• Composites Research
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• v.16 no.1
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• pp.13-18
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• 2003

Prediction of composite fatigue life is not a straightforward matter, depending on various failure modes and their interactions. In this paper, a methodology is presented to predict fatigue life and residual strength of composite materials based on Phenomenological Model(non-linear fatigue damage model). It is assumed that the residual strength is a monotonically decreasing function of the number of loading cycles and applied fatigue stress ratio and the model parameters(strength degradation parameter and fatigue shape parameter) are assumed as function of fatigue life. Then S-N curve is used to extract model parameters that are required to characterize the stress levels comprising a randomly-ordered load spectrum. Different stress ratios (${\sigma}_{min}/{\;}{\sigma}_{max}$) are handled with Goodman correction approach(fatigue envelope) and the residual strength after an arbitrary load cycles is represented by two parameter weibull functions.

• Geomechanics and Engineering
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• v.9 no.3
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• pp.373-395
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• 2015

Comprehensive results from cyclic plate loading at a diameter of 300 mm supported by layers of geocell are presented. The plate load tests were performed in a test pit measuring $2000{\times}2000mm$ in plane and 700 mm in depth. To simulate half and full traffic loadings, fifteen loading and unloading cycles were applied to the loading plate with amplitudes of 400 and 800 kPa. The optimum embedded depth of the first layer of geocell beneath the loading plate and the optimum vertical spacing of geocell layers, based on plate settlement, are both approximately 0.2 times loading plate diameter. The results show that installation of the geocell layers in the foundation bed, increase the resilient behavior in addition to reduction of accumulated plastic and total settlement of pavement system. Efficiency of geocell reinforcement was decreased by increasing the number of the geocell layers for all applied stress levels and number of cycles of applied loading. The results of the testing reveal the ability of the multiple layers of geocell reinforcement to 'shakedown' to a fully resilient behavior after a period of plastic settlement except when there is little or no reinforcement and the applied cyclic pressure are large. When shakedown response is observed, then both the accumulated plastic settlement prior to a steady-state response being obtained and the resilient settlements thereafter are reduced. The use of four layers of geocell respectively decreases the total and residual plastic settlements about 53% and 63% and increases the resilient settlement 145% compared with the unreinforced case. The inclusion of the geocell layers also reduces the vertical stress transferred down through the pavement by distributing the load over a wider area. For example, at the end of the load cycle of the applied pressure of 800 kPa, the transferred pressure at the depth of 510 mm is reduced about 21.4%, 43.9%, 56.1% for the reinforced bases with one, two, and three layers of geocell, respectively, compared to the stress in the unreinforced bed.

• Journal of People, Plants, and Environment
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• v.23 no.2
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• pp.179-189
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• 2020

In order to increase the indoor air purification effect of plants, plants need to be placed on 5-10% of indoor spaces. To increase the density and utilization of plants in indoor spaces, studies on bio-wall, a vertical green wall system, have been recently conducted. The purpose of this study was to investigate the growth characteristics of 7 indoor plants introduced to the system and their rooting zones at different irrigation cycles. This study was conducted to investigate a proper irrigation cycle for the continuous maintenance of bio-wall systems. The conditions of their growth environment were maintained as follows: light intensity, 20-50 μmol·m^-2·s^-1 PPFD; and temperature, 20 - 25℃. For fertilization, Hyponex diluted with water at the ratio of 1:1,000 was supplied to plants. Irrigation was treated at intervals of 1, 3, 5, and 7 days for 1 hour at a time. As a result, there was no significant difference in the growth of plants between different irrigation cycles. Dieffenbachia 'Marianne' showed a significant decrease in the number of leaves at the irrigation cycle of 7 days. In addition, the chlorophyll content was relatively low at the irrigation cycle of 7 days. In terms of the color of leaves, a decrease in L value and b value and an increase in a value were observed, resulting in changes in brightness and color. Ardisia pusilla 'Variegata' showed a slightly higher photosynthetic activity and stomatal conductance when it was watered every day and once per 5 days, while Epipremnum aureum showed a relatively higher photosynthetic activity and stomatal conductance at the irrigation cycle of 3 days. In the case of root activity, it was found that the longer irrigation cycle, the higher root activity compared to daily irrigation. The development of roots of Peperomia clusiifolia was promoted by watering at long intervals. However, in the case of Aglaonema 'Siam-Aurora', the total number of roots decreased at the interval of 7 days. In conclusion, a proper irrigation cycle for the sustainable maintenance of vertical bio-wall systems seems to be 3 days.

