• International Journal of Highway Engineering
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• v.17 no.3
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• pp.77-83
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• 2015

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.6
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• pp.612-618
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• 2019

In the unmanned vehicle industry, the market is exploding due to the rapid development of public and private demands along with the technological development of the 4th Industrial Revolution. In addition, unmanned mobiles are being used for communication services. In this paper, we analyzed the communication performance of unmanned aerial vehicle according to the characteristics of Doppler frequency. The Doppler frequency was calculated using the geometric model of the unmanned aerial vehicle, and the Doppler frequency of 10km, 30km, 300km, 1000km per hour and the BER performance by AWGN were measured by considering the unmanned high speed unmanned vehicle based on the position of the controller. The Doppler frequency model uses a Dent model and adds additive white Gaussian noise (AWGN) to check the bit errors of the transmitter and receiver. Low speed unmanned vehicles generally exhibited a BER performance of 0.2, while high speed unmanned vehicles generally exhibited a BER performance of 0.06. As the frequency band increases at the same speed, the BER performance increases, and when the speed increases in the same frequency band, the BER performance decreases. This is confirmed by the simulation results to predict theoretically predictable BER performance. In the frequency bands of 2.6 GHz, 5 GHz, and 28 GHz, the BER characteristics by Doppler frequency and the BER characteristics by controller function are verified. effect was confirmed.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.3
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• pp.45-53
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• 2003

Ships and ocean structures are subjected to random loads caused by irregular waves. The irregularity of amplitude from random loading affects on fatigue crack growth and fatigue life. However the effects of irregularity of loading on fatigue including random loading have not been explained exactly. Therefore in this paper crack growth tests on DENT specimens under constant-amplitude loading including a single tensile overload are conducted to investigate the effect of overload on crack growth rate. The size of plastic zone and crack growth rate before and after a single tensile overloading are measured using ESPI system. Crack growth retardation model that is characterized by crack growth length and the size of plastic zone was proposed and compared with test result. From the research, the validity of proposed model is examined on crack growth retardation, and consequently fatigue life.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.521-522
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• 2006

Occlusal loading is considered as the main factor of noncarious cervical lesions. The goal of this study is to identify stress distribution using three dimensional finite element analysis, when occlusal loading is applied on the cervical lesion of human tooth. A finite element model was constructed from micro-CT image and three kinds of static force(500 N) were assumed. In all cases stress concentrates on the same area in the cement-enamel junction. This finding is consistent with published experimental results.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.306-311
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• 2003

A growing fatigue crack is known to be retarded on application of an overload cycle. The retardation may be characterized by the total number of cycles involved during retardation and the retarded crack length. The overload ratio plays an important role to influence the retardation behavior. The objective of the present investigation is to study the effect of different overload ratio on the retardation behavior. For DENT(double edge notched tension) specimens and ESET(eccentrically-loaded single edge crack tension) specimens, fatigue crack growth tests are conducted under cyclic constant-amplitude loading including a single tensile overloading with different overload ratios. The proposed crack retardation model predicts crack growth retardation due to a single tensile overloading. The predictions are put into comparison with the experimental results to confirm the reliability of this model.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.3
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• pp.56-61
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• 2010

Recently, UV pulse laser is widely used in micro machining of the research, development and industry field of IT, NT and BT products because the laser short wavelength provides not only micro drilling, micro cutting and micro grooving which has a very fine line width, but also high absorption coefficient which allows a lot of type of materials to be machined more easily. To analyze the dynamic deformation during a very short processing time, which is nearly about several tens nanoseconds, the commercial Finite Element Analysis (FEA) code, LS-DYNA 3D, was employed for the computitional simulation of the UV laser micro machining behavior for thin copper material in this paper. A finite element model considering high strain rate effect is especially suggested to investigate the micro phenomena which are only dominated by mechanically pressure impact in disregard of thermally heat transfer. From these computational results, some of dynamic deformation behaviors such as dent deformation shapes, strains and stresses distributions were observed and compared with previous experimental works. These will help us to understand micro interaction between UV laser beam and material.

