• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.419-427
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• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.11
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• pp.990-999
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• 2013

Previous studies based on the theoretical evidence and based on the empirical data have been constantly revealing related factors affecting visual fatigue in viewing 3D images. however, the measurement data coupled with the factors that affect the viewers to feel fatigue is insufficient. this study research that the viewers feel the visual functional data is based on subjective fatigue such as IPD, AC/A ratio, and the degree of phoria and the effects on variance in these data, is to examine the correlation between these data. based on the average score of subjective fatigue which is $6.00{\pm}3.88$, total fatigue points from 0 up to 6 is classified as a group not appealing for the fatigue and from 7 up to 16, they were classified as the fatigue appealing group. the results showed no difference in satisfaction of the images by each subjective fatigue, IPD and far phoria. AC/A ratio was higher from the fatigue not appealing group, near phoria was higher from the fatigue appealing group. after watching 3D images, the fatigue not appealing group showed a tendency of higher increase of exophoria. correlations appeared in this experiment showed that AC/A ratio and near phoria are closely related to level of subjective fatigue which feel when watching 3D images. when watching 3D images based on two data appear to be able to predict the fatigue, even during content production fatigue reduce the data dimensions to be used as the main basis is expected.

• Korean Journal of Applied Biomechanics
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• v.22 no.3
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• pp.349-356
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• 2012

This study aimed to assess the effects of progressive lumbar stability exercises and lumbar stability exercises on changes in the transversus abdominis muscle thickness and lower extremity muscle fatigue index in soccer players. Ten subjects were assigned to undergo training in each of the 2 groups, namely, the progressive lumbar stability exercise group and lumbar stability exercise group. Each intervention session lasted for 30 min, and 4 sessions were conducted in a week for 6 weeks for soccer players of S. University in Jeonnam, Korea. Changes in the transversus abdominis muscle thickness and lower extremity muscle fatigue index were measured using ultrasound and surface electromyogram. The results of the ultrasound measurement for the transversus abdominis muscle thickness indicated that progressive lumbar stability exercises were more effective than lumbar stability exercises. The results of the lower extremity muscle fatigue index measurements using surface electromyogram indicated that the fatigue index decreased in the progressive lumbar stability exercise group. Progressive lumbar stability exercise is believed to have put more workload during the shaking of the limbs, leading to increased stability and increased efficiency of the lower extremity muscle, thereby decreasing the fatigue index. Therefore, progressive lumbar stability exercises can be an effective measure for preventing injuries and improving the game performance of sports players by increasing the transversus abdominis muscle thickness and decreasing the lower extremity muscle fatigue index.

• The Journal of Information Systems
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• v.26 no.4
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• pp.39-62
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• 2017

Purpose The purpose of this study is to investigate the factors which affect users' fatigue and reluctant intention of using a SNS. In particular, this study focused on the fatigue of SNS users, as the recent excessive use of SNS has led to negative effects such as invasion of privacy, addition and social overload. fatigue This research will explain how producing adverse effects by using SNS caused psychological and mental depression. Previous researches explained that mental fatigue associated with SNS is not simple one and it is complicated with various psychological factors. Considering this fact, this study introduced a behavioral economics concept and a social comparison theory in the research model. Design/methodology/approach For research purposes, this study developed research hypotheses in order to empirically examine the factors that affect SNS users' fatigue and reluctant intention. The empirical research was based on a poll done through 800 research candidates in the SNS fields and the final 451 responses were collected and used in statistical data analysis. The adaptability, trust, and validity to measurement model were verified and the structural relationship in the research model was analyzed through these 451 responses. Findings First of all, maintenance fatigue of SNS had a positive significant effect on coupling and fatigue of SNS and information privacy had a non-significant effect on fatigue. Second, coupling had a negative significant effect on rational inattention, however, perceived cost had a non-significant effect on rational inattention. Third, lateral/upward comparison had a positive significant on user's negative emotions. Meanwhile, user's negative emotions did not have a significant effect on rational inattention.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.167-175
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• 1988

The principle objective of this study is to evaluate the fatigue behavior of structural steel components of highway bridges subjected to service stresses. The main aspects of this investigation are; 1) a measurement and statistical analysis of service stress cycles observed in highway bridge. 2) fatigue tests under equivalent constant-amplitude(CA) loading and simulated variable-amplitude(VA) loading 3) a evaluation of the fatigue behavior under VA-loading by eqivalent root mean cube (RMC) stress range. Theoretically, the RMC model is adequate in evaluation of fatigue behavior under VA-loading, because the regression coefficient (m) of crack growth rate is 3 approximately. The result of fatigue test shows that the RMC model is fitter than the current RMS model in fatigue evaluation under VA-loading. The interaction effects and sequence effects under VA-loading affect little fatigue life of structural components. As the transition rate of stress ranges is higher, the crack growth rate is higher.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.69-77
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• 1996

