내구연한이 도래한 아스팔트 혼합물은 사용자의 주행성 및 안전성 확보를 위해 주기적인 유지·보수를 실시한다. 과거에는 유지·보수 과정에서 발생된 폐아스팔트 혼합물을 각종 건설현장에서 단순 매립재로서 활용하였으나, 재활용 아스팔트 혼합물의 배합설계 기술이 확립된 이후에는 도로포장재료로서의 재활용되어왔다. 하지만 현재 시공된 재활용 아스팔트 혼합물 또한 내구연한이 다가옴에 따라 노화된 재활용 아스팔트 혼합물의 처리방안 수립이 필요한 시점이다. 본 연구에서는 한번 재활용된 아스팔트 혼합물이 기존의 재활용 배합설계법으로 반복적인 재활용이 가능한지 검증해보고자 하였다. 이를 위해 아스팔트 혼합물의 물성을 결정하는 가장 큰 요인 중 하나인 아스팔트의 물성이 노화 및 재생을 반복할때 어떻게 변하는지를 시험을 통해 분석하였다. 아스팔트 바인더의 노화를 모사하기 위해 공용성등급시험에 사용되는 단기노화 장비(Rolling Thin Film Oven, RTFO)와 장기노화 장비(Pressure Aging Vessel, PAV)을 활용하 였다. 노화된 아스팔트의 회생을 위한 재생첨가제 사용량은 국토부 시공지침의 배합설계법을 참고하였다. 실험결과, 노화된 바인더는 회생시 원바인더에 비해  sin는 감소하였으나, 회생된 바인더 간에는 유사한 결과값을 보였다. 반면 단기노화 시료는 회생이 반복 됨에 따라  sin이 감소한 경향을 보였으며, 장기노화시료는 회생이 반복되어도  sin가 유사한 것으로 확인되었다.

In this study, we designed and manufactured a large angular contact ball bearing (LACBB) with low deformation using JIS-SUJ2 steel and analyzed changes in its structural characteristics and chemical composition upon heat treatment. The bearing was produced by hot forging and heat treatment including a quenching and tempering (Q/T) process, and its properties were analyzed using 4 mm thick specimens. A difference in the size distribution of the carbide in the outer and inner parts of the bearing was observed and it was confirmed that large and non-uniform carbide was distributed in the inner part of the bearing. After heat treatment, the hardness value of the outer part increased from 13.4 HRC to 61 HRC and the inner part increased from 8.0 HRC to 59.7 HRC. As a result of X-ray diffraction (XRD) measurements, the volume fraction of the retained austenite contained in the outer part was calculated to be 3.5~4.8 % and the inner part was calculated to be 3.6~5.0 %. The surface chemical composition and the content of chemical bonds were quantified through X-ray photoelectron spectroscopy (XPS), and a decrease in C=C bonds and an increase in Fe-C bonds were confirmed.

The need for lightweight yet strong materials is being demanded in all industries. Carbon fiber-reinforced plastic is a material with increased strength by attaching carbon fiber to plastic, and is widely used in the aerospace industry, ships, automobiles, and civil engineering based on its low density. Carbon-reinforced fiber plastic is a material widely used in parts and manufactured products, and structural analysis simulation is required during design, and application of actual material properties is necessary for accurate structural analysis simulation. In the case of carbon-reinforced fiber plastics, it is reported that there is a porosity of around 0.5% to 6%, and it is necessary to check the change in material properties according to the porosity and pore shape. It was confirmed by applying the method. It was confirmed that the change in elastic modulus according to the porosity was 10.7% different from the base material when the porosity was 6.0%, and the Poisson's ratio was confirmed to be less than 3.0%. It was confirmed that the elliptical spherical pore derived different material properties from the spherical pore depending on the pore shape, and it was confirmed that the shape of the pore had to be confirmed to derive equivalent material properties.

Epoxy-based composites find extensive application in electronic packaging due to their excellent processability and insulation properties. However, conventional epoxy-based polymers exhibit limitations in terms of thermal properties and insulation performance. In this study, we develop epoxy-based siloxane/silica composites that enhance the thermal, mechanical, and insulating properties of epoxy resins. This is achieved by employing a sol–gelsynthesized siloxane hybrid and spherical fused silica particles. Herein, we fabricate two types of epoxy-based siloxane/ silica composites with different siloxane molecular structures (branched and linear siloxane networks) and investigate the changes in their properties for different compositions (with or without silica particles) and siloxane structures. The presence of a branched siloxane structure results in hardness and low insulating properties, while a linear siloxane structure yields softness and highly insulating properties. Both types of epoxy-based siloxane/silica composites exhibit high thermal stability and low thermal expansion. These properties are considerably improved by incorporating silica particles. We expect that our developed epoxy-based composites to hold significant potential as advanced electronic packaging materials, offering high-performance and robustness.

