• Composites Research
• /
• v.13 no.2
• /
• pp.30-39
• /
• 2000

It is difficult for civil engineer to apply composite materials of laminated type to structure for civil construction because of complicated theory although those have much merit. A simple method by which one can predict "exact" values of the natural frequency of vibration of laminated plates is presented. Many laminates with particular orientations have negligible values of $B_{16}$ and $B_{26}$ as the number of plies increases. Such laminates, with $D_{16}$ = $D_{26}$ ->0 can be solved by the same equation as for the special orthotropic laminates(1991,1995). If the quasi-isotrpic constants are used, It is possible to simplify analysis procedure since the equations for isotropic plates can be used. Use of some coefficients can produce "exact" values for laminates with such configuration. This coefficient, in fact, represents the effect of the anisotropy of the laminate. D. H. Kim proposed to use a correction factor, he developed, to produce "exact" solution out of the approximate solution obtained by using the quasi-isotropic constants(1995). In this paper, the fiber orienation studied is [$\alpha$/$\beta$/$\beta$/$\gamma$/$\alpha$/$\alpha$/$\beta$]r, with $\alpha$=-$\beta$, and $\gamma$${\gamma}$=$0^{\circ}$ or $90^{\circ}$ and the above-mentioned method is used to obtain the natural frequencies of plates with such orientations, and detailed result is presented for the use of engineers.nted for the use of engineers.

• Journal of the Korean Society for Precision Engineering
• /
• v.33 no.6
• /
• pp.439-445
• /
• 2016

Carbon fiber reinforced plastic (CFRP) composites have been widely used due to their great strength, stiffness and light weight. However, due to its anisotropy and inhomogeneous properties the machining process of CFRP composites is typically more complex than that of regular metals. Since there are many defects, such as delamination and tool wear during the machining process of CFRP composites, the optimization of this process is essential in improving the productivity. In this study, orthogonal machining of CFRP composites was performed to identify the machining characteristics of these materials. In addition, an experimental observation of delamination was investigated through the use of scanning electron microscopy (SEM). In these experiments, the cutting forces were measured and analyzed to determine the difference between machining of CFRP composites and metals. The comparison between the numerical models and experimental results was performed in terms of the maximum cutting forces.

• Composites Research
• /
• v.13 no.2
• /
• pp.81-90
• /
• 2000

For automotive applications, a sandwich sheet which was made of a 5182 aluminum alloy (AA5182) sheet and a polypropylene (PP) sheet, AA5182/PP/AA5182, has been developed. In order to evaluate its formability, the forming limit diagrams (FLD) of the 5182 aluminum alloy sheet with 0.2mm thickness and the sandwich sheet with 1.2mm thickness have been obtained based on the modified Marciniak-Kuczynski (M-K) theory. To account for the anisotropy of the sheet, Hill's 1948 yield function has been applied. The FLD of the sandwich sheet was predicted to be better than that of the AA5182 sheet, which was well confirmed by experiments.

• Steel and Composite Structures
• /
• v.21 no.4
• /
• pp.703-753
• /
• 2016

The ratcheting behavior was studied experimentally for Z2CND18.12N elbow piping under cyclic bending and steady internal pressure. Dozens of cyclic plasticity models for structural ratcheting responses simulations were used in the paper. The four models, namely, Bilinear (BKH), Multilinear (MKIN/KINH), Chaboche (CH3), were already available in the ANSYS finite element package. Advanced cyclic plasticity models, such as, modified Chaboche (CH4), Ohno-Wang, modified Ohno-Wang, Abdel Karim-Ohno and modified Abdel Karim-Ohno, were implemented into ANSYS for simulating the experimental responses. Results from the experimental and simulation studies were presented in order to demonstrate the state of structural ratcheting response simulation by these models. None of the models evaluated perform satisfactorily in simulating circumferential strain ratcheting response. Further, improvement in cyclic plasticity modeling and incorporation of material and structural features, like time-dependent, temperature-dependent, non-proportional, dynamic strain aging, residual stresses and anisotropy of materials in the analysis would be essential for advancement of low-cycle fatigue simulations of structures.

• Composites Research
• /
• v.25 no.1
• /
• pp.9-13
• /
• 2012

In this research, biomechanical characteristics of the bone tissue are experimentally investigated. By using specimens of the bovine bone, the mechanical properties are obtained through tension and shear tests. In experiments, non-homogeneous and anisotropic properties with respect to longitudinal and transversal directions are observed. Moreover, the viscoelastic behavior in which modulus and strength properties are dependent on strain rates is analyzed. It is expected that a numerical damage model of the bone be efficiently established based on the results.

