• 한국기계가공학회지
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• 제20권4호
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• pp.127-134
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• 2021

In this study, the adhesive fracturing characteristics of a DCB specimen due to single and heterogeneous bonding materials under tearing load was investigated. The experiments were conducted to examine the fracturing properties of the adhesive DCB specimen. As an experimental condition, a forced displacement of 3mm/min was applied to one side while the other side was fixed. As a result of the experiment, it was found that the AL6061-T6 material was superior to the CFRP material in terms of maximum stress, specific strength, and energy release rate when compared to the adhesive fracturing property of a single material. We tested CFRP-AL, a heterogeneous bonding material, and compared its experimental results to the results from the single materials. Based on these results, CFRP-AL with a heterogeneous bonding material was observed to have the superior structural safety compared to single materials for the mode III fracture type.

• 한국안전학회지
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• 제38권3호
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• pp.20-26
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• 2023

Fiber-reinforced composite materials with carbon, glass, and aramid fibers are widely applied to industrial field structures due to their excellent properties. However, carbon fibers are vulnerable to external impacts, whereas aramid fibers degrade when exposed to water. This study evaluated carbon/aramid fiber composites degraded and damaged by high-temperature saline environments using acoustic emission (AE). The test specimen was molded using an autoclave and immersed in seawater at 70 ℃ for 224 days. In order to imitate the damage, a 3-mm-diameter hole was drilled using a diamond drill. Additionally, the specimen with the perforation was repaired by patch attachment processing. Three-point bending was used to conduct the flexural experiment, and an AE sensor with a 150-kHz resonance frequency was attached to evaluate the damage and the effect of patch attachment. AE accumulative counts obtained at the maximum load were 69.2, 67.1, and 91.2 for a high-temperature seawater deteriorated condition, a hole specimen, and a repaired patch specimen, respectively. Furthermore, the maximum amplitude of AE was detected at low values of 28 dB, 31.3 dB, and 30.3 dB.

• 한국항공우주학회지
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• 제50권7호
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• pp.455-463
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• 2022

세계 각국에서는 위성용 카메라 등 고신뢰성을 요구하는 카메라에 대한 연구개발 필요성이 높아짐에 따라 시편시험 수행을 통해 광기구 구조물과 광학부품 간 접착강도 물성치의 신뢰성을 확보해오고 있다. 다만 널리 활용되고 있는 시편형상은 취성 경향이 높은 유리 및 유리세라믹 소재에의 적용에 적합하지 않아 접착강도 한계값 도달 전 유리 부분 응력집중으로 인한 소재 자체 깨짐 현상이 정확한 접착강도 획득에 어려움을 유발한다. 본 연구에서는 유리 소재 자체 파단이 발생한 시편시험 결과를 바탕으로 다양한 시편형상에 대한 전단시험 환경에서의 응력분포 특성을 해석적으로 분석하였다. 이를 통해 유리부의 응력집중을 완화할 수 있는 형상적 특징을 도출하여 시편시험으로 검증가능한 접착 전단강도의 범위를 개선하였다.

• 소성∙가공
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• 제31권1호
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• pp.17-22
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• 2022

Hot stamping is widely used to manufacture structural parts to satisfy requirements of eco-friendly vehicles. Recently, hot forming technology using uncoated steel sheet is being studied to reduce cost and solve patent problems. In particular, research is focused on process technology capable of suppressing the generation of an oxide layer. To evaluate the oxide layer in the hot stamping process, Gleeble testing machine can be used to evaluate the oxide layer by controlling the temperature history and the atmosphere condition. At this time, since cooling by gas injection is impossible to protect the oxide layer on the surface of a specimen, research on a method for securing a quenching speed through natural cooling is required. This paper proposes a specimen shape design method to secure a target quenching speed through natural cooling when evaluating the oxide layer of an un-coated boron steel sheet by Gleeble test. For the evaluation of the oxide layer of the un-coated steel sheet through the Gleeble test, dog-bone and rectangular type specimens were used. In consideration of the hot stamping process, the temperature control conditions for the Gleeble test were set and the quenching speed according to the specimen shape design was measured. Finally, the quenching speed sensitivity according to shape parameter was analyzed through regression analysis. A quenching speed prediction equation was then constructed according to the shape of the specimen. The constructed quenching speed prediction equation can be used as a specimen design guideline to secure a target quenching speed when evaluating the oxide layer of an un-coated boron steel sheet by the Gleeble test.

