• Advanced Composite Materials
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• v.16 no.4
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• pp.283-298
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• 2007

Environment-friendly composites reinforced with bagasse fiber (BF), a kind of natural fiber as the remains from squeezed sugarcane, were fabricated by injection molding and press molding. As appropriate matrices for injection molding and press molding, polypropylene (PP) and polycaprolactone-cornstarch (PCL-C) were selected, as a typical recyclable resin and biodegradable resin, respectively. The mechanical properties of BF/PP composites were investigated in view of fiber mass fraction and injection molding conditions. And the mechanical properties and the biodegradation of BF/PCL composites were also evaluated. In the case of injection molding, the flexural modulus increased with an increase in fiber mass fraction, and the mechanical properties decreased with an increase in cylinder temperature due to the thermal degradation of BF. The optimum conditions increasing the flexural properties and the impact strength were $90^{\circ}C$ mold temperature, 30 s injection interval, and in the range of 165 to $185^{\circ}C$ cylinder temperature. On the other hand, as to BF/PCL-C fully-green composites, both the flexural properties and the impact strength increased with an increase in fiber mass fraction. It is considered that the BF compressed during preparation could result in the enhancement in mechanical properties. The results of the biodegradability test showed the addition of BF caused the acceleration of weight loss, which increased further with increasing fiber content. This reveals that the addition and the quantities of BF could promote the biodegradation of fully-green composites.

• Structural Engineering and Mechanics
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• v.21 no.6
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• pp.737-765
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• 2005

This paper presents a theoretical model for the behavior of partially confined axi-symmetric reinforced concrete members subjected to axial load. The analysis uses the theories of elasticity and plasticity to cover the full range of the concrete behavior. Analysis of the elastic range of the problem involves boundary conditions that are defined along a relatively simple geometry. However, extending the analysis into the plastic range involves difficulties that arise from the irregular geometry of the boundary between the plastic zone and the elastic zone, a boundary which is also changing as the axial load increases. The solution is derived by replacing the discrete steel ties with an equivalent tube of thickness $t_{eq}$ and by analyzing the concrete cylinder, which is uniformly confined by the equivalent tube. The equivalency criterion initiates from a theoretical analysis of the problem in its elastic range where further finite element analysis shows that this criterion is valid also for the plastic range of the cylinder material. According to the proposed model, the efficiency of the lateral reinforcement can be evaluated by the equivalent thickness $t_{eq}$. Comparison with published test results of confined reinforced concrete stress-strain curves shows good agreement between the test and the analytical results.

• Computers and Concrete
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• v.27 no.3
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• pp.225-239
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• 2021

Carbon fiber reinforced polymer (CFRP) has extensive use in strengthening reinforced concrete structures due to its high strength and elastic modulus, low weight, fast and easy application, and excellent durability performance. Many studies have been carried out to determine the performance of the CFRP confined concrete cylinder. Although studies about the prediction of confined compressive strength using ANN are in the literature, the insufficiency of the studies to predict the strain of confined concrete cylinder using ANN, which is the most appropriate analysis method for nonlinear and complex problems, draws attention. Therefore, to predict both strengths and also strain values, two different ANNs were created using an extensive experimental database. The strength and strain networks were evaluated with the statistical parameters of correlation coefficients (R2), root mean square error (RMSE), and mean absolute error (MAE). The estimated values were found to be close to the experimental results. Mathematical equations to predict the strength and strain values were derived using networks prepared for convenience in engineering applications. The sensitivity analysis of mathematical models was performed by considering the inputs with the highest importance factors. Considering the limit values obtained from the sensitivity analysis of the parameters, the performances of the proposed models were evaluated by using the test data determined from the experimental database. Model performances were evaluated comparatively with other analytical models most commonly used in the literature, and it was found that the closest results to experimental data were obtained from the proposed strength and strain models.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.441-456
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• 2016

This work reports wave propagation in the nanocomposite cylinders that reinforced by straight single-walled carbon nanotubes based on a mesh-free method. Moving least square shape functions have been used for approximation of displacement field in weak form of motion equation. The straight carbon nanotubes (CNTs) are assumed to be oriented in specific or random directions or locally aggregated into some clusters. In this simulation, an axisymmetric model is used and also the volume fractions of the CNTs and clusters are assumed to be functionally graded along the thickness. So, material properties of the carbon nanotube reinforced composite cylinders are variable and estimated based on the Eshelby-Mori-Tanaka approach. The effects of orientation, aggregation and volume fractions of the functionally graded clusters and CNTs on dynamic behavior of nanocomposite cylinders are studied. This study results show that orientation and aggregation of CNTs have significant effects on the effective stiffness and dynamic behaviors.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.290-297
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• 2002

