• 대한기계학회논문집A
• /
• 제36권7호
• /
• pp.751-757
• /
• 2012

사용조건에서 수명시험을 수행할 경우 시험시간이 많이 소요되므로 사용조건보다 가혹한 스트레스 조건을 추가하여 가속수명시험을 수행하면 시험시간을 단축시킬 수 있다. 수명에 영향을 미치는 스트레스를 선정하여 각 스트레스의 사용조건과 가속조건에서 시험을 수행할 경우 가속 스트레스간에 교호작용이 존재할 수 있다. 그러나 기존의 연구에서는 2가지 이상의 가속 스트레스를 부과하여 가속수명시험을 수행할 경우 교호작용을 고려하지 않은 경우와 가속 수명에 대한 모델식을 제시한 연구들이 대부분이다. 본 논문에서는 기계류 부품의 수명에 영향을 미치는 가속 스트레스를 선정한 후 교호작용을 고려한 시험계획에 따라 가속수명시험을 수행한 자료를 이용하여 가속 계수와 가속 스트레스간의 관계식을 산출하는 방법을 제시하고자 한다. 또한 본 논문에서 제시한 교호작용을 고려한 가속시험방법과 가속 계수를 산출할 수 있는 모델식을 이용하여 복합적인 가속수명시험 수행시 쉽게 적용하고 결과를 산출할 수 있는 기초가 될 것으로 기대된다.

• Geomechanics and Engineering
• /
• 제10권6호
• /
• pp.775-791
• /
• 2016

The indirect tensile strengths (ITSs) of different cemented paste backfill mixes with different curing times were determined by considering crack initiation and fracture toughness concepts under different loading conditions of steel loading arcs with various contact angles, flat platens and the standard Brazilian test jaw. Because contact area of the ITS test discs developes rapidly and varies in accordance with the deformability, ITSs of curing materials were not found convenient to determine under the loading apparatus with indefinite contact angle. ITS values increasing with an increase in contact angle can be measured to be excessively high because of the high contact angles resulted from the deformable characteristics of the soft paste backfill materials. As a result of the change of deformation characteristics with the change of curing time, discs have different contact conditions causing an important disadvantage to reflect the strength change due to the curing reactions. In addition to the experimental study, finite element analyses were performed on several types of disc models under various loading conditions. As a result, a comparison between all loading conditions was made to determine the best ITSs of the cemented paste backfill materials. Both experimental and numerical analyses concluded that loading arcs with definite contact angles gives better results than those obtained with the other loading apparatus without a definite contact angle. Loading arcs with the contact angle of $15^{\circ}$ was found the most convenient loading apparatus for the typical cemented paste backfill materials, although it should be used carefully considering the failure cracks for a valid test.

• Physical Therapy Rehabilitation Science
• /
• 제7권4호
• /
• pp.164-171
• /
• 2018

Objective: The purpose of this research was to determine the immediate effects of wearing a foot-pressure-based insole (FPBI) on ankle dorsiflexion range of motion (DFROM), postural sway, and muscle activation in healthy individuals with genu varum. Design: Cross-sectional study. Methods: This study was conducted on thirteen adults, with six male and seven females subjects. The mean age was 24.08 years. Foot pressure was measured to apply the FPBI and the weight bearing lunge test was performed with the application of a flat insole (FI) and FPBI. Examination was randomly performed in four conditions to measure both postural sway and muscle activation. All participants applied both the FI and FPBI with four conditions. The four conditions were as follows: 1) Romberg test posture with eyes closed, 2) Romberg test posture with eyes opened, 3) dominant single leg standing with eyes opened, and 4) non-dominant single leg standing with eyes opened. Results: For ankle DFROM between the FI and FPBI, a significant increase was observed in both the dominant and non-dominant leg (p<0.05). For postural sway between the FI and FPBI in the Romberg test posture with eyes closed and dominant single leg standing with eyes opened conditions, a significant decrease was observed (p<0.05). However, the postural sway between FI and FPBI in the Romberg test posture with eyes opened and non-dominant single leg standing with eyes opened, no significant decrease was observed. Also, there were no significant effects on muscle activation between the application of the FI and FPBI. Conclusions: The result showed that FPBI immediately improved ankle DFROM and postural sway. It seems that FPBI may improve genu varum in healthy individuals with genu varum.