In order to respond to environmental pollution, developed countries, including Korea, have begun to conduct research to utilize hydrogen energy. For mass transfer of hydrogen energy, storage as liquid hydrogen is advantageous, and in this case, the volume can be reduced to 1/800. As such, the transportation technology of liquefied hydrogen for ships is expected to be needed in the near future, but there is no commercialized method yet. This study is a study on the technology to test the performance of the components constituting the membrane type storage container in a cryogenic environment as a preparation for the above. It is a study to find a way to respond by analyzing in advance the problems that may occur during the shear test of adhesives. Through this study, the limitations of ISO4587 were analyzed, and in order to cope with this, the specimen was supplemented so that fracture occurred in the adhesive, not the adhesive gripper, by using stainless steel, a low-temperature steel, to reinforce the thickness. Based on this, shear evaluation was performed under conditions lowered to minus 243℃, and it was confirmed that the breaking strength was higher at cryogenic temperatures.

PURPOSES : The process of extracting and recovering an asphalt binder from an asphalt mixture is harmful to the human body and can affect the properties of the asphalt binder owing to the presence of residual solvent quantities. This study was conducted to determine the properties of aged asphalt binders based on rejuvenator content without extracting and recovering the asphalt binders using RAP mortar. METHODS : After extracting and recovering aged binders from waste asphalt, a rejuvenator was added at a certain rate to evaluate the physical and rheological properties of the binder based on the added amount. RESULTS : When the rejuvenator content was greater than necessary, the absolute viscosity was not properly measured owing to the behavior of the rejuvenator. The phase angle was measured to be almost 90°, thus indicating that it acted as a liquid . In addition, the shear strain and nonrecovery compliance also increased significantly. CONCLUSIONS : If an excess rejuvenator quantity was added to the aged binder, the absolute viscosity was not properly measured, the phase angle was measured to be almost 90°, and the shear strain increased significantly. It is also necessary to conduct the same tests on different types of RAPs to ensure that the results of this study are reasonable.

예로부터 식품과 한약재로 널리 활용되어 온 매실은 호흡급등형 과실로 수확 후 상온에서 보관하면 며칠 내로 황변이 발생하고 물러지는 등 후숙이 빠르게 진행된다. 본 연구는 이러한 후숙이 진행될 때 수확 당시 색도가 품질과 영양적인 측면에 미치는 영향과 보관 조건에 따른 변화의 정도를 비교･분석하고자 한다. 이를 위해 같은 날에 수확한 매실을 색도에 따라 청매와 황매로 구분하고 상온, 냉장, 냉동 보관하는 동안에 발생되는 물리･화학적인 변화를 조사하였다. 수확 당일의 측정값과 비교하여 10~15% 이상 변하는데 소요되는 시간을 고려하면, 매실의 물성 변화는 저장기간 전반에 걸쳐 수확일의 색도 차이에 따라 뚜렷한 영향을 받지 않는 것으로 나타났다. 모든 저장 온도 조건에서 수확일과 비교한 실험일의 경도 감소가 가장 두드러졌고, 색도와 사과산의 변화도 빠르게 진행되었으나, 가용성 고형분과 pH의 변화는 거의 나타나지 않았다. 매실은 상온 보관의 경우 대략 4일 이내, 냉장 저장의 경우 대략 20일 이내에서 물성의 변화가 약 10% 이하로 적게 나타나며 품질을 유지하는 것으로 나타났다. 냉동 저장의 경우 색도와 경도는 저장 초기에 급격히 변하지만, 다른 물성은 대체로 장기간 유지되었다. 따라서 본 연구 결과를 토대로 저장 조건에 따른 물성 변화를 고려하여 매실의 저장 방법과 적절한 사용 시기를 결정할 것을 제안한다.

