• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.814-821
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• 2015

The purpose of this study is to estimate crack reduction properties of covering concrete with fibers in basement. Air contents, slump, compressive strength, tensile strength and plastic shrinkage has been tested to conduct the optimum addition ratio and type of fiber. The results is a following. For the properties of air contents, all of the specimens added fibers shown the higher than plain concrete. For the flowability, slump decreased about 40-80% when all of the specimens added fibers. For the strength properties, the specimens added nylon fiber shown higher compressive and tensile strength about 5-15% comparing with other concrete. For the plastic shrinkage, cracking decreased when the fiber added comparing with plain concrete. Especially, when nylon fiber added in the concrete, the plastic shrinkage did not occurred. For the overall consideration, when the addition ratio of nylon fiber is 0.6%, the press concrete is identified as showed optimum properties.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.213-224
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• 2018

In this study, a series of accelerated creep tests (SIM) was carried out on geosynthetic strip reinforcements with folding grooves having different tensile strengths (15 kN, 25 kN, 35 kN, 50 kN, 70 kN, and 90 kN) to analyze creep characteristics and to assess creep reduction factors. In particular, long-term creep tests were conducted on geosynthetic strip reinforcements with 25 kN tensile strength, which is widely used, to compare and analyze the accelerated creep test results. As a result, the creep reduction factor increased with an increasing design life of reinforcement. In addition, geosynthetic strip reinforcement using the same material and manufacturing method showed similar creep reduction factors at the same design life for different tensile strengths. When both long-term and accelerated creep test data were used, the creep reduction factors from the accelerated test were estimated to be 5.9%~7.1% less than those from the long-term creep test for the design life ranging from 50 to 100 years.

• Textile Coloration and Finishing
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• v.10 no.5
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• pp.39-47
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• 1998

The purpose of this study was to investigate the effect of alkali treatment on EG solution of polyester/silk union cloth(P/S cloth) . Tensile strength, moisture regain, crease resistance, and reduction ratio of the treated P/S cloth were measured. The results of this study were as follows ： 1) The weight loss of P/S cloth treated with EG solution was three times higher than those of P/S cloth treated with $H_2O$. The weight loss of P/S cloth was increased greatly with increasing concentration of NaOH, temperature, and time. Favorable weight reduction of treating condition could be obtained when lower concentration of NaOH was used with longer time. 2) If it was added $H_2O$ on EG solution, weight loss of polyester increased, while those of silk decreased. In addition, decreasing ratio of tensile strength warp direction (polyester) was lower, while those of weft direction(silk) was higher. 3) Moisture regain of P/S cloth treated with EG solution increased with weight loss up to 10% . Crease resistance of P/S cloth was the highest at weight loss of 10~15%.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.253-258
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• 1994

The effect of hole size and hole-to-hole distance in the braided and laminated composite was studied in terms of tensile strength, pin bearing strength, and flexural strength of S2-glass fiber braided polyester. The tensile strength reduction with hole size was well fitted with he Whitney and Nuismer's prediction for the laminated composite. The characteristic distance was measured to be about 1.6mm for braided composite and 1.8mm for laminated one. The effect of distance between the centers of two circu lar holes on tensile strength was negligible when the distance between these two holes was larger than 4 times of the diameter of circular hole for both braided and laminated composite. The side effect was diminished when the center of hole was located 3 times farther than the diamet.er of the hole. The pin bearing strengths was decreased with the size of pin hole for both braided and laminated composite.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.77-84
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• 2007

In this paper presented, a design method of sandwich slab bridge of simple supported made by composite materials. Many of the bridge systems, including the girders and cross-beams, and concrete decks behave as the special orthotropic plates. Such systems with sections, boundary conditions other than Navier or Levy solution types, or with irregular cross sections, analytical solution is very difficult to obtain. Thus, Finite Difference Method is used for analysis of the pertinent problem. For the design of bridge made by the composite materials, cross-section is used the form-core shape because of this shape is economical and profitable, and for output of the stress value used F.D.M. Based the experimental of a composite specialist, an equation expressing the rate of decrease of tensile strength of glass fibers based on increase of mass was obtained. From these equations, one can estimate the rate of tensile strength reduction due to increased size. Tasi-Wu failure criterion for stress space is used. Strength-failure analysis procedure, using these reduced tensile strength, is presented.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.15-22
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• 1998