• Journal of Periodontal and Implant Science
• /
• 제29권1호
• /
• pp.95-102
• /
• 1999

The purpose of this study was to observe histopathologically the influence of advanced periodontitis on pulp tissue, and to conclude the correlation between the results with clinical manifestations. The samples were teeth with over 7mm pocket depth and over 50% radiographic bone loss. These were diagnosed to have very poor prognosis and thus planned to be extracted. Those with any of following conditions were excluded from the samples, loss of vitality, periapical pathology, restoration or prosthesis, dental caries, and attrition or abrasion. It was because these conditions could affect pulp without any correlation with periodontal disease. For the experiment, 17 teeth from 11 patients were selected. Average age of patient was 47. Each tooth was examined for following categoris; pocket depth, gingival recession, electric pulp test, mobility, percussion test, sensitivity test. The extracted teeth were fixed buffered neutral formalin solution. It was decalcified using 4% nitric acid. Sliced histological samples observed using light microscope, for pulp status, and severeity of inflammation. 4 samples were excluded due to histologic sample discrepency. Thus 13 samples were subject to observation. 4 showed normal conditions. Focal reversable pulpitis was shown in 5 samples. Chronic pulpitis was observed 1 sample. Pulpal abscess was observed in 3 samples.

• 한국건설순환자원학회논문집
• /
• 제5권1호
• /
• pp.29-36
• /
• 2017

이 연구의 목적은 알칼리 활성화제의 종류와 양생방법에 따라 나타나는 고로슬래그 기반 섬유보강 복합재료의 압축강도 및 인장거동에 대해 실험적으로 조사하는 것이다. 이를 위하여 알칼리 활성화제 2종류의 배합과 2가지 양생방법을 결정하였고, 밀도 실험, 압축강도 실험과 일축인장 실험을 수행하였다. 실험 결과, 규산나트륨을 사용한 경우 수산화칼슘과 탄산나트륨을 혼합하여 사용한 경우에 비하여 강도, 인장변형성능, 인성 측면에서 우수한 것으로 나타났으며, 활성화제 종류에 따라 양생방법에 의한 영향이 다르게 나타나는 것을 확인하였다.

• 아동학회지
• /
• 제7권1호
• /
• pp.67-84
• /
• 1986

The purpose of the present research was to investigate cross-modal transfer, especially tactual-to-visual transfer in infancy and to study the relation between failure of cross-modal transfer performance and length of familiarization period. The subjects of this study were 60 infants, 10 boys and 10 girls at each level: six, nine, and twelve months of age. All were normal, healthy, full-term babies. The mothers' educational achievement was controlled at more than 12 years of schooling. There were two separate experimental conditions, one 30-sec and one 60-sec familiarization period. Each experimental condition consisted of a tactual familiarization and a visual recognition memory test. Each child was presented with these 2 sets of cross-modal stimuli in one of the 2 experimental conditions. Infants' visual responses in the visual recognition memory test were videotaped for 20 seconds. Visual fixation time to novel and familiar stimuli was observed throughout the test. The data was analyzed with t-test, percentage of total fixation time to novel stimuli, and ANOVA. The results showed that: 1) Significant differences were found in the cross-modal transfer performance from touch to vision between the 3 age groups. This is, 6 and 9 month old infants didn't show cross-modal transfer in the 30-sec condition, but 12 month old infants did show cross-modal transfer in the 30-second. 2) In all 3 age groups, no significant differences were found in cross-modal transfer performance between the two conditions.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2003년도 춘계학술대회 논문집
• /
• pp.729-732
• /
• 2003

