatively. Hence, in this study, test method simulating operating conditions of contact wire by Minsung Kang and etc. is used to evaluate the fatigue characteristics of copper alloy contact wire. Also, test results is compared with the result of Minsung Kang's research on pure copper contact wire.