• Composites Research
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• v.14 no.1
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• pp.1-7
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• 2001

In this study, damage evaluation of glass fiber reinforced thermoplastic composites was investigated with acoustic emission method. Specimens of 1.7mm thickness laminate were made from PET and 7 layers o171ass fabrics. Notch and impact loading were added to the specimen and normal tensile test and tensile test with the dead load were carried out. AE signal was measured as the functions of notch ratio to the width0 and impact energy in order to find out the correlation between fracture mode and AE parameters. The result has shown that low amplitude of AE signal was due to the microcrack of matrix and its growth, whereas the amplitude in the mid range was the response to the delamination and interfacial separation. In the range of high amplitude above 90dB. the fracture of glass fabric was found. Tensile strength decreased with increasing notch ratio to the width and impact energy because of tile effect or delamination, the cracking of matrix and stress concentration. In proportion to the size of damaged area. AE signal showed its wider range of frequency and energy as well as increased number of hits.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.105-105
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• 2010

자동차 차체부품에 적용되는 플라스틱 소재는 강도와 내마모성, 내충격성의 충분한 물성확보가 필요하며, 이에 플라스틱 소재의 기계적 특성 향상을 위해 유리 섬유가 다량 함유된 복합소재적용이 증가하고 있다. 반면 플라스틱이 고강도화함에 따라 제품 성형을 위한 사출 금형을 손상시키는 사례가 빈번하게 발생하고, 소재의 유동성 저하에 따른 사출 불량이 증가하고 있어 고강성 플라스틱 복합소재에 대응하는 고경도, 고내마모 특성이 부여된 사출 금형의 개발이 시급한 실정이다. 특히 사출 금형에 사용되는 소재는 기존 소재에 비해 우수한 내마모성과 함께 고광택을 유지하는 것이 더욱 중요해졌으며, 이에 따라 유럽, 일본과 국내 연구진에 의해 다양한 연구가 진행되고 있다. 그 중에서도 일본에서 개발되어 국내에도 소개된 래디칼 질화는 기존 질화법에 표면의 화합물 층만을 제어하는 것으로 다소의 표면 광택 효과는 있으나, 플라스틱 사출에 그대로 적용하기에는 무리가 따르므로 그 용도가 극히 제한적이다. 본 연구에서 적용한 나노 질화기술은 0.1torr 이하의 고진공에서 고밀도의 플라즈마 에너지를 발생시키는 방법으로 화합물층이 없는 나노 크기의 질화층을 소재 표면에 형성시키는 기술로서, 처리 후에도 표면의 색상 및 광택의 변화가 없는 것을 특징으로 한다. 또한 표면 경도 및 피로 특성을 향상시킴으로써 금형의 내구 수명을 향상시킬 것으로 기대된다. 본 연구에서는 KP4 금형 소재를 사용하여 플라즈마 이온 질화 시험 조건에 따른 소재의 경도 및 내마모 특성을 파악하고, 미세 조직 분석 및 XRD 분석 등을 통해 내마모 특성 향상에 대한 기본 특성을 평가하였다. 또한 인장시험을 통해 인장강도, 항복강도 및 연신율을 파악하고, 이를 토대로 고주기 피로시험을 실시함으로써 S-N curve를 얻고, 이를 통해 피로 강도 및 피로 수명에 미치는 나노 질화 처리의 영향을 파악하고자 하였다. 플라즈마 이온 질화 시험은 질소와 수소 비율($N_2:H_2$), 진공도, Screen bias voltage, Bias voltage를 변화시켰으며, 챔버 온도는 $400^{\circ}C$로 고정하였으며, 처리시간도 3시간으로 고정하였다. 질소와 수소의 비율은 3:1일 때 최고의 내마모 특성을 보였으며, 진공도는 내마모 특성에 큰 영향을 미치지 않는 것으로 관찰되었다. KP4의 초기 경도값은 약 302 Hv인 반면 최적의 나노 질화처리를 거친 시편에서는 800Hv 이상의 Vickers 경도값을 보였다. SEM 미세조직 분석과 EPMA를 통한 성분 분석을 시행한 결과 표층으로부터 약 $1.5{\mu}m$의 나노질화층을 확인할 수 있었다.

