• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.46-55
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• 2021

Concrete structures can cause various problems as the number of common years increases when exposed to external extreme climate conditions. Among these problems, freezing and thawing occur due to the action of extreme climate factors such as heavy rain and heavy snow, which have become the most problematic in recent years. In this study, we present a rapid freezing and thawing test method of concrete in the air, referring to KS F 2456, as Seoul exhibits very dry weather during the period of freezing and thawing. Concrete test specimens and RC beams were fabricated to perform rapid freezing and thawing of 0, 100, 200, and 300 cycles, and the performance evaluation confirmed the degradation of each subject in material and member units. The design strength of 24 MPa, which performs rapid freezing and thawing in the air up to 300 cycles, decreases by 5.24 MPa (21%), and as rapid freezing and thawing in the air increases the stress burden on reinforced concrete bending members, reducing the energy absorption (dissipation) ability of structures due to earthquakes.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.3
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• pp.49-53
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• 2022

Ultra-thin glass (UTG) has been widely used in foldable display as a cover window for the protection of display and has a great potential for rollable display and various flexible electronics. The foldable display is under impact loading by bending and touch pen and exposed to other external impact loads such as drop while people are using it. These external impact loads can cause cracks or fracture to UTG because it is very thin under 100 ㎛ as well as brittle. Cracking and fracture lead to severe reliability problems for foldable smartphone. Thus, this study constructs finite element analysis (FEA) model for the pen drop test which can measure the impact resistance of UTG and conducts mechanical modeling to improve the reliability of UTG under impact loading. When a protective layer is placed to an upper layer or lower layer of UTG layer, stress mechanism which is applied to the UTG layer by pen drop is analyzed and an optimized structure is suggested for reliability improvement of UTG layer. Furthermore, maximum principal stress values applied at the UTG layer are analyzed according to pen drop height to obtain maximum pen drop height based on the strength of UTG.

• Journal of the Korean Wood Science and Technology
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• v.2 no.2
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• pp.25-31
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• 1974

1. Various gluing qualities applying Resorcinol Plyophen #6000 were studied on aiming the strength relationships of laminated woods resulted by single species [poplar (Populus deltoides), larch(Larix leptolepis)], mixed species of (poplar and larch), preservatives, treated poplar the scarf joint with mixed species of poplar and larch and the scarf joint treated with preservatives. 1. 1 On the block shear and on the DVL tension test, the mean wood failure ratio showed an excellent value i.e., above 65% and the tangential strength for larch was higher than that of radial, but it was reversed for poplar as shown in Tables 1 and 2. 1. 2 The lamina treated with Na-PCP reduced slightly the strength but the limited strength allowed for manufacturing laminated wood was not influenced by treating Na-PCP as shown in Tables 3 and 4. 1. 3 The safe scarf ratio in the plane scarf joint was above 1/12 for larch and 1/6 for poplar regard less of the chemical treatment or untreatment as shown in Tables. 5, 6, 7 and 8. 2. In the normal and boiled state, the gluing quality of the laminated wood composed of single[poplar (Populus deltoides), larch (Larix leptolepis)] and double species (poplar and larch) glued with Resorcinol Plyophen #6000 were measured as follow, and also represented the delamination of the same laminated wood. 2.1 The normal block shear strength of the straight and curved laminated wood (in life size) were more than three times of the standards adhesion strength. And, the value of the boiled stock was decreased to one half of the standard shear adhesion strength, but it was more than twice the standard strength for the boiled stock. Thus, it was recognized that the water resistance of the Resorcinol Plyophen #6000 was very high as shown in Tables 9 and 10. 2. 2 The delamination ratio of the straight and curved laminated woods in respect of their composition were decraesed, in turn, in the following order i. e., larch, mixed stock (larch+poplar) and poplar. The maximum value represented by the larch was 3.5% but it was below the limited value as shown in Table 11. 3. The various strengthes i.e., compressive, bending and adhesion obtainted by the straight laminaced wood which were constructed by five plies of single and double species of lamina i. e., larch (Larix leptolepis) and poplar (Populus euramericana), glued with urea resin were shown as follows: 3. 1 If desired a higher strength of architectural laminated wood composed of poplar (P) and larch (L), the combination of the laminas should be arranged as follows, L+P+L+P+L as shown in Table 12. 3.2 The strength of laminated wood composed of laminas which included pith and knots was conside rably decreased than that of clear lamina as shown Table 13. 3.3 The shear strength of the FPL block of the straight laminated wood constructed by the same species which were glued with urea adhesives was more than twice the limited adhesion strength, thus it makes possible to use it for interior constructional stock.

