• Composites Research
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• v.35 no.3
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• pp.188-195
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• 2022

This paper proposes a multiscale process-structural analysis methodology and applies to a battery housing part made of the short fiber-reinforced and fabric-reinforced composite layers. In particular, uncertainties of the material properties within the microscale representative volume element (RVE) were considered. The random spatial distribution of matrix properties in the microscale RVE was realized by the Karhunen-Loeve Expansion (KLE) method. Then, effective properties of the RVE reflecting on spatially varying matrix properties were obtained by the computational homogenization and mapped to a macroscale FE (finite element) model. Morever, through the hybrid process simulation, a FE (finite element) model mapping residual stress and fiber orientation from compression molding simulation is combined with one mapping fiber orientation from the draping process simulation. The proposed method is expected to rigorously evaluate the design requirements of the battery housing part and composite materials having various material configurations.

• Composites Research
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• v.35 no.2
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• pp.61-68
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• 2022

Composite materials have been used in aerospace industry and many applications because of many advantages such as specific strength and stiffness and corrosion resistance etc. However, it is vulnerable to impacts, these impact lead to formation of cracks in composite laminate and failure of structures. In this paper, we analyzed Mode I fracture toughness of Carbon/Epoxy laminates using acoustic emission signal. DCB test was carried out to analyze Mode I failure characterization of Carbon/Epoxy laminates, and AE sensor was attached to measure AE signal induced by failure of specimen. Fracture toughness was calculated using cumulative AE energy and measured crack length using camera. The calculated fracture toughness was applied in FE model and the result of FE analysis compared with DCB test results. The results show good agreement with between FEM and DCB test results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.109-114
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• 2008

This paper presents the development status of a subscale precooled turbojet engine "S-engine" for the hypersonic cruiser and space place. S-engine employs the precooled-cycle using liquid hydrogen as fuel and coolant. It has $23cm{\times}23cm$ of rectangular cross section, 2.6 m of the overall length and about 100 kg of the target weight employing composite materials for a variable-geometry rectangular air-intake and nozzle. The design thrust and specific impulse at sea-level-static(SLS) are 1.2 kN and 2,000 sec respectively. After the system design and component tests, a prototype engine made of metal was manufactured and provided for the system firing test using gaseous hydrogen in March 2007. The core engine performance could be verified in this test. The second firing test using liquid hydrogen was conducted in October 2007. The engine, fuel supplying system and control system for the next flight test were used in this test. We verified the engine start-up sequence, compressor-turbine matching and performance of system and components. A flight test of S-engine is to be conducted by the Balloon-based Operation Vehicle(BOV) at Taiki town in Hokkaido in October 2008. The vehicle is about 5 m in length, 0.55 m in diameter and 500 kg in weight. The vehicle is dropped from an altitude of 40 km by a high-altitude observation balloon. After 40 second free-fall, the vehicle pulls up and S-engine operates for 60 seconds up to Mach 2. High altitude tests of the engine components corresponding to the BOV flight condition are also conducted.

• Journal of Korean Society for Quality Management
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• v.49 no.2
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• pp.113-125
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• 2021

Purpose: This study focused on reality and quality improvement of aviation security equipment performance certification system. Methods: For this propose, we analyzed aviation security equipment performance certification system related legislations. Using analyzed data, we suggested advancement plan of aviation security equipment performance certification system. Results: In results, South Korea has been implementing aviation security performance certification system since October 2018. Parts for improvement of system are mutual certification with major countries that operate aviation security equipment performance certification systems, the spread of the defense industry's system, development of similar substances for handling explosives, and introduction of preliminary inspections. Conclusion: The research result could be used as a basic data for upgrading Korea's aviation security performance certification system.

