• Composites Research
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• v.19 no.4
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• pp.7-14
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• 2006

Interfacial shear strength between epoxy and carbon fiber has been analyzed utilizing the microbond specimen with an epoxy micro-droplet adhered onto single carbon fiber. The interfacial shear stress distributions along the fiber/matrix interface were calculated by finite element analysis using three kinds of finite element models such as droplet model, circular-crosssection model and pull-out model. Conclusions were obtained as follows. (1) Interfacial shear stress distribution showed that larger stresses were concentrated in the fiber/matrix interface for microbond test than for pull-out test. Thus, debonding at the fiber/matrix interface during microbond test was liable to occur at low load level. (2) Microbond test showed higher interfacial strength which was caused by various effects of micro-droplet geometry and size as well as stress concentration in the region contacting with the micro-vise tip.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.639-642
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• 1999

Pullout test known as Lok test among the test methods to evaluate concrete strength strength is a test method which is used to decide the form removal time by assessing the early strength of concrete in a new construction, or to control the quality of newly placed concrete. This method has inconvenience to place inserts on the form work in advance, however, the placing work is quite simple and it has advantage that the strength can be measured at field as long as the inserts are placed. In this study, the first step is to investigate the properties of test method itself, by performing the laboratory test which covers deviation of the method and factors affecting the results, etc. The second step is to correlate the result with cylinder strength and other NDT methods such as rebound hammer, ultrasonic method, etc. And that, the results are compared with foreign results to find the differences between the two. In this research, new factors such as moisture content, area of aggregate failure cross section and area of aggregate separation cross section, etc as well as wate-cement ratio and age are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.752-760
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• 2000

Mechanical press joining has been used in sheet metal joining processes because of its simple process and possibility of joining dissimilar metals, such as steel and aluminum. The strength of mechanical press joining varies with joining conditions. The optimum joining conditions considering tensile-shear and peel-tension strength have to be established to assure the reliability in the joining strength. Therefore, optimization of joining conditions has been investigated for improving joining strength of sheet metal. It is possible to obtain optimum strength from improvement on the joining strength of peel-tension mechanical press joint under multiaxial stress states.

• Composites Research
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• v.31 no.4
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• pp.139-144
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• 2018

Long Fiber-reinforced composites have advantages of excellent production efficiency and formability of complex shapes compared to conventional continuous fiber reinforced composite materials. However, if we need to make complicated composite shapes or to assemble parts made of different materials, a variety of joining methods are needed. In general, long fiber prepreg sheet (LFPS) contains mold release agent to facilitate demolding after thermoforming. Therefore, mechanical fastening is required in addition to the adhesive bonding to get proper joining strength. In this study, we proposed a stainless steel insert for co-cure bonding which cures LFPS and bonds the stainless steel insert through thermoforming process. The wing of the insert which is spread during the thermoforming process induces adhesion and mechanical wedging effect and serves as a hook to resist the pulling force. The burn-out method was used to confirm the unfolded state of the stainless steel insert wings inserted into the composite material. The static pull-out test was performed to quantitatively evaluate the joining strength. From these experimental results, the condition which guarantees the most appropriate joining strength was derived.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.165-173
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• 2008

One of the most important requirements for reinforced concrete constructions is the bond behavior between concrete and reinforcement. For practical application, it is very important to study bond behavior of reinforcing bars in recycled aggregate concrete (RAC). Thirty six pull-out tests were carried out in order to investigate the bond behaviour between recycled coarse aggregate concrete (RCAC) and deformed bars. RCA replacement ratios (i.e., 0%, 30%, 60% and 100%) and positions of deformed bar (i.e., vertical and horizontal position) were considered as variables in this paper. Each specimen was in the form of a cube, with edges of 150 mm in length and for the pull-out tests, a deformed bar, 13 mm in diameter, was embedded in the center of each specimen. Based on the test results, the bond strength between the RCAC and deformed bars were influenced by both RCA replacement ratios and positions of deformed bars. It was found that under the equivalent mix proportion (i.e., the mix proportions are the same, except for different RCA replacement ratios), the bond strength between the RCAC and the ribbed bar has no obvious relation with the RCA replacement ratio, whereas the positions of deformed bars have a significant effect on the bond behavior between the RCAC and deformed bars. Under the condition of same RCA replacement ratio, the specimen of horizontal reinforcement at upper position (HU type) appear considerably low bond stress.

• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.725-734
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• 2017

This paper investigated the effects of rebar corrosion on bond performance between rebar and two different concrete mixes (compressive strengths of 20.7 MPa and 44.4 MPa). The specimen was designed as a rebar centrally embedded in a 200 mm concrete cube, with two stirrups around the rebar to supply confinement. An electrochemical accelerated corrosion technique was applied to corrode the rebar. 120 specimens of two different concrete mixes with various reinforcing steel corrosion levels were manufactured. The corrosion crack opening width and length were recorded in detail during and after the corrosion process. Three different loading schemes: monotonic pull-out load, 10 cycles of constant slip loading followed by pull-out and varied slip loading followed by pull-out, were carried out on the specimens. The effects of rebar corrosion with two different concrete mixes on corrosion crack opening, bond strength and corresponding slip value, initial slope of bond-slip curve, residual bond stress, mechanical interaction stress, and energy dissipation, were discussed in detail. The mean value and coefficient of variation of these parameters were also derived. It was found that the coefficient of variation of the parameters of the corroded specimens was larger than those with intact rebar. There is also obvious difference in the two different concrete mixes for the effects of rebar corrosion on bond-slip parameters.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.33-40
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• 1988

The new technique has been used to determine the soil-reinforcement interaction. The testing apparatus is essentially a triaxial cell fitted with the capability to house a hollow cylinderical sample. A hollow cylinderical sand specimen with a concentrical layer of reinfarcing material sandwitched in the middle is used in this investigation. The reinforcement is fastened at the base. The hollow specimen can be viewed as a "unit sheet" of a soil-reinforcement composite system of infinite horizontal extent. Axial load as well as inner and outer chamber pressures can be applied to perform a test. The specimen is first subjected to an isotropic stress state corresponding to the overburden pressure. Next, an extension test by reducing the axial load is carried out. The specimen is "loaded" to failure by either the breakage of reinforcing material (tensile failure) or slippage which takes place at the soil-reinforcement interface (i.e. the overcoming of the bonding capacity). Since the reinforcement is fastened at its lower end to the base, any tendency of relative movement between the reinforcement and the sand during an extension test can induce tensile force in the reinforcement thus forming a "reversed pull-out" test condition. Preliminary test results have demonstrated positively of the new approach to test the soil-reinforcement interaction. Reinforcing elements of different extensibility were used to study the deformbility of reinforced soil. Furthermore, both the breakage and the pull-out modes of failure were observed.

• Composites Research
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• v.18 no.4
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• pp.59-65
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• 2005

This report is on the Reinforcing System(MFRI) for Concrete Structure using FRP ROD & High-Performance Mortar. The main characteristic of this system is as follow. First, the fiber rods in this system have seven times greater tensile strength than general reinforcing steel bars(re-bar) and the weight is a fifth lighter. Camels coated on the fiber rods' surfaces to improve adhesive strength and pull-out strength. Second, high strength shotcrete mortar is has very good workability and low rebound rate. After installing the Fiber Rods, Shotcrete mortar Is applied or sprayed to finish reinforcement. Finally, MFRI system has excellent fire-resisting performance and sogood tolerance against external environment by inserting fiber rods and reinforcing materials into mortar which has high compressive strength. It is applied to bridge slab, utility box and tunnel of civil engineering works, and beam and slab of building structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.965-970
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• 2002

The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures. Carbon fiber is attractive for this application due to its good tensile strength, resistances to corrosion, and low weight. Generally bond strength and behavior between concrete and carbon fiber mesh(CFM) is very important, because of the enhanced bond of CFM. Therefore if bond strength is sufficient, it will be expected to enhance reinforcement effect. If insufficient, reinforcement effect can not be enhanced because of bond failure between concrete and CFM. This study is to investigate the bond strength of CFM to the concrete using direct pull-out test and tensile-shear test. The key variables of the experiment are the location of clip, number of clips and thickness of cover mortar. The general results indicate that the clip anchorage technique for increasing bond strength with CFM appear to be effective to maintain the good post-failure behavior.

• Advances in concrete construction
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• v.7 no.3
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• pp.191-201
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• 2019

Bamboo concrete bond behaviour is investigated through pullout test in this work. The bamboo strip to be used as reinforcement inside concrete is first treated with chemical adhesive to make the bamboo surface impermeable. Various surface coatings are explored to understand their water repellant properties. The chemical action at the bamboo concrete interface is studied through different chemical coatings, sand blasting, and steel wire wrapping treatment. Whereas mechanical action at the bamboo concrete interface is studied by developing mechanical interlock. The result of pullout tests revealed a unique combination of surface treatment and grooved bamboo profile. This combination of surface treatment and a grooved bamboo profile together enhances the strength of bond. Performance of a newly developed grooved bamboo strip is verified against equivalent plain rectangular bamboo strip. The test results show that the proposed grooved bamboo reinforcement, when treated, shows highest bond strength compared to treated plain, untreated plain and untreated grooved bamboo reinforcement. Also, it is observed that bond strength is majorly influenced by the type of surface treatment, size and spacing of groove. The changes in bamboo-concrete bond behavior are observed during the experimentation.