This study aims at analyzing the property of the structural body bonded with alumimum foam by the utilization of the aluminum foam of closed type used generally with impact absorbent. The structural bodies bonded with the aluminum foam of DCB and TDCB are designed in this study, and then the fatigue analysis and experiment are carried out. At fatigue analysis, the maximum load happens at all of each specimen models when the fatigue life of 0 to 50 cycle is proceeded. And from the point of time that the maximum load happens, the load at the bonded surface is seen to be decreased in cases of analysis and experiment. As the specimen thickness is increased, the maximum load happened at specimen is increased. It is confirmed that the result of fatigue analysis becomes similar to that of fatigue experiment for verification. It is thought that the study data on various specimen thicknesses can be secured simply without the extra fatigue experimental procedure. By using this study result, the mechanical properties of the structural bodies bonded with the alumimum foams of DCB and TDCB with mode Ⅲ type can be thought to be analyzed effectively.

This study is on the structural analysis and fatigue evaluation of Re-EV engine cam shaft used to drving range extended electric vehicle. Recently, Electric vehicle is very important for driving extended. Specially this study is upgrade of cam shaft to improve durability and fatigue life.

Aging aircraft structures are inevitably exposed to environment for a long time facing many potential problems, including corrosion and wide spread fatigue damage, which in turn cause the degradation of flight safety. In this study, the environmental surface damages on aging aircraft structures induced during service were quantitatively analyzed. Additionally, S-N fatigue tests were performed with center hole specimens extracted from aging aircraft structures. From the results of quantitative analyses of the surface damages and fatigue tests, it is concluded that corrosion pits initiated during service reduce the fatigue life significantly. Finally, using the fracture mechanics and the EIFS (equivalent initial flaw size) concepts, the remaining fatigue life was predicted based on actual fatigue test results.

목적: 본 연구에서는 식물성 약재인 차즈기 추출물의 눈 피로 개선에 대한 양안시기능 평가를 해보고자 한다. 방법: 선천성 또는 만성질환이 없고 내과적인 진찰결과 병적 증상 또는 소견이 없는 사람 중에 서 임상병리 검사 및 활력징후가 정상범위에 속하며 등가구면 굴절이상도가 –3.00D 이상인 피 험자 30명을 대상으로 본 실험을 진행하였다. 피험자들은 차즈기 추출물을 구강 섭취하는 실 험군과 위약(placebo)을 구강 섭취하는 대조군의 총 2개의 그룹으로 15명씩 나뉘어 무작위로 ‘시험물질 → 위약 투여군’과 ‘위약 → 시험물질 투여군’으로 배정하여 각각 일주일 동안 구강 섭취하도록 하였다. 500mg의 차즈기 추출물과 대조군인 위약(placebo)을 각각 복용하고, 체내 에 흡수되는 시간을 감안하여 2시간 후 시각적 근거리 작업을 2시간 동안 진행한 후에 폭주근 점과 조절근점, 양안조절용이성 검사를 실시하였다. 검사는 3회 측정한 평균값으로 SPSS 21.0 프로그램을 이용하여 p<0.05 수준에서 통계적 유의성을 검증하였다. 결과: 시각적 근거리 작업 전과 후의 평균 폭주근점 변화를 비교한 결과, 차즈기 추출물을 복 용 했을 때는 7.80±2.33 cm에서 6.94±2.16 cm로 –0.86±0.16 cm만큼 감소하는 유의성을 보였고, 위약을 복용했을 때는 8.18±2.26 cm에서 9.41±2.20 cm로 +1.23±0.75 cm만큼 증 가하는 유의성을 보였다. 평균 조절근점 변화를 비교한 결과에서는, 차즈기 추출물을 복용했을 때 우안에서는 -0.85±1.32 cm, 좌안에서는 -0.71±1.21 cm, 양안에서는 –0.69±1.46 cm로 통계적으로 조절근점이 유의하게 감소하는 변화를 보였으며, 위약을 복용했을 때는 우안은 +0.73±0.79 cm, 좌안은 +0.83±1.12 cm, 양안은 +0.67±0.84 cm로 조절근점이 유의하게 증 가하는 변화를 보였다. 마지막으로 평균 양안조절용이성 변화를 비교한 결과, 차즈기 추출물을 복용했을 때는 +1.27±2.41 cpm의 변화를 보여 통계적으로 유의하게 증가하였으나, 위약을 복용했을 때는 –0.07±2.57 cpm로 통계적으로 유의할 정도의 차이는 아니지만 감소하는 경향 을 볼 수 있었다. 결론: 차즈기 추출물에서 위약에 비해 통계적으로 유의하게 평균 폭주근점의 증가를 억제하는 것으로 나타나 폭주력 개선에 효과가 있는 것을 알 수 있었고, 평균 조절근점 또한 감소하였으 므로 조절력 개선에도 효과를 보이는 것으로 확인할 수 있었다. 평균 양안조절용이성 역시 차 즈기 추출물에서 증가하였으므로 조절 부담에 의한 눈의 피로도를 개선하는데 효과를 보이는 것으로 나타나 차즈기라는 식물성 약재가 눈에 미치는 긍정적인 효과에 대한 연구가 필요할 것으로 사료된다.

