• 열처리공학회지
• /
• 제9권3호
• /
• pp.161-168
• /
• 1996

The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.168-173
• /
• 2004

Fretting is a kind of surface degradation mechanism observed in mechanical components and structures. The fretting damage decrease in 50-70% of the plain fatigue strength. This may be observed in aircraft, automobile and nuclear power plant used in special environment and various loading conditions. In the present study, the characteristics of the fretting fatigue are investigated using the two aluminum alloy(Al2024-T3511 and Al7050-T7451). Through the experiment, it is found that the fretting fatigue strength of the Al7050-T7451 alloy decreased about 50% from the plain fatigue strength, while the fretting fatigue strength of the Al2024-T3511 alloy decreased about 45%. The tire track was widely observed in fracture surface area of oblique crack which was induced by contact pressure. These results can be the basic data to the structural integrity evaluation of aluminum alloy subjected to fretting damage.

• 한국기계가공학회지
• /
• 제9권1호
• /
• pp.25-34
• /
• 2010

Fretting damage reduces fatigue life of the material due to low amplitude cyclic sliding and changes in the contact surfaces of strongly connected machine and structures such as bolt, key, fixed rivet and connected shaft, which have relative slip of repeatedly very low frequency amplitude. In this study, the fretting fatigue behavior of 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were evaluated. The plain fatigue test and fretting fatigue test under cyclic bending load carried out commercial bending fatigue tester and specially devised equipments to cause fretting damage. From these experimental work, the following results obtained: (1) The plain fatigue limit for stress ratio R=-l was about 151MPa. (2) In case of fretting fatigue, fatigue limit for stress ratio R=-l about 72MPa, the fatigue limit for R=0 about 81MPa, and the fatigue limit for R=0.3 about 93MPa. (3) The fatigue limit reduction rates by the fretting damage were about 52%(R=-1), 46%(R=0) and 38%(R=0.3) respectively. (4) The fatigue limit reduction rate decreased with stress ratio increase. In fretting bending test, as stress ratio increased, occurrence of initial oblique crack by fretting decreased or phased out, so that fracture surfaces were formed by plain fatigue crack occurrence, and such tendency was notable as stress amplitude increased. (5) Tire tracks and rubbed scars were observed in the fracture surface and contacted surface.

• Steel and Composite Structures
• /
• 제25권3호
• /
• pp.327-335
• /
• 2017

To gain more knowledge of aluminum foam sandwich structure and promote the engineering application, aluminum foam sandwich consisting of 7050 matrix aluminum foam core and 304 stainless steel face-sheets was studied under three-point bending by WDW-T100 electronic universal tensile testing machine in this work. Results showed that when aluminum foam core was reinforced by 304 steel face-sheets, its load carrying capacity improved dramatically. The maximum load of AFS in three-point bending increased with the foam core density or face-sheet thickness monotonically. And also when foam core was reinforced by 304 steel panels, the energy absorption ability of foam came into play effectively. There was a clear plastic platform in the load-displacement curve of AFS in three-point bending. No crack of 304 steel happened in the present tests. Two collapse modes appeared, mode A comprised plastic hinge formation at the mid-span of the sandwich beam, with shear yielding of the core. Mode B consisted of plastic hinge formation both at mid-span and at the outer supports.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 1997년도 제8회 학술강연회논문집
• /
• pp.87-94
• /
• 1997

로켓트 추진기관 단조부품용 $\psi$ 370mm급 알루미늄합금 7175 빌레트의 국산화개발과 관련한 용해주조기술 현황과, 합금설계와 미량원소첨가가 품질과 제작수율개선에 미치는 영향을 분석하였다. 미량의 Be첨가는 용탕의 유동성을 개선하고 미세기공량을 감소시켜 단조성을 개선할 것으로 기대되며, 불순물인 Fe/Si 비를 제어하면 주조균열생성을 크게 억제하는 것으로 나타났다. 현재의$\psi$370mm합금 빌레트의 품질수준은 전반적으로 양호하지만, 단조품의 최종물성 개선과 용해주조 조건 정립을 위한 합금설계, 열해석 등의 체계적인 연구와 노하우습득이 필수적으로 요구되며, 이는 향후 예상되는$\psi$ 650급의 대형빌레트의 개발과 7050적용에 이용될 것으로 판단된다.

