• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1220-1226
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• 2001

This study investigates the effects of the pre-strain level on mechanical properties of the solid-phase formed thermoplastic composite. A uniaxial solid-phase forming was performed at the temperature of 125$\^{C}$ and at the constant cross-head speed of 3mm/sec. The composite sheet was formed to various pre-strain levels of 10%, 20%, and 30%. Tension, flexural, and impact tests were carried out to characterize the material properties of a solid-phase formed part. Tensile and flexural strengths decreased with increasing the pre-strain level, while impact strength increased. Various microstructures of the formed part explained the above material behavior.

• Design & Manufacturing
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• v.15 no.3
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• pp.39-44
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• 2021

In molding of continuous fiber-reinforced thermoplastic composites, it is very difficult to impregnate between the reinforcements and the matrix since the matrix has a high melting temperature and high viscosity. Therefore, most of composite molding processes are divided in the manufacturing processes of intermediate materials called prepreg and the forming of products from intermediate materials. The divided process requires additional facilities and thermoforming, and they increase the cycle time and cost of composite products. These problems can be resolved by combining the continuous fiber-reinforced composite molding process with injection molding. However, when a composite material is manufactured by inserting woven fabric into the injection mold, poor impregnation occurs on the surface of the molded product. It affects the properties of the composites. In this paper, through an impregnation experiment using cores with different heat transfer rates and pore densities, the reason for the poor impregnation was confirmed, and molding experiments were conducted to produce composite with improved surface impregnation by inserting the mesh. And also, the surface impregnation and deformation of composites molded using different types of mesh were compared with each other.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.27-32
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• 2013

According to the composition of LTCC material, though it was thought that bulk defect which was made in forming process effects on the densification during the sintering, it was not reported systemically. In this study, we evaluated crystal structure, 3 point bending strength, hardness and microstructure of the samples by uniaxial pressing and tape casting using the commercial powders of the crystallizing glass and the glass/ceramic composite. In the case of glass/ceramic composite, Viox-001 powder with residual glass in the sintering, 3 point bending strength was similar regardless of forming process due to fill the bulk defect by residual glass. In the case of crystallizing glass, MLS-22, because glass phase was small in the sintering, glass did not fill the pore in the sample by uniaxial pressing process, therefore, the 3 point bending strength of it was 167 MPa. However, the 3 point bending strength of the sample by tape casting was 352 MPa and much higher. Meanwhile, crystal structure and hardness were similar regardless of forming process.

• Composites Research
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• v.17 no.6
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• pp.28-36
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• 2004

Micro-tow deformation during forming of PVC foam-fabric composite sandwich structure is investigated to find out the correlation between forming condition and material deformation. The foams used in this research are PVC foams which have 4 different densities and the fabric composite is Carbon/epoxy prepreg which is plain weave (3k) as a skin material. Tow parameters such as crimp angle and tow amplitude are measured using microscope and a proper image tool and are compared with each other. In order to find out the effect of foam deformation during forming on tow deformation the compressive tests of foams are performed in three different environmental temperatures ($25^{\circ}C$, $80{\circ}C$, $125^{\circ}C$). The microscopic observation results show that the micro tow deformations are quite different from each other with respect to the foam density and forming pressure.

• Journal of the Korean Ceramic Society
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• v.32 no.9
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• pp.989-994
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• 1995

Rigid porous carbon fiber composites with the uniform pore size distribution were prepared by vacuum forming from water slurries containing carbonized PAN fibers, a phenolic resin and ceramic binders. The composites were designed to use for highly efficient carbon fiber filters for particulate filtration and gas adsorption. As the as-received carbon fibers of 1mm in length were milled to an approximate average length of 300${\mu}{\textrm}{m}$, modulus of rupture (MOR) of the composite filter was increased from 1MPa to the value larger than 5 MPa. Modulus of rupture (MOR) for the composite filter fabricated using the milled carbon fiber was increased from 5 MPa to 10 MPa as the carbonization temperature of the PAN fiber was raised from 90$0^{\circ}C$ to 140$0^{\circ}C$. The air permeability and an average pore size of the composite filter were increased from 40 to 270cc/min.$\textrm{cm}^2$ and from 35 to 80${\mu}{\textrm}{m}$, respectively, as the apparent porosity increased from 80 to 95%. It was shown that the MOR of the carbon fiber composite filter was dependent primarily on the average length of carbon fiber, carbonization temperature and the type of bonding materials.