• 예술인문사회 융합 멀티미디어 논문지
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• 제8권3호
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• pp.589-596
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• 2018

현대 사회에서 의식주 중에서 구조물이나 운송수단은 중요한 역할을 가진다. 만약 구조물이나 운송수단에 작은 크랙이라도 생기고 크랙이 진전되면 그 부품들이 파괴되어 큰 사고를 야기할 수 있다. 이러한 상황을 방지하기 위한 본 연구에서는 크랙의 진전에 따른 파손 경향을 조사하기 위하여 시험편을 이용하였다. CT 시험편의 재질로는 요즘 각광받는 복합재료인 단방향 탄소섬유 강화플라스틱을 사용하였다. 시험편 모델은 단방향성 섬유로서 적층각도를 주었고 적층각도는 [60/-60/60/-60]순으로 지정하였다. 해석 조건으로는 하단부의 홀을 고정시킨후 상단부 홀을 15mm의 강제 변위를 가하였다. 본 연구 결과로는 구조용 강, 구리, 티타늄, 알루미늄 순으로 등가응력과 전단응력이 높게 나왔다. 이러한 결과는 이종재료로 만들어진 CT 시험편의 파손을 검증하는 데 유용하게 사용될 수 있다고 사료된다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(2)
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• pp.154-159
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• 1998

In order to assess the susceptibility of the environmentally assisted cracking(EAC) on SA508 Cl.3 steel in primary water condition, potential step test and slow strain rate test(SSRT) were conducted in a simulated crack tip condition. In this test, anodic dissolution was dominant in the crack tip environments. Proposed simple dissolution model is a modification of Hishida's anodic dissolution model at the plastic zone. One can predict actual crack growth rate with the smooth specimen through this model.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.685-688
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• 2006

As the concrete structure being large-sized and/or high-strengthened, the control of the hydration and curing temperature is made much account. This study, analysing the concrete temperature history from cylindric specimen and mock-up structures, investigates the effect of the early age curing condition and the optimum method of curing temperature control on mass concrete.

• 한국기계연구소 소보
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• 통권20호
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• pp.89-104
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• 1990

This study was carried out to obtain the most optimum conition in vacuum sintering of M2 HSS powder, by analysis of sintering characteristics and fracture strength in several conditions. The conclusion deduced from this study are as follows; -Boron was more effective element than graphite; at this time, the optimum amount of addition was 0.05 wt% -The optimum condition of sintering temperature and time were 1190- $1200^{\circ}C$ and 1-1.25hr, respectively -Fracture strength of vacuum sintered and heat-treated specimen in the most optimum condition was 2-2.5KN/ $mm^2$

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.227-230
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• 1998

The interfacial breakdown between two internal dielectric surfaces represents one of the major causes of failure for power cable joint. In order to better understand this phenomenon, breakdown experiments were performed for each interfacial condition at Epoxt/EPDM interface found in cable. The specimen were Epoxy resin and EPDM generally used in cable joint. The interface conditions were three parts. First condition was the pressure of interface, we used the value of 1, 2, 3, 4, 5[kg/cm$^2$]. For the second condition, the sanding condition was treated with sand paper #220, #600, #1200. Finally, we observed the breakdown according to the presence of silicon oil at the interface.

• 연구논문집
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• 통권29호
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• pp.185-194
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• 1999

The shape and thickness distribution according to the pressure-time curve were carried out using the FEM and experiment. Also, mechanical properties were investigated. The square cup parts have been formed with pressure-time curve generated by result of analysis. The tensile strength and elongation have been investigated according to applied pressure conditions using the tensile test specimen obtained from the superplastic formed cup. We can use to predict the shape of formed part under the applied pressure using the FEM analysis. In the case of optimum pressure condition, the thickness distribution and mechanical properties were improved. From this study, we can find the important of optimum pressure-time condition. We have investigated about the forming of airplane part and fuel tank for motorcycle. If the applied load used in boundary conditions was appropriate, the simulation result coincides with the formed part. However, it is very difficult to define the pressure condition in complicated shape. Thus, it is need to develop the optimum pressure condition for superplastic forming.