• Advanced Composite Materials
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• v.17 no.3
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• pp.215-224
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• 2008

The present study aims to design a multilayer microstrip antenna with composite sandwich construction and investigate fatigue behavior of this multilayer SAS (surface antenna structure) that was asymmetric sandwich structure for the next generation of structural surface technology. This term, SAS, indicates that the structural surface becomes an antenna. Constituent materials were selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, antenna elements inserted into structural layers were designed for satellite communication at a resonant frequency of 12.2 GHz. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue life curve of the SAS was obtained. The experimental results of bending fatigue were compared with single load level fatigue life prediction equations and in good agreement. The SAS concept is can be extended to give a useful guide for manufacturers of structural body panels as well as antenna designers.

• Structural Engineering and Mechanics
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• v.26 no.3
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• pp.343-361
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• 2007

This article presents a numerical tool for dimensioning two-threaded fasteners connecting prismatic parts subjected to fatigue tension loads that are coplanar with the screw axis. A simplified numerical model is developed from unidirectional finite elements, modeling the connected parts and screws with bent elements and the elastic contact layer between the parts with springs. An algorithm updating the contact stiffness matrix, calculating forces and displacements at each node of the structure and thus normal stresses in the screws in both static and fatigue is further developed using C language. An experimental study is also conducted in parallel with the numerical approach to validate the developed model assumptions, the numerical model and the 3D finite element results. Since stiffness values for the compressive zones in the parts are analytically difficult to determine, a statistical software method is used, from which a tuning factor is derived for identifying these stiffness values. The method is also applied to set out the influence of each parameter on the fatigue behaviour of each screw. Finally, the developed model will be used to establish a new, sophisticated, fast and accurate tool for dimensioning bolted mechanical structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.475-480
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• 1997

It is common to assum identical allowable safety factors in static strength, defined by mean stress and in fatigue, defined by stress amplitude. Under the load with asymmetrical cycles the safety factor is not the same. In this paper, with the consideration of unequal allowable safety factors a general method for estimating fatigue reliability of a machine element under a combined state of stress is derived based on the theory proposed by Prof. Kececioglu and normal distribution. The calculation of fatigue reliability for limited life is discussed with example.

• Journal of the Korean Society for Railway
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• v.8 no.6 s.31
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• pp.495-499
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• 2005

Fatigue behavior of reinforced concrete(RC) elements has been experimentally and analytical investigated. Fatigue behavior is influenced by a longitudinal reinforcement ratio, strength of concrete and a load ratio Pu/Po. The purpose of this study to propose an empirical formula for the fatigue behavior on the basis of experimental results. Also an analytical method to predict the crack propagation of RC beams has been developed based on the relationships between bond stress and slip.

• International Journal of Automotive Technology
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• v.8 no.3
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• pp.309-317
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• 2007

In this study, we conducted a vibration fatigue analysis of the lower control arm in a vehicle suspension system. The vehicle was driven during the tests so that the dynamic effects could be taken into account. The dynamic load of the frequency domain was superimposed on the frequency response analysis. We performed a virtual proving ground test using multi-body dynamics, along with a finite element analysis and fatigue life predictions. Shape optimization was also considered using the design of the experimental approach, and a response surface analysis was performed to improve the durability performance of the lower control arm. We identified the elements that had the most influence on the optimal shape of the finite element model and analyzed the sensitivity of those elements. Then the optimal points that minimized the amount of damage to the areas of interest were determined through a response surface analysis. The results suggested that the fatigue life of the model increased as its mass was not increased excessively, and demonstrated that these design procedures yielded an appropriate optimized lower control arm model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1078-1084
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• 2005

The relationship between fatigue crack opening behavior and the reversed plastic zone sizes is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack, where the contact elements are used in the mesh of the track tip area. The smaller element size than reversed plastic zone size is used fer evaluating the distribution of reversed plastic zone. In the author's previous results the FEA could predict the crack opening level, which crack tip elements were in proportion to the theoretical reversed plastic zone size. It is found that the calculated reversed plastic zone size is related to the theoretical reversed plastic zone size and crack opening level. The calculated reversed plastic zone sizes are almost equal to the reversed plastic zone considering crack opening level obtained by experimental results. It can be possible to predict the crack opening level from the reversed plastic zone size calculated by finite element method. We find that the experimental crack opening levels correspond with the opening values of contact nodes on the calculated reversed plastic zone of finite element simulation.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.20 no.1
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• pp.15-20
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• 2014

Background: The purpose of this study was to investigate the effect of differing insole height on the electromyographic (EMG) activity and muscle fatique in tibialis anterior and gastrocnemius a lot of repeat college students from the desk during a sit to stand activity. Methods: For the 20 subjects (males), let them wear insole in order. Using EMG equipment measured the difference in muscle activity and muscle fatigue degree. All subjects measured for 3 seconds in standing up from the chair. It's measured total 3 times. Results: The summary of results stated above is as follows: It's sitting to standing activity when there were no significant differences between the muscles. But sitting activity in muscle fatigue-calf muscle during standing activity correlated only. Conclusion: The results of this study, the height of an adult male lead in adequate to maintain a healthy foot function and health elements of effective and aesthetic elements based on a significance in that it presents.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.103-112
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• 1994

Various kinds of fatigue failures of ocean structures were reported and the importance of fatigue life estimation at the design state is significantly recognized and various kinds of analysis approaches have been discussed. In this paper characteristics of the simplified method proposed here and the spectral method are studied and the elements of the approach are discussed. The merits and demerits of the forementioned analysis schemes are studied and the relating parameters such as SCF and S-N curves are also investigated. The simplified fatigue analysis approach and tile spectral fatigue analysis technique is applied for the analysis of bracing members of typical semi-submersible drilling rig structure for the verification of the usage of two methods and the sensitivity study has been performed using the simplified method. The result from the spectral analysis give a more realistic picture of the fatigue life of the offshore structure considered here.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1455-1460
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• 2006

The relationship between fatigue crack growth behavior and cyclic crack tip opening displacement is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the growth behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. We investigate the relationship between the reversed plastic zone size and the changes of the cyclic crack tip opening displacement along the crack growth. We investigate the effect of the element size when predict fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The cyclic crack tip opening displacement is related to fatigue crack opening behavior.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.05a
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• pp.31-36
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• 1998

It is very important to have exact informations on the properties and characteristics of the sintered steel as a new material of machine elements. The bending fatigue tests are performed for sintered steel bend specimens and spur gears, which are notched by using a slicing blade. The fatigue test at a constant stress amplitude is performed by using an electrohydraulic servo-controlled pulsating tester Consequently, the S-N curves are obtained and the fatigue strength. is compared with flaw depth. Accordingly, this study presents the fatigue strength of sintered spur gears, the critical notch depth of sintered steel and the effects of flaw depth on the bending fatigue strength. The enhancement of fatigue strength due to carburized treatment is clarified.