• Composites Research
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• v.27 no.4
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• pp.158-167
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• 2014

Final goal of this research is to establish the database for correlation factors which connects the test and analysis results of shear buckling allowables for composite plate. To accomplish the goal, extensive test and analysis works are required. In this paper, as the first step, a frame-type fixture for shear buckling test was designed and validated through the test and analysis. Final configuration of the fixture were determined via parametric study on the effect of specimen size, cross-sectional dimensions, and number of fastening bolts on the shear buckling load. Results of the study showed the designed frame-type fixture successfully induces the shear buckling of composite plate. However, there were deviations between the test results and analysis results for ideal case under pure shear load, which were mainly caused by the difference in plate sizes for both cases. The difference were larger in the plates with larger hole and simply supported boundary condition. It is concluded from the results that while the designed fixture can be used for the clamped plates with acceptable accuracy, it shows larger difference in the simply supported plates.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1059-1064
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• 2012

In this study, tensile tests were performed on specimens that simulated the cold-bending and heat-treatment of pipe bends to understand the mechanical properties of pipe bends manufactured by cold-bending followed by heat-treatment for relieving residual stress. The strength and ductility of cold-worked materials were respectively found to be higher and lower than those of the parent material although heat-treatment was carried out to relieve residual stress. In addition, the increase in strength and decrease in ductility were proportional to the applied strain levels for cold-working. It was thus inferred that the intrados and extrados regions of pipe bends that were cold-bended and heat-treated show higher strength and lower ductility compared to the parent straight pipe and that the mechanical properties at the crown region are nearly the same as those of the parent straight pipe.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.704-709
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• 2001

Experimental methods to determine non-linear properties of rubber materials for finite element analysis is discussed. In simple tension tests, dumbbell specimens are generally used to obtain states of pure tension strain. It is shown that the strip specimens of which length is over 10 times of the width can be also used. In simple compression tests, the effect of the friction between the test specimen and the platens is investigated. the new test method with the tapered platen is proposed in order to overcome the effect of friction and it is verified by experimental and finite element analysis results. In pure shear tests, it is shown that the width of the specimen must be at least 10 times of the height. The mechanical conditioning is suggested to stabilize the properties of the rubber materials. Also, engine mount for automotive is analyzed and experimented for each cases.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.119-127
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• 1999

The objective of this study is to simulate the fracture behavior of composite structure bonded with more than 2 different cementitious materials. For this, concrete and cement were stacked and bonded in a direction perpendicular to loading and specimens were tested. Each constituent material of concrete and cement was fabricated independently also, and three point bending and indirect tensile tests were carried out for the acquisition of measured values applicable to the proposed model. As a result of comparing theoretical results and experimental ones, it was found that the proposed model derived from fictitious crack theory can be used to predict the fracture behavior of composite structures on the vases of well agreement with experimental results. It was also noted that the degree of improvement of fracture energies and strengths is greatly dependent on the stacking sequence of layers composing of a composite structure. Thus, it can be concluded that brittleness or ductility of a composite structure can be accomplished by a proper arrangement of layers on one's purpose throughout the proposed analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.2001-2005
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• 2005

The tensile test is generally used to measure mechanical properties with conventional fracture test. This test is extremely certain method to measure Young's modulus, yield strength, tensile strength and so on. ASTM, by international standard, prescribes two classes of tensile tests in tubular products. One is method that specimens aren't done by any process with Tube-shape. The other is that specimens are made on process for C-shape. In this paper, we would like to present the new-shape specimens for the tensile test. The presented specimen's shape is that put two pieces of C-shape specimens together. Besides a load point and a support point are fixed like Tube-shape specimens. This shape of specimen has a difference that existing specimen is made on one-step process out this specimen is made on two-step process. This shape is considered that stress concentration phenomenon occurs at the reduced section if a specimen is made on one step process.

