• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.636-641
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• 2010

A preburner for the staged combustion in the high performance liquid rocket engine is being developed and strength experiments and finite element analyses on specimens, which simulate the brazing joint of the preburner, were performed and the results were compared. One specimen simulate the joints near oxygen injectors of head by the funance brazing and two specimens the joints of the combustion chamber cooling channel by vacuum brazing. The experiments were burst ones with strain gauges.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.27-27
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• 1999

본 연구에서는 초음파 Immersion법을 이용하여 복합재 연소관내에 존재하는 결함을 검출하는 방법에 대하여 연구하였으며, 이를 위하여 FRP의 delamination, FRP-EPDM간의 미접착을 모사한 모의 결함 시편을 제작하여 시험하였다. 먼저 복합재료에 대한 초음파 시험방법을 최적화하기 위하여 가장 검출 감도가 좋은 탐촉자의 적용 주파수조건 및 물거리를 구하였으며, 이들 최적 조건으로 모의 결함 시편을 A, B, C-Scan하여 결함을 검출 분석하였다. 그리고 시험 자료를 바탕으로 데이터 값을 분석함으로써 복합재료에서의 음파 속도, 음향 임피던스, 반사율 및 투과율 등 복합재료의 초음파 특성을 산출하였으며, 동 시편에 대한 X-ray 필름을 촬영하여 그 결과를 초음파 시험 결과와 비교 분석하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1461-1469
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• 2011

Using three-dimensional (3-D) FE analyses, this paper provides a method for analyzing the effects on stresses and strains produced by angular and concentric misalignment of a test specimen for a torsion test. To quantitativele compare of the FE results, the average bending strain for the angular, concentric, and combined misalignment was proposed. To verify the effects of axial misalignment of the test specimens, we used both circular and tubular specimens. From the FE results, we proposed general predictions for the effects caused by the various types of axial misalignment and its direction. In addition, we confirmed the effect of initial yielding moment based on the initial yielding condition for axial misalignment of specimens in torsion tests.

• Composites Research
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• v.37 no.2
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• pp.126-131
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• 2024

The moisture absorption rate and structural strength changes of oven-cured composite skin based on closed molds were studied. Moisture absorption was performed on specimens with and without filler applied. The specimens were exposed to moisture for up to 231 days. Tensile and compression tests were conducted with and without filler application. As a result of the test, the moisture absorption rates of the tensile and compressive specimens without filler were 2.4 and 0.3% higher, respectively, than those with the filler applied. The tensile and compressive strengths of the specimen without filler applied were average 305 MPa and 139 MPa, respectively, and the tensile and compressive strengths of the specimen with filler applied were 313 MPa and 166 MPa, respectively, appeared high.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.2
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• pp.1-11
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• 1997

During hydroproof test of composite pressure vessel, acoustic emission signal was measured and analyzed to evaluate structural integrity of composite motor case. When pressure was held for 1 min. at constant pressure from low pressure level to high pressure level, the pattern of hit rate of good composite pressure vessel is increased with higher value than that of bad composite pressure vessel. This report also presents detection possibility of burst location approximately in the range of 25∼36％ of burst pressure using energy rate. In case that it is difficult to detect burst location of composite motor case, it is possible to detect burst location, i.e. structurally weak location of composite pressure vessel with applying same pressure lower than maximum expected operating pressure(MEOP) repeatedly.

• Composites Research
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• v.23 no.5
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• pp.15-21
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• 2010

In this study, repair and maintenance schemes of the damaged composite structure was investigated, and a repair process of the carbon/epoxy laminate composite structure was investigated numerically and experimentally. The composite laminates were damaged by drop weight type impact test machine. The damaged composite structure was repaired using external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.1
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• pp.25-31
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• 2011

In the tensile test necking occurs at the maximum load point and non-uniform stress state is generated in this section. The equivalent stress becomes quite different from the axial stress as necking proceeds. Methods for obtaining the true stress-true strain curves, by overcoming difficulties due to the necking phenomena, have been developed by many authors. One of the methods based on the finite element analysis simulation is a very promising method. In this paper, general-purpose finite element program is used to simulate the tensile test. A round specimen and a flat specimen prepared from the same steel block are tested and simulated. The true stress-true strain curves are determined without assuming that the material follows Hollomon's law.

• Composites Research
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• v.37 no.2
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• pp.76-85
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• 2024

In this paper, a composite maintenance robot using carbon fiber spray method was developed that automatically sprays mixture was created for repair to damaged areas to repair them. To develop a robot, a repair process was developed in which a mixture of milled carbon fiber, epoxy resin, and hardener is sprayed and consolidated on the damaged area. To automate the repair process, an EOAT based on a collaborative robot was developed that can automatically suction and spray the mixture onto the damaged area. To evaluate the repair performance of the robot, 0° and 90° unidirectional specimens were manufactured and tested in accordance with ASTM D3039. Tests were performed on undamaged specimen, damaged specimen, and repaired specimen by a robot after damaged. As a result of the specimen test, the tensile strength of the 0° and 90° specimens was recovered by 10% and 90% after repair. Based on the test results, the repair performance of the developed composite maintenance robot was verified.

• Journal of the Korean Ceramic Society
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• v.36 no.3
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• pp.225-230
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• 1999

Ball-on-3-ball 시험에서 이축 강도를 결정하기 위한 방법에 대해 고찰하였다. 알루미나 시편을 이용하여 ball-on-3-ball 시험과 poston-on-3-ball 시험을 하여 이축 강도를 측정하였다. piston-on-3-ball 시험에서의 강도 식과 등가 반지름을 이용하여 계산한 ball-on-3-ball 시험에서의 이축 강도와, piston-on-3-ball 시험에서의 이축 강도를 분산 분석(ANOVA)한 결과, 두 평균이 동일하다고 할 수 있었다. 따라서, ball-on-3-ball 시험에서의 이축 강도는 piston-on-3-ball 시험에서의 강도 식과 등가 반지름을 이용하여 계산할 수 있다. 또한, 유한 요소법을 이용하여 ball-on-3-ball 시험시 시편에 인가되는 응력 분포를 고찰해 보았다.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.17-25
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• 2005

The bender element method is an experimental technique to determine very small strain ($<10^{-3}\%$), elastic shear modulus of a soil, $G_{max}$ by measuring the velocity of shear wave propagation through a sample. Bender elements have been applied as versatile transducers to measure small strain modulus of wet or dry soils in various laboratory apparatus. In this paper, bender element (BE), resonant column (RC) and torsional shear (TS) tests were performed on Toyoura sand at various testing conditions using the modified Stokoe type RC/TS testing equipment capable of performing BE test. Based on the results, applicabilities of the testing method using bender element were evaluated by comparing the values of $G_{max}$ obtained from RC/TS and BE testing methods. For more dependable evaluation, the loading frequency of each testing method was considered for the results obtained for samples in saturated condition by adapting Biot's theory.