콘크리트는 우수하고 뛰어난 내구성에 의해 구조물 건설에 가장 많이 사용되는 재료 중 하나이다. 오늘날 급격한 경제의 발전 및 도시화 등에 의해 오늘날 구조물은 대형화 및 고층화되고 있다. 이에 따라 고강도, 고경량, 고내구 콘크리트 개발에 대한 다양한 연구가 진행되고 있다. 특히 나노소재가 첨 가된 콘크리트는 나노소재에 의해 미세공극이 충진되어 강도 및 내구성이 우수한 것으로 알려져있다. 그러나 기존 나노소재가 적용된 콘크리트는 단위중량이 높아 이를 구조물에 적용시 자중을 증가시키 는 단점이 있다. 이에 본 연구에서는 입자 직경이 10-100 μm이지만 입자 내부의 공극이 있어 단위 중량이 0.6t/m3인 Micro hollow sphere가 잔골재로 사용된 고경량, 고강도 콘크리트의 염화물 침투 특성을 평가하였다. 본 연구에서 사용된 실험변수로써 Micro hollow sphere의 잔골재 치환량(0%, 42%, 100%)가 고려되었으며, 이 시편의 단위중량은 각각 2.37 t/m3, 1.89 t/m3, 1.62 t/m3이다. Micro hollow sphere가 사용된 콘크리트의 염화물 침투 특성은 NT-Build 492 시험을 통해 평가되었다. 실 험결과 Micro hollow sphere 치환율이 0%, 42%, 100%인 실험체의 단위중량은 염화이온 확산계수는 각각 4.45 x10-13 m2/s, 2.57 x10-13 m2/s, 1.4x10-13 m2/s로 Micro hollow sphere 치환량이 증 가함에 따라 염화이온 침투 저항성이 증가하는 것으로 확인되었다. 따라서, Micro hollow sphere를 이용한다면 단위중량이 작으며 내구성이 큰 고경량, 고내구 콘크리트 배합이 가능할 것으로 판단된다.

In recent automobile development, vehicle weight reduction has become a very important goal. Seat weight reduction is a large portion of vehicle weight reduction. In this study, a specimen tensile tests were conducted on the Almag material, which is an alloy of aluminum and magnesium, and also conducted on SAFH440, SAFH 590, SAFC780, and SAFH980, which are mild steel materials used in the seat frame. The tensile specimen tests were carried out in two speed; 2mm/s and 4mm/s, and the obtained stress to strain curve was converted to the analysis material card of true stress to true strain curve to be used in the seat structural analysis. The constructed analysis material card was used in the specimen tensile finite element analysis, and the analysis result was able to obtain the stress to strain curve similar to the test result.

The curb weight of electric trucks is more than 10% higher than that of conventional internal combustion engine trucks due to the motor and battery. For this reason, cargo box developed for small electric trucks is required weight reduction, and cargo door that can reduce weight and maintain strength are being developed. In this paper, we designed the lightweight cargo door, confirmed the stability of the door through structural analysis, and developed a cargo box door that was more than 25% lighter by applying composite materials such as Sheet Molding Compound(SMC) and Fiber Reinforced Plastic(FRP).

High-entropy alloys (HEAs) are characterized by having five or more main elements and forming simple solids without forming intermetallic compounds, owing to the high entropy effect. HEAs with these characteristics are being researched as structural materials for extreme environments. Conventional refractory alloys have excellent hightemperature strength and stability; however, problems occur when they are used extensively in a high-temperature environment, leading to reduced fatigue properties due to oxidation or a limited service life. In contrast, refractory entropy alloys, which provide refractory properties to entropy alloys, can address these issues and improve the hightemperature stability of the alloy through phase control when designed based on existing refractory alloy elements. Refractory high-entropy alloys require sufficient milling time while in the process of mechanical alloying because of the brittleness of the added elements. Consequently, the high-energy milling process must be optimized because of the possibility of contamination of the alloyed powder during prolonged milling. In this study, we investigated the hightemperature oxidation behavior of refractory high-entropy alloys while optimizing the milling time.

In general, a large mirror without weight reduction in large optical or space telescope systems can increase the system’s weight or lead to significant deformation of the mirror surface. Thus, it is imperative to pursue lightweight design strategies. In this paper, the structure design of a spherical mirror, a diameter of 600mm and a mirror radius of 2,000mm, was investigated to reduce weight and minimize deformation. To establish load paths for internal and external loads, stiffeners were added across the lateral supports. This approach effectively reduced both weight and deformation caused by gravity. Weight reduction and reduction percentages were quantified, and the mirror deformation was evaluated by using finite element analysis (FEA). The proposed structures were compared with honeycomb structures for weight reduction. This evaluation allowed to assess the deformation characteristics and the potential advantages of the proposed structures for lightweight mirrors.