The K-R design curve is an engineering method of linear-elastic fracture analysis under plane-stress loading conditions. By the way, linear-elastic fracture mechanics (LEFM) is valid only as long as nonlinear material deformation is confined to a small region surrounding the crack tip. Like general steels, it is virtually impossible to characterize the fracture behavior with LEFM, in many materials. Critical values of J contour integral or crack tip opening displacement (CTOD) give nearly size independent measures of fracture toughness, even for relatively large amounts of crack tip plasticity. Furthermore, the crack tip opening displacement is the only parameter that can be directly measured in the fracture test. On the other. the crack tip opening angle (CTOA) test is similar to CTOD experimentally. Moreover, the test is easier to measure the fracture toughness than other method. The shape of the CTOA curve depends on material fracture behavior and, on the opening configuration of the cracked structure. CTOA parameter describes crack tip conditions in elastic-plastic materials, and it can be used as a fracture criterion effectively. In this paper, CTOA test is performed for steel JS-SS400 hot-rolled thin plates under plane-stress loading conditions. Special experimental apparatuses are used to prevent specimens from buckling and to measure crack tip opening angle for thin compact tension (CT) specimens.

• 열처리공학회지
• /
• 제20권4호
• /
• pp.181-186
• /
• 2007

Effect of heat treatment conditions on formability and property of warm hydroformed parts for Al 6061 extruded tubes was investigated in this study. For the investigation, as-extruded, fully annealed and T6-treated Al 6061 seamless tubes were prepared. To evaluate the warm hydroformability, uni-axial tensile test and free bulge test were performed at various pre- and post-heat treatment conditions. And the tensile test specimens were obtained from hexagonal prototype hydroformed parts at $250^{\circ}C$. As a result, hydroformability of fully annealed tube is 25% higher than that of extruded tube. The tensile strength and strain of hydroformed part reach to 330 MPa and 12%, respectively, when the part was T6 treated after warm hydroforming. However, the hydroformability of T6 pre-treated tube is relatively low due to the decreased elongation, 8%.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
• /
• pp.603-608
• /
• 1997

Studies on the second-order analysis of reinforced concrete columns have been chiefly dealt with symmetric section under uniaxial loading. In practical situations, however, columns are subjected to biaxial loadings. Therefore, for more accurate prediction of the behavior of concrete columns under biaxial loading, the interaction between bending moments of major and minor axes should be considered. Recently Kim & Lee proposed a numerical method of predicting the behavior of concrete columns under biaxial loading. In this paper, to investigate the behavior of concrete columns under biaxial loading and verify the validity of proposed method, a series of test were carried out for sixteen tied reinforced columns with 100${\times}$100mm square and 200${\times}$100mm rectangular sections under various loading conditions. The length of columns was 1,300mm and the concrete strength was 28MPa. The boundary conditions at the both ends were hinged and end eccentricities were equal(400mm). Proposed numerical analyses applied to the test piece were performed to predict behavior of concrete columns with square and rectangular sections under various loading conditions. Test results were also compared with those using the moment magnifier method in ACI code. The test results showed that the moment magnifier method is conservative.

• 한국정밀공학회지
• /
• 제32권1호
• /
• pp.49-55
• /
• 2015

Recently, many researchers and industry are looking for ways to decrease the use of lubricants because of economical and environmental reasons. One of the lubrication technologies is the MQL method. This study presents a research of MQL and Wet milling processes of Al 6061 material. For this experiment, the test specimen is suggested, and various machining conditions are applied. And, shape of micro-pattern which has been recently spotlighted is included in the test specimen. In order to compare MQL with Wet machining, several milling experiments were carried out, varying feed rate, cutting speed, depth of cut, etc. Finally, the surface roughness results of machining tests according to the process conditions were measured. It is expected that the results of machining experiments can be used to predict the surface roughness of various MQL milling processes.