• Computers and Concrete
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• v.24 no.4
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• pp.369-378
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• 2019

This paper aims to present an analytical model to predict the static analysis of laminated reinforced composite plates subjected to sinusoidal and uniform loads by using a simple first-order shear deformation theory (SFSDT). The most important aspect of the present theory is that unlike the conventional FSDT, the proposed model contains only four unknown variables. This is due to the fact that the inplane displacement field is selected according to an undetermined integral component in order to reduce the number of unknowns. The governing differential equations are derived by employing the static version of principle of virtual work and solved by applying Navier's solution procedure. The non-dimensional displacements and stresses of simply supported antisymmetric cross-ply and angle-ply laminated plates are presented and compared with the exact 3D solutions and those computed using other plate theories to demonstrate the accuracy and efficiency of the present theory. It is found from these comparisons that the numerical results provided by the present model are in close agreement with those obtained by using the conventional FSDT.

• Advances in nano research
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• v.12 no.2
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• pp.117-137
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• 2022

Effect of thickness stretching on free vibration, bending and buckling behavior of carbon nanotubes reinforced composite (CNTRC) laminated nanoplates rested on new variable elastic foundation is investigated in this paper using a developed four-unknown quasi-3D higher-order shear deformation theory (HSDT). The key feature of this theoretical formulation is that, in addition to considering the thickness stretching effect, the number of unknowns of the displacement field is reduced to four, and which is more than five in the other models. Two new forms of CNTs reinforcement distribution are proposed and analyzed based on cosine functions. By considering the higher-order nonlocal strain gradient theory, microstructure and length scale influences are included. Variational method is developed to derive the governing equation and Galerkin method is employed to derive an analytical solution of governing equilibrium equations. Two-dimensional variable Winkler elastic foundation is suggested in this study for the first time. A parametric study is executed to determine the impact of the reinforcement patterns, nonlocal parameter, length scale parameter, side-t-thickness ratio and aspect ratio, elastic foundation and various boundary conditions on bending, buckling and free vibration responses of the CNTRC plate.

• Advances in nano research
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• v.15 no.2
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• pp.175-189
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• 2023

The under-evaluation structure includes a functionally graded porous (FGP) core which is confined by two piezoelectric carbon nanotubes reinforced composite (CNTRC) layers. The whole structure rests on the Pasternak foundation. Using quasi-3D hyperbolic shear deformation theory, governing equations of a sandwich plate are driven. Moreover, face sheets are subjected to the electric field and the whole model is under thermal loading. The properties of all layers alter continuously along with thickness direction due to the CNTs and pores distributions. By conducting the current study, the results emerged in detail to assess the effects of different parameters on buckling of structure. As instance, it is revealed that highest and lowest critical buckling load and consequently stiffness, is due to the V-A and A-V CNTs dispersion type, respectively. Furthermore, it is revealed that by porosity coefficient enhancement, critical buckling load and consequently, stiffness reduces dramatically. Current paper results can be used in various high-tech industries as aerospace factories.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.2
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• pp.46-51
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• 2015

Since it is impossible to predict earthquakes, they involve more casualties and property damage compared to meteorological disasters such as heavy snow and heat waves, which can be predicted through weather forecasts. This has highlighted the need for seismic design and reinforcement. Recently, the use of composite materials as reinforcement has surged because steel plate reinforcement and section enlargement are likely to result in increased weight and physical damage to structures. This study evaluates the seismic performance of panels created from composite materials, and their guide systems. The specimens were miniature versions of actual steel structures, and displacement loads were applied in the transverse direction. Seismic performance was found to improve when structures were reinforced with seismic panels.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.461-466
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• 2013

Advanced fiber-reinforced laminated composites are widely used in various fields of engineering to reduce weight. The material property of each ply is well known; specifically, it is known that ply is less reliable than metallic materials and very sensitive to the loading direction. Therefore, it is important to consider this uncertainty in the design of laminated composites. In this study, reliability analysis is conducted using COMSOL and MATLAB interactions for a laminated composite plate for the case in which the tip deflection is the design requirement and the material property is a random variable. Furthermore, the efficiency and accuracy of the approximation method is identified, and a probabilistic sensitivity analysis is conducted. As a result, we can prove the applicability of the advanced design method for the stabilizer of an underwater vehicle.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.160-166
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• 1994

In general, the problems of strengthening and repairing of deteriorated or damaged reinforced concrete members are usually worked out in situ by externally bounding steel plates using epoxy resins, which has been recognized to be one of effective and convenient methods. But the disadvantages of strengthening/repairing concrete members with externally bonded steel plates include ; (a) deterioration of the bond at the steel-concrete interface caused by the corrosion of steel ; (b) difficulty in manipulating the plate at the construction site ; (c) improper formation of joints, due to the limited delivery lengths of the steel plates ; and etc. Therefore these difficulties eventually have led to the concept of replacing the steel plates by fiber-reinforced composite sheets which are characterized by their light weight, extremely high stiffness, excellent fatigue properties, and outstanding corrosion resistance. In the paper, for the reliability assessment of reinforced concrete beams externally strengthened by carbon fiber plastic(CFRP) laminates, an attempt is made to suggest a limit state model based on the strain compatibility method and the concept of fracture mechanics. And the reliability of the proposed models is evaluated by using the AFOSM method. The load carrying capacity of the deteriorated and/or damaged RC beams is considerably increased. Thus, it may be stated that the post-strengthening of concrete beams with externally bonded CFRP materials may be one of very effective way of increasing the load carrying capacity and stiffeness characteristics of existing structures.