• Women's Health Nursing
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• v.7 no.2
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• pp.169-187
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• 2001

This study was performed to probe the effect of exercise program on muscle strength, endurance, flexibility, pain, disability level and life satisfaction in female teachers of elementary school who complain of low back pain. For this study, 44 female teachers aged 30-50 years with mechanical low back pain of 6 months' duration, who had the structural normalities in the lumbar spine, were recruited from April 1 to July 10 1999. Twenty three out of them were assigned to the experimental group and twenty one to the control group. The exercise program consisted of education on right postures, the etiology and diagnosis of low back pain, and exercise intervention such as muscle relaxation, elongation and strengthening. With 8 weeks program, the subjects received two sessions of education and six sessions of group exercise in the 1st week, while three sessions of group exercise and four sessions of individual exercise weekly and two sessions of education during the later 7 weeks. The muscle strength and endurance were measured by Cybex 770, the flexibility by flexibility measurement machine, the intensity of pain by Visual Analogue Scale (VAS), the level of disability by Oswestry low back pain disability scale, depression by Beck depression inventory (BDI), and life satisfaction by Life satisfaction index-Z. Study measurements were taken before and after 8 weeks exercise program. Data were analyzed using paired t-test, t-test, and ANCOVA. The results were as follows ; 1. The flexors and extensors peak torque and flexors peak torque per body weight of experimental group were significantly increased at test velocities $30^{\circ}$/sec, $60^{\circ}$/sec compared with those of control group. There was no significant difference in extensors peak torque per flexors peak torque at $30^{\circ}/sec$, $60^{\circ}/sec$ between experimental and control group. 2. The flexors and extensors total work and flexors total work per body weight of experimental group were significantly increased at $120^{\circ}/sec$, compared with those of control group. 3.The flexibility of lumbar spine in experimental group was significantly increased compared with that of control group. The pains in anterior, posterior, left lateral and right lateral bending and in rotation of experimental group were significantly increased compared with those of control group. 4. The Oswestry disability scores of experimental and control group were significantly decreased, and there was no difference in the Oswestry disability score change between experimental and control group. 5. The scores of BDI of experimental group were significantly decreased compared with those of control group. Life satisfaction index-Z scores of experimental group were not changed, but those of control group were significantly decreased. There was no difference in the score change of Life satisfaction index-Z between experimental and control group. 6. ANCOVA analysis for the data variables of inhomogeneous baseline represented that there was no significant difference in extensors peak torque and extensors total work at $120^{\circ}/sec$ and extensor total work per body weight at $120^{\circ}/sec$ change between experimental group and control group. These findings indicate that the exercise program could be effective in increasing the muscle strength, endurance, flexibility and decreasing pain, improving depression in female teachers of elementary school with chronic low back pain. It is suggested that the exercise program could be an essential factor for the effective nursing intervention to the patients suffered from chronic low back pain.

• The korean journal of orthodontics
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• v.36 no.2 s.115
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• pp.145-152
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• 2006

The purpose of this study was to evaluate electroless plating as a method of increasing the diameter of an orthodontic wire in comparison with eletroplating. After pretreatment plating of the 0.016 inch stainless steel orthodontic wire, electroless plating was performed at $90^{\circ}C$ until the diameter of the wire was increased to 0.018 inch. During the process of electroless plating, the diameter of the wire was measured every 5 minutes to examine the increasing ratio of the wire's diameter per time unit. And to examine the uniformity, the diameter at 3 points on the electroless-plated orthodontic wire was measured. An X-ray diffraction test for analyzing the nature of the plated metal and a 3-point bending test for analyzing the physical property were performed. The electroless-plated wire group showed a increased tendency for stiffness, yield strength, and ultimate strength than the electroplated wire group. And there was a statistically significant difference between the two groups for stiffness and ultimate strength. In the electroless-plated wire group, the increasing ratio of the diameter was $0.00461{\pm}0.00003mm/5min$ (0.00092 mm/min). In the electroplated wire group, it was $0.00821{\pm}0.00015mm/min$. The results of the uniformity test showed a tendency for uniformity in both the plating methods. The results of this study suggest that electroless plating of the wire is closer to the ready-made wire than electroplating wire in terms of the physical property. However, the length of plating time needs further consideration for the clinical application of electroless plating.

• Composites Research
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• v.33 no.5
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• pp.296-301
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• 2020

Laminated composite materials have excellent in-plane properties, but are vulnerable in thickness directions, making it easy to delamination when bending and torsion loads are applied. Thickness directional reinforcement methods of composite materials that delay delamination include Z-pinning, Stitching, Tufting, etc., and typically Z-pinning and Stitching method are commonly used. The Z-pinning is reinforcement method by inserting metal or carbon pin in the thickness direction of prepreg, and the conventional stitching process is a method of reinforcing the mechanical properties in the thickness direction by intersecting the upper and lower fibers on the preform. In this paper, I-fiber stitching method, which complement and improve weakness of Z-pinning and Stitching method, was proposed, and the static strength of composite single-lap joints using I-fiber stitching process were evaluated. The single-lap joints were fabricated by a co-curing method using an autoclave vacuum bag process. The thickness of the composite adherend was fixed, and 5 types of specimens were manufactured with varying the stitching pattern (5×5, 7×7) and angle (0°, 45°). From the test, the failure load of the specimen reinforced by the I-fiber stitching process was increased by up to 143% compared to that of specimen without reinforcement.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.10
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• pp.192-199
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• 2000