Vibration experiments have been performed to observe the analytic characteristics of power How finite element method(PFFEM) for the reinforced cylindrical structure. For this, the vibration experimental results are compared with the numerical solutions obtained by PFFEM in medium-to-high frequency ranges. Input Power into the experimental structure is measured using the impedance head adhered to the exciter, and that input power is used for the vibration analysis. Using the developed PFFEM program(PFADS), the reinforced cylindrical structure modeled by beam and plate elements is analyzed, and very reliable results for PFFEM are obtained by the comparisons of the experimental results.

• 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.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.137-140
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• 2005

Resin transfer molding (RTM) is one of the most popular processes for producing fiber reinforced polymer composites. In the manufacture of complex thick composite structures, analysis on flow front advancement on the resin impregnating the multi-layered fiber preform is helpful for the optimization of the process. In this study, three-dimensional mold filling simulation of RTM is carried out by using CVFEM (Control Volume Finite Element Method). On the assumption of isothermal flow of Newtonian fluid, Darcy’s law and continuity equation are used as governing equations. Different permeability tensors employed in each layer are obtained by experiments. Numerically predicted flow front is compared with experimental one in order to validate the numerical results. Flow simulations are conducted in the two mold geometries, rectangular plate and hollow cylinder. Permeability tensor of each layer preform in Cartesian coordinate system is transformed to cylinder coordinates system so that the flow within the multi-layered preforms of the hollow cylinder can be calculated exactly. Our emphasis is on the three dimensional flow analysis for circular three-dimensional braided preform, which shows outstanding mechanical properties such as high impact strength and toughness compared with other conventional two-dimensional laminar-structured preforms.

• KSTLE International Journal
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• v.8 no.2
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• pp.29-34
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• 2007

Recently, requirements relating to performance, environment and noise in the oil hydraulic system of the heavy construction equipment have been reinforced continuously. In order to solve these technical trends, studies on the system compactness, operation under high pressure and great rotating speed, electronic control, substitute oil, and noise reduction have been progressed briskly. Among these recent studies, the system operation under high pressure is quite difficult to carry into effect due to mechanical limitations; that is, for realizing the system operation in the hydraulic pump under high pressure, the improvements or innovations on the design techniques, the manufacturing techniques, and the lubrication performance of the working oil are required. Accordingly, in this study, the stress distribution and optimum design factors under the maximum pressure were discussed by using stress analysis on the cylinder block of the hydraulic axial piston pump, which is one of the most important relative sliding regions.

• Architectural research
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• v.17 no.1
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• pp.41-48
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• 2015

Early investigations focused mainly on manipulating the confinement effect to develop a reinforced concrete column with lateral hoops. Based on this legacy model, Li's model incorporated the additional confinement effect of a steel jacket. However, recent experiments on plain concrete cylinders with steel jackets revealed relatively large discrepancies in the estimates of strength enhancement and the post-peak behavior. Here, we describe a modified constitutive law for confined concrete with an unbonded external steel jacket in terms of three regions for the loading stage. We used a two-phase heterogeneous concrete model to simulate the uniaxial compression test of a $150mm{\times}300mm$ concrete cylinder with three thicknesses of steel jackets: 1.0 mm, 1.5 mm, and 2.0 mm. The proposed constitutive model was verified by a series of finite element analyses using a finite element program. The damaged plasticity model and extended Drucker-Prager model were applied and compared in terms of the level of pressure sensitivity for confinement in 3D. The proposed model yielded results that were in close agreement with the experimental results.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.143-144
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• 2016

The core drilling method is considered to be the most effective and common method of assessing the compressive strength of concrete in existing reinforced concrete buildings for structural repair and retrofit. In general, core specimens within reinforcing bars are not permitted in the regulations with regard to assessing concrete strength even if the core specimens can contain the bars in some cases. The purpose of this study is to investigate the effects of the reinforcement arrangement on the concrete compressive strength as a basic research to propose the quantitative criteria of strength for core specimens containing reinforcements. To complete the basic research, cylinder specimens inserted in a variety of reinforcement arrangements were prepared and tested.