• 한국군사과학기술학회지
• /
• 제5권4호
• /
• pp.67-77
• /
• 2002

This paper introduces the calibration results of the fatigue crack growth models for damage tolerance analysis of the aircraft structures. Generalized Willenborg model and Wheeler model are calibrated with experimental data tested under the load spectrum of a trainer. The retardation factors such as, shut-off ratio in Generalized Willenborg model and shaping exponent in Wheeler model, are evaluated for aluminum alloys AL2024-T3511, AL7050-T7451 and AL7075-T73511. It is shown that the retardation effect of the crack growth rate depends on the yield strength of material and the maximum stress in the load spectrum. Generalized Willenborg model and Wheeler model give satisfactory prediction of crack growth life but the calibration of the experimental parameters with test is required.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2000년도 추계학술대회 논문집
• /
• pp.90-93
• /
• 2000

Al ally 7050 has been developed for higher strength and improved property against stress-corrosion cracking. Since the use of this alloy becomes more important for forged aircraft structural components. $\phi$ 65mm extruded billet has been forged for a highly-stressed aircraft parts. After forging processing and heat treatment, the forged parts showed undesirable microstructure caused by severe local grain coarsening at the surface layer and heavily-localized metal flow, the analysis of resulted in degraded mechanical properties. The above results have been compared to simulation by using the DEFORM-3D and those showed the thermomechamical processing must be optimized in terms of forging temperature, strain rate and deformation amount. To prevent the grain coarsening at the surface layer $\varepsilon$ heavily-localized grain flows.

• 소성∙가공
• /
• 제25권1호
• /
• pp.5-11
• /
• 2016

The control of the roll velocities is essential in maintaining stability during ring rolling, but such control is difficult. The determination of the best roll velocities can be helped with the use of FE simulations and processing maps, which give the useful information such as power dissipation and flow instability for hot metal forming processes. In the current study, the workability of 7050 aluminum alloy is evaluated by using processing map. With the developed information, the stability of the ring rolling condition, called the Constant Growth Velocity Condition (CGVC), is evaluated.

• 한국식품영양과학회지
• /
• 제46권9호
• /
• pp.1122-1127
• /
• 2017

바나나 껍질과 파인애플 껍질에서 식품의 향에 가장 많이 사용되는 ethyl butyrate를 합성할 수 있는 ester synthetase의 최적 조건을 확립하고자 반응표면분석(response surface methodology, RSM)을 사용하였다. RSM 분석 결과 바나나 껍질에서 회수한 ester synthetase의 ethyl butyrate 합성 최적 조건은 ethanol의 농도가 38.7050 mM, butyric acid의 농도가 50.9019 mM, 반응시간이 4.3662시간일 때 최대 예측값은 45.8199 mM이었다. 파인애플 껍질에서 회수한 ester synthetase의 ethyl butyrate 합성 최적 조건은 ethanol의 농도가 54.6502 mM, butyric acid의 농도가 58.7638 mM, 반응시간이 4.7436시간일 때 최대 예측 값은 65.1087 mM임을 알 수 있었다. 결론적으로 ethyl butyrate 합성을 위해서는 바나나 껍질에서 회수한 ester synthetase보다는 파인애플 껍질에서 회수한 ester synthetase가 더 효율이 높음을 알 수 있었다. 앞으로 이들의 연속 대량 생산을 위해서 효소의 고정화 방법과 연속적인 기질 투입을 위한 기술 등의 개발이 더 이루어진다면 천연향 원료의 개발이 가능할 것으로 판단된다.

• 농업과학연구
• /
• 제1권1호
• /
• pp.5-8
• /
• 1974

인삼(人蔘)의 육종(育種)을 위(爲)한 몇가지 기초정보(基礎情報)를 얻기 위(爲)하여 국내(國內) 육성계통(育成系統) 16계통(系統)을 대상(對象)으로 하여 조사(調査) 분석(分析)하였던 바 그 결과(結果)를 요약(要約)하면 다음과 같다. 1. 인삼(人蔘)의 각 주요(主要) 양적(量的) 형질중(形質中) 경장(莖長)이(0.7050) 가장 높은 유전력(遺傳力)을 보였고 반면 엽장(葉長)의 유전력(遺傳力)이 (0.5674) 가장 낮았다. 2. 엽장(葉長)과 경직경간(莖直徑間)의 유전형(遺傳型) 상관(相關)이 (0.9844) 가장 높았고, 엽장(葉長)과 경장간(莖長間)의 유전형(遺傳型) 상관(相關)이 (0.8649) 가장 낮았으나 표현형(表現型) 상관(相關)에 있어서는 경장(莖長)과 경직경간(莖直徑間)이 (0.8788) 가장 높았으며 경장(莖長)과 경직경간(莖直徑間)이 (0.7950) 가장 낮았다. 3. 각 형질간(形質間)의 공유전력은 경장(莖長)과 경직경간(莖直徑間)이 가장 높았으며 엽장(葉長)과 경장간(莖長間)이 가장 낮은 값을 나타내었다. 4. 재식위치(栽植位置)에 따르는 각 형질(形質)의 변이(變異) 정도(程度)는 경장(莖長)이 가장 컸던 반면 경직경(莖直徑)에서 가장 적은 경향(傾向)이 있다.