• 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.

• Magazine of the Korean Society of Agricultural Engineers
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• v.36 no.3
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• pp.74-83
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• 1994

A series of isotropic consolidation tests, undrained and drained triaxial compression tests was carried out to investigate the physical characteristics and behaviours of marine silty sands collected from the western coast of Korea. This study also included a theoretical development of the constitutive equation to evaluate stress-strain relationship and volume change of silty sands. The results and main conclusions of the study are summarized as follows; 1. Isotropic compression and swelling index are linearly decreased with an increase in relative density. 2. Both undrained shear strengh and elastic modulus are increased with an increase in relative density and confining pressure. 3. Internal friction angles obtained from drained and undrained compression tests of the soils are proportional to relative density. 4. The phenomenon of dilatancy of each sample is less profound when confining stress is increased but more profound when relative density is increased. 5. The slope of critical state lines is 1.78 for Saemangum, 1.70 for Siewha and 1.26 for Sukmoon sands. 6. In this study, Drucker-Praper type criterion is used and hardening function of Cap model is modified by hyperbolic fuction. This will improve a lack of physical meaning of hardening parameters in conventional Cap model. 7. A newly developed constitutive equation to the forementioned silty sands and checked its applicability. This is in good agreement with the measured data.

• Korean Journal of Materials Research
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• v.21 no.12
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• pp.650-654
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• 2011

In this paper, the effects of conventional and newly developed elastomer modified underfill materials on the mechanical shock reliability of BGA board assembly were studied for application in mobile electronics. The mechanical shock reliability was evaluated through a three point dynamic bending test proposed by Motorola. The thermal properties of the underfills were measured by a DSC machine. Through the DSC results, the curing condition of the underfills was selected. Two types of underfills showed similar curing behavior. During the dynamic bending reliability test, the strain of the PCB was step increased from 0.2% to 1.5% until the failure circuit was detected at a 50 kHz sampling rate. The dynamic bending reliability of BGA board assembly using elastomer modified underfill was found to be superior to that of conventional underfill. From mechanical and microstructure analyses, the disturbance of crack propagation by the presence of submicron elastomer particles was considered to be mainly responsible for that result rather than the shear strength or elastic modulus of underfill joint.

• Structural Engineering and Mechanics
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• v.67 no.2
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• pp.165-173
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• 2018

A simple predicted model using a modified Shear-lag method was used to represent the moisture absorption effect on the stiffness degradation for $[0/90]_{2s}$ composite laminates with transverse cracks and under flexural loading. Good agreement is obtained by comparing the prediction model and experimental data published by Smith and Ogin (2000). The material properties of the composite are affected by the variation of temperature and moisture absorption. The transient and non-uniform moisture concentration distribution give rise to the transient elastic moduli of cracked composite laminates. The hygrothermal effect is taken into account to assess the changes in the normalised axial and flexural modulus due to transverse crack. The obtained results represent well the dependence of the stiffness properties degradation on the cracks density, moisture absorption and operational temperature. The composite laminate with transverse crack loaded in axial tension is more affected by the hygrothermal condition than the one under flexural loading. Through this theoretical study, we hope to contribute to the understanding of the moisture absorption on the composite materials with matrix cracking.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.3
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• pp.53-59
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• 2021

In vibration-free vehicles such as limousine buses, the vibration is minimized by installing an air spring instead of the leaf spring used in the existing freight cars to prevent the damage to the loaded cargo from shocks generated during movement. In the existing vehicles, steel structures support the air spring system. This study was aimed at replacing the steel structures used in the Z-spring by carbon fiber and glass fiber reinforced plastics. In addition, the mechanical properties (elastic modulus, tensile strength, and shear strength) of carbon fiber and glass fiber prepreg were derived using specimens molded with the corresponding prepreg. The final goal was to develop a material lighter than the conventional steel material but with enhanced mechanical properties. Although the CF prepreg exhibited excellent mechanical properties, the production cost was extremely high. To overcome this limitation, hybrid composites with GF prepreg were examined, which are expected to be promising future materials.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2408-2417
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• 2022

The nanoindentation behavior of P92 steel with thermomechanical treatment under 3.5 MeV Fe¹³⁺ ion irradiation at room temperature, 400 and 700 ℃ was investigated. Pop-in behavior is observed for all the samples with and without irradiation at room temperature, while the temperature dependence of pop-in behavior is only observed in irradiated samples. The average load and penetration depth at the onset of pop-in increase as the irradiation temperature increases, in line with the results of the maximum shear stress. Irradiation induced hardening is exhibited for all irradiated samples, but there is a significant reduction in the hardness of sample irradiated at 700 ℃ in comparison to the samples irradiated at room temperature and 400 ℃. The ratio of hardness to elastic modulus for all samples decreases with increasing penetration depth except for samples at 700 ℃. With the increasing of irradiation temperature, the ratio of the irreversible work to the total work gradually decreases. In contrast, it increases for samples without irradiation.

