• Composites Research
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• v.33 no.6
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• pp.377-382
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• 2020

The free vibration characteristics of corrugated laminated composite plates with axial stiffeners is investigated using the Rayleigh-Ritz method. The plate is stiffened by beams with open cross-section area. The equivalent homogenization model is used for the corrugated laminated composite plates. This homogenization model is treated a corrugated plate as an orthotropic plate that has different material properties in two perpendicular directions. The motion of equivalent plate is represented on the basis of the first order shear deformation theory (FSDT) to account for the effect of rotary inertia and transverse shear deformation. Stiffeners are considered as discrete elements to predict the local vibration mode to be generated by the presence of stiffeners. To validate the proposed analytical approach, natural frequencies and vibration mode shapes from the analytical method are compared with those from the FEA by ANSYS.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.241-250
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• 2007

In case of retrofitting a concrete structure subjected to blast load by using retrofit materials such as FRP (fiber-reinforced polymer), appropriate ductility as well as raising stiffness must be obtained. But the previous approximate and simplified models, which have been generally used in the design and analysis of structures subjected to blast load, cannot accurately consider effects on retrofit materials. Problems on the accuracy and reliability of analysis results have also been pointed out. In addition, as the response of concrete and reinforcement on dynamic load is different from that on static load, it is not appropriate to use material properties defined in the previous static or quasi-static conditions to in calculating the response on the blast load. In this study, therefore, an accurate HFPB (high fidelity physics based) finite element analysis technique, which includes material models considering strength increase, and strain rate effect on blast load with very fast loading velocity, has been suggested using LS-DYNA, an explicit analysis program. Through the suggested analysis technique, the behavior on the blast load of retrofitted concrete walls using CFRP (carbon fiber-reinforced polymer) and GFRP (glass fiber-reinforced polymer) have been analyzed, and the retrofit capacity analysis has also been carried out by comparing with the analysis results of a wall without retrofit. As a result of the analysis, the retrofit capacity showing an approximate $26{\sim}28%$ reduction of maximum deflection, according to the retrofit, was confirmed, and it is judged ate suggested analysis technique can be effectively applicable in evaluating effectiveness of retrofit materials and techniques.

• Composites Research
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• v.12 no.5
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• pp.54-64
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• 1999

This study investigated the impact behaviors of the stitched sandwich composites under the low energy impact by the use of drop weight impact tester. These sandwich composites condidted of the glass fabric faces with a urethane foam core. The upper face and the lower face were stitched to combinr through the core thickness direction using the polyester reinforcements. Four types of the stitched sandwich composites, each having a different core thickness, were tested to determine the effects of the core thickness. The impact conditions were changes with the variations of the mass and drop height of the impact tup. The test results showed that the core thickness and the impact condidtions such as the drop height and the mass of the impact tup affected the impact force, the contact time, and the strain behaviors of the stitched sandwich composites. The stitched sandwich composites are able to avert the damage and also maintain the structural integrity even thouth the presence of the damage owing to the through-the-thickness reinforcements. However, it is important to improve the wetting ability of the stitched reinforcements so that the conventional structures are substituted for the stitched sandwich composites effectively.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.233-236
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• 2002

An efficient method was developed in this study to obtain optimal stacking sequences, thicknesses, and minimum weights of stiffened laminated composite shells under combined loading conditions and stiffener layouts using genetic algorithms (GAs) and finite element analyses. Among many parameters in designing composite laminates determining a optimal stacking sequence that may be formulated as an integer programming problem is a primary concern. Of many optimization algorithms, GAs are powerful methodology for the problem with discrete variables. In this paper the optimal stacking sequence was determined, which gives the maximum critical buckling load factor and the minimum weight as well. To solve this problem, both the finite element analysis by ABAQUS and the GA-based optimization procedure have been implemented together with an interface code. Throughout many parametric studies using this analysis tool, the influences of stiffener sizes and three different types of stiffener layouts on the stacking sequence changes were throughly investigated subjected to various combined loading conditions.