• Composites Research
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• v.36 no.5
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• pp.321-328
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• 2023

This study developed the in-situ stamp-forming process using the multi-axis robotic arm to fabricate thermal composite parts. Optimal fabrication parameters with the multi-axis robotic arm were determined using finite element analysis and these parameters were further refined through the practical manufacturing process. A comparison between the manufactured parts and finite element analysis results was conducted regarding thickness uniformity and wrinkle distribution to confirm the validity of the finite element analysis. Additionally, to evaluate the formability of the manufactured composite parts, measurements of crystallinity and porosity were taken. Consequently, this study establishes the feasibility of the In-situ stamp-forming consolidation using a robotic arm and verifies the potential for producing composite parts through this process.

• Current Industrial and Technological Trends in Aerospace
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• v.6 no.2
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• pp.60-68
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• 2008

The characteristic and properties of materials are rapidly degraded when subjected to the synergistic effects of the space environment such as atomic oxygen, radiation, vacuum and thermal cycling. In order to understand the mechanism of material property variation in space environment and to develop new space materials applicable to the future space program, advanced space organizations such as NASA, ESA and JAXA have been continuing many researches on material test specimens used on ISSE(International Space Station Experiment) or LDEF(Long Duration Exposure Facility). In this paper, the selection requirements and verification trend of materials in space applications

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.518-522
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• 2012

Hyaluronic acid (HA) microbeads were synthesized by dropping 0.5 wt% of sodium hyaluronate dissolved in NaOH into 0.2 vol% of divinyl sulfone dissolved in 2-methyl-1propanol at a speed of 0.005 ml/min. HA microbeads were collected from a divinyl sulfone crosslinker solution stirred at 200 to 400 rpm for 5 h at temperatures from room temperature to $60^{\circ}C$ at intervals of $10^{\circ}C$. The crosslinked microbeads were then cleaned thoroughly using distilled water and ethanol. SEM results revealed that the microbeads were white-colored spheres. The 3-D porous network structure of the microbeads became dense with an increase in the crosslinking temperature; however, no dependence of the crosslinking temperature on the microbead size was detected. The extent of swelling decreased from 970% to 670% with an increase in the crosslinking temperature from room temperature to $60^{\circ}C$, most likely due to the increase in the degree of crosslinking.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.643-651
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• 2017

Four types of high Mn TWIP(Twinning Induced Plasticity) steels were fabricated by varying the Mn and Al content, and the tensile properties were measured at various strain rates and temperatures. An examination of the tensile properties at room temperature revealed an increase in strength with increasing strain rate because mobile dislocations interacted rapidly with the dislocations in localized regions, whereas elongation and the number of serrations decreased. The strength decreased with increasing temperature, whereas the elongation increased. A martensitic transformation occurred in the 18Mn, 22Mn and 18Mn1.6Al steels tested at $-196^{\circ}C$ due to a decrease in the stacking fault energies with decreasing temperature. An examination of the tensile properties at $-196^{\circ}C$ showed that the strength of the non-Al added high Mn TWIP steels was high, whereas the elongation was low because of the martensitic transformation and brittle fracture mode. Although a martensitic transformation did not occur in the 18Mn1.9Al steel, the strength increased with decreasing temperature because many twins formed in the early stages of the tensile test and interacted rapidly with the dislocations.

• Nuclear Engineering and Technology
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• v.50 no.5
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• pp.683-689
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• 2018

To evaluate equipment survivability of the polymer Viton, used in sealing materials, the effects of its thermal degradation were investigated in severe accident (SA) environment in a nuclear power plant. Viton specimens were prepared and thermally degraded at different SA temperature profiles. Changes in mechanical properties at different temperature profiles in different SA states were investigated. The thermal lag analysis was performed at calculated convective heat transfer conditions to predict the exposure temperature of the polymer inside the safety-related equipment. The polymer that was thermally degraded at postaccident states exhibited the highest change in its mechanical properties, such as tensile strength and elongation.

• Journal of Korea Foundry Society
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• v.11 no.1
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• pp.15-25
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• 1991