• Composites Research
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• v.21 no.1
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• pp.40-45
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• 2008

Rubber hose assembly for automotive hydraulic brake during operation is subject to combined stresses of cyclic pressure, cyclic bending and torsion as well as thermal load. The rubber hose is composed of ethylene-propylene diene monomer(EPDM) rubber layers reinforced by polyvinyl acetate(PVA) braided fabrics. A durability tester with loading rigs for inducing the above cyclic stresses was used to investigate failure mechanisms in the rubber hose assembly. Failure examination was performed at every 100 thousands cycles of bending and torsion. Hose samples were sectioned with a diamond-wheel cutter and then polished. The polished surface was observed by optical microscope and scanning electron microscope (SEM). Some interfacial delamination with a length of about 1mm along the interface between EPDM rubber and PVA fabrics was shown at the test cycles of 400,000. The delamination induced some cracking into the outer rubber skin layer to leading the final rupture of the hose.

• International Journal of Concrete Structures and Materials
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• v.6 no.2
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• pp.123-134
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• 2012

There is significant concern in the engineering community regarding the safety and effectiveness of fiber-reinforced polymer (FRP) strengthening of RC structures because of the potential for brittle debonding failures. In this paper, previous research programs conducted by other researchers were reviewed in terms of the debonding failure of FRP laminates externally attached to concrete. This review article also discusses the influences on bond strength and failure modes as well as the existing experimental research and developed equations. Based on the review, several important conclusions were re-emphasized, including the finding that the bond transfer strength is proportional to the concrete compressive strength; that there is a certain bond development length that has to be exceeded; and that thinner adhesive layers in fact lower the chances of a concrete-adhesive interface failure. It is also found that there exist uncertainty and inaccuracy in the available models when compared with the experimental data and inconsistency among the models. This demonstrates the need for continuing research and compilation of data on the topic of FRP's bond strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.2917-2925
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• 2000

Tensile strength and failure process of composite materials depend on the variation in fiber strength, matrix properties and fiber-matrix interfacial shear strength. A Monte-Carlo simulation considering variation in these factors has been widely used to analyze such a complicated phenomenon as a strength and simulated the failure process of unidirectional composites. In this study, a Monte Carlo simulation using 2-D and 3-D(square and hexagonal array) model was performed on unidirectional graphite/epoxy and glass/polyester composites. The results simulated by using 3-D hexagonal array model have a good agreement with the experimental data which were tensile strength and failure process of unidirectional composites.

• Tribology and Lubricants
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• v.18 no.5
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• pp.351-356
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• 2002

The surfaces of machine components in sliding contact such as bearing, gears and pistons etc. frequently operate under the condition of mixed lubrication due to high load, high speed and slip. These machine components often undergo the inception of scuffing in practical application. The scuffing failure is a critical problem in modern machine components, especially for the requirement of high efficiency and small size. However, it is difficult to find a universal mechanism to explain all scuffing phenomena because there are so many factors affecting the onset of scuffing. In this study, scuffing experiments are conducted using Acoustic Emission(AE) measurement by an indirect sensing approach to detect scuffing failure. Acoustic Emission(AE) signal has been widely utilized to monitor the interaction at the friction interface. Using AE signals we can get an indication about the state of the friction processes, about the quality of solid and liquid layers on the contacting surfaces in real time. The FFT(Fast Fourier Transform) analyses of the AE signal are sued to understand the interfacial interaction and the relationship between the AE signal and the state of contact is presented.

• Structural Engineering and Mechanics
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• v.56 no.3
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• pp.473-490
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• 2015

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-to-concrete bonded joints. The section analysis that considers the effect of concrete's tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

• Korean Journal of Metals and Materials
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• v.47 no.8
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• pp.500-507
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• 2009

Pb-free solder has recently been used in electronics in efforts to meet environmental regulations, and a number of Pb-free solder alloy choices beyond the near-eutectic SnAgCu solder are now available. With increased demand for thin and portable electronics, the high cost of alloys containing significant amounts of silver and their poor mechanical shock performance have spurred the development of low Ag SnAgCu solder, which provides improved mechanical performance at a reasonable cost. Although low Ag SnAgCu solder exhibits significantly higher fracture resistance under high-strain rates, little thermal fatigue data exist for this solder. Therefore, it is necessary to investigate thermal fatigue reliability of low Ag SnAgCu solder under variation of thermal stress in order to allow its implementation in electronic products with high reliability requirements. In this study, the reliability of Sn0.3Ag0.7Cu(SAC0307), a low Ag solder alloy, is discussed and compared with that of Sn3Ag0.5Cu(SAC305). Three sample types and six samples size are evaluated. Mechanical properties and microstructure of the solder joint are investigated under thermal shock cycles. It was observed that the mechanical strength of SAC0307 dropped slightly with thermal cycling relative to that of SAC305. This reveals that the failure mode of SAC0307 is different from that SAC305 under this critical condition.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.535-544
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• 2016

This paper aims at examining the effects of sustained load and elevated temperature on the time-dependent deformation of a carbon fiber reinforced polymer (CFRP) sheets bonded to concrete as well as the pull-off strength of single-lap shear specimens after the sustained loading period using digital images. Elevated temperature during the sustained loading period resulted in increased slip of the CFRP composites, whereas increased curing time of the polymer resin prior to the sustained loading period resulted in reduced slip. Pull-off tests conducted after sustained loading period showed that the presence of sustained load resulted in increased pull-off strength and interfacial fracture energy. This beneficial effect decreased with increased creep duration. Based on analysis of digital images, results on strain distributions and fracture surfaces indicated that stress relaxation of the epoxy occurred in the 30 mm closest to the loaded end of the CFRP composites during sustained loading, which increased the pull-off strength provided the failure locus remained mostly in the concrete. For longer sustained loading duration, the failure mode of concrete-CFRP bond region can change from a cohesive failure in the concrete to an interfacial failure along the concrete/epoxy interface, which diminished part of the strength increase due to the stress relaxation of the adhesive.

