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The effect of repair patches with different geometric shapes on bonding strength was investigated. Four shapes of patches were considered: rectangular patch (RP), triangular patch (TP), inv...

Epoxy polymers are actively used in high-end technological applications. However, a major drawback of epoxies is their brittle mechanical behavior especially at cryogenic temperatures. Here we report a novel filler (GO-PDA) of poly ( p- phenylenediamine) (PDA) nano-sized particles attached to graphene oxide (GO) sheets. Chemical analysis showed the attachment of PDA particles to GO through amidation of carboxylic groups. Transmission electron microscopy showed that PDA particles are uniform and spherical of ≈70 nm in size. Selected area electron diffraction showed that these particles are crystalline. Mechanical properties of epoxy/GO-PDA composite are tested at 25 °C (RT) and −120 °C (CR) temperatures. Young's modulus was not remarkably affected by GO-PDA addition. However, strength, fracture strain and toughness showed improvement at relatively low GO-PDA wt%. Microstructural analysis of fractured surfaces showed that the fracture mechanism is dependent on testing temperature. GO-PDA has a very good strengthening and toughening effects for epoxy without compromising the modulus both at RT and CR.

Damaged wind turbine blades are repaired conventionally using a hand lay-up method with epoxy, where the bonding strength is not high. Epoxy has poor curing characteristics at low temperatures. The infusion method with polyester was proposed. Infusion method is believed to distribute resin uniformly. Polyester is used because it hardens better than epoxy at low temperatures. At room temperature, the proposed method increased the bonding strength by 77.7% compared to the conventional method. Using the proposed method at 15 and 5°C, the bonding strength increased compared to the conventional method. This paper proposes a new method for repairing wind turbine blades, even at temperatures where the conventional method cannot be used because epoxy resin does not harden. The bonding strength of the proposed method at low temperatures is higher than that of the conventional method at room temperature.

For a hydrogen engine to be successfully commercialized in a short period of time, it must have power on the same level as gasoline engines, almost no NOx emissions, and high efficiency. This simultaneous achievement would be possible with the use of low temperature combustion, which supercharges an ultra-lean mixture, because NOx from a hydrogen engine is thermally produced. However, increasing the energy input for higher output produces backfire, which is a significant problem for hydrogen-fueled engines with external mixture, and why the simultaneous achievement of high output and low-exhaust is not easily accomplished. This research investigated the potential of simultaneously achieving high output, similar to the output of a gasoline engine, without backfire, by using a complex valve timing variation and lean boosting. The study achieved almost zero NOx emission and high efficiency in a single cylinder engine built for research purposes with a valve timing variation system. Experimental results revealed that retarding the intake valve opening timing could control the backfire generated when increasing the output of the hydrogen engine, and the method above is also effective with lean boosting. Stable combustion in the lean region of Φ = 0.2, which can reduce temperature below the NOx generation temperature, was possible due to the large ultra-lean limit of hydrogen. In addition, the exhaust was almost NOx free due to the low temperature combustion, by supercharging the ultra-lean mixture under high power operation similar to that of gasoline. The above results verified that almost pollution-free emission without backfire, and simultaneous high power and efficiency could be achieved in a hydrogen engine through a method of intake valve timing retardation and lean overcharging.