The design of multi-stage gear drives is a time-consuming process because it includes more complicated problems, which are not considered in the design of single-stage gear drives. The designer has no determine the number of reduction stages and the gear ratios of each reduction stage. In addition, the design problems include not only dimensional design but also configuration design of gear drive elements. There is no definite rule or principle for these types of design problems. Thus the design practices largely depend on the sense and the experiences of the designer, and consequently result in undesirable design solution. A new and generalized design algorithm has been proposed to support the designer at the preliminary phase of the design of multi-stage gear drives. The proposed design algorithm automates the design process by integrating the dimensional design and the configuration design process. The algorithm consists of four steps. In the first step, the user determines the number of reduction stages. In the second step, gear ratios of every stage are chosen using the random search method. The values of the basic design parameters of a gear are chose in the third step by using the generate and test method. Then the values of the dimensions, such as pitch diameter, outer diameter and face width, are calculated for the configuration design in the next step. The strength and durability of each gear is guaranteed by the bending strength and the pitting resistance rating practices by using AGMA rating formulas. In the final step, the configuration design is carried out using simulated annealing algorithm. The positions of gears and shafts are determined to minimize the geometrical volume (size) of a gearbox while avoiding interferences between them. These steps are carried out iteratively until a desirable solution is acquired. The proposed design algorithm is applied to the preliminary design of four-stage gear drives in order to validate the availability. The design solution has considerably good results in both aspects of the dimensional and the configuration design.

• Journal of Animal Environmental Science
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• v.14 no.1
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• pp.61-68
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• 2008

The roof structural model of liquid manure storage tank was designed to improve a structural safety and an ability of resistance to corrosion by the bad environmental condition with high humidity and high gas concentration. Due to corrosion of a general steel, the 5 years used materials were reduced to one-third of a new material in the result of a bending strength test. Some structural materials were tested to evaluate a strength and an anti-corrosion, and stainless steel pipe (STS439), steel angle with zinc hot dipping, rectangular steel pipe covered with FRP (Fiberglass Reinforced Plastics) resin were selected finally. A stainless steel is more expansive about $3{\sim}5$ times than general structural steel. But its durability under heavy corrosive environment is expected twice as long as general steel. The roof models were designed as closed cone type for each of the three structural materials. In the result of a FEM (Finite Element Method) structural analysis for the developed models, the safe snow depth was higher 2.3 times than a general roof structure, when elements of equal section modulus were used.

• Journal of dental hygiene science
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• v.15 no.4
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• pp.407-412
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• 2015

This study investigated flexural properties of indirect Gum-shade composite resins for esthetic improvement. The material utilized in this study was Crea.lign, Twiny flow and Twiny paste (TP). Ten specimens were fabricated with a dimension of $25{\times}2{\times}2mm$ according to the ISO 4049. After fabrications, specimens were stored in the distilled water for 24 hours at the temperature of $37^{\circ}C$. Three-point bending test was performed in universal testing machine (Instron 3344; Instron, USA) at a crosshead speed of 1 mm/min until the failure occurred. TP exhibited a higher flexural strength (FS) and flexural modulus (FM) compared to the flowable materials. There were significant differences among the three materials in FS and FM. However, there was no significant difference in work of fracture (WOF) in all tested materials (p>0.05). In Weibull analysis, TP showed the greatest Weibull modulus which means a higher reliability of the materials. Also, Gum-shade composite resins revealed a strong correlation in all flexural properties. There was a positive correlation in FS-FM ($r^2=0.99$) and a negative correlation between FS-WOF and FM-WOF ($r^2>0.97$). Therefore, this confirmed that flexural property was important for mechanical behavior evaluation and useful information. To addition, this improved among mechanical properties correlation of materials as important factor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.624-629
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• 2016

A brake lever in a basic railway brake system is an important safety device that delivers braking force from the brake cylinder to the brake pad. The safety guidelines for designing rolling stock only qualitatively describe that the brake lever should have sufficient strength. Each train has a different type of brake lever. One brake lever that was designed with a factor of safety of 1.27 has failed, so the material was changed to increase the strength. Therefore, the stress distribution and weak points of the lever were identified by theoretical analysis. and structural analysis. Different brake lever designs were examined for KTX high-speed trains, which have a split-type structure, as well as for electric locomotives, which use an electric multiple unit (EMU) with a unity-type structure. A fracture test was also done to look at the relationship between the vertical stress and the bending stress during braking. The results were used to find a safety factor to apply to each train and suggest quantitative minimum guidelines. We also looked at changing the unity-type EMU brake lever to the split type under the same conditions and analyzed how much the design change affected the factor of safety.