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.37-46
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• 2017

PURPOSES : A composite pavement utilizes both an asphalt surface and a concrete base. Typically, a concrete base layer provides structural capacity, while an asphalt surface layer provides smoothness and riding quality. This pavement type can be used in conjunction with rollercompacted concrete (RCC) pavement as a base layer due to its fast construction, economic efficiency, and structural performance. However, the service life and functionality of composite pavement may be reduced due to interfacial bond failure. Therefore, adequate interfacial bonding between the asphalt surface and the concrete base is essential to achieving monolithic behavior. The purpose of this study is to investigate the bond characteristics at the interface between asphalt (HMA; hot-mixed asphalt) and the RCC base. METHODS : This study was performed to determine the optimal type and application rate of tack coat material for RCC-base composite pavement. In addition, the core size effect, temperature condition, and bonding failure shape were analyzed to investigate the bonding characteristics at the interface between the RCC base and HMA surface. To evaluate the bond strength, a pull-off test was performed using different diameters of specimens such as 50 mm and 100 mm. Tack coat materials such as RSC-4 and BD-Coat were applied in amounts of 0.3, 0.5, 0.7, 0.9, and $1.1l/m^2$ to determine the optimal application rate. In order to evaluate the bond strength characteristics with temperature changes, a pull-off test was carried out at -15, 0, 20, and $40^{\circ}C$. In addition, the bond failure shapes were analyzed using an image analysis program after the pull-off tests were completed. RESULTS : The test results indicated that the optimal application rate of RSC-4 and BD-Coat were $0.8l/m^2$, $0.9l/m^2$, respectively. The core size effect was determined to be negligible because the bond strengths were similar in specimens with diameters of 50 mm and 100 mm. The bond strengths of RSC-4 and BD-Coat were found to decrease significantly when the temperature increased. As a result of the bonding failure shape in low-temperature conditions such as -15, 0, and $20^{\circ}C$, it was found that most of the debonding occurred at the interface between the tack coat and RCC surface. On the other hand, the interface between the HMA and tack coat was weaker than that between the tack coat and RCC at a high temperature of $40^{\circ}C$. CONCLUSIONS : This study suggested an optimal application rate of tack coat materials to apply to RCC-base composite pavement. The bond strengths at high temperatures were significantly lower than the required bond (tensile) strength of 0.4 MPa. It was known that the temperature was a critical factor affecting the bond strength at the interface of the RCC-base composite pavement.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.1-10
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• 2016

The use of materials for modern lightweight auto-bodies is becoming more complex than hitherto assemblies. The high strength materials nowadays frequently used for more specific fields such as the front and rear sub frames, seat belts and seats are mounted to the assembled body structure using bolt joints. It is desirable to use nuts attached to the assembled sheets by projection welding to decrease the number of loose parts which improves the quality. In this study, nut projection welding was carried out between a nut of both boron steel and carbon steel and ultra-high strength hot-stamped steel sheets. Then, the joints were characterized by optical and scanning electron microscope. The mechanical properties of the joints were evaluated by microhardness measurements and pullout tests. An indigenously designed sample fixture set-up was used for the pull-out tests to induce a tensile load in the weld. The fractography analysis revealed the dominant interfacial fracture between boron steel nut weld which is related to the shrinkage cavity and small size fusion zone. A non-interfacial fracture was observed in carbon steel nut weld, the lower hardness of HAZ caused the initiation of failure and allowed the pull-out failure which have higher in tensile strengths and superior weldability. Hence, the fracture load and failure mode characteristics can be considered as an indication of the weldability of materials in nut projection welding.

• Journal of Industrial Technology
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• v.24 no.A
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• pp.165-171
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• 2004

Latex modification of concrete provides the material with higher flexural strength, as well as high bond strength and reduced water permeability. However, If the thermal expansion properties of overlay concrete (latex-modified concretes) are big different from that of substrate (ordinary portland cement concrete), these would cause a big interfacial stresses and result in premature failure. Therefore, the purposes of this study were to investigate thermal expansion characteristics of latex-modified concrete with cement types. The result of thermal expansion showed the coefficient of thermal expansion of concretes increased with latex inclusion. The coefficient of thermal expansion of RSLMC was a little smaller than that of LMC, which might be due to the finer cement grain, compacter internal, and stiffer properties of concrete. However, the coefficients of LMC and RSLMC were quite similar to that of ordinary cement concrete. Thus, this would not cause an interfacial stresses and will enable to ensure long-term performance of concrete bridge deck overlays.