• Journal of the Korean Society of Clothing and Textiles
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• v.18 no.4
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• pp.549-559
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• 1994

The purpose of this study was to study accumlated residual soils which may be one of the causes for yellowing of worn cloths. Wear and wash tests of white cotton undershirts were repeated at 30 households sellected at random over a period of 60 days. Laundry conditions were similar to home laundry habits in a fact-finding survey, using a powdery heavy duty detergent containing no enzymes or enzymes. The subjects in this study were survey of laundry actual condition, the undershirts from prior to and after the final washing was measured residual soils, $L^*a^*b^*$ value and mellowness index of CIE system. D3ta were analysed by simple correlation analysis of wear and wash cycle, residual soils, whiteness The results obtained were summarized as follows: 1. Using pattern of washing machine, Presoaking was no singinificant differnece in general characteristics of survey respondent. Laundry frequency was significant difference in income level, occupation of housewives whether or not. Use of cold and hot water was significant difference in residence shape. 2. The analyzed consequences of recognition and actual behavior in connection with laundry were found variables each other to have independence or not. 3. Amount of residual sebum soils is using non-enzyme detergent were much more than in using enzyme detergent, increased linearly with increase of the number of wear and wash cycles. 4. Residual protein soils with increase of the number wear and wash cycles less than in laundering more easy than sebum soils. Since accumulated residual sebum soils were much more than residual protein soils. 5. Increase of residual soils was raised mellowness index and diminshed whiteness. yellowness index of residual sebum soils was higher than protein soils. If increase of whiteness will be incresed, amount of residual sebum soils will be decreased sebum soils. Because amount of residual sebum soils much more than protein soils, yellowness index of residual sebum soils was more higher than that of protein soils.

• Restorative Dentistry and Endodontics
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• v.29 no.3
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• pp.267-272
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• 2004

The purpose of this in vitro study was to evaluate the effect of surface defects and cross-sectional configuration of NiTi rotary files on the fatigue life under cyclic loading. Three NiTi rotary files ($K3^{TM},{\;}ProFile^{\circledR},{\;}and{\;}HERO{\;}642^{\circledR}$) with ＃30/.04 taper were evaluated. Each rotary file was divided into 2 subgroups : control (no surface defects) and experimental group (artificial surface defects), A total of six groups of each 10 were tested. The NiTi rotary files were rotated at 300rpm using the apparatus which simulated curved canal (40 degree of curvature) until they fracture. The number of cycles to fracture was calculated and the fractured surfaces were observed with a scanning electron microscope. The data were analyzed statistically. The results showed that experimental groups with surface defects had lower number of cycles to fracture than control group but there was only a statistical significance between control and experimental group in the $K3^{TM}$ (p<0.05), There was no strong correlation between the cross-sectional configuration area and fracture resistance under experimental conditions. Several of fractured files demonstrated characteristic patterns of brittle fracture consistent with the propagation of pre-existing cracks. This data indicate that surface defects of NiTi rotary files may significantly decrease fatigue life and it may be one possible factor for early fracture of NiTi rotary files in clinical practice.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.1
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• pp.7-14
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• 2023

We investigated the effect of multiple tempering on the microstructure and mechanical properties of AISI 4340 steel. The austenitized and quenched AISI 4340 steels were tempered at 550, 600, and 650℃ for 1, 2, and 4 h by single-tempering (ST). The multiple tempering was conducted for 4 h by double-tempering (DT, 2 h + 2 h), and quadruple-tempering (QT, 1 h + 1 h + 1 h + 1 h). As tempering temperature increases, yield strength and ultimate tensile strength decrease and elongation increases due to recovery and recrystallization of martensite and coarsening of carbides. At 550℃, as the number of tempering cycles increases, the yield strength and tensile strength decrease at the expense of fracture elongation. At 600 and 650℃, the yield strength and tensile strength increase with increasing the number of tempering cycles while fracture elongation maintains similar values. The multiple tempering at the same tempering time of 4 h improves the modulus of toughness at all tempering temperatures, which is presumed to be due to the change in carbide precipitation behavior by multiple tempering.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.2
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• pp.142-149
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• 2005

[ $LiNiO_2$ ] was mixed with $TiO_2$ or ZnO for the preparation of a cathode. The electrochemical properties of the cathode were investigated and the effects of the addition of $TiO_2$ or ZnO were discussed. The first discharge capacity decreased as the quantity of the added $TiO_2$ or ZnO increased. It is probably due to the decrease in the area of reaction interface according to the increase in the amount of the added oxide. When 2wt.% and 5wt.% of oxides are added, the discharge capacity increased as the number of cycles increased. It is considered that this results from the increase in the area of reaction interface because the oxide is detached from the $LiNiO_2$ with the increase in the number of cycles. The 1wt.% $TiO_2$ or ZnO-added $LiNiO_2$ had a larger first charge capacity than $LiNiO_2$. This is considered to result from the deintercalation of Li ions in the Ni sites along with the Li ions in the Li sites.

