• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• 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.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.9 no.1
• /
• 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
• /
• v.25 no.3
• /
• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1997.04a
• /
• 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.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.5 no.4
• /
• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.10a
• /
• 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.

• Transactions of Materials Processing
• /
• v.25 no.1
• /
• 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.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.46 no.9
• /
• pp.1122-1127
• /
• 2017

Currently, the consumer trends are increasing towards "natural" in all food systems. Therefore, in the flavor industry, the production of flavor esters by "natural" methods are needed. On the other hand, "natural flavor" is expensive to produce because of the limited natural source. Recently, the flavor obtained from the enzyme or microbial could be represented as "natural flavor". Ethyl butyrate is used most frequently as a fruity aroma in drinks and the processed food industry. In this study, ethyl butyrate was synthesized enzymatically using the ester synthetase obtained from the waste of pineapple and banana peel. The ethyl butyrate production optimization was analyzed using a response surface methodology. The enzyme reaction variances were composed of the ethanol content, butyric acid content, and reaction time. As a result, in ester synthetase obtained from banana peel, the maximum predicted production amounts were 45.8199 mM at an ethanol content of 38.7050 mM, butyric acid content of 50.9019 mM, and reaction time of 4.3662 h. In ester synthetase obtained from pineapple peel, the maximum predicted production was 65.1087 mM at an ethanol content of 54.6502 mM, butyric acid content of 58.7638 mM, and reaction time of 4.7436 h. In conclusion, ethyl butyrate production was shown the more useful using the ester synthetase obtained from pineapple peel than that from banana peel.

• Korean Journal of Agricultural Science
• /
• v.1 no.1
• /
• pp.5-8
• /
• 1974

To obtain several foundamental information for the breeding of Korean Ginseng. 16 line selecteds in Korea were investigated and analyzed. The results obtained are as follows : 1. In all quantitative genetic characters of Korean Ginseng, the stem length showed the highest heritability(0.7050) and the leaf length the lowest(0.5674). 2. The genotypic correlation was showen the highest value (0.8649) at between the leaf length and the stem diameter and the lowest value(0.8649) at between the leaf length and the stem length, but the phnotypic correlation was shown the highest value (0.8788) at between the stem length and the stem dimeter and the lowest value (0.7950) at between the leaf length and stem length. 3. The co-heritability between the stem length and the stem diameter showed the highest value(0.6124) and that between the leaf length and the stem length showed the lowest value(0.5471). 4. The inter-class correlation among the planting location showed the highest value at the stem length and the lowest value at the stem diameter.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.26 no.1
• /
• pp.82-88
• /
• 2017

In 2016, a handmade vehicle called to the VF-3 was designed and manufactured as a formula typed car. Prior to manufacturing and assembly, the impact attenuator was analyzed through ANSYS LS-DYNA, and the results were applied to the VF-3. The dynamical performance of the VF-3, such as the acceleration and circling simulations, was also assessed through MSC-ADAMS. The results were applied and compared after the Korean Society of Automotive Engineers (KSAE) competition. There was only a 0.8 s difference in the acceleration test. In order that the frame was not twisted by thermal deformation, Argon-TIG welding was used and a zig was designed. Another zig was designed to have the exact position for the hardpoints in the suspension system. Most of the parts were made with aluminum 7050 for reduced weight. The VF-3 won the third prize in the 2016 KSAE Student Handmade Vehicle competition.