• Polymer(Korea)
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• v.24 no.4
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• pp.564-570
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• 2000

The waste FRP occured in the fabrication of SMC (sheet molding compound) bathtubs and the waste polyurethane foam occured in electronic manufacture and waste insulator were applied as a soundproof and light weight pannel in the waste FRP unsaturated polyester matrix resin composites to recycle. The effect of filler contents on the mechanical properties and interfacial phenomena of the filler and matrix on the composites was evaluated. The tensile strength of composites reached its maximum value of 82.34 MPa when the filler content was 70 wt%, and the more content of reinforcement is increased, the more tensile modulus was decreased. The flexural strength and modulus of composites, reinforced 70 wt% with filler content, were dominant compared to the other samples to 72.5 MPa, 958.4 MPa respectively. When composite of reinforced 70 wt% with filler content, it was confirmed that pull out phenomena and cracks did not occur in the interface of reinforcement and matrix resin through the SEM observation. Also, waste FRP and urethane foam were dispersed well into matrix resin as filler.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.53-59
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• 2018

This study analyzed the field applicability through the combination of environment-friendly grid-typed reinforcements and pre-mixed fiber with filler. The film of the grid-typed reinforcement is made by recycled PE resin. And, Ascon fiber is obtained the dispersion by pre-mixing of filler. To be able to recognize in advance the various circumstances that could arise in the construction of the road pavement layer, we conducted a basic field application test of the (Mock Up) pavement layer. As a result, it was found that the pavement with environment-friendly grid-typed reinforcement and dispersive fiber construction had improved strength, stress, and rutting resistance. It is consistent with the strength and stress results of the actual test of the mock up specimen. It is expected to perform an effective role in the safety as well as the use of environment-friendly fibers in actual construction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.630-648
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• 1992

The minimum weight design for simply-supported isotropic or symmetrically laminated stiffened cylindrical shells subjected to various loads (axial compression or combined loads) is studied by a nonlinear mathematical search algorithm. The minimum weight design in accomplished with the CONMIN optimizer by Vanderplaats. Several types of buckling modes with maximum allowable stresses and strains are included as constraints in the minimum weight design process, such as general buckling, panel buckling with either stingers or rings smeared out, local skin buckling, local crippling of stiffener segments, and general, panel and local skin buckling including stiffener rolling. The approach allows the consideration of various shapes of stiffening members. Rectangular, I, or T type stringers and rectangular rings are used for stiffened cylindrical shells. Several design examples are analyzed and compared with those in the previous literatures. The unstiffened glass/epoxy, graphite/epoxy(T300/5208), and graphite/epoxy aluminum honeycomb cylindrical shells and stiffened graphite/epoxy cyindrical shells under axial compression are analyzed through the present approach.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.246-250
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• 1999

항공기 날개 및 동체의 보강재로 사용되는 스트링거가 압축하중을 받게되면 플렌지와 웹에서의 부분좌굴이 발생하고 이는 좌굴이 발생하지 않은 부분에 과도한 하중이 걸리게 하여 스트링거의 전체적인 하중지지능력을 현저히 감소시킨다. 이러한 손상의 형태가 크리플링(Crippling)이다. (중략)

• Composites Research
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• v.35 no.4
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• pp.269-276
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• 2022

In this paper, a composite stiffened panel was fabricated using a three-dimensional weaving method that can reduce the risk of delamination, and mechanical properties such as buckling load and natural frequency were investigated. The preform of the stringer and skin of the stiffened panel were fabricated in one piece using T800 grade carbon fiber and then, resin (EP2400) was injected into the preform. The compression test and natural frequency measurement were performed for the stiffened panel, and the results were compared with the finite element analyses. In order to compare the performance of 3D weaving structures, the stiffened panels with the same configuration were fabricated using UD and 2D plain weave (fabric) prepregs. Compared to the tested buckling load of the 3D woven panel, the buckling loads of the stiffened panels of UD prepreg and 2D plain weave exhibited +20% and -3% differences, respectively. From this study, it was confirmed that the buckling load of the stiffened panel manufactured by 3D weaving method was lower than that of the UD prepreg panel, but showed a slightly higher value than that of the 2D plain weave panel.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.483-491
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• 2008

The effectiveness of a new fiber-steel composite plate designed specifically to be used for strengthening of reinforced concrete members has been investigated. Twelve reinforced concrete beams were tested. Seven of the beams were strengthened with carbon fiber-steel composite plate(CSP), four of the beams were strengthened with glass fiber-steel composite plate(GSP), and one beam was used as a control specimen. The experimental results showed that new strengthening system controls the premature debonding and provides a more ductile failure mode than other conventional strengthening systems. The observed ductility ratios were $3.01\sim3.81$ and $3.55\sim4.95$ for strengthened beam with CSP and GSP, respectively. The maximum load was increased by 115% and 107% for strengthened beam with CSP and GSP, respectively, comparing with control beam. In addition, experimental and analytical results were well agreed.