• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.537-546
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• 2010

This research work contributed to a study for the procedure and methodology to assess the fatigue durability for a composite torque link of helicopter landing gear, which was newly developed and fabricated by the resin transfer moulding technique to interchange with metal component. The simulated load spectrum anticipated to be applied to the torque link during its operation life was generated using an advanced method of probabilistic random process, and the fatigue durability was evaluated by the strength degradation approach on the basis of material test data. The full scale fatigue test was also performed and compared with the analysis results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.167-174
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• 2008

The objective of this study is to verify whether the composite action is sufficiently strong to withstand at the interface and the structural behavior of LB-DECK panel with field concrete slab strengthened with main reinforcing bars. Static and fatigue tests are performed for LB-DECK panels with varied shapes and amounts of rebars, and the results are compared with those of field concrete panel(FCP). The test results indicate that the LB-DECK panel with 1.5 times of more rebars inside significantly increase the overall stiffness. LB-DECK penel usually shows on average 52.1 percent of improved stiffness compared with the FCP. The fatigue test results also show that the LB-DECK panel can withstand two-million cycles of repeated loads without any damage.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.15-21
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• 2011

It is required to accumulate experimental datum that make the theories easy to general technicians in order to use composite material widely on construction field. Therefore, we intend to present base technologies that evaluate static and fatigue performance according to the FRP deck section and offer the basis datum for FRP deck analyses and the design standards. As results of static tests, it can be shown that specimen with fabric direction has higher rigidity than that with normal to fabric direction and convergence for the datum. Due to this reason, it has more stable behavior by structural characteristics of matrix arrangement during destruction. For the fatigue tests, we found that by increasing the number of test repetition, test specimen with fabric direction had an crack just before the destruction, and the contact surface was detached.

• Elastomers and Composites
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• v.47 no.3
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• pp.194-200
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• 2012

Rubber components have been widely used in automotive industry as anti-vibration components for many years. These subjected to fluctuating loads, often fail due to the nucleation and growth of defects or cracks. To prevent such failures, it is necessary to understand the fatigue failure mechanism for rubber materials and to evaluate the fatigue life for rubber components. The objective of this study is to develop the durability analysis process for vulcanized rubber components, which is applicable to predict fatigue life at initial product design step. The determination method of nonlinear material constants for FE analysis was proposed. In order to investigate the applicability of the commonly used damage parameters, fatigue tests and corresponding finite element analyses were carried out and strain energy density was proposed as the fatigue damage parameter for rubber components. The fatigue analysis for automotive rubber components was performed and the durability analysis process was reviewed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.781-785
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• 2015

In this study, a newly developed ultrasonic fatigue test was performed for durability assessment of polyoxymethylene engineering plastic, which has a high crystallization rate and degree of crystallization. Fatigue strength of POM (polyoxymethylene) was performed on a piezoelectric UFT developed by Mbrosia Co., Ltd(1), operating at a high frequency of 20 kHz. The test results showed a fatigue limit of 5.0~6.0 MPa under fatigue testing at R = -1, 20kHz; and, electron microscopy revealed the size effect by risk volume and fractured dimple structure after the coalescence of micro-voids through the crazing effect, which occurs during the failure of a polymer.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.337-345
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• 2006

In this study, to evaluate fatigue characteristics of developed composite bridge deck, compression fatigue test at girder support and flexural fatigue test for the 2.8m-long flexural test model were carried out. For the test specimen, DB 24 truck load was applied up to 2,000,000 cycles. In the compression fatigue test, behavior at deck tube and its bonded connection were evaluated. In the flexural fatigue test, deck behavior at mid-span and girder connection were evaluated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.938-946
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• 1989

Using the CT specimen of carbon steel(SM45C), we estimated the fatigue crack propagation behavior in stable crack propagation range. Furthermore the fatigue crack propagation rate, Acoustic Emission(AE) count rate, and fractography characteristics were also compared among others. The following results were confirmed by experimental observation. Near-threshold stress intensity factor range(.DELTA. $K_{th}$) is influenced by stress ratio but not at the upper limit of stable crack propagation range. As stress intensity factor range(.DELTA.K) and(or) stress amplitude increase (s), both crack propagation rate(da/dN) and AE count rate(dn/dN) increase. Effective stress intensity factor range(.DELTA. $K_{off}$) determined from the crack closure point measurement by AE method is useful for the evaluation of fatigue crack propagation rate. Fractography in stable crack propagation range showed striation, and agreed with the crack propagation rate obtained either by experiment of by the results of microscopic measurements.s.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.751-758
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• 2017

The behavior of fatigue crack growth of nickel-based powder metallurgy superalloy that could be used in aircraft turbine disc is investigated at room temperature, and $650^{\circ}C$ considering real operating conditions. The direct current potential drop(DCPD) method was used to measure the crack length of material in real time according to ASTM E647. Tests were performed with various stress ratios (0.1 and 0.5). Experimental results show that stress ratio, and temperature all affect the behavior of fatigue crack growth. As the stress ratio and temperature increase, the fatigue crack growth rate of nickel-based powder metallurgy superalloy also increases. Results were compared and reviewed with fatigue crack growth rates of other nickel-based superalloy materials (Inconel-100) that were studied in previous papers. Fractography analysis of the fractured specimens was performed using as SEM.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.2
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• pp.81-93
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• 2020

The fatigue characteristics of glass fiber reinforced plastic (GFRP) composites were studied under repeated loads using the finite element method (FEM). To realize the material characteristics of GFRP composites, Digimat, a mean-field homogenization tool, was employed. Additionally, the micro-structures and material models of GFRP composites were defined with it to predict the fatigue behavior of composites more realistically. Specifically, the fatigue characteristics of polybutylene terephthalate with short fiber fractions of 30wt% were investigated with respect to fiber orientation, stress ratio, and thickness. The injection analysis was conducted using Moldflow software to obtain the information on fiber orientations. It was mapped over FEM concerned with fatigue specimens. LS-DYNA, a typical finite element commercial software, was used in the coupled analysis of Digimat to calculate the stress amplitude of composites. FEMFAT software consisting of various numerical material models was used to predict the fatigue life. The results of coupled analysis of linear and nonlinear material models of Digimat were analyzed to identify the fatigue characteristics of GFRP composites using FEMFAT. Neuber's rule was applied to the linear material model to analyze the fatigue behavior in LCF regimen. Additionally, to evaluate the morphological and mechanical structure of GFRP composites, the coupled and fatigue analysis were conducted in terms of thickness.

• Journal of Korean Society of Steel Construction
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• v.15 no.6 s.67
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• pp.629-637
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• 2003

This s paper presented the results of the three phases of fatigue tests to determine the fatigue strength of in-plane welded gusset joints, which are the most common details inevitably existing in the region of high stress range. A total of 57 fatigue specimens with varying thickness and strengths were made and tensile fatigue tests performed. One full-scale beam fatigue test was also performed. The validity of the fatigue strength of those details in the specification was confirmed, with the effects of thickness of flanges and welded attachments, length of attachments, and strength of applied steel examined. The characteristics of crack initiation and propagation were also observed. The test result was evaluated by comparing it with other test data and fatigue criteria of other countries. To determine the degree of stress concentration in the weld toe depending on geometric configuration such as attachment length and transition radius, analyses were performed. Compared to the present specification, analytical results indicate the need to revise and subdivide the detail categories.