• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.69-73
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• 2003

A open section thick composite beam model is suggested in this study. In the model, the primary and secondary warping and transverse shear effects are incorporated. The rigidities associated with thick channel composite beam and thin channel composite beam are obtained and compared. The results show that the difference among rigidities of the thick and thin composite beams increase as the wall thickness increases.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.167-171
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• 2005

The thick open section composite beams are used extensively as load carrying members and stiffeners of structural elements. However, most of studies on thick composite beams are limited only to closed section beams. In this study, an open cross-section thick-walled composite beam model which includes coupled stiffness, transverse shear, and warping effects is suggested and the deflections associated with the thick-walled composite beams and thin-walled composite beams are obtained and compared with the finite element analysis results. The correlation between thin and thick walled composite beam was achieved for two different layup configurations which are the circumferentially asymmetric stiffness (CAS) and circumferentially uniform stiffness (CUS) beams.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.49-52
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• 2000

A new composite manufacturing technique which combines winding and curing together is studied and analyzed. This method is especially suited to the manufacture of thick composite materials in which thermal spiking is a common problem. An experimental apparatus was designed and built for use with a filament winder to continuously cure a thick composite cylinder. A hoop-wound composite cylinder with 152 mm wall thickness was manufactured and embedded thermocouples and strain gages were monitored throughout the cure process. The experimental data were compared with analytical results.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.480-485
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• 2004

The applications of composite materials have increased over the past few decades in a variety of structures that require high ratio of stiffness and strength to weight ratios. Recently the thick open section composite beams are used extensively as load carrying members and stiffeners of structural elements. However, most of studies on thick composite beams are limited only to closed section beams. In this study, an open cross-section thick-walled composite beam model which includes coupled stiffness, transverse shear, and warping effects is suggested and the deflections associated with the thick-walled composite beams and thin-walled composite beams are obtained and compared with the finite element analysis results.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.202-206
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• 2005

Most of studies on the open section composite beams are confined to the thin composite beams. There are some works focused on the thick composite beams but they are limited only to closed section beams. Therefore, it is required to develop an appropriate model to analyze the thick open section composite beams. In this study, the cantilever beams of two specific lay-up configurations are considered which are the circumferentially asymmetric stiffness (CAS) and circumferentially uniform stiffness (CUS) beams. Under the torsional loading, loading induced deformations are obtained for the thick beams using the suggested model. The model includes coupled stiffness and secondary warping effects. The results are compared with those obtained using thin beam model to observe the thickness effects. Those results are also compared with the finite element analysis results.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.129-132
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• 2001

Fiber waviness is one of manufacturing defects encountered frequently in thick composite structures. It affects significantly on the behavior as well as strength of thick composites. The effects of fiber waviness on tensile/compressive nonlinear elastic behavior and strength of thick composite with fiber waviness are studied theoretically and experimentally. FEA(Finite Element Analysis) models are proposed to predict tensile/compressive nonlinear behavior and strength of thick composites. In the FEA models, both material and geometric nonlinearities were incorporated into the model using energy density, iterative mapping and incremental method. Also Tsai-Wu criteria was adopted to predict the strength of thick composites with fiber waviness. Tensile and compressive tests were conducted on the specimens with uniform fiber waviness. It was observed that the degree of fiber waviness in composites significantly affected the nonlinear behavior and strength of the composites

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.139-142
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• 2004

The fabric composite rings for nozzle parts of solid rocket motors should be thick to endure high temperature and pressure of combustion gas. Since the thermal residual stresses developed during manufacturing of the axi-symmetric composite structures increase as the thickness increases and eventually induce failures during storage and operation, the estimation of the residual stresses is indispensable for design and manufacture of the thick composite nozzle parts. In this paper, thick fabric rings made of carbon fabric phenolic composites were fabricated in a hydroclave and in an autoclave using a multi-step pre-compaction process to minimize draping. The residual stresses distributed in the rings were measured by the radial-cut method and it was found that the compaction reduces the residual stresses in the composite ring.

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.2
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• pp.65-72
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• 2003

Composite sabot can increase the penetration performance of APFSDS projectile by reduction of the sabot weight. However, it has a thick-sectioned lamination and the lamination structure is different from those of the conventional composite parts. In this study, modeling technique for a thick and radially-laminated composite part has been applied in the finite element analysis of composite sabot. Four models of composite lamination for the sabot have been proposed and evaluated for their structural strength.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.176-179
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• 2003

This paper deals with the optimum design of thick-walled multi-layered composite tubes by minimizing the process-induced residual stresses under some constraints of structural stiffnesses. An analytic model based on quasi-static thermoelasticity is adopted for the calculation of the residual stresses in the multi-layered composite tubes. The numerical results of optimization show that, in the case of cross-ply CFRP tubes, the residual stresses can be reduced to a certain level by controlling ply thicknesses. However, the optimized tubes may be susceptible to cracking because the transverse residual stress is still large in a strength-based sense. To further suppress the residual stresses, the effects of stacking sequence, wall thickness and axial pretension on the optimum solutions are examined.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.258-263
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• 1999

In this study, the numerical and experimental investigations were conducted to understand ultrasonic wave propagation and to evaluate the degree of fiber waviness in thick composites nondestructively. The path, energy and traveling time of insonified wave were predicted by adopting the ray and plane wave theories. In the analysis, the composites were assumed to have continuous fiber with sinusoidal waviness in a matrix and were modeled as stacks of infinitesimally short length off-axis elements with varying fiber orientation along the length direction. From the experiments on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness, the energy distributions of received wave were obtain for the various positions of transmitter. It was observed that the energy of wave was converged to the adjacent peaks of fiber waviness. The location where maximum energy of wave was detected from the experiments showed good agreement with the location obtained from theoretical predictions. Finally, the test procedure was Proposed to evaluate fiber waviness in thick composites by considering the energy of wave and relative distance between transmitter and receiver.