목 적: 본 연구는 스마트폰을 이용한 근거리 시작업 후 눈피로와 관련된 EEG(뇌파)의 특성을 알아보고 눈 피로의 객관적 지표로서 활용가능성을 확인하고자 한다. 방 법: 20-30세 남녀 대학생 24명을 대상으로 2시간 동안 스마트폰을 통한 근거리 시작업 전 과 후의 EEG를 측정하였다. EEG를 측정하기 위해 전형적인 10-20 방법을 참조하여 4개 채널 의 전극을 Fp1, Fp2, Pz, Oz 위치에 부착하였으며, 측정장비는 (주)락싸 4채널 (QEEG LXE-3204)를 사용하였다. 실험이 시작되면 피험자는 모니터의 흰 바탕화면을 응시하도록 하였 으며, 화면우측 중앙에 검정색점이 1초간 제시 후 사라진 다음 “루”글자가 화면 좌측 중앙에 2초간 나타나도록 하여 안구의 단속운동이 이루어지도록 하였다. 피험자가 실험에 임하고 있음 을 확인하기 위해 피험자에게 “루”글자가 나타났다 사라지면 스페이스바를 가능한 한 빨리 눌 러서 반응하도록 하였다. 화면에 제시된 자극에 대한 키보드 반응이 1초 이상 걸린 시행은 분 석에서 제외하였다. 또한 앞선 시행이 다음시행에 미치는 영향을 방지하기 위해서 “루”글자가 사라진 후 검정색점 이 나타나기까지 간격을 7초로 유지하였다. 결과: 4개 채널 각각에 대하여 “루”글자가 나타날 때를 기준으로 획득된 조건별 50회의 데이 터에 대해 조건별 평균 파형을 계산하여 ERP분석을 수행한 결과, Pz와 Oz채널에서 P3 성분의 실험조건 간 차이가 시각적으로 확인되었다. Pz 채널과 Oz 채널 모두 정점이 나타나는 시간은 두 조건에서 모두 비슷하였으나 P3성분의 정점크기가 스마트폰을 이용한 근거리 시작업 후에 상대적으로 작게 나타났다(p<0.05). 결론: 시각과 연관된 후두엽 부위의 Pz와 Oz 모두에서 근거리 시작업 후 눈피로가 증가하는 요인으로 유추해 볼 수 있는 P3성분의 상대적으로 낮은 정점크기를 확인 할 수 있었다. 이는 눈 피로와 관련된 객관적 지표로서 활용이 가능할 것이라 생각된다.