The fatigue crack initiation behavior of plasma ion nitrided SACM645 steel was investigated through the rotary bending fatigue test and residual stress measurement by XRD. It was shown by XRD and EPMA that the plasma ion nitrided surface was composed of ${\gamma}^{\prime}(Fe_4N)$phase and ${\varepsilon}(Fe_{2-3}N)$phase, and that the nitrogen atoms existed in Fe matrix in diffusion layer. The OM, SEM and Auger spectroscopy showed that the depth of compound layer, mixed compound and diffusion layer, and diffusion layer was $8{\mu}m$, $30{\mu}m$ and $300{\mu}m$, respectively. However, the microhardness test showed that the depth of hardened layer was $500{\mu}m$. The tensile strength of the ion nitrided SACM645 was lower than that of the unnitrided SACM645, and the ion nitrided specimen was fractured without plastic deformation. The nitrided SACM645 showed much poorer low cycle fatigue properties than the unnitrided one. In rotary bending fatigue, the fatigue strength of the ion nitrided SACM645 was higher than that of the unnitrided specimen, and the fatigue crack initiation sites changed by applied fatigue stress levels. The XRD result showed that the ion nitrided SACM645 has the compressive residual stress from surface to $600{\mu}m$ deep and the tensile residual stress from $600{\mu}m$ to deeper site. It is thought that crack initiation takes place at the point where the total stress of residual stress and applied stress is maximum.

• Fashion & Textile Research Journal
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• v.25 no.2
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• pp.185-198
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• 2023

The purpose of this study is to obtain information necessary for the development of patient clothes that can reduce physical fatigue of caregivers by quantitatively measuring the muscle load and fatigue. The patient clothes used in this study can be broken down into three types: A type (back center zipper open suit), B type (top-to bottom separated patient clothes), and C type (front zipper open suit). The EMG measurement sites are as follows: hand muscle (brachioradialis), upper arm (biceps, triceps), shoulder (anterior deltoid, medial deltoid, posterior deltoid, upper trapezius), and waist (erector spinae); additionally, the EMG signals were measured. Through this experiment, muscle load, muscle energy consumption, and muscle fatigue generation tendency were analyzed. The results of the study revealed that the C type patient clothes required the most strength in the muscles of the shoulders, upper arms, hands, and back when being put on and taken off compared to other patient clothes. The A type clothes required a relatively large force in opening the zipper. In terms of muscle energy consumption, B type generally called for more strength when it came to the zip-up and putarmsup motions. With regard to the cover the body and put legs/hips up motions, C type used the highest amount of muscle energy, whereas A type used relatively little energy. In terms of the occurrence of muscle fatigue during the putting on and taking off of the patient's clothing, there was a difference in the area and degree of muscle fatigue in the A, B, and C types, and there was also a tendency for muscle fatigue to occur when performing repetitive movements.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.3
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• pp.218-223
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• 2007

The dissipation of high-power ultrasonic energy at the faces of the defect causes an increase in temperature. It is resulted from localized selective heating in the vicinity of cracks because of the friction effect. In this paper the measurement of size and direction of crack using UET(Ultrasound Excitation Thermography) is described. The ultrasonic pulse energy is injected into the sample in one side. The hot spot, which is a small area around the crack tip and heated up highly, is observed. The hot spot, which is estimated as the starting point of the crack, is seen in the nearest position from the ultrasonic excitation point. Another ultrasonic pulse energy is injected into the sample in the opposite side. The hot spot, the ending point of the crack, is seen in the closest distance from the injection point also. From the calculation of the coordinates of both the first hot spot and the second hot spot observed, the size and slope of the crack is estimated. In the experiment of STS fatigue crack specimen(thickness 14mm), the size and the direction of the crack was measured.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.8
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• pp.708-713
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• 2011

U.S. nuclear regulatory commission(NRC) regulatory guide(RG) 1.20 requires a comprehensive vibration assessment program(CVAP) for use in verifying the structural integrity of reactor vessel internals(RVI) for flow-induced vibrations prior to commercial operation. The CVAP program consist of vibration and fatigue analysis, a vibration measurement program, an inspection program, and a correlation of their results. One of the main purposes of the analysis program is to select measurement locations, however measurement locations can not be determined by only analysis results, therefore we developed selection criteria of measurement locations for advanced power reactor 1400(APR1400) RVI CVAP, It will be used to select measurement locations and instrument types for APR1400 RVI CVAP.

• Journal of Broadcast Engineering
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• v.19 no.2
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• pp.215-226
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• 2014

The 3D technology has been spread slowly and the reason would be attributed to the fact that most commercialized 3D displays require 3D glasses. There have been various researches on human factors of glass type 3D display. In this study we measured and modeled crosstalk as well as 3D visual fatigue induced by mobile glassless 3D display. Crosstalk as well as visual fatigue varied depending on horizontal position of the 3D mobile display. Measured crosstalk was relative low around the center of the display and it increased at the side of the display. Similar results were found in the measurement of 3D visual fatigue and discomfort. These results imply that human factors should be considered in the process of design and evaluation of mobile 3D displays.