• Composites Research
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• v.23 no.6
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• pp.61-66
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• 2010

In this paper, the variation of mechanical properties of T800 carbon/epoxy composites according to the forming pressure, which was referred to previous studies on a filament winding process, were investigated. The specimens of all the tests were fabricated by an autoclave de-gassing molding process controlling forming pressure (absolute pressures of 0.1MPa, 0.3MPa, 0.7MPa including vacuum) and water jet cutting after fabricating composite laminates. Various tensile tests were performed for in-plane properties and interlaminar properties were also measured by using Iosipescu test jig. Fiber volume fraction was measured to correlate the property variation and the forming pressure. This properties are expected to be utilized in the design of Type III pressure vessel for hydrogen vehicles which uses the same carbon fiber (T800 carbon fiber) for the filament winding process.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.59.4-60
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• 2016

Recent galaxy simulations suggest several scenarios in which the inner structure of late-type galaxies (LTGs) is linked to global quenching. Exactly what mechanism governs the bulge quenching is, however, still under debate due to the lack of observational clues. In this study, we utilize a sample of ~1,300 LTGs in the local universe (0.02 < z < 0.2) from SDSS 7, and classify them into star-forming, AGN-hosting, and composite types and into barred and unbarred galaxies. We also examine each subgroup's specific star forming rate (sSFR), stellar mass and compactness using a data set matched with the advanced sSFR catalog by Chang et al. (2015). We find that while star-forming and composite galaxies show no detectable difference between barred and unbarred galaxies, barred AGNs have much lower sSFR than unbarred AGNs at given stellar mass and compactness, Such tendency is stronger for more massive and/or more concentrated galaxies. The results indicate that most AGN-driven quenching is triggered by growth of the bar structure, consistent with the previous simulations of bars.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1385-1389
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• 2005

This paper describes the design, analysis and manufacture procedure of the composite blade for hingeless rotor system of unmanned helicopters. Helicopter rotor system is the key structural unit that produces thrust and control forces for intended flight conditions. In this work, a hingeless rotor system is adopted, and base on the design requirements for rotor system, composite blade section design and calculation of material properties were performed. In order to avoid the unstable state such as resonance, vibration characteristics of rotor system were analyzed. Finally, this paper describes the forming and manufacture of composite blade.

• Composites Research
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• v.26 no.1
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• pp.42-47
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• 2013

In this study, an economical and effective processing technique to form multiple dimples on the surface of a composite part, which are known to be useful to improve aerodynamic performance and heat dissipation. Forming dimples on the surface using molds is an expensive processing because forming multiple tiny positive spheres on the surface of the mold requires much time and effort. In this study, plates with multiple round holes are utilized as a core to form dimples on the carbon/epoxy composite skin covering the core. A vacuum bagging process is used to apply pressure on the surface while curing. Composite parts which have multiple dimples on the surface can be utilized in the field which needs high aerodynamic performance and heat dissipation ability such as high speed sports car bodies.

• Steel and Composite Structures
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• v.24 no.3
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• pp.351-358
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• 2017

Due to the increasing competition, automotive manufacturers have to manufacture highly safe and light vehicles. The parts which make up the body of the vehicle and absorb the energy in case of a crash, are usually manufactured with sheet metal forming methods such as deep drawing, bending, trimming and spinning. The part may get thinner, thicker, folded, teared, wrinkled and spring back based on the manufacturing conditions during manufacturing and the type of application methods. Transferring these effects which originate from the forming process to the crash simulations that are performed for vehicle safety simulations, makes accurate and reliable results possible. As a part of this study, firstly, the one-step and incremental sheet metal forming analysis (deep drawing + trimming + spring back) of vehicle front bumper beam and crash boxes were conducted. Then, crash performances for cases with and without the effects of sheet metal forming were assessed in the crash analysis of vehicle front bumper beam and crash box. It was detected that the parts absorbed 12.89% more energy in total in cases where the effect of the forming process was included. It was revealed that forming history has a significant effect on the crash performance of the vehicle parts.