The chassis frame generally consists of side members, cross beams, and several mounting brackets. Strength and fatigue behaviors of welded joints between members and brackets in a frame are a very complex phenomena, which comes basically due to the structural geometry, non-homogeneous material, and welding residual stresses. Therefore, the prediction of fatigue life for the welded structure is very difficult compared to that for the simple geometry. This paper presents the structural and fatigue analysis results for a body frame and welded joints under system durability loads. In order to fatigue assessment of welded joints, local stress approach is used for its simplicity, which is based on the several empirical S-N curves that are associated with welded joint types and loading modes. The estimated fatigue cycles of the welded areas in a frame were satisfied the target cycles under system load conditions.

This paper studies on the effect of kurtosis on fatigue life. A typical vibration test machine uses a normal distribution signal. However, the vibration signal generated in the actual operating environment is a non-normal distribution signal with kurtosis. In this paper, a signal which has the same power spectral density, but has different kurtosis is generated using the Zero Memory Non-Linear(ZMNL) method. The power spectral densities of these two signal will coincide within ±3dB. Fatigue damage spectrum(FDS) computed with a normal distribution signal and FDS computed with a non-normal distribution signal generated using the ZMNL method are compared. FDS computed using the normal distribution signal of kurtosis 3 will show a big difference over the 100Hz with FDS computed using the signal of kurtosis 6. This paper shows through such FDS comparison that a difference in fatigue life prediction may result in if a vibration profile which does not consider kurtosis occurring in the operating environment of a product is used in a vibration test.

As aluminum foam has the most superior absorption of impact energy, this material has been used at automobile and airplane. If aluminum foam is used by jointing bolt and nut, it can be broken. Therefore, it is more effective to bond aluminum foam and other materials by adhesive. In this study, the fatigue fracture simulation through ANSYS program is carried out on the aluminum foam specimen bonded with adhesive as the type of DCB Mode Ⅲ. There are four kinds of specimens with the types of DCB Mode Ⅲ in this study. The thicknesses of four specimens are 35mm, 45mm, 55mm and 65mm. In cases of specimen thicknesses of 35mm, 45mm, 55mm and 65mm, the maximum loads are shown as ±0.2kN, ±0.55kN, ±1kN and ±1.2kN respectively. As the specimen thickness increases, the maximum loads increase. The results of fatigue experiment as specimen thickness of 55mm can be shown to approach the simulation results by confirming the simulation results of this study. So, The simulation data can be applied in order to investigate the mechanical property at DCB specimen with the type of Mode Ⅲ.

Fatigue crack growth rate tests were conducted as a function of temperature, dissolved hydrogen (DH) level, and frequency in a simulated PWR environment. Fatigue crack growth rates increased slightly with increasing temperature in air. However, the fatigue crack growth rate did not change with increasing temperature in PWR water conditions. The DH levels did not affect the measured crack growth rate under the given test conditions. At 316 oC, oxides were observed on the fatigue crack surface, where the size of the oxide particles was about 0.2 μm at 5 ppb. Fatigue crack growth rate increased slightly with decreasing frequency within the frequency range of 0.1 Hz and 10 Hz in PWR water conditions; however, crack growth rate increased considerably at 0.01 Hz. The decrease of the fatigue crack growth rate in PWR water condition is attributed to crack closure resulting from the formation of oxides near the crack tips at a rather fast loading frequency of 10 Hz.

