• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.363-375
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• 2015

This research investigated the effects of diameter and material of energy frame on the impact velocity or strain rate of Strain Energy Frame Impact Machine (SEFIM). The impact speed of SEFIM have been clearly affected by changing the diameter and material of the energy frame. The reduced diameter of the energy frame clearly increased the impact velocity owing to the higher strain at the moment of coupler breakage. And, titanium alloy energy frame produced the fastest speed of impact among three materials including steel, aluminum and titanium alloys because titanium alloy has faster wave velocity than steel. But, aluminium energy frame was broken during impact tests. In addition, the tensile stress versus strain response of high performance fiber reinforced cementitious composites at higher and wider strain rates between 10 and 72 /sec was successfully obtained by using four different energy frames.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.571-578
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• 2016

Recently, review on viability of various industrial by product and natural materials as raw material for concrete has been actively done in aspect of environment-friendly issue and depletion of natural resource. This study conducted fundamental study on the possibility of utilizing mud flat as admixture and filling material for concrete. First, chemical analysis on the viability of mud flat as admixture was done and the researchers compared it with the substance of fly ash and blast furnace slag. According to the result, substance content was proven to be inadequate. In addition, as the replacement rate of mud flat increased, compressive strength and tensile strength decreased. According to the estimated result of chemical substance analysis, possibility of utilizing mud flat as admixture was low. According to the result of experiment done as filling material, 10% ~ 30% replacement rate of mud flat manifested more than 8 Mpa of compressive strength of block which may be utilized for secondary product. However, additional experiment such as making block is required afterward. According to the result of flow experiment, as the replacement rate of mud flat increased, flow value decreased, and through chloride content analysis test, it was proven that mud flat is inappropriate to be applied as steel beam using structure since it has high content of sodium. It may be utilized as products that does not use steel beam such as internal brick.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.313-320
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• 2013

In this study, performance of fiber-reinforced polymer-modified mortar was studied for the development of eco-friendly materials for high performance repair and reinforcement. The general cement mortar and eco-friendly UM resin was mixed with a certain percentage for increased durability. To increase the strength of the polymer-modified mortar, PVA fiber, steel fiber and hybrid fiber were added at a constant rate. Hybrid fiber is contains the same percentage of PVA fiber and steel fiber. In order to determine the strength properties of fiber-reinforced polymer-modified mortar, the compressive strength test, the splitting tensile strength test and the flexural strength test were performed. And, in order to determine the durability properties of fiber-reinforced polymer-modified mortar, water absorption test and chemical resistance test were performed. From the experimental results, polymer-modified mortar using UM resin was improved durability. And the tensile strength and flexural strength increased, which were the vulnerability of fiber reinforced polymer-modified mortar. From this study, fiber-reinforced polymer-modified mortar using eco-friendly UM resin can be used to repair and reinforcement for the external exposure of concrete structures to improve the durability.

• Elastomers and Composites
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• v.40 no.2
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• pp.93-103
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• 2005

In this study, surface treatment of the elastomeric matrix was investigated to develop a substituting material for steel dynamic damper of automobile. The key technology is to get ultra high density elastomeric compound in order to substitute steel dynamic damper. The optimum matrix material(chloroprene rubber) and filler(metal powder) were selected for this. The several properties of elastomeric compound were examined. According to the results, the $t_{s2}$ of filled elastomeric compound was decreased with increasing the filler loading whereas the $t_{90}$ was increased. Also, tensile strength and rebound resilience were decreased with filler loading. To solve the problem of high filler loading, the photo grafting technique was employed on elastomeric matrix. The degree of grafting was determined by FTIR-ATR. Also, the filler surface was modified by chemical etching and the surface morphology was examine by SEM. After chemical treatment of filler, the particle size analyzer was used to examined the particle size, size distribution, and morphology of the modified filler.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.65-73
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• 2011

Microstructural characteristics of two high strength (600 MPa & 800 MPa) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 MPa grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 MPa and 800MPa grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was $0.7{\mu}m$. The 800 MPa grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 MPa grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 MPa grade weld metal.

• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.29-34
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• 2006

Elastic modulus, tensile and bond capacities are important factors for developing an effective reinforcing action of a flexural member as a reinforcing material for concrete structures. Reinforcement must have enough bond capacity to prevent the relative slip between concrete and reinforcement. This paper presents an experimental study to clarify the bond capacity of prestressed carbon fiber reinforced polymer(CFRP) rod manufactured by an automatic assembly robot. The bond characteristics of CFRP rods with different pitch of helical wrapping were analyzed experimentally. As the result, all types of CFRP rods show a high initial stiffness and good ductility. The mechanical properties of helical wrapping of the CFRP rods have an important effect on the bond of these rods to concrete after the bond stress reached the yield point. The stress-slip relationship analyzed from the pull-out test of embedded cables within concrete was linear up to maximum bond capacity. The deformation within the range of maximum force seems very low and was reached after approximately 1 mm. The average bond capacity of CF20, CF30 and CF40 was about 12.06 MPa, 12.68 MPa and 12.30 MPa, respectively. It was found that helical wrapping was sufficient to yield bond strengths comparable to that of steel bars.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.1
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• pp.30-37
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• 2015

The need to consider torsion in the design of members of a structure has recently been increasing; therefore, many studies on torsion have been carried out. Recent research was focused on the torsional performance of concrete according to the reinforcing materials used. Of particular interest, are torsion studies of beams made of SFRC(steel fiber reinforced concrete), and there has been increasing use of SFRC at construction sites. In contrast, research on the composite PVA-ECC (polyvinyl alcohol-engineered cementitious composite) has only covered its mechanical performance, though it exhibits excellent tensile-strain performance (better than SFRC). Therefore, research on the torsion of concrete beams retrofitted using PVA-ECC is lacking. In this study, the behavior characteristics and performance of reinforced-concrete beams retrofitted by PVA-ECC was investigated experimentally. The experimental results show that the resistance to torsional cracking is increased by PVA-ECC. In addition, the strain on the rebar of the specimen was found to be reduced.

• Journal of the Korean Society of Safety
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• v.30 no.3
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• pp.7-12
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• 2015

CFRP composites are used as primary structural members in various industrial fields because their specific strength and specific stiffness are excellent in comparison to conventional metals. Their usage is expanding to high added-value industrial fields because they are more than 50% lighter than metals, and have excellent heat resistance and wear resistance. However, when CFRP composites suffer impact damage, destruction of fiber and interface delamination occur. This causes an unexpected deterioration of strength, and for this reason it is very difficult to ensure the reliability of the excellent mechanical properties. Therefore, for the destruction mechanism in bending with impact damage, this study investigated the reinforcement data regarding various external loads by identifying the consequential strength deterioration. Specimens were damaged by impact with a steel ball propelled by air pressure. Decrease in bending strength caused by the tension and compression of the impact side, and depending on the lamination direction of fiber and interface inside the specimen. From the bending test it was found that the bending strength reduced when the impact energy increased. Especially in the case of compression on the impact side, as tensile stress occurred at the damage starting point, causing rapid failure and a substantially reduced failure strength.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.2
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• pp.47-52
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• 2010

Miniaturization and lightweight are increasingly the recent trend in the manufacture of electric appliances and machine parts. So technology of micro joining for joining materials is indispensable. This paper gives a description of an experimental study of the ultrasonic welding of metals. In ultrasonic metal welding, high frequency vibrations are combined with pressure to join two materials together quickly and securely, without producing significant amount of heat. Ultrasonic metal welder consists of Transducer, Booster, and Horn that are designed very accurately to get the natural frequencies and vibration mode. In this study, The horn was designed and analyzed the natural frequency by the modal analysis and harmonic analysis. And using a fiber optic sensor, we measured the amplitude and analyzed the Fast Fourier Transformed result. Using the horn, Ultrasonic metal welding between Ni sheet and Ni sheet of 0.1mm thickness was accomplished under the optimal conditions of static pressure 0.15MPa, vibration amplitude 45% and welding time of 0.28s. This result can be used for ultrasonic metal welding in manufacturing industry.

• Transactions of Materials Processing
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• v.23 no.8
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• pp.495-500
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• 2014

Magnesium alloys are currently expected to be widely used for weight reduction of cars and as high efficient materials in the automotive and electronics industries. Although the specific strength of magnesium is excellent, it cannot be easily formed at room temperature due to its HCP structure. However in order to improve the formability of magnesium, it is necessary to investigate its formability in the warm temperature range. In the current study, the aim was to add to the magnesium property database so that the mass production of a magnesium car body can be accomplished. Warm tensile tests were conducted and the forming limit diagram was determined to confirm formability characteristics of magnesium AZ31B alloy sheet. In addition the bending formability and the magnesium damping capacity were evaluated for AZ31B and compared to SPRC440E which is a sheet steel used for car bodies.