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.173-189
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• 2023

For a given structural geometry, the stiffness and damping parameters of the soil and the dynamic response of the structure may change in the face of an equivalent linear soil behavior caused by a strong earthquake. Therefore, the influence of equivalent linear soil behavior on the impedance functions form and the seismic response of the soil-structure system has been investigated. Through the substructure method, the seismic response of the selected structure was obtained by an analytical formulation based on the dynamic equilibrium of the soil-structure system modeled by an analog model with three degrees of freedom. Also, the dynamic response of the soil-structure system for a nonlinear soil behavior and for the two types of impedance function forms was also analyzed by 2D finite element modeling using ABAQUS software. The numerical results were compared with those of the analytical solution. After the investigation, the effect of soil nonlinearity clearly showed the critical role of soil stiffness loss under strong shaking, which is more complex than the linear elastic soil behavior, where the energy dissipation depends on the seismic motion amplitude and its frequency, the impedance function types, the shear modulus reduction and the damping increase. Excellent agreement between finite element analysis and analytical results has been obtained due to the reasonable representation of the model.

• Transactions of Materials Processing
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• v.32 no.6
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• pp.367-375
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• 2023

Composite materials, known for their excellent mechanical properties and lightweight characteristics, are applied in various engineering fields. Recently, efforts have been made to develop an automotive battery protection panel using a plain-woven composite composed of glass fiber and polypropylene to reduce the weight of automobiles. However, excessive warpage occurs during the GF/PP compression molding process, which makes car assembly challenging. This study aims to develop a model that predicts the warpage during the compression molding process. Obtaining out-of-plane properties such as elastic or shear modulus, essential for predicting warpages, is tricky. Existing mechanical methods also have limitations in calculating these properties for woven composite materials. To address this issue, finite element analysis is conducted using representative volume elements (RVE) for woven composite materials. A warpage prediction model is developed based on the estimated physical properties of GF/PP composite materials obtained through representative volume elements. This model is expected to be used for reducing warpages in the compression molding process.

• Journal of Korean Society of Steel Construction
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• v.14 no.6
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• pp.803-811
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• 2002

Current composite steel and concrete bridges are designed using full-interaction theory assuming there is no relative slip, between the steel and concrete components along their interface, because of the complexities of partial-interaction analysis techniques. However, in the assessment of existing composite bridges this simplification may not be warranted as it is often necesary to extract the correct capacity and endurance from the structure. This may only be achieved using partial-interaction theory which tuly reflects the behaviour of the structure. In this paper, Parametric analyses have been carried out in order to confirm the partial-interaction curvatures with deflection effect using the finite element method. Therefore, the model is considered for simply supported steel and concrete composite bridges with a uniform distribution of connectors subjected to a single concentrated load. For the case studies, this study applicate a parameters such as the number and space of stud shear connector and elastic modulus of concrete slabs. From this study, it is known that partial-interaction effect was in the increase to the increasing the deflection of composite bridges, and stiffness and strength of slab concrete considering the occurrence of crack effect seriously to the partial-interaction behavior.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.2 s.17
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• pp.57-63
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• 2005

In case of general structures, it has been known that the strain amplitude band experienced by the base in a state of service load is less than 1% and most of the base show low, strain amplitude behavior less than 0.01%. In this study examining the influence affected to dynamic behavior in a condition of the low strain amplitude of unsaturated decomposed granite soils, the resonant column test, using some samples in Su-won area, has been performed for each degree of saturation resulted from different void ratios and confined stress. It is found out that the minimum value of the damping ratio occurred in roughly $17{\sim}18%$ according to void ratios regardless of confined pressure in the same manner with the case of the maximum shear elastic modulus; and it is estimated that for the influence of surface tension in the optimum degree of saturation, the damping ratio appears to be least.