Damage to gas and fire protection piping systems can lead to secondary disasters after an earthquake, so their seismic design is crucial. Accordingly, various types of seismic restraint installations are being devised, and a new suspended piping trapeze restraint installation has also recently been developed in Korea. In this study, a cyclic loading test was performed on the developed trapeze support system, and its performance was evaluated according to ASHRAE 171, the standard for seismic and wind restraint design established by the American Society of Refrigeration and Air Conditioning Engineers (ASHRAE). The three support system specimens did not break or fracture, causing only insignificant deformations until the end of the experiment. Based on the experimentally rated strength and displacement performance, this trapeze support system is expected to control the seismic movement of piping during an earthquake.

해양레저활동 인구증가 및 관련 산업의 급성장으로 인해 레저 선박을 접안하는 계류시설과 부유체를 기반으로 하는 해상부유 식 펜션 등 레저시설 수요가 증가하고 있으며, 이러한 연안에서 사용되는 부유체는 대부분 경량 부유체로서 중량이 상대적으로 경량이므 로 연안으로 유입되는 파(Wave)와 상재 하중에 의해 쉽게 경사가 발생하여 안정성이 낮아 안전사고가 빈번히 발생하고 있다. 이런 문제점 에 대한 해결방안으로 부유체의 운동저감장치를 연구하여 알리고자 한다. 본 연구논문에서는 부유체에 운동저감장치(기압차를 이용한 운 동저감장치)를 부착하여 운동저감효과를 부착하지 않은 부유체와 비교하는 방식으로 효과를 분석하였다. 효과분석은 전산해석시험으로 분석하여 부유체의 안정성 증가방법을 연구하고 그 효과를 검증해 보았다. 시험결과 분석결과 기압차를 이용한 운동저감장치를 부착한 부유체가 운동저감장치를 부착하지 않은 부유체보다 파랑에 대한 운동량이 저감되어 부유체의 안정성이 증가된 것으로 분석되었다. 이러 한 부유체의 운동저감 장치는 무동력 선박뿐만 아니라 동력선, 반잠수식 선박에서도 유용하게 사용될 것으로 판단되어 다양한 분야에 적 용하여 연구를 진행할 계획이다.

Lightweight face recognition models, as one of the most popular and long-standing topics in the field of computer vision, has achieved vigorous development and has been widely used in many real-world applications due to fewer number of parameters, lower floating-point operations, and smaller model size. However, few surveys reviewed lightweight models and reimplemented these lightweight models by using the same calculating resource and training dataset. In this survey article, we present a comprehensive review about the recent research advances on the end-to-end efficient lightweight face recognition models and reimplement several of the most popular models. To start with, we introduce the overview of face recognition with lightweight models. Then, based on the construction of models, we categorize the lightweight models into: (1) artificially designing lightweight FR models, (2) pruned models to face recognition, (3) efficient automatic neural network architecture design based on neural architecture searching, (4) Knowledge distillation and (5) low-rank decomposition. As an example, we also introduce the SqueezeFaceNet and EfficientFaceNet by pruning SqueezeNet and EfficientNet. Additionally, we reimplement and present a detailed performance comparison of different lightweight models on the nine different test benchmarks. At last, the challenges and future works are provided. There are three main contributions in our survey: firstly, the categorized lightweight models can be conveniently identified so that we can explore new lightweight models for face recognition; secondly, the comprehensive performance comparisons are carried out so that ones can choose models when a state-of-the-art end-to-end face recognition system is deployed on mobile devices; thirdly, the challenges and future trends are stated to inspire our future works.

Thermal protection systems (TPS) are a group of materials that are indispensable for protecting spacecraft from the aerodynamic heating occurring during entry into an atmosphere. Among candidate materials for TPS, ceramic insulation materials are usually considered for reusable TPS. In this study, ceramic insulation materials, such as alumina enhanced thermal barrier (AETB), are fabricated via typical ceramic processing from ceramic fiber and additives. Mixtures of silica and alumina fibers are used as raw materials, with the addition of B4C to bind fibers together. Reaction-cured glass is also added on top of AETB to induce water-proof functionality or high emissivity. Some issues, such as the elimination of clumps in the AETB, and processing difficulties in the production of reusable surface insulation are reported as well.