• Structural Engineering and Mechanics
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• v.40 no.1
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• pp.105-120
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• 2011

The strengthening and rehabilitation of reinforced concrete structures with externally bonded carbon fibre reinforced polymer (FRP) laminates has shown excellent performance and, as a result, this technology is rapidly replacing steel plate bonding techniques. This paper addresses this issue, and presents results deals with the influence of external bonded CFRP-reinforcement on the time-dependent behavior of reinforced concrete beams. A total of eight reinforced concrete beams with cracked and un-cracked section, with and without externally bonded CFRP laminates, were investigated for their creep and shrinkage behavior. All the beams considered in this paper were simply supported and subjected to a uniform sustained loading for the period of six months. The main parameters of this study are two types of sustained load and different degrees of strengthening scheme for both cracked and un-cracked sections of beams. Both analytical and experimental work has been carried out on strengthened beams to investigate the cracking and deflection performance. The applied sustained load was 56% and 38% of the ultimate static capacities of the un-strengthened beams for cracked and un-cracked section respectively. The analytical values based on effective modulus method (EMM) are compared to the experimental results and it is found that the analytical values are in general give conservative estimates of the experimental results. It was concluded that the attachment of CFRP composite laminates has a positive influence on the long term performance of strengthened beams.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1238-1245
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• 1988

Friction and wear characteristics of short fiber reinforced and particulate filled composites were investigated experimentally. Two kinds of fiber composites, chopped graphite fiber reinforced PAI(polyamide-imide) and glass fiber reinforced PAI, and a particulate composite, TiO$_{2}$ powder filled PAI, were selected for the friction and wear test since these are important engineering materials based on a new high temperature engineering plastic. All the specimens were cut into proper size for cylinder-on-plate type wear test. Frictional forces were measured by employing a load transducer and wear rates were calculated by measuring weight loss during wear test. The experimental results are reported in this paper and carefully discussed to explain the friction and wear behavior qualitatively. The frictional behavior is interpreted by considering four basic friction components which are believed to the genesis of friction and the wear behavior is explained by applying delamination theory of wear.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.171-178
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• 2019

Fiber-reinforced polymer (FRP) composites have proved to be reliable as strengthening materials. Most of existing studies used single types of FRP composites. Therefore, in this experimental study, carbon FRP sheet, aramid FRP sheet, and hybrid FRP plate including glass fibers were fabricated, and the effect of pre-stressed FRP composites on flexural strengthening of reinforced concrete (RC) beams was investigated. In total, eight RC beam specimens were fabricated, including one control beam (specimen N) without FRP composites and seven FRP-strengthened beams. The main parameters were type of FRP composite, the number of anchors used for pre-stressing, and thickness of FRP plates. As a result, the beam strengthened with pre-stressed FRP plate showed superior performance to the non-strengthened one in terms of initial strength, strength and stiffness at yielding, and ultimate strength. As the number of anchors and thickness of FRP plate (i.e., amount of FRP plates) increased, the strengthening effect increased as well. When hybrid FRP plates were pre-stressed, the strengthening effect was higher in comparison with pre-stressed single type FRP plate.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.215-221
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• 2017

An electromagnetic (EM) wave absorber reduces the possibility of radar detection by minimizing the radar cross section (RCS) of structures. In this study, a radar absorbing structure (RAS) was applied to the leading edge of a blended wing body aircraft to reduce RCS in X-band (8.2~12.4GHz) radar. The RAS was composed of a periodic pattern resistive sheet with conductive lossy material and glass-fiber/epoxy composite as a spacer. The applied RAS is a multifunctional composite structure which has both electromagnetic (EM) wave absorbing ability and load-bearing ability. A two dimensional unit absorber was designed first in a flat-plate shape, and then the fabricated leading edge structure incorporating the above RAS was investigated, using simulated and free-space measured reflection loss data from the flat-plate absorber. The leading edge was implemented on the aircraft, and its RCS was measured with respect to various azimuth angles in both polarizations (VV and HH). The RCS reduction effect of the RAS was evaluated in comparison with a leading edge of carbon fabric reinforced plastics (CFRP). The designed leading edge structure was examined through static structural analysis for various aircraft load cases to check structural integrity in terms of margin of safety. The mechanical and structural characteristics of CFRP, RAS and CFRP with RAM structures were also discussed in terms of their weight.