• Polymer(Korea)
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• v.24 no.5
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• pp.673-681
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• 2000

Electrically conductive composites have been prepared by treating fabrics with oxidizing agent and exposing them to aniline, which deposited a substantial amount of conductive polymer within the interstices of the material. However the conductivity of the composite fabrics was limited by the irregular deposition of the conductive polymer layer. To improve the conductivity of polyaniline/nylon 6 composite fabrics, we modified the surface characteristics of nylon 6 fabrics by various plasma treatments and increased diffusion and adsorption of aniline by ultrasonic treatments. By the oxygen plasma treatment, attachment of functional groups such as C-O and C-OH increased on the surface of nylon 6 fiber, which promoted adhesion to polyaniline resulting in the higher add-on and electrical conductivity. Electrical conductivities of polyaniline/nylon 6 composite fabrics were highly increased by ultrasonic treatment, which assisted the diffusion of aniline into the inside of nylon fabrics by cavitation and vibration. Also, the effects of monomer concentration and the number of deposition cycles on the nylon 6 fabric conductivity Were investigated. As a result, the fabric conductivity increased with the monomer concentration and the number of polymerization deposition cycles.

• Restorative Dentistry and Endodontics
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• v.44 no.2
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• pp.22.1-22.8
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• 2019

Objectives: The aim of this study was to investigate the effect of glide path preparation with PathFile and ProGlider nickel-titanium (NiTi) files on the cyclic fatigue resistance of WaveOne NiTi files. Materials and Methods: Forty-four WaveOne Primary files were used and divided into four groups (n = 11). In the first group (0 WaveOne), the WaveOne Primary files served as a control group and were not used on acrylic blocks. In the 1 WaveOne Group, acrylic blocks were prepared using only WaveOne Primary files, and in the PF+WaveOne group and PG+WaveOne groups, acrylic blocks were first prepared with PathFile or ProGlider NiTi files, respectively, followed by the use of WaveOne Primary files. All the WaveOne Primary files were then subjected to cyclic fatigue testing. The number of cycles to failure was calculated and the data were statistically analyzed using one-way analysis of variance (ANOVA) and the Tukey honest significant difference multiple-comparison test at a 5% significance level. Results: The highest number of cycles to failure was found in the control group, and the lowest numbers were found in the 1 WaveOne group and the PF+WaveOne group. Significant differences were found among the 1 WaveOne, PF+WaveOne, and control groups (p < 0.05). No statistically significant differences were found between the PG+WaveOne group and the other three groups (p > 0.05). Conclusion: Glide path preparation with NiTi rotary files did not affect the cyclic fatigue resistance of WaveOne Primary files used on acrylic blocks.

• Economic and Environmental Geology
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• v.30 no.4
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• pp.353-362
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• 1997

P wave velocities of core samples from the Pocheon granite were measured before and after applications of cyclic loading. Then. distribution of the pre-existing microcracks and microcracks developed due to the cyclic loading was investigated by analyzing P wave velocity anisotropies and microscopic observations from thin sections. Anisotropy constants were calculated with three different ways: (1) $C_A$ between the maximum and the minimum velocities, (2) $C_AI$ between velocities measured along the axial direction and the average of six velocities measured in the planes perpendicular to the loading axis (rift plane) and (3) $C_AII$ between the maximum and the minimum velocities measured in the plane perpendicular to the loading axis. Among anisotropy constants. $C_AI$ was the most effective anisotropy constant to identify the rift plane whose orientation is parallel to the pre-existing microcracks as well as the distribution of stress induced microcracks. $C_AI$ decreased after cyclic loading and the relationship between $C_AI$ and number of cycles shows comparatively coherent negative trends. indicating that stress induced microcracks are aligned perpendicular to the orientation of pre-existing microcracks and that the amounts are proportional to the number of loading cycles. The difference of anisotropy constants before and after cyclic loading was effective in delineating the level of cracks and we called it Induced Crack Index. Velocity measurements and microscopic observations show that anisotropy was caused mainly due to microcracks aligned to a particular direction.