본 논문에서는 재료 점소성-손상모델을 기반으로 한 피로균열 진전속도(FCGR) 전산 평가법을 제안한다. 7% 니켈강 재료 거동을 모사하는 점소성-손상모델을 소개하고, 이의 유한요소해석 플랫폼에의 적용을 위해 상용 유한요소해석 프로그램인 ABAQUS에서 제공하는 사용자 정의 재료 서브루틴(UMAT)에 재료모델을 탑재하였다. 개발 UMAT의 검증을 위해 7% 니켈강 재료 인장시험 시뮬레이션을 수행하였으며, 이를 통해 재료정수를 획득하였다. 또한, 피로하중에 따른 손상해석에 있어 계산 시간 단축을 위한 jump-in-cycles 과정과 임계 손상 값 조정 및 피로 예비 균열 시뮬레이션을 수행하였고 이들 과정을 개발 UMAT에 탑재하여 해석을 수행하였다. 개발 UMAT을 활용하여 7% 니켈강의 상온 FCGR 테스트 시뮬레이션을 수행하였으며, 균열길이(a)와 주기 수(number of cycles)의 관계 및 1 cycle 당 균열성장량(da/dN)과 응력확대계수 진폭(ΔK)의 관계 등의 결과를 실험결과와 비교하여 검증하였다.

Recently, the light weight and the safety of automobile are the important targets of automotive design and the parts for car have been substituted the plastic or the porous material for the steel material. As the aluminium foam has many pores at its surface, it has the fatigue property of bonded face which differs from general material. In this study, two dimensional model is designed and performed with the fatigue analysis as the variable(θ value) becomes the slant angle of bonded face at the specimen with the aluminium foam. As the analysis result on the models with the slant angles of 6°, 8° and 10°, the bonding forces are disappeared when the fatigue loads are repeated during 4000 cycle, 4500cycle and 5000cycle respectively. By comparing with the analysis results of three models, the fatigue cycle to endure fatigue load becomes larger as the slant bonded angle becomes higher. So, the structural safety can be seen by applying only as only a simulation of finite element method instead of the experiment where much cost and time is spent. In this study, the configuration of aluminum foam is designed with the shape of TDCB Mode II. The shear fatigue strength of the bonded structure can be evaluated by the analysis program of ANSYS.

본 연구에서는 2D 화면과 3D화면으로 각각 제시된 운전 시뮬레이션 환경에서 운전자의 종적 차량통제, 주관 적 피로감 및 지각된 현실감에서의 차이를 비교하였다. 본 연구의 결과들을 요약하면 다음과 같다. 첫째, 실험참 가자들은 미리 정해진 네 가지 수준의 목표속도(60, 80, 100 및 120km/h)를 유지할 때 3D 조건보다는 2D 조건에 서, 그리고 목표속도가 낮을수록 목표속도에 비해 더 빠르게 운전하였고, 이러한 경향은 목표속도 조건과 상관없 이 일정하였다. 둘째, 선행차량과의 차간거리 유지수행에 대한 분석 결과, 2D 조건에 비해 3D 조건에서 실험참가 자들은 선행차량과 더 근접한 차간거리를 유지하며 주행하였는데, 특히 선행차량의 주행속도가 비교적 느렸던 조건(즉, 60km/h)에 비해 비교적 빨랐던 조건(즉, 80 및 100km/h)에서 이러한 경향이 두드러졌다. 셋째, 속도 유지 과제와 선행차량과의 차간거리 유지수행 모두에서 2D 조건에 비해 3D 조건에서 실험참가자들이 경험하는 피로 감의 수준이 더 높았으나 주관적 현실감에 대한 평가에서는 두 가지 과제 모두에서 2D와 3D 조건에 따라 유의 한 차이가 관찰되지 않았다.

PURPOSES : This research describes how to predict the life cycles of fatigue cracking based on NCHRP Report 704 as well as modified harmony search (MHS) algorithm. METHODS : The fatigue cracking regression model of NCHRP Report 704 was used in order to calculate the ESAL (Equivalent Single Axle Load) numbers up to pavement failure, based on using material parameters, composite modulus, and surface pavement thickness. Furthermore, the MHS algorithm was implemented to find appropriate material parameters and other structural conditions given the number of ESALs, which is related to pavement service life. RESULTS: The case studies show that the material and structural parameters can be obtained, resulting in satisfying the failure endurance of asphalt concrete structure, given the number of ESALs. For example, the required ESALs such as one or two millions are targeted to satisfy the service performance of asphalt concrete pavements in this study. CONCLUSIONS : According to the case studies, It can be concluded that the MHS algorithm provides a good tool of optimization problems in terms of minimizing the difference between the required service cycles, which is a given value, and the calculated service cycles, which is obtained from the fatigue cracking regression model.