In this paper, the mechanical properties according to the rCF weight percent(10, 20, 30, 40, 50wt%) of the rCFRP specimen were evaluated and analyzed. First, to prepare rCFRP specimens, pellets were prepared according to the type of weight percent, and rCFRP tensile specimens according to ASTM D638 were prepared using an injection molding machine. Tensile tests were performed on each of 10 specimens according to weight percent conditions, and tensile strength and modulus of elasticity were calculated. For a detailed analysis of the correlation between the internal structure of the specimen and the mechanical properties, the weight percent to the constituent materials of the rCFRP specimen was calculated using mCT and used for the analysis of mechanical properties. For a more detailed analysis, a detailed analysis of the mechanical properties of rCFRP was performed through the fracture surface analysis of the specimen using FE-SEM.

Conversion to modern hydrogen energy is required, and research on liquefied hydrogen cargo containment systems is needed for large-capacity transport and storage. In this study, changes in the mechanical properties of the adhesive required for storage and transport in liquid hydrogen were confirmed. The lap shear test was performed by realizing cryogenic conditions in a small chamber using liquid nitrogen and liquid helium. There was an increase of 11.0% in the -180℃ condition compared to room temperature, and an increase of 1.8% in the -230℃ condition compared to the -180℃ condition was confirmed. In the case of shear strain, it is known that it decreases as the temperature goes down. As a result of the experiment, it was confirmed that the value at room temperature and the value at -180℃ reduced the shear strain by 5.0%, and -230˚ compared to the -180℃ condition. An increase of 1.5% was confirmed in the C condition. In the case of the specimen tested at -230℃, the deformation in the gripper part was larger than in other tests, and it is judged that the maximum shear strength and shear strain were affected. In addition, in this study, there is a limitation in the experiment at -230°C rather than 253°C, which is the boiling point of hydrogen

In modern times, where problems due to environmental pollution are continuously occurring, hydrogen is in the spotlight as the energy of the future. Hydrogen is an eco-friendly energy resource that does not even generate CO2, and is actively supporting research to utilize hydrogen energy at the national level. This study is a study on the cryogenic mechanical properties of the elements constituting the cargo hold during the transportation of liquid hydrogen. Among the various components, the evaluation of mechanical properties of the cryogenic adhesive under liquid helium conditions was confirmed. The related contents are summarized as follows. As a result of performing SSRT by curing the adhesive, it was confirmed that tensile strength and maximum strain were increased at cryogenic temperature (-230°C) compared to room temperature (25°C). It was confirmed that the adhesive-hardened specimen showed a brittle fracture mode at both room temperature and cryogenic temperature during tensile. Improvements in this study, such as pores occurring during adhesive curing, the use of standard specimens, and experiments at -253°C, the boiling point of hydrogen, exist, and are planned to be carried out in subsequent studies.

This study is related to the development of lightweight automotive materials that were carried out to develop eco-friendly vehicles worldwide. High-strength aluminum alloy is used as one of the significant lightweight materials in the field of transportation machinery, and it is used as a lightweight material in various areas, including automobiles. The A356 alloy used in this study is an excellent aluminum alloy material that has widely used as a high strength aluminum alloy material in various forming methods. In this study, to examine the characteristics of the two alloys in which Mn and Sr elements were added to the A356 alloy and the A356 alloy, both alloys were manufactured by metal mold casting, which is a gravity casting method. The obtained specimens were heat-treated under the same conditions. In this study have investigated of the microstructure analysis, thermal analysis, crystal phase analysis, and mechanical property evaluation were performed to confirm how the added Mn and Sr elements influenced the microstructure, precipitate formation, and mechanical properties.

This study has related to lightweight automobiles due to global warming with the reduction of fossil fuel reserves are rapidly progressing around the automobile industry. This study has revealed the relationship for the mechanical properties via the analyzed microstructure, precipitated phase variation of the wheel hub of a commercial vehicle manufactured using molten forging technology using A356 and A357 alloys, which are high-strength Al-Si-Mg base cast aluminum alloys. Differential scanning calorimetry has performed to analyze the precipitation amount of each alloy that influences the mechanical properties of aluminum alloy. The XRD analysis has measured for the microstructure's crystal phase on A356 and A357 alloys. In this paper has evaluated to compare the properties of the A356 alloy and the A357 alloy for the mechanical properties. The A356 alloy has confirmed that a microstructure is finer than A357 alloy, and a quantity of precipitated material is more than A357 alloy. Therefore, this study confirmed that the A356 alloy has better mechanical properties than the A357 alloy.