>> In order to develop a universal cryogenic piston pump of small size for increasing utilization of liquidhydrogen, dynamic compression performance of piston pump were evaluated and improvements were also discussedfor piston rod and piston tip. The cryogenic piston pump has crosshead structure and inclined cup shape pistontip. As the results, it was found that i) insulation of heat flow from piston-rod part is required for stable operationⅱ) improving the self-clearance adjustment effect of piston tip and reducing piston eccentricity were desirableto promote pumping pressure and operating range. Key words : Piston pump(피스톤펌프), Cryogenic and high pressure type(초저온 및 고압형), Piston shape(피스톤형상), Heat isolation structure(열차단 구조), Heat flow(열유입), Vapor(기화) † Corresponding author : jtlee@skku.edu [ 접수일 : 2014.6.10 수정일 : 2014.6.28 게재확정일 : 2014.6.30 ]Copyright ⓒ 2014 KHNES 1. 서 론 액화수소는 단위 질량 및 부피당의 에너지밀도가 높아 다가올 수소경제에서 차지하는 역활이 클 것으로 평가되고 있는 에너지저장물질이다 1) . 액체수소 이용시스템에는 압송장치가 필수이므로 이용율을 높이기 위해서 다양한 요구조건에 대응할 수 있는 범용의 액체수소 압송시스템이 요구된다 . 이를 위해 저자들은 일부 액체수소펌프 기술선진국에서만 개발하고 있는 피스톤형의 소형 고압 액체수소피스톤펌프의 연구에 착수하였다

적층 세라믹 반도체의 제조 공정에서 사용되는 연속 소성로의 체임버를 설계하였다. 소성과정에서 발생하는 이물질의 효과적인 배출을 위하여 사용되는 질소 기체의 흡배기구, 소성되는 재료의 아래와 위에 위치한 열선 등이 각각의 체임버에 들어가게 된다. 본 연구에서는, 흡배기구의 개수, 체임버 바닥과 아래 열선 사이의 간격 (h1), 아래 열선과 소성 재료 사이의 간격 (h2), 소성 재료와 위 열선과의 간격 (h3), 열선의 온도, 열선의 개수 및 간격 등을 설 계변수로 사용하였다. 체임버 내부에서 질소 기체가 난류가 아닌 층류를 가장 잘 형성하는 방향으로 흡배기구의 개수 를 결정하였다. 재료의 이송 위치에서 온도를 섭씨 1,300도로 가장 균일하게 유지할 수 있는 방향으로 나머지 설계변 수들 (h1, h2, h3, 열선의 온도, 열선의 개수 및 간격 등)의 값을 결정하였다. 설계된 체임버를 제작하여 열전대를 사용 하여 온도를 측정하여 보았다. 측정된 온도는 섭씨 1,300도에서 섭씨 ±2.2 도의 범위 내에서 온도를 균일하게 유지함 을 확인하였다.

In order to achieve simultaneously the ultra-low NOx, the high power and the high efficiency in a hydrogen-fueled engine with SI and the external mixture, the effects of low temperature combustion, performance and exhaust are compared and analyzed by the application of the lean boosting. As the results, the decrease rate of the high temperature in the hydrogen is less decreased than the other fuels by high constant-volume specific heat. However, when the conditions of 1.7bar and ${\Phi}

In an attempt to enhance the mechanical properties of epoxy/graphene-based composites, the interface was engineered through the functionalization of graphene oxide (GO) sheets with p-phenylenediamine; this resulted in p-phenylenediamine functionalized graphene oxide (GO–pPDA). The morphology and chemical structure of the GO–pPDA sheets were studied by spectroscopic methods, thermal analysis, X-ray diffraction, and transmission electron microscopy. The characterization results show the successful covalent functionalization of GO sheets through the formation of amide bonds. In addition, p-phenylenediamine were polymerized on graphene sheets to form crystalline nanospheres; this resulted in a GO/poly(p-phenylenediamine) hybrid. The mechanical properties of the epoxy/GO–pPDA composite were assessed. Although the Young's modulus showed improvement, more significant improvements were observed in the strength, fracture strain, and plane-strain fracture toughness. These improvements were attributed to the unique microstructure and strong interface between GO–pPDA and the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43821.

It was found that the pure hydrogen-air pre-mixture was self-ignited at a high compression ratio without any assisting method in room temperature, thus refuting the preconception that compression ignition of hydrogen engine was impossible. Therefore, in order to analyze the correlation of compression ignition condition at cold start with hydrogen HCCI engine clearly, the possibility of compression igniting compression ratio is investigated with the change of equivalence ratio and engine speed, experimentally. As the results, it is confirmed that the possibility of compression-igniting compression ratio at cold start was decreased by increasing equivalence ratio due to decreasing auto-ignition temperature. In addition, it is grasped that the possibility of compression-igniting compression ratio at cold start is decreased around 14.9% by increasing engine speed at same supply energy.

