• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.4
• /
• pp.126-132
• /
• 2018

As means to increase the use of concrete with recycled coarse aggregate (RCA), this study aims to evaluate the applicability for flexural strengthening of reinforced concrete beam with high-strength concretes and RCA on which FRP plates, used for repair and strengthening of old and low-durability reinforced concrete structures, is applied. In order to increase the adhesive force of epoxy and FRP plate, FRP plate was installed according to Near-Surface-Mounted (NSM) method. 12 specimens were manufactured using substitution rate of RCA (30%), concrete strengths (40MPa, 60MPa), diameters of deformed bar (D10, D13), and types of FRP plate (AFRP, CFRP) as variables to analyse flexural performance according to FRP plate and substitution rate of recycled aggregate. As a result, in all specimens, specimens strengthened by FRP plate showed a maximum of 17% increase in performance compared to specimens without FRP plate and strengthening performance of CFRP was found to be higher than AFRP. When modulus of rupture was used, the value of cracking moment was similar to that of the reference equation. As bending moment of some specimens strengthened by FRP plate failed to satisfy the criteria of KCI 2012 and ACI 440-2R, additional experiment is deemed as necessary.

• Composites Research
• /
• v.18 no.3
• /
• pp.38-46
• /
• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6A
• /
• pp.457-464
• /
• 2011

An experimental study was performed to evaluate the possibility of using stiff type PolyUrea(PU) on RC slab as a strengthening material. Stiff type PU(STPU) was sprayed on the bottom surface of the slab specimens, which were then attached with CFRP or GFRP sheets. Also the evaluation of the bond capacity, the single most influential parameter on strengthening of RC structures, was carried out the flexural capacity evaluation test results showed that the load carrying capacity of the PU specimen was greater and less than the unstrengthened and FRP sheet attached specimens, respectively. The STPU specimens showed a ductile flexural behavior in the plastic displacement range. With respect to bond capacity, the bond strength of all of the specimen exceeded the code required bond strength of 1.5 MPa. Also, the STPU sprayed specimen without using epoxy resin did not peel off when the tensile grip was applied for testing. The stability of the PU bond failure indicate a good bond strength of PU when applied to concrete.

• Composites Research
• /
• v.33 no.4
• /
• pp.228-233
• /
• 2020

In this paper, a single lap shear test was performed using a glass fiber reinforced composite material (GFRC). Pencil lead drawn paper sensor (PLDPS) was applied for single lap shear test being performed. Bisphenol-A epoxy and amine hardener were used as adhesives combining with composite materials. To make a difference in adhesive properties, the adhesive was cured under different conditions. PLDPS was made of a 4B pencil on A4 paper. Because graphite in a pencil was an electrically conductive substance, electric resistance (ER) could be measured. A change in ER was observed by a position where a PLDPS was attached to single lap shear specimens. It was confirmed that the change in ER was different depending on two attached positions and was observed by lap shear strain as well. In case the lap shear strain was large, the change in ER of PLDPS was high. This was because the larger the extension of the adhesive part, the larger the degree of bending of the specimen and thus the larger the distance change between two electrodes.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.16 no.3
• /
• pp.485-492
• /
• 2021

The wind turbines with a rated capacity of 50kW or less are generally considered as small class. Small wind turbines are an attractive alternative for off-grid power system and electric home appliances, both as stand-alone application and in combination with other energy technologies such as energy storage system, photovoltaic, small hydro or diesel engines. The research objective is to develop the 50kW scale wind turbine blades in ways that resemble as closely as possible with the construction and methods of utility scale turbine blade manufacturing. The mold process based on wooden form is employed to create a hollow, multi-piece, lightweight design using carbon fiber and fiberglass with an epoxy based resin. A hand layup prototyping method is developed using high density foam molds that allows short cycle time between design iterations of aerodynamic platforms. A production process of five blades is manufactured and key components of the blade are tested by IEC 61400-23 to verify the appropriateness of the design. Also, wind system with developed blades is tested by IEC 61400-12 to verify the performance characteristics. The results of blade and turbine system test showed the available design conditions for commercial operation.