Lightweight steel is a crucial material that is being actively studied because of increased carbon emissions, tightening regulations regarding fuel efficiency, and the emergence of UAM, all of which have been recently labeled as global issues. Hence, new strategies concerning the thickness and size reduction of steel are required. In this study, we manufacture lightweight steel of the Fe-Mn-Al-C system, which has been recently studied using the DED process. By using 2.8 wt.% low-Mn lightweight steel, we attempt to solve the challenge of joining steel parts with a large amount of Mn. Among the various process variables, the laser scan power is set at 600 and 800W, and the laser scan speed is fixed at 16.67 mm/s before the experiments. Several pores and cracks are observed under both conditions, and negligibly small pores of approximately 0.5 μm are observed.

본 논문에서는 1차원 오일러 보 요소(Euler-Bernoulli Beam Element)를 이용한 회전익기 축계에 대한 중량 최적설계를 수행하였다. 회전 축계의 특성을 고려해 비틀림(Torsion)과 베어링과 같은 축지지 강성 및 플랜지(Flange) 질량을 모두 고려하였고, 동적 안전성 확 보를 위해 고유치 해석을 수행하여 임계속도(Critical Speed)와 기어박스로부터 오는 치 변형 가진을 회피할 수 있도록 하였다. 축의 길 이는 고정된 상태에서 두께와 반경을 조절하여 중량 최적화를 수행하였으며, 최적화 과정은 2단계로 나누어 진행하였다. 1단계에서 는 비틀림 강도를 제약조건으로 하여 중량을 최적화한 후 2단계에서는 축계 안정성 확보 기준(Headquarters, U.S. Army Material Command, 1974)에 따라 축의 비틀림 강도에 대한 제약조건을 만족시키며, 축의 1차 모드가 임계속도를 회피할 수 있도록 축 1차모드 와 임계속도의 차이가 최대가 되도록 최적화를 진행하였다. 주어진 1차원 보 요소를 이용하여 최적설계를 한 결과를 3차원 유한요소 모델과 실제 제작된 축게의 시험결과와 비교하여 제안된 방법을 검증하였다.

The sub-frame is located on the lower body of a monocoque type vehicle and serves as an engine and suspension, and is an important object part that receives a lot of load. The existing press-type sub-frame has a large number of parts for assembling, which causes an increase in cost. Changing the machining form of this part from the existing press-type machining method to the hydro-forming machining method has the advantage of reducing the cost and weight at the same time due to the reduction of the process. Therefore, in this study, the purpose of this study is to change the design so that the sub-frame of the existing press type can be changed to the hydro-forming process method. To this end, we intend to present a design method by analyzing the effect on the rigidity of the sub-frame using the existing machining method through shape optimization analysis.

PURPOSES : Recently, the generation of industrial by-products has been increased owing to the increase in electrical power consumption. This experimental study investigated a special mortar development using outstanding benefits of porous structures in heavy oil fly ash (HOFA) and bottom ash (BA) to reduce heat transfer and weight of tunnel repair mortar. METHODS : Based on the concept of materials usable for this objective being porous and light, the physical and chemical properties of heavy oil fly ash and bottom ash were analyzed to determine the application possibility for tunnel repair mortar. In addition to satisfying this primary requirement, the research aimed at determining the relationships between the characteristics of porous structures and effectiveness of reducing weight and thermal conductivity. This study was undertaken on the use of bottom ash as fine aggregate and heavy oil ash as filler in mortar mix proportion. Four different levels of bottom ash (25%, 50%, 75%, 100%, and 5%), and 10%, 15%, and 20% of heavy oil fly ash were investigated to determine the proper replacement amount within the designed specification. According to the analytic results on the effectiveness of both by-products and chemical additives, the repair mortar with optimum mixture proportion was investigated using various tests including thermal conductivity and porosity. RESULTS : The use of porous by-products increased the demand for mixing water in obtaining the required flowability, but the compressive strength did not decrease significantly in proportion by adding an amount of bottom ash. Based on the results, bottom ash can be replaced with aggregate as much as 50%, but adding an amount of heavy oil ash is suggested as below 10% in formulation. CONCLUSIONS : The optimized repair mortar, which was produced by conclusive formulation, was evaluated as a high-performance material to repair tunnels with the effectiveness of porous and remarkable physical properties.