• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.367-374
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• 2019

Drying shrinkage in the hardened cement is known to change in volume by decreasing the moisture content in the hardened body, and it is known that the higher the W / C and the higher the content of the paste, the larger the drying shrinkage. In the case of ECC, more drying shrinkage occurs compared to concrete, since it does not contain coarse aggregate. Since ECC is an important material for tensile performance, the effect of restrained tensile stress on mechanical tensile behavior should be considered. The purpose of this study is to analyze the effect of stress caused by restraint on the tensile behavior of ECC. The mechanical properties of the specimens were tested by uniaxial tension tests with different restraints. As a result, the difference of tensile behavior according to restraint stress was observed and the cause was analyzed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.198-203
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• 2020

Cracking due to material behavior like drying shrinkage easily occurs since tensile strength in concrete is very low at initial curing stage. In this paper, workability such as air content and slump was evaluated on CFC(Cellulose Fiber Concrete) with 0.0 ~ 2.0% of fiber addition, and the tests for tensile/compressive strength were performed. With increasing addition ratio of fiber, air content and slump kept similar level to 1.0kg/㎥ of addition ratio, and this trend was effective to 2 hours after mixing. Strength was enhanced with increasing addition ratio, which showed 7.0 ~ 9.0% for compressive strength and 7.0 ~ 22.0% for tensile strength, respectively. The tensile strength increased relatively more, which show the addition of cellulose fiber was very effective to crack resistance. The workability in CFC can be guaranteed for 2 hours in the following conditions like 2 minutes of mixing period and 1.0kg/㎥ of addition ratio of fiber.

• Journal of Powder Materials
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• v.17 no.6
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• pp.456-463
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• 2010

This paper describes the results of the application of Cr-Diamond-like carbon (DLC) films for efficiency improvement through surface modification of spur gear parts in the hydraulic gear pump. Cr-DLC films were successfully deposited on SCM 415 substrates by a hybrid coating process using linear ion source (LIS) and magnetron sputtering method. The characteristics of the films were systematically investigated using FE-SEM, nano-indentation, sliding tester and AFM instrument. The microstructure of Cr-DLC films turned into the dense and fine grains with relatively preferred orientation. The thickness formed in our Cr buffer layer and DLC coating layer were obtained the 487 nm and $1.14\;{\mu}m$. The average friction coefficient of Cr-DLC films considerably decreased to 0.15 for 0.50 of uncoated SCM415 material. The hardness and surface roughness of Cr-DLC films were measured 20 GPa and 10.76 nm, respectively. And then, efficiency tests were performed on the hydraulic gear pump to investigate the efficiency performance of the Cr-DLC coated spur gear. The experimental results show that the volumetric and mechanical efficiency of hydraulic gear pump using the Cr-DLC spur gear were improved up to 2~5% and better efficiency improvement could be attributed to its excellent microstructure, higher hardness, and lower friction coefficient. This conclusion proves the feasibility in the efficiency improvement of hydraulic gear pump for industrial applications.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.51 no.1
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• pp.59-65
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• 2006

The impermeable seed coat is valuable trait in soybean because impermeable seed retain viability for longer period than permeable seed under adverse conditions such as delayed harvest or prolonged storage. Soybean seeds of various size showing different seed hardness were examined for their water absorption and seed viability under adverse storage conditions. Of one hundred thirty nine genotypes, eight types of seeds having different seed hardness and seed size were used as material. Soybean genotypes showing high hard seed rate, GSI13125 (89%), GSI10715 (54%), and GSI10284 (42%), were slow in water absorption and low in the electroconductivity of seed leachate in distilled water. Germination of GSI10284 and GSI13125 that have higher hard seed rate was less affected by CSVT and artificial aging treatment indicating higher seed storability. The higher storing ability of both collections was confirmed by electroconductivity test for leachate. GSI10122 showed low seedling emergence when the seeds were artificially aged. This genotype was considered as to having a poor storing ability based on difference of electroconductivity before and after artificial aging. Among tests conducted in the experiment, CSVT could be used for determining storage life in legumes. In conclusion, water absorption property of seed was strongly related to the hardness that is directly related to the seed viability and storing ability in soybean seed.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.566-574
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• 2016

Fiber metal laminates, which are hybrid materials consisting of metal sheets and composite layers, have contributed to aerospace and automotive industries due to their reduced weight and improved damage tolerance characteristics. In this study, the impact performance of the laminates, which are comprised of a self-reinforced polypropylene and two aluminum sheets, and the pure aluminum alloy sheet material were investigated experimentally via numerical simulation. In order to compare the impact performance, the laminates and aluminum alloy were examined by assessing the impact force, energy time histories, and specific energy absorption. ABAQUS is a commercial software that is used to simulate the actual drop-weight tests. Based on this study, it is noted that the impact performance of the laminates was superior to that of the aluminum alloy. In addition, a good agreement between the experimental and numerical results can be achieved when the impact force and energy time histories from the experiments and the numerical simulations are compared.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3633-3642
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• 2015