• Polymer(Korea)
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• v.25 no.1
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• pp.63-70
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• 2001

The objective of this study was to investigate the effect of cure type on the processing and physical properties under conditions of similar stress-strain properties. On the carbon black filled natural rubber(NR) based compound, the induction time decreased, but the cure rate became fast with increasing loading of sulfur donor agent. Tensile strength was little affected on the curing type. However, elongation generally decreased with increasing accelerator. Effect of cure type on the blow-out properties was followings: CV

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.607-612
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• 2017

Recently, additive manufacturing (AM) technology, also known as 3D printing technology, has attracted attention as an innovative production method to fabricate functional components having complex shapes with saving materials. In particular, a fabrication of poly lactic acid (PLA) parts through a fused deposition modeling (FDM) technique has attracted much attention in the medical field. In this paper, an experimental study on the identification of dominant process parameters influencing mechanical properties of PLA parts fabricated by the FDM process is conducted, and their optimal values for maximizing the mechanical properties are obtained. Three process parameters are considered in this research, namely, layer thickness, a part orientation and in-fill. It is known that thin layer thickness, part orientation diagonal to the tension direction, and full in-fill are optimal conditions to maximize the mechanical properties.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.42.1-42.1
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• 2009

오스테나이트 스테인리스강은 우수한 내식성 및 기계적 특성으로 인해 구조용 재료로 널리 사용되고 있다. 표준원전 경수로의 경우 가압기 밀림관소재로 Nb 안정화 오스테나이트 스테인리스강인 type 347 스테인리스강이 사용되고 있다. 그러나 원전배관에서는 운전중 배관내 온도편차에 의한 열응역과 하중변화에 의한 기계적하중에 의해 피로손상을 받는다. 일반적으로 범용 오스테나이트 스테인리스강(AISI 304, 316)의 피로균열 성장거동에 대한 연구결과는 국내외적으로 다수 축적되어 있으나 type 347 탄소, 질소 함량에 따른 기계적 특성 및 피로균열성장 연구는 매우 미비하다. 따라서 본 연구에서는 탄소와 질소의 함량에 따른 기계적거동을 평가하고, 이에 따른 피로균열전파속도를 관찰하여 스테인리스강의 정확한 피로균열전파속도 곡선을 제시하고자 한다. 실험에 사용된 시편은 두께 5mm, 폭 25.4mm CT시편을 사용하였으며, 1mm의 예비균열을 주었다. 그리고 실험온도는 상온과 원전가동온도인 $316^{\circ}C$에서 실시하였으며, 주파수는 10Hz를 주었다. 실험결과 각 함량에 따른 type 347의 미세조직 관찰결과 기지내에 압연방향을 따라 조대한 석출물의 흐름이 관찰되었으며, 크기나 분포가 큰 차이를 보였다. C+N 함량이 낮은 시편은 주로 $0.1\;{\mu}m$ 이하의 미세한 입자들이 오스테나이트 기지조직의 입내와 입계에 고르게 분포되어 있었다. 그러나 C+N 함량이 높은 시편의 경우에는 $0.1\;{\mu}m$ 이하의 미세한 입자들과 함께 국부적으로 $1\sim10\;{\mu}m$의 조대한 입자들이 분포하고 있는 것이 관찰되었다. 그리고 질소의 함량이 높아짐에 따라 인장강도는 증가하였으며, 피로시험결과 고온에서 실험한 피로균열성장률 곡선이 상온보다 높게 나타남을 확인할 수 있었다. 그리고 질소가 적게 첨가되고 탄소의 함량이 많을수록 피로균열성장률은 ASME 곡선보다 낮게 나타났다.