• Journal of Aerospace System Engineering
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• 제8권3호
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• pp.41-46
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• 2014

Fatigue evaluations for the rotor blades of commercial or military rotorcraft have been carried out using the safe life concept since 1950s. Particularly, in the case of a rotor blade made of a composite material, a highly reliable fatigue life could be predicted by evaluation the cumulative damage using combination of fatigue life curve and load spectrum. However, there is a limit in adequately evaluating the strength reducing phenomena caused by damages or defects generated during the manufacturing process or impact damage induced by operational usages, using only the safe life concept. In this study, the fatigue evaluation process based on the damage tolerance concept is described and illustrated by means of successful application to substantiate the retirement time of composite rotor blades.

• Proceedings of the Korean Society For Composite Materials Conference
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.115-118
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• 2000

The development of high-strength fibers such as boron/epoxy and carbon/epoxy and adhesives has made it possible to repair cracked metallic plates by bonding reinforcing patches to the plate over the crack. In this study, aluminum 6061-T6 alloy plates with the high strength are applied to specimens with a cracked bolt hole to study the effect of diverse patch materials on the fatigue behavior of this structure. Additionally, the observation of the effort of different patch sizes on the specimen was performed. The results shows that the patch repair can improve the static strength by about 17% and the fatigue life by 200% compared with non-repaired case. And it was also revealed that the patching method along to crack growth direction is mort efficient in cost and weight reduction.

• Steel and Composite Structures
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• 제20권6호
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• pp.1173-1182
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• 2016

The objective of this work was to evaluate the ductile cracked structures with bonded composite patch used in probabilistic elastic plastic fracture mechanics subjected to tensile load. The finite element method is used to analyze the stress intensity factors for elastic case, the effect of cracks and the thickness of the patch ($e_r$) are presented for calculating the stress intensity factors. For elastic-plastic the Monte Carlo method is used to predict the distribution function of the mechanical response. According to the obtained results, we note that the stress variations are important factors influencing on the distribution function of (J/Je).

• Steel and Composite Structures
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• 제12권2호
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• pp.129-147
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• 2012

In this paper, the thermal buckling analysis of rectangular composite laminated plates is investigated using the Differential Quadrature (DQ) method. The composite plate is subjected to a uniform temperature distribution and arbitrary boundary conditions. The analysis takes place in two stages. First, pre-buckling forces due to a temperature rise are determined by using a membrane solution. In the second stage, the critical temperature is predicted based on the first-order shear deformation theory. To verify the accuracy of the method, several case studies were used and the numerical results were compared with those of other published literatures. Moreover, the effects of several parameters such as aspect ratio, fiber orientation, modulus ratio, and various boundary conditions on the critical temperature were examined. The results confirm the efficiency and accuracy of the DQ method in dealing with this class of engineering problems.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1541-1547
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• 2006

An efficient procedure to obtain the optimal stacking sequence and the minimum weight of stiffened laminated composite curved panels under several loading conditions and stiffener layouts has been developed based on the finite element method and the genetic algorithm that is powerful for the problem with integer variables. Often, designing composite laminates ends up with a stacking sequence optimization that may be formulated as an integer programming problem. This procedure is applied for a problem to find the stacking sequence having a maximum critical buckling load factor and the minimum weight. The object function in this case is the weight of a stiffened laminated composite shell. Three different types of stiffener layouts with different loading conditions are investigated to see how these parameters influence on the stacking sequence optimization of the panel and the stiffeners. It is noticed from the results that the optimal stacking sequence and lay-up angles vary depending on the types. of loading and stiffener spacing.