PURPOSES: The objective of this paper is to select the confidential intervals by utilizing the second moment reliability index(Hasofer and Lind; 1974) related to the number of load applications to failure which explains the fatigue failure and rut depth that it indicates the permanent deformation. By using Finite Element Method (FEM) Program, we can easily confirm the rut depth and number of load repetitions without Pavement Design Procedures for generally designing pavement depths. METHODS : In this study, the predictive models for the rut depth and the number of load repetitions to fatigue failure were used for determining the second moment reliability index ( ). From the case study results using KICTPAVE, the results of the rut depth and the number of load repetitions to fatigue failure were deducted by calculating the empirical predictive equations. Also, the confidential intervals for rut depth and number of load repetitions were selected from the results of the predictive models. To determine the second moment reliability index, the spreadsheet method using Excel’s Solver was used. RESULTS : From the case studies about pavement conditions, the results of stress, displacement and strain were different with depth conditions of layers and layer properties. In the clay soil conditions, the values of strain and stresses in the directly loaded sections are relatively greater than other conditions. It indicates that the second moment reliability index is small and confidential intervals for rut depth and the number of load applications are narrow when we apply the clay soil conditions comparing to the applications of other soil conditions. CONCLUSIONS : According to the results of the second moment reliability index and the confidential intervals, the minimum and maximum values of reliability index indicate approximately 1.79 at Case 9 and 2.19 at Case 22. The broadest widths of confidential intervals for rut depth and the number of load repetitions are respectively occurred in Case 9 and Case 7.

Eating breakfast provides crucial nutrition for brain function and helps promote overall health. It is especially critical in growing adolescents, as it is known to form good eating habits and better study habits. This study investigated the effects of skipping breakfast on nutritional state, fatigue level, and attention level. A cross-sectional study was conducted in 2010 on total of 828 adolescents composed of 414 boys and 414 girls. Students who ate breakfast never to twice per week were placed in the breakfast-skipper group while students who ate breakfast more than five times per week were included in the breakfast-eater group. Students performed a self-reported questionnaire on food behaviors, amount of food consumption, fatigue level, attention deficient hyperactivity disease (ADHD) level by Conners-Wells’ Adolescent Self-Report Scales, depression scale, and self-esteem level. Statistical analysis was conducted using the SAS program (version 9.1). A total of 135 boys (32.6%) and 138 girls (33.3%) were included in the breakfast-skipper group, whereas 241 boys (58.2%) and 223 girls (53.9%) were included in the breakfast-eater group. The breakfast-skipper group showed irregular food behaviors and lacked nutrients. Specifically, energy (p< .001), protein (p< .001), dietary fiber (p< .001), calcium (p< .01), vitamin A (p< .01), thiamin (p< .05), niacin (p< .001) levels in boy breakfast-skippers were statistically lower compared to boy breakfast-eaters. Intakes of all nutrients except fat in girl breakfast-skippers were statistically lower than in girl breakfast-eaters. Girl breakfast-skippers (41.3%) showed significantly higher fatigue risks compared to girl breakfast-eaters (21.5%). Low attention level was also observed only in girls in the breakfast-skipping group. Moreover, students in the breakfast-skipper group showed higher scores for depression and low self-esteem (p< .001). In conclusion, skipping breakfast has effects on young adolescents’ nutrition, manifesting as high fatigue level and low attention level, especially in girls.

