• Applied Chemistry for Engineering
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• v.24 no.4
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• pp.363-369
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• 2013

In this work, the effects of ozone treatments on mechanical interfacial properties of carbon fibers-reinforced nylon-6 matrix composites were investigated. The surface properties of ozone treated carbon fibers were studied by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Mechanical interfacial properties of the composites were investigated using critical stress intensity factor ($K_{IC}$). The cross-section morphologies of ozone-treated carbon fiber/nylon-6 composites were observed by scanning electron microscope (SEM). As a result, $K_{IC}$ of the ozone-treated carbon fibers-reinforced composites showed higher values than those of as-received carbon fibers-reinforced composites due the enhanced $O_{1s}/C_{1s}$ ratio of the carbon fiber by the ozone treatments. This result concludes that the mechanical interfacial properties of nylon-6 matrix composites can be controlled by suitable ozone treatments on the carbon fibers.

• Polymer(Korea)
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• v.37 no.1
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• pp.61-65
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• 2013

In this work, the anodic oxidation of carbon fibers was carried out to enhance the mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites. The surface characteristics of the carbon fibers were studied by FTIR, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Also, the mechanical interfacial properties of the composites were studied with interlaminar shear strength (ILSS), critical stress intensity factor ($K_{IC}$), and critical strain energy release rate ($G_{IC}$). The anodic oxidation led to a significant change in the surface characteristics of the carbon fibers. The anodic oxidation of carbon fiber improved the mechanical interfacial properties, such as ILSS, $K_{IC}$, and $G_{IC}$ of the composites. The mechanical interfacial properties of the composites anodized at 20% sulfuric/nitric (3/1) were the highest values among the anodized carbon fibers. These results were attributed to the increase of the degree of adhesion at interfaces between the carbon fibers and the matrix resins in the composite systems.

• Composites Research
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• v.15 no.3
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• pp.30-38
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• 2002

Fiber Bragg grating(FBG) like other optical fiber sensors also has the merit of embedding capability. To increase their actual value related to embedding capability, this paper reported the reliability and signal characteristics of FBGS embedded in composite laminates. The microphotographs of embedded optical fibers visualized the embedding environments of stripped optical fibers and coated optical fibers. Based on these microphotographs and cure monitoring performed using FBGs, we could understand that the main cause breaking the unique Bragg condition of low-birefrigence FBG were residual stress artier curing and reported the stale of stress/strain of optical fiber quantitatively. The cure monitoring also showed the history of splitting peak of a stripped FBG along cure processing. In addition, we could obtain a transverse insensitive grating(TIG) with ease by recoating a stripped FBG. TIG has good advantage for real-time signal processing.

• Steel and Composite Structures
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• v.44 no.5
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• pp.707-720
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• 2022

In the present work, bending and free vibration analyses of multilayered functionally graded (FG) graphene platelet (GPL) and fiber-reinforced hybrid composite beams are carried out using the parabolic function based shear deformation theory. Parabolic variation of transverse shear stress across the thickness of beam and transverse shear stress-free conditions at top and bottom surfaces of the beam are considered, and the proposed formulation incorporates a transverse displacement field. The present theory works only with four unknowns and is computationally efficient. Hamilton's principle has been employed for deriving the governing equations. Analytical solutions are obtained for both the bending and free vibration problems in the present work considering different variations of GPLs and fibers distribution, namely, FG-X, FG-U, FG-Λ, and FG-O for beams having simply-supported boundary condition. First, the matrix is assumed to be strengthened using GPLs, and then the fibers are embedded. Multiscale modeling for material properties of functionally graded graphene platelet/fiber hybrid composites (FG-GPL/FHRC) is performed using Halpin-Tsai micromechanical model. The study reveals that the distributions of GPLs and fibers have significant impacts on the stresses, deflections, and natural frequencies of the beam. The number of layers and shape factors widely affect the behavior of FG-GPL-FHRC beams. The multilayered FG-GPL-FHRC beams turn out to be a good approximation to the FG beams without exhibiting the stress-channeling effects.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.48 no.3
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• pp.14-22
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• 2016

Pulping is a stage that can change fibrous raw materials into pumpable slurry. Recovered paper can be defibrated to individual fibers by shear stress generated by rotation of a rotor and water. Disintegration of recovered paper is more complicated than that of chemical pulp. When disintegration of recovered paper is poor, screening and cleaning efficiency will be worse and properties of paper will also be deteriorated. Therefore, pulping is an important treatment for improvement of availability of recovered paper and process runnability. In this study, degrees of disintegration of KOCC obtained from a linerboard mill was analyzed with a pilot-scale screen. Flake removal of KOCC slurry was performed by a pilot screen. Simple pumping action gave a positive effect on disintegration of KOCC. After pumping for 10 minutes, paper strength increased without the change of water retention value and fibrillation of KOCC slurry. This phenomena can be explained by modification of hornified surface of KOCC fibers by shear stress generated by pumping. Consequently, disintegration efficiency of KOCC can be enhanced by control of retention time at pulper or an agitation power at chests of papermaking process.