The failure of display modules in cellular phones due to drop impact depends on the materials, stiffnesses and shapes of the phones. In the early development stage of cellular phones, the behavior of the display modules due to drop impact is tested using jigs where the display modules are installed. In this study, jigs of cellular phones for drop impact test of OLED modules were designed. The material, thickness and number and orientation of ribs were considered as design variables. Jigs were designed in a way that responses of modules due to drop impact were similar to those of modules in cellular phones. The maximum principal stresses at the upper glasses of modules were considered as responses, which were analyzed using a commercial software ABAQUS/Explicit. The drop impact analysis at the height of 1.5 meters showed that the responses of OLED module in the developed jig were in a good agreement with those in cellular phone.

Some design changes were made to enhance the uniformity of temperature distribution inside the chamber of semiconductor test equipment. The design changes include the installation of adjustable airflow controller inside the chamber, the alignment of the centers of heater and match plate, the change in the size and the shape of holes in match plate base, and the addition of new holes of 2 mm diameter in order to allow airflow directly to the temperature sensors. In order to verify their effects, the temperature distributions inside the chambers were measured using 32 RTD sensors before and after the design changes. The temperature distributions were in the ranges of 87.1 to 91.5℃ (90±2.9℃) and 89.5 to 90.8℃ (90±0.8℃) before and after the design changes, respectively. The above temperature distribution after design changes was maintained for longer than 15 minutes, which satisfied the target temperature range of 90±1℃ for longer than 10 minutes.

Food allergies are classified as IgE-mediated food allergies (IFAs) and non-IgE-mediated food allergies (NFAs). Recently, oral immunotherapy (OIT) has been found to be successful for treating both IFA and NFA, especially using interferon (IFN) gamma. This study was designed to clarify the clinical characteristics of IFA and NFA and compare the therapeutic characteristics of OIT using subcutaneously administered IFN-gamma for both types of food allergy. In this study, 148 patients were categorized into the IFA and NFA group following food challenge, skin-prick test and food-specific IgE tests. The patients were then treated using protocols specific for IFA and NFA using subcutaneous IFN-gamma injection as a randomized controlled trial. The principle of complete allergy resolution at prior dose in the case of IFA was also evaluated. Only the patients with IFA and NFA treated with OIT using IFN-gamma achieved tolerance successfully. Tolerance was achieved from low-dose range in IFA and in high-dose range for NFA. Complete tolerance was not obtained without achieving complete allergy resolution at each dose of the allergen before increasing the dosage in IFA. Both IFA and NFA can be successfully treated with OIT using IFN-gamma but show different clinical and therapeutic characteristics. IFN-gamma is necessary for the tolerance induction but not for tolerance maintenance. Additional study for the mechanisms of tolerance induction by IFN-gamma is needed.

A method for identification of flexible joints in vehicle structures is presented. The method identifies the most important parameters of a joint model and estimates their values by using displacement measurements of the overall structure. Thus, the method can be used to develop simple, design-oriented joint models that are suitable for preliminary structural design. The viability of the proposed method is demonstrated by applying it to plane frame structures with flexible joints. Nomenclature b = vector of parameter estimates bj = vector of parameter estimates obtained by using the y'th data subset C — covariance matrix Cjb — covariance matrix of parameters obtained by the jth data subset / = force vector K = global stiffness matrix Kj = stiffness matrix of a joint KR = stiffness matrix of the vehicle structure without joints u = vector of displacements um = vector of measured displacements u = vector of estimated displacements jc = vector of regressor variables Z = matrix of sensitivity derivatives of the displacements with respect to the parameters of the joints j8 = vector of parameters of a joint model y = the vector of transformed joint parameters in principal direction analysis e = vector of measurement errors (n) = combinations of n objects taken m at a time Subscripts b = vector of parameter estimates s = vector of measurement errors