The effects of shot peening an the fatigue strength are studied in this paper. Applying the multistage shot peening on the material. the relation between the residual stress and fatigue strength compressive is investigated. Observing tensile strength elongation. reduction of area. hardness. and roughness. the results can be summarized as follows ; 1.The change of mechanical properties is small before and after the shot peening is carried out. The change of hardness is also small in high hardness material. 2.The surface roughness does not affect the fatigue strength. but the surface roughness is improved by multi-stage shot peening. 3.The fatigue strength of multi-stage shot peening material is 756MPa and is 1.78 times higher than that of un-peened material. 4.The maximum compressive residual strength of multi-stage shot peening material is -792MPa the fatigue strength seems to be improved by residual stress.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.1
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• pp.75-81
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• 1998

We have studied internal quality including chemical compositions, microscopic structure and nonmetallic inclusion of test materials. We have analyzed tensile strength value, hardness value, impact value etc. In analyzing internal quality, all of the test materials showed typical ferrite+pearlite structure. But nonmetallic inclusion showed oxide and sulfide inclusions in medium carbon steels, and sulfide inclusion is S-free cutting steels. In ca+ S-free cutting steels, the calcium aluminate and sulfide complex inclusion had low-melting points as deformation of sulfide and oxide inclusion is existed. It was found that tensile strength and hardness give maximum value in medium carbon steels, where as minimum in Ca + -free cutting steels. But values of elongation, reduction of area impact are reverse. Fracture surface of impact specimen is ductile in free cutting steels but brittle in medium cabon steels.

• Proceedings of the KAIS Fall Conference
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• 2011.05b
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• pp.679-682
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• 2011

The effects of heat input(1.5~3.6kJ/mm) and postweld heat treatment(PWHT, $600^{\circ}C$, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strength and CVN impact energy of as-welded specimens decreased with increasing heat input. The fine-grained acicular ferrite was mainly formed in the low heat input while polygonal and side plate ferrites were dominated in the high inputs. Meanwhile, tensile strength and hardness of PWHT weldments decreased due to the coarsening of microstructure and reduction of residual stresses.

• Proceedings of the KIEE Conference
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• 2005.11b
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• pp.226-229
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• 2005

본 논문에서는 송전선로 도체의 경년열화(thermal deterioration)를 평가하기 위해 확률적 기법을 도입하였다. 선로의 경년열화를 나타내기 위해 선로의 장력(tensile strength) 감소를 계산하며 이는 해당 선로의 과거 전류 이력과 선로가 위치한 지역의 과거 기상데이터 및 부하량의 변화를 통해 산출한다 첫째로, 과거 데이터를 통해 확률분포를 구한 후 모든 데이터는 통계적으로 서로 간에 독립적이라는 가정 하에 Monte-Carlo Simulation을 수행하였다. 둘째로, 과거 데이터의 이력을 시간순서대로 추종하여 1시간 단위로 장력변화를 누적하는 순차적 계산(dynamic calculation)을 수행하였으며 그 결과를 MCS 기법과 비교하였다 주로 백분율로 표현하는 도체의 장력 감소분은 송전선로의 수명을 결정하는데 사용할 수 있는 중요한 지수이때, 계통계획에 있어서 유용한 기준으로 사용할 수 있을 것이다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.159-163
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• 2006

The effects of annealing temperature and time on mechanical properties and microstructures were studied in cold drawn pearlitic steel wires containing 0.84wt% Si. Annealing was performed from $200^{\circ}C$ to $450^{\circ}C$ with different time of 30sec, 1min, 15min and 1hr. The increase of tensile strength at low temperature was related with strain ageing. The decrease of tensile strength at high annealing temperature was related with spherodization of cementite and the occurrence of recovery of the lamellar ferrite in the pearlite. The improvement of ductility was connected with spherodization of cementite plate in pearlite and recovery process by reduction of high dislocation density at short time annealing temperature of $400^{\circ}C$.