• Korean Journal of Materials Research
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• v.14 no.1
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• pp.13-18
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• 2004

Titanium alloys are the one of promising candidate materials for medium high temperature parts in the aircraft, automobile, petrochemistry and electrochemistry because of their high strength with low density in medium high temperature. In this study, the effects of aging and heat treatments on the mechanical properties of Ti-15-3 alloy in medium high temperature, which was $400^{\circ}C$, were studied. Solid solution treatment was performed at $8000^{\circ}C$ of $\beta$ phase region for 1 h and the alloy was quenched in water. The alloy was aged at $5000^{\circ}C$ of $\alpha$ and $\beta$ two-phase region for 1, 2, 4, 8, ... and 100 h to increase the mechanical property. The $\beta$ single phase was observed at all parts of specimens in Ti-15-3 alloy after ST. As the aging at $500^{\circ}C$, fine precipitates of a phase was generated from matrix of $\beta$ phase and the microstructure was consisted of weaving structure such as Widmanstiitten a phase. The most suitable aging time is 24h in$ 400^{\circ}C$. At this time, strength is 1164 MPa and elongation is about 12%. In room temperature, elongation of Ti-15-3 alloy aged at $500^{\circ}C$ for 16 h is poor (=3%) in spite of high tensile strength (1458 MPa).

• Korean Journal of Materials Research
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• v.34 no.3
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• pp.175-183
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• 2024

Geopolymer, also known as alkali aluminum silicate, is used as a substitute for Portland cement, and it is also used as a binder because of its good adhesive properties and heat resistance. Since Davidovits developed Geopolymer matrix composites (GMCs) based on the binder properties of geopolymer, they have been utilized as flame exhaust ducts and aircraft fire protection materials. Geopolymer structures are formed through hydrolysis and dehydration reactions, and their physical properties can be influenced by reaction conditions such as concentration, reaction time, and temperature. The aim of this study is to examine the effects of silica size and aging time on the mechanical properties of composites. Commercial water glass and kaolin were used to synthesize geopolymers, and two types of silica powder were added to increase the silicon content. Using carbon fiber mats, a fiber-reinforced composite material was fabricated using the hand lay-up method. Spectroscopy was used to confirm polymerization, aging effects, and heat treatment, and composite materials were used to measure flexural strength. As a result, it was confirmed that the longer time aging and use of nano-sized silica particles were helpful in improving the mechanical properties of the geopolymer matrix composite.

• Journal of Preventive Medicine and Public Health
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• v.30 no.2 s.57
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• pp.356-368
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• 1997

In effort to determine whether aircraft noise can have health effects such as hearing loss, hypertension and psychological stress, a total of 111 male professors and administrative officers working a college near a military airport in Korea(exposed group) and a total of 168 males and 112 females matched by age groups(control groups) were analyzed. Personal noise exposure and indoor and outdoor sound level of jet aircraft noise were measured at the exposed are3. And pure tone, air conduction test and measurement of blood pressure were given to the exposed(males) and matched control groups (males and females). BEPSI(Brief Encounter Psychological Instrument) and psychological response to aircraft noise were examined for the exposed group. The noise dosimetry results revealed time-weighted averages(TWAs) that ranged from 61 to 68 dBA. However the levels encountered during taking off jet airplanes reached 126 dBA for two half minutes time period. Th, audiometric, test showed that mean values of HTL(hearing threshold level) in exposed group at every frequency(500, 1,000, 2,000, 4,000, and 8,000 Hz were much lower than them of male and female control groups. And in old age groups, interaction of age and noise was observed at 8,000 Hz in both ears(p<0.05). Conclusively, aircraft noise does not appear to induce hearing loss directly in high frequency, but may decreased hearing threshold level by interaction of aging process and noise exposure. However, difference of mean values of exposed and control groups on blood pressure was not significantly. In psychological test, annoyance was the most severe psychological response to noise in exposed group, but mean value of BEPSI was not correlated with job duration in exposed group.

• Journal of the military operations research society of Korea
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• v.36 no.1
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• pp.91-102
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• 2010

Doubler repair is one of the frequently applied methods to repair cracks which occur at the structure of aircraft weapon systems. The requirement of the doubler repair for some of aging aircraft has increased more recently. However very few researches have been conducted until now. In this paper, the effect of the various doubler repair methods was evaluated. Especially, the relationship between the array of revet and the effect of stress concentration was investigated. To calculate variation of the stress with different repair methods, commercial FEA program was utilized. As a result, it was shown that the main factor for the variation of stress is pitch and number of revet line. Furthermore the optimized array of revet for the specific geometries of doubler was suggested.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.163-168
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• 2001