• Journal of Magnetics
• /
• v.12 no.1
• /
• pp.35-39
• /
• 2007

A highly sensitive magnetic sensor using the Giant MagnetoImpedance effect has been developed. The sensor performance is studied and estimated. The sensor circuitry consists of a square wave generator (driving source), a sensing element in a form of composite wire of a 25 $\mu$m copper core electrodeposited with a thin layer of soft magnetic material ($Ni_{80}Fe_{20}$), and two amplifier stages for improving the gain, switching mechanism, scaler circuit, an AC power source driving the permeability of the magnetic coating layer of the sensing element into a dynamic state, and a signal pickup LC circuit formed by a pickup coil and an capacitor. Experimental studies on sensor have been carried out to investigate the key parameters in relation to the sensor sensitivity and resolution. The results showed that for high sensitivity and resolution, the frequency and magnitude of the ac driving current through the sensing element each has an optimum value, the resonance frequency of the signal pickup LC circuit should be equal to or twice as the driving frequency on the sensing element, and the anisotropy of the magnetic coating layer of the sensing wire element should be longitudinal.

• Composites Research
• /
• v.20 no.5
• /
• pp.13-19
• /
• 2007

Fiber-reinforced thermoplastic composites not only approach almost near to the strength of thermosetting composite but also has excellent productivity, recycling property, and impact resistance, which are pointed as weaknesses of thermosetting composites. The study for strength calculation of one direction fiber-reinforced thermoplastic composites and the study measuring precisely fiber orientation distribution were presented. Need the systematic study for the data base that can predict mechanical properties of composite material and fiber orientation distribution by the fiber content ratio was not constructed. Therefore, this study was investigated what affect the fiber content ratio and fiber orientation distribution have on the strength of composites. Fiber-reinforced thermoplastic composites by changing fiber orientation distribution and the fiber content ratio were made. Tensile strength ratio of $0^{\circ}$ direction of fiber-reinforced composites increased being proportional the fiber content and fiber orientation function as change from isotropy(J=0) to anisotropy(J=1). But, tensile strength ratio of $90^{\circ}$ direction by separation of fiber filament decreased when tensile load is imposed fur width direction of reinforcement fiber length direction.

• Composites Research
• /
• v.18 no.1
• /
• pp.38-44
• /
• 2005

In this paper, the group velocity dispersion curves of the $S_o$ symmetric mode in unidirectional CFRP plate was calculated as varying the propagating direction. The group velocity curve was obtained with the group velocities of the $S_o$ symmetric mode corresponding to 0.2 MHz-mm under the first cut-off frequency in the dispersion curves, and corrected by introducing the slowness curve. The velocities of the $S_o$ symmetric mode in the unidirectional CFRP plate were measured as varying the propagating direction and compared with the col?rotted group velocity curve. The measured velocities were good agreement with the corrected group velocity curve except near the fiber direction which was called the cusp region. It implies that the direction of the group velocities incline toward the fiber direction of the unidirectional CFRP plates when the propagation direction is not accorded with the principal axis. It is supposed that this phenomenon rerults from the preferential propagating the energy toward the direction with the faster propagation velocity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.4
• /
• pp.347-355
• /
• 2014

Thermal problems that are directly related to the lifetime of an electronic device are becoming increasingly important owing to the miniaturization of electronic devices. To solve thermal problems, it is essential to study thermal stability through thermal diffusion and insulation. A honeycomb sandwich plate has anisotropic thermal conductivity. To analyze the thermal deformation and temperature distribution of a system that employs a honeycomb sandwich plate, the thermal and elastic properties need to be determined. In this study, the thermal and elastic properties of a honeycomb sandwich plate, such as thermal conductivity, coefficient of thermal expansion, elastic modulus, Poisson's ratio, and shear modulus, are predicted. The properties of a honeycomb sandwich plate vary according to the hexagon size, thickness, and material properties.

• Polymer(Korea)
• /
• v.24 no.6
• /
• pp.860-868
• /
• 2000

In this work, the electro-magnetic interference (EMI) characteristics of PAN-based carbon fibers-reinforced composites are investigated with difference to manufactural parameters, i.e., fiber grade, fiber orientation angle, and laminating method. As a result, EMI shielding effectiveness (SE) of the composites greatly depends on a fiber orientation in composite angle. Especially, the fiber grade affects SE of composites in case of orientation angle of 0$^{\circ}$. Then the SE become greater as the change of electric character according to the arrangement directions, i.e., electrical anisotropy in the same constituent materials. This is due to the skin effect which is represented in the surface of electro-magnetic wave in high-frequency range. In all cases according to lamination methods, the composites represents SE of 83~98% over. Whereas, in symmetric and unsymmetric laminate structures, the SE decreases slightly as the laminate angles of composites increases. On the contrary. the repeating laminates structure shows the opposite tendency. Especially, 90$^{\circ}$ repeating laminate structure shows the SE more than 90% over the measuring frequency.