• Journal of the Korean Wood Science and Technology
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• 제21권2호
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• pp.31-37
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• 1993

Composites of styrene polymers with woody fibers were prepared, and the effect of compatibilizers on their mechanical properties was evaluated. To improve the compatibility of wood fibers and the matrix polymers, styrene-maleic anhydride copolymer(SMA) and maleic anhydride-modified polymers were used as compatibilizers. As results, maleic anhydride-modified polystyrene and SMA were proved to improve the tensile strength of the molded composites, and also were evaluated as good compatibilizers for the wood fiber polystyrene composite. Cellulosic fiber (dissolving pulp) provided better reinforcement than lignocellulosic fiber(thermomechanical pulp). On the contrary in the case of the composite of wood fiber and acrylonitrile-butadiene styrene copolymer(ABS), SMA and maleic anhydride-modified acrylonitrile-butadiene-styrene copolymer(MABS) did not act as compatibilizers. However, MABS was evaluated as a good polymer matrix to make wood fiber reinforced composite. The tensile properties of the composites of wood fiber and MABS were superior than those of wood fiber-ABS composites.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제13권6호
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• pp.423-429
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• 2003

On this study. we improved the efficiency applying algorithm that is repeatedly using table of orthogonal array in discrete design space and filling a defect of gradient method in continuous design space. we showed optimal ply angle that maximized 1st natural frequency of CFRP laminated composite plate without a hole and with a hole by each aspect ratio. In the case of CFRP laminated composite plate without a hole, we confirmed the reliance and efficiency of algorithm in comparison with the result of optimization achievement repeatedly using statistical table of orthogonal array of experimental design and the BFGS optimal design method.

• Steel and Composite Structures
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• 제29권4호
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• pp.493-508
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• 2018

Free vibration analysis of super-elliptical composite thin plates was investigated. Plate is formed by symmetrical quasi-isotropic laminates. Rayleigh-Ritz method was used for parametric analysis based on the governing differential equations of Classical Laminated Plate Theory (CLPT). Simply supported and clamped boundary conditions at the periphery of plates were considered. Parametric study was performed for the effect of different lamination type, aspect ratio, thickness and super-elliptical power on natural frequencies. Convergence study and validation of isotropic case were achieved. A number of design parameters like different dimensions, structure systems, panel sizes, panel thicknesses, lamination sequences, boundary conditions and loading conditions must be considered in the production of composite ships. The number of possible combinations practically may be so high that a parametric study should be carried out in order to determine the optimum design parameters rapidly during the preliminary design stage. The use of Rayleigh-Ritz method could make this parametric study possible. Thereby it might be decreasing the consumption of time, material and labor. Certain results for some different super-elliptical powers presented in tabulated form in Appendix for designers as well.

• Steel and Composite Structures
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• 제19권2호
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• pp.503-519
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• 2015

This paper presents an optimization process using Genetic Algorithm (GA) for minimum weight by selecting suitable standard sections from a specified list taken from American Institute of Steel Construction (AISC). The stress constraints obeying AISC-LRFD (American Institute of Steel Construction-Load and Resistance Factor Design), lateral displacement constraints being the top and inter-storey drift, mid-span deflection constraints for the beams and geometric constraints are considered for optimum design by using GA that mimics biological processes. Optimum designs for three different space frames taken from the literature are carried out first without considering concrete slab effects in finite element analyses for the constraints above and the results are compared with the ones available in literature. The same optimization procedures are then repeated for the case of space frames with composite (steel and concrete) beams. A program is coded in MATLAB for the optimization processes. Results obtained in the study showed that consideration of the contribution of the concrete on the behavior of the floor beams results with less steel weight and ends up with more economical designs.

• Journal of the Korea Concrete Institute
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• 제27권5호
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• pp.501-510
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• 2015

Composite construction of precast concrete and cast-in-place concrete is currently used for the modular construction. In this case, the use of steel fiber reinforced concrete (SFRC) could be beneficial for precast concrete. However, the shear strength of such composite members (SFRC and cast-in-place concrete) is not clearly defined in current design codes. In the present study, steel fiber composite beam tests were conducted to evaluate the effect of steel fibers on the composite members. The test variables are the area ratio of SFRC and shear reinforcement ratio. The test results showed that when minimum horizontal shear reinforcement was used, the shear strength of composite beams increased in proportion to the area ratio of steel fiber reinforced concrete. However, because of the steel fiber, the composite beams were susceptible to horizontal shear failure. Thus, minimum horizontal shear reinforcement is required for SFRC composite beams.