Single-base propellants contain a single energetic component: nitrocellulose. Accurate predictions of propellant shelf-life should result in cost savings in terms of human and material resources. This study derived an optimized kinetic model reaction order that described stabilizer consumption and estimated propellant shelf-life. High temperature accelerated aging tests gave an optimum reaction order value of 1.15481, from which the minimum standard error of a linear regression estimate of 16.284 was obtained. At normal storage temperature of $21-30^{\circ}C$, propellants should have a safe shelf-life of 140 years, and a minimum of 35 years. It is necessary to consider the temperature range in ammunition storage areas to predict propellant shelf-life more accurately.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.6134-6141
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• 2014

This study analyzed the gap in perception between communication with parents and filial piety according to the general characteristics of teenagers. The test subjects were high school students from academic and vocational school from different districts of Seoul. A survey was conducted from March to July of 2014 to 290 high school students. Data analysis was conducted on the SPSSWIN 18.0 program using a t-test, one-way analysis of variance, correlation analysis, and other tests. The empirical analysis of the experiments were verified at the significance level of 5%. First, communication with fathers differed significantly depending on the school division, economic class, religion; and communication with mothers differed significantly depending on school division, grade-level, academic performance, domestic discipline, and economic class. Second, the perception of filial piety showed a significant positive correlation with the communication with the mother; and with the communication with the father. The implication of this study is that better communication between the parents and teenagers correlate with the higher filial piety according to the general characteristics of teenagers, and should become a central material for policy.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.35-43
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• 2012

In general, load carrying capacity, one of the load & resistance capacities in bridges, has more margins than the load carrying capacity evaluated with theoretical methods, unless there are severe damages, defects or material deterioration phenomena that can have a great impact on the behavior of bridges. However, errors have been already included in the current processes of loading tests and structural analysis for measuring load carrying capacity, thus devaluing the reliability of response adjustment factor. Therefore, this study found out the problems of existing electric resistance strain and displacement sensors in sensor suite to solve the problems with sensors and the errors in the appropriateness of structural analysis model, thereby leading to the changes into an optical fiber smart sensor with excellent performance. Besides, the study attempted to ensure the accuracy of response adjustment factor by selecting the optimal models through the interpretation of various structural analysis models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.111-119
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• 2016

Rebound hammer test, SonReb method and concrete core test are most useful testing methods for estimate the concrete compressive strength of deteriorated concrete structures. But the accuracy of the NDE results on the existing structures could be reduced by the effects of the uncertainty of nondestructive test methods, material effects by aging and carbonation, and mechanical damage by drilling of core. In this study, empirical procedure for verifying the in-situ compressive strength of concrete is suggested through the probabilistic analysis on the 268 data of rebound and ultra-pulse velocity and core strengths obtained from 106 bridges. To enhance the accuracy of predicted concrete strength, the coefficients of core strength, and surface hardness caused by ageing or carbonation was adopted. From the results, the proposed equation by KISTEC and the estimation procedures proposed by authors is reliable than previously suggested equation and correction coefficient.

• Restorative Dentistry and Endodontics
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• v.40 no.2
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• pp.123-127
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• 2015

Objectives: Glide path preparation is recommended to reduce torsional failure of nickel-titanium (NiTi) rotary instruments and to prevent root canal transportation. This study evaluated whether the repetitive insertions of G-files to the working length maintain the apical size as well as provide sufficient lumen as a glide path for subsequent instrumentation. Materials and Methods: The G-file system (Micro-Mega) composed of G1 and G2 files for glide path preparation was used with the J-shaped, simulated resin canals. After inserting a G1 file twice, a G2 file was inserted to the working length 1, 4, 7, or 10 times for four each experimental group, respectively (n = 10). Then the canals were cleaned by copious irrigation, and lubricated with a separating gel medium. Canal replicas were made using silicone impression material, and the diameter of the replicas was measured at working length (D0) and 1 mm level (D1) under a scanning electron microscope. Data was analysed by one-way ANOVA and post-hoc tests (p = 0.05). Results: The diameter at D0 level did not show any significant difference between the 1, 2, 4, and 10 times of repetitive pecking insertions of G2 files at working length. However, 10 times of pecking motion with G2 file resulted in significantly larger canal diameter at D1 (p < 0.05). Conclusions: Under the limitations of this study, the repetitive insertion of a G2 file up to 10 times at working length created an adequate lumen for subsequent apical shaping with other rotary files bigger than International Organization for Standardization (ISO) size 20, without apical transportation at D0 level.