• Archives of Pharmacal Research
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• v.27 no.8
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• pp.867-872
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• 2004

Oxidative stress due to reactive oxygen species (ROS) can cause oxidative damage to cells. Cells have a number of defense mechanisms to protect themselves from the toxicity of ROS. Mitochondria are especially important in the oxidative stress as ROS have been found to be constantly generated as an endogen threat. Mitochondrial defense depends mainly on super-oxide dismutase (SOD) and glutathione peroxidase (GPx), whereas microsomal defense depends on catalase (CAT), which is an enzyme abundant in microsomes. SOD removes superoxide anions by converting them to $H_2O$$_2$, which can be rapidly converted to water by CAT and GPx. Also, GPx converts hydroperoxide (ROOH) into oxidized-glutathione (GSSG). Ovariectomized (OVX) rats are used as an oxidative stress model. An ovariectomy increased the levels of MDA, one of the end-products in the lipid peroxidative process, and decreased levels of the antioxidative enzymes； SOD, CAT and GPx. However, Chondroitin sulfate (CS) decreased the levels of MDA, but increased the levels of SOD, CAT and GPx in a dose-depen-dent manner. Moreover, inflammation and cirrhosis of liver tissue in CS- treated rats were sig-nificantly decreased. These results suggest that CS might be a potential candidate as an anti oxidative reagent.

• Journal of Families and Better Life
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• v.11 no.1
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• pp.119-133
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• 1993

Based on the Double ABCX model of family stress and adaptation this study was to investi-gate the intercorrelations among and the relative magnitutide of variables associated with diffe-rent levels of adaptation to conflict with mothers-in-law reported by daughter-in-law. Frequency of conflict was selected as a stressor(aA) Resource factor(bB) in this study was self-efficacy. Four types of blame(self-behavior self-character other people and impersonal world blame) were selected as perception factors(cC). The adaptation factors(xX) were the level of daughter-in-law's psychological well-being and marital adjustment. Data for this research were questionnaire responses from 151 daughters-in-law who lived in Seoul. The results of correlational analyses indicated that most variables were significantly correlated with each other. In addition results of the path analysis on daughter-in-law's psychological well-being indicated that higher scores on the psychological well-being were significantly associa-ted with(a) greater self-behavior blame for the conflict and (b) less ascription of blame to the impersonal world. Frequency of conflict influenced psychological well-being indirectly th-rough self-behavior blame and impersonal blame both of which were also found to mediate the effect of self-efficacy on the level of psychological well-being. However although all indepen-dent variables were significantly correlated with marital adjustment no variables had direct effects on marital adjustment.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.16-22
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• 2004

Dimethyl Ether (DME) has been considered as one of the most attractive alternative fuels for a compression ignition engine. The major advantage of DME-fuelled engine is a great potential for soot-free combustion without sacrificing an inherent high thermal efficiency of diesel engine, despite a necessity for modification of the conventional fuel injection system. An experimental study on DME and conventional diesel sprays was conducted by employing a common-rail type fuel injection system with a 5-holes sac type nozzle, including a constant volume vessel pressurized with nitrogen gas. The injection rates of DME and diesel fuel were recorded with the Bosch type injection rate meter. The injection delay of DME was shorter than that of diesel fuel. The measured injection rates of DME and diesel fuel were correlated with spray penetrations. The prediction method of spray penetration was established using the injection rates, which was verified with the Dent's penetration model and found to agree well for DME case.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.81-93
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• 1989

The present study attempts to develop the theoretical model for the damage estimation of offshore tubular members which are subjected to the accidental impact loads due to collision, falling objects and so on. For the reasons of the simplicity of the problem being considered, however, this paper postulates that the accidental load can be approximated to be the quasi-static one, in which dynamic effects are negelcted. Based upon the theoretical and experimental results which are obtained from the present study as well as the existing literature, the load-displacement relations taking the interaction effect between the local denting and the global bending deformation into account are presented in the explicit form when the concentrated lateral load acts on the tubular member whose end condition is supposed to be rotation ally free and axially restrained, in which membrane forces develop. Thus, the practical estimation of damage deformation for the local denting and the global bending damage of tubular members against the accidental loads is possible and also the collision absorption capability of the member can be calculated by performing the integration of the area below the given load-displacement curves, provided that all the energy is dissipated to the deforming the member itself.