• Structural Engineering and Mechanics
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• v.46 no.2
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• pp.295-322
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• 2013

Steel fiber reinforced self-compacting concrete (SFRSCC) is a relatively new composite material which congregates the benefits of self-compacting concrete (SCC) technology with the profits derived from the fiber addition to a brittle cementitious matrix. Steel fibers improve many of the properties of SCC elements including tensile strength, toughness, energy absorption capacity and fracture toughness. Modification in the mix design of SCC may have a significant influence on the SFRSCC mechanical properties. Therefore, it is vital to investigate whether all of the assumed hypotheses for steel fiber reinforced concrete (SFRC) are also valid for SFRSCC structures. Although available research regarding the influence of steel fibers on the properties of SFRSCC is limited, this paper investigates material's mechanical properties. The present study includes: a) evaluation and comparison of the current analytical models used for estimating the mechanical properties of SFRSCC and SFRC, b) proposing new relationships for SFRSCC mixtures mechanical properties. The investigated mechanical properties are based on the available experimental results and include: compressive strength, modulus of elasticity, strain at peak compressive strength, tensile strength, and compressive and tensile stress-strain curves.

• Fibers and Polymers
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• v.6 no.2
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• pp.169-173
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• 2005

Low temperature plasma (LTP) treatment was applied to wool fabric with the use of a non-polymerizing gas, namely oxygen. After the LTP treatment, the fabric properties including low-stress mechanical properties, air permeability and thermal properties, were evaluated. The low-stress mechanical properties were evaluated by means of Kawabata Evaluation System Fabric (KES-F) revealing that the tensile, shearing, bending, compression and surface properties were altered after the LTP treatment. The changes in these properties are believed to be related closely to the inter-fiber and inter-yam frictional force induced by the LTP. The decrease in the air permeability of the LTP-treated wool fabric was found to be probably due to the plasma action effect on increasing in the fabric thickness and a change in fabric surface morphology. The change in the thermal properties of the LTP-treated wool fabric was in good agreement with the above findings and can be attributed to the amount of air trapped between the yams and fibers. This study suggested that the LTP treatment can influence the final properties of the wool fabric.

• Coupled systems mechanics
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• v.12 no.2
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• pp.151-165
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• 2023

In this study, a simple method for the determination of the shear correction factor for composites beam with a rectangular cross section is presented. The plane stress elasticity assumption is used after simplifications of the expression of the stress distribution in the beam. The different fiber orientation angle and volume fraction are considered in this work. The studied structure is subjected to various loading type (thermal and hygrothermal). The numerical results obtained show that there is a dependence of the shear coefficient on the orientation of the fibers. The evolution of the shear correction factors depends not only on the orientation of the fibers and also on the volume fraction and the environment. the advantage of this developed formula of the shear correction factor is to obtain more precise results and to consider several parameters influencing this factor which are neglected if the latter is constant.

• Steel and Composite Structures
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• v.44 no.6
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• pp.817-828
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• 2022

In this study, considering dissipated energy in fracture process zone (FPZ), a novel criterion based on maximum strain energy release rate (SER) for orthotropic materials is presented. General case of in-plane loading for cracks along the fibers is assumed. According to the experimental observations, crack propagation is supposed along the fibers and the reinforcement isotropic solid (RIS) concept is employed as a superior model for orthotropic materials. SER in crack initiation and propagation phases is investigated. Elastic properties of FPZ are extracted as a function of undamaged matrix media and micro-crack density. This criterion meaningfully links between dissipated energy due to toughening mechanisms of FPZ and the macroscopic fracture by defining stress intensity factors of the damaged zone. These coefficients are used in equations of maximum SER criterion. The effect of crack initiation angle and the damaged zone is considered simultaneously in this criterion and mode II stress intensity factor is extracted in terms of stress intensity factors of damage zone and crack initiation angle. This criterion can evaluate the effects of FPZ on the fracture behavior of orthotropic material. Good agreement between extracted fracture limit curves (FLC's) and available experimental data proves the ability of the new proposed criterion.

• Composites Research
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• v.23 no.4
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• pp.35-43
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• 2010

The purpose of this paper is to develop a Hybrid Fiber-reinforced High Strength Lightweight Cementitious Composite (HFSLCC) incorporated with lightweight filler and hybrid fibers for lightness and high ductility. Optimal ingredients and mixture proportion were determined on the basis of the micromechanical analysis and the steady-state cracking theory considering the fracture characteristics of matrix and the interfacial properties between fibers and matrix. Then 4 mixture proportions were determined according to the type and amount of fibers and the experiment was performed to evaluate the mechanical performance of those. The HFSLCC showed 3% of tensile strain, 4.2MPa of ultimate tensile stress, 57MPa of compressive strength and $1,660kg/m^3$ of bulk density. The mechanical performance of HFSLCC incorporated with PVA fibers of 1.0 Vol.% and PE fibers of 0.5 Vol.% is similar to those of the HFSLCC incorporated with fibers of 2.0 Vol.%.