Due to aging, adhesively bonded and riveted aircraft lap joints can contain distends, cracks around rivet holes, fatigue induced flaws, and corrosion. It is required for the safety of aircraft to inspect these defects through the whole region of mint in rapid speed. Bond quality or adhesively bonded and riveted aluminum lap splice joints is investigated using non-contact remote ultrasonic nondestructive evaluation (NDE). Non-contact ultrasonic tests are performed using laser generation and air-coupled transducer detection. A Q-switched Nd:YAG laser and a periodic transmission mask are used to generate a selected Lamb mode. The Lamb wave is generated on one side of the lap splice joint, propagates along the plate, interacts with the joint and is detected on the other side by a micromachined air-coupled capacitance transducer. Analysis of recorded signals allows to evaluate the condition of the bond.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.8
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• pp.551-557
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• 2022

LRU (Line Replacement Unit) modifications are often required for military aircraft due to aging. Recently, LRU modifications were proceeded for KA-O (Armed Airborne Controller) by replacing the ejection seat and adding avionic equipment, which made the aircraft's operational CG (Center of Gravity) on fuel consumption curve become out of the range of the specification requested. The off-ranged CG should be corrected by introducing an appropriate method. This study proposes a procedure for revising and verifying the empty weight CG altered due to LRU modification for small military aircraft (e.g., KA-O). In the proposed method, first, the change of empty weight CG of KA-O due to the LRU modifications is comprehensively examined. Then, several ballast masses are added to the engine mount strut to restore the empty weight CG on the fuel consumption curve to a safe operational range. The installations are verified via stress and fatigue analysis for various operating conditions. Considering that open information is not very available for the revision of empty weight CG, this study is valuable because it presents an established procedure for correcting and verifying empty weight CG during aircraft modification.

• 한국항공운항학회:학술대회논문집
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• 2016.05a
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• pp.202-208
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• 2016

최근 5년간 발생한 국적 항공기 사고 23건 중 헬기사고가 16건으로 전체 항공사고의 70%를 차지한다. 현재 국내에서 고정익 항공기 549대, 회전익 항공기 186대가 각각 운영(군 경찰 보유헬기 제외)되고 있음을 감안하면 회전익 항공기 사고가 훨씬 높은 편이며, 고정익 항공기 가동시간에 비하여 가동률이 매우 낮은 회전익 항공기를 고려하면 비행시간당 항공기 사고 비율은 회전익 항공기가 월등하게 높은 편이다. 또한 고정익 항공기의 평균기령은 10.9년인데 비하여 산림항공본부를 비롯한 헬기운영업체에서 운영 중인 회전익 항공기의 평균기령은 18.9년으로 회전익 항공기가 전체적으로 노후화 되어 있으나, 국적항공사에 운영 중인 노후 항공기 관리프로그램을 회전익 항공기 운영사에서는 운영하지 않고 있다. 따라서 본 연구를 통하여 노후 항공기 운영현황을 검토하여 노후 회전익 항공기 운영기준을 수립하고 노후 회전익 항공기의 정비프로그램을 정립하여 회전익 항공기의 지속감항성을 확보할 수 있는 방안과 수명주기 설정을 마련하고자 한다.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.34-46
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• 1999

전 세계적으로 항공기의 노후화에 따른 안전성 확보와 수명연장을 위한 대책 연구가 활발하다. 미국의 경우 군용기 (주로 수송기)의 평균수명은 40년을 넘어서고 있으며 이들은 아직도 $20{\sim}30년$ 더 사용될 예정이다. 민간항공기의 경우에도 군용기만큼은 아니지만 노후화하고 있기는 마찬가지이다. 수명연장을 위해 여러가지 비파괴검사 기술이 활용되고 있으며, 새로운 비파괴 시험 평가 검사 방법들이 속속 개발되고 있다. 항공기의 안전을 위협하는 기체구조 손상의 2대 주범으로는 부식과 피로를 꼽을 수 있으며, 이를 탐지하고 평가하기 위한 경제적인 검사방법에 대한 연구가 미국을 중심으로 활발하게 진행되고 있는데, 이에 대한 최근 현황을 살펴본다.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.63-66
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• 2000

This research addresses study on thermal residual stress of a composite patch repair of the edge cracked aluminium panel of aging aircraft. Composite patch repair is an efficient and economical technique to improve the damage tolerance of cracked metallic structures. These are thermal residual stresses due to the mismatch of coefficient of thermal expansion, and these are affected by the curing cycle of patch specimen. In this study, three curing cycles were selected for F.E. analysis. This study features the effect on composite patch and aluminum by thermal residual stress during crack propagation in aluminum plate.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.27 no.4
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• pp.65-72
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• 2019

There is concern about the increased risk of accidents from manual investments due to ground handling service operators, aging equipment and manpower shortages. Therefore, it is necessary to improve the quality of ground treatment services and safety management at the airport. Therefore, this study analyzed the domestic and overseas ground operation status and the license handling procedure of aircraft handling business. In addition, a case study on the evaluation system of international organizations examined the applicability of the certification body to the Korean situation. It is practical in that it provides policy implications for improving the quality of groundwork not covered in previous studies. This is expected to improve the constitution, improve quality, improve airport operations, and operate safely.