The effect of alpha phase on the fatigue properties of Fe-29%Ni-17%Co low thermal expansion alloy was investigated. Two kinds of alloys (Base alloy and Alpha alloy) were prepared by controlling the minimal alloy composition. Microstructure observation, tensile, high-cycle fatigue, and low-cycle fatigue results were measured in this study. The Base alloy microstructure showed typical austenite γ phase. Alpha alloy represented the dispersed phase in the austenite γ matrix. As a result of tensile testing, Alpha alloy was found to have higher strengths (Y.S. & T.S.) and lower elongation compared to those of the Base alloy. High cycle fatigue results showed that Alpha alloy had a higher fatigue limit (360MPa) than that (330MPa) of the Base alloy. The Alpha alloy exhibited the superior high cycle fatigue property in all of the fatigue stress conditions. SEM fractography results showed that the alpha phase could act to effectively retard both fatigue crack initiation and crack propagation. In the case of low-cycle fatigue, the Base alloy had longer fatigue life in the high plastic strain amplitude region and the Alpha alloy showed better fatigue property only in the low plastic strain amplitude region. The fatigue deformation behavior of the Fe-29%Ni-17%Co alloy was also discussed as related with its microstructure.

This study empirically examines how much effect levels of fatigue and stress of a construction worker have on disaster risks from the perspective of human factors concerning construction disaster risks. To achieve the purpose of this study, a survey was conducted with respect to construction workers working at large construction sites within the metropolitan area. The retrieved survey data were analyzed by using the statistical software programs, SPSS 18.0 and AMOS 8.0. The results of this study do not definitively lead to the conclusion that the level of fatigue or stress of construction workers result in disaster risks. However, it does show that the results vary depending upon the individual approach and treatment of stress and fatigue. In particular, this study revealed that disaster risk levels could increase through unsafe behavior intentions which were established as a mediator variable. Also, with respect to unsafe behavior intentions of construction workers leading to disaster risks, when examining the results that the level of mental fatigue, occupational stress and social-psychological stress of construction workers had a greater significant effect than the level of physical fatigue, this study demonstrates the importance of psychological and mental issues that could be easily overlooked with respect manual labor workers.

The purpose of this study was to investigate the effects of smartphone use on muscle fatigue and tenderness in the cervical erector spinae (CES) and the upper trapezius (UT) and on the cervical range of motion among subjects with and without neck muscle pain. The subjects were 30 smartphone users in their 20 s who -were assigned to either an experimental group with neck muscle pain or a control group without neck muscle pain. Muscle fatigue and tenderness in the CES and the UT as well as the subjects’ cervical range of motion were measured before and after 20-min smartphone sessions in a sitting position. In a between-group comparison of muscle fatigue, the experimental group showed a significantly greater decrease in median frequency in the CES and the right UT after smartphone use (p<.05). Regarding the assessment of muscle tenderness after smartphone use, the experimental group showed a statistically significant decrease in the pressure-pain threshold (PPT) in all muscles (p<.05), whereas the control group showed a significantly decreased PPT in the right CES and the UT (p<.05). The assessment of the cervical range of motion revealed a statistically significant reduction in the cervical flexion-extension and left lateral flexion in the experimental group (p<.05) after smartphone use. However, there was no significant change in the cervical range of motion in the control group (p>.05) after smartphone use. When compared with the control group, the experimental group demonstrated greater changes in cervical extension, lateral flexion, and rotation, except for cervical flexion (p<.05). In conclusion, when smartphone users have pre-existing neck muscle pain, the use of a smartphone further increased muscle fatigue and tenderness in the neck and reduced PPT and the cervical range of motion.

In this study, the specimen of tapered double cantilever beam(TDCB) with aluminum foam is designed and shearing fatigue strength is based on the investigation of static behaviour analysis under the condition of mode Ⅱ. These specimen models have length and width of 200 mm and 25 mm. The inclined angles of adhesive face at the specimens are 6°, 8 °and 10°. As the inclined angle becomes higher, the time for which the model can not be broken during fatigue load becomes longer. The shearing strength of TDCB bonded structure with aluminum foam applied by shearing fatigue load can be evaluated through finite element method.