PURPOSES: Knowing the scope of deterioration of the concrete slab around spalling is important in determining the size of the partial-depth repair. The change in the material properties of the concrete slab, according to the severity of spalling and distance from spalling, is analyzed herein by performing non-destructive and destructive tests at the field and in the laboratory. METHODS: The test slabs were determined by finding spallings with high or medium severity. The relative elastic modulus was measured near the spalling, far from spalling, and around the slab center using an impact echo equipment. The core specimens were obtained at the measurement positions. An absorption test was performed for the core specimens, while the impact echo and dynamic modulus tests were performed for the upper and lower parts of the core specimens under dry or saturated conditions. A compressive strength test was also performed for the upper and lower parts of the core specimens. RESULTS : The absorption coefficient, relative elastic modulus, relative dynamic modulus, and relative compressive strength worsened as the measurement position became closer to the spalling distress and top of the slab. The worse material properties were measured for the spalling with a higher severity. The moisture condition of the specimens scarcely affected the material properties. CONCLUSIONS : The impact echo test results obtained at the field showed a high correlation with the results of the absorption, impact echo, dynamic modulus, and compressive strength tests performed in the laboratory. Accordingly, a quicker and a more convenient nondestructive soundness evaluation of concrete pavements is expected to be realized using the field impact echo test method.

To fabricate the 5182 aluminum-polymer sandwich panels, the strength of 5182 aluminum panels, which are the skin sheets that constitutes the sandwich composite panels, is changed according to the degree of heat treatment after rolling, and the characteristics of sandwich panel are also changed. In addition, in the stress-strain curves of the sandwich panel, the serration behavior observed in the 5182 aluminum alloy sheet is also observed. This serration behavior causes surface roughness during sheet forming, which is a serious problem in application to automotive body sheet. In this study, the tensile properties of the 5182 aluminum sandwich panels at room and elevated temperature were carefully investigated by tensile test. It can be found that when the aluminum surface sheets having insufficient heat treatment time is applied, the serration behavior does not completely disappear from the temperature of the room temperature to 160℃.

화석연료로부터 기인한 환경오염에 대한 대응과 더불어 신재생에너지 공급의무화제도의 시행은 재생연료유 등 신재생에너지의 활용도를 증대시켰다. 부생연료유(2호)와 정제연료유(감압)는 국내 법령으로 엄격히 규제되고 있으며, 부생연료유(2호)를 혼합한 정제연료유(감압)의 물성변화를 시험하였다. 부생연료유(2호)를 1 : 1로 혼합한 정제연료유(감압)의 물성분석 결과, 국내 폐기물관리법에서 규정하고 있는 품질기준을 만족하였다. 다만, 연료와 관련한 추가항목 시험결과에서 높은 방향족 함량을 나타내었다. 연료내 높은 방향족 함량은 사용기기의 고무류 파손이나 연소 시 그을음, 매연 등이 발생할 가능성이 높을 것으로 보인다.

항공유는 문제가 발생 시 대형사고로 이어질 수 있기 때문에 다른 수송용 연료보다 더 엄격히 관리되고 있다. 항공유의 품질기준은 국내의 한국산업표준(KS), 미국재료협회(ASTM)와 국제운송협회(IATA)에서 각각 규정하고 있다. 2016년부터 2017년까지 국내 정유사의 5개 공장에서 생산되는 항공유에 대하여 방향족 함량, 황 함량 및 증류성상 등 6개 항목에 대하여 품질분석을 실시하였다. 국내에서 생산된 항공유는 품질기준에 적합한 것으로 나타났으며, 연간 일정하게 유지되고 있었다. 국제기준인 ASTM과 IATA의 품질기준과 비교했을 때, 방향족 함량은 국내 KS 기준이 ASTM 및 IATA 설정기준보다 1.5 wt% 엄격하게 설정되어 있으나 이 기준을 충분히 만족시키는 것으로 나타났다. 또한, 황 함량, 증류성상 및 인화점 등 나머지 항목들도 국내와 국제기준을 모두 충족하는 것으로 나타났다.

본 연구에서는 탄소나노튜브/화이버/폴리머 복합소재 구조에 대한 재료 물성 및 강성 추정을 다룬다. 수정된 Halpin-Tsai 모델을 적용한 멀티 스케일 해석은 탄소나노튜브의 함유량 비율, CNT 두께-길이 비율, 화이버 부피 함유량, 그리고 화이버 보강각도 변화에 따라서 수행되었다. 본 연구에서 제시한 멀티-스케일 접근방법은 기존 모델을 적용하여 얻은 결과와 비교하여 검증하였다. 매개변수 해석을 통하여 CNT의 적절한 함유량은 적층된 CNTFPC 구조의 구조성능의 향상시킬 수 있는 중요한 특성을 규명하였다.