Jin Ho Choi

Weight Optimization of Composite Flat and Curved Wings Satisfying Both Flutter and Divergence Constrains

Aeroelastic tailoring studies using effective computational method with genetic algorithm have been conducted to find an optimized lamination set which give minimum structural weight. The efficient and robust computational system for the flutter optimization has been developed using the coupled computational method based on the micro genetic algorithm. It is shown that the wing structural weight with both divergence and flutter constrains can be significantly reduced using composite materials with proper optimum lamination compared to the case of isotropic wing model.

Relation between Surface Roughness and Overlap Interval in Fused Deposition Modeling

Rapid prototyping (RP) can efficiently fabricate high level models with complex shapes. Hence the RP has been widely applied in various industrial fields. However, as the technology is inherently performed by layered manufacturing process, the surface quality of the RP part is not satisfactory to use general industrial purpose. This is the reason that surface roughness problem has been key issue in RP. In this paper, relation between surface roughness and overlap interval is investigated based on a surface roughness formulation in fused deposition modeling (FDM). Additionally, effects of surface angle and filament shape are analyzed and discussed to predict surface roughness distribution by the overlap interval variation.

A Study on the Crack Propagation of Composite Materials Using a Planar Piezo Sensor

As fiber-reinforced composite materials are widely used in aircraft, space structures, and robot arms, studies that investigate NDT methods are growing in importance as they seek to improve the reliability and safety of these methods. It is very important to measure the defect sizes and to decide their tolerance ranges. Acoustic emission (AE) can evaluate these defects by detecting the emitting strain energy when the elastic waves are generated by the initiation and growth of a crack, plastic deformation, fiber breakage, matrix cleavage, or delamination. In this paper, 8 × 8 planar piezo sensors were manufactured and the crack initiation and propagation of the AE signals were experimentally investigated using these sensors. An electronic circuit able to amplify and control the 64 channel AE signals was designed and manufactured. The amplified 64 channel AE signals were output into light emitting diodes (LEDs) and stored on an optical film. From the ensuing tests, it was demonstrated that the initiation lo...As fiber-reinforced composite materials are widely used in aircraft, space structures, and robot arms, studies that investigate NDT methods are growing in importance as they seek to improve the reliability and safety of these methods. It is very important to measure the defect sizes and to decide their tolerance ranges. Acoustic emission (AE) can evaluate these defects by detecting the emitting strain energy when the elastic waves are generated by the initiation and growth of a crack, plastic deformation, fiber breakage, matrix cleavage, or delamination. In this paper, 8 × 8 planar piezo sensors were manufactured and the crack initiation and propagation of the AE signals were experimentally investigated using these sensors. An electronic circuit able to amplify and control the 64 channel AE signals was designed and manufactured. The amplified 64 channel AE signals were output into light emitting diodes (LEDs) and stored on an optical film. From the ensuing tests, it was demonstrated that the initiation location and transmitting path of AE signals in composite materials could be detected effectively by the planar piezo electric sensor.

Progressive Failure Analysis of Unidirectional-Fabric Laminated Composite Joints under Pin-Loading

A two-dimensional progressive failure analysis is conducted to predict the failure loads and modes of carbon-epoxy composite joints under pin-loading. An eight-node laminated shell element is used for the finite element modeling. Post-failure stiffness is evaluated based on the complete unloading model combined with various failure criteria. The comparison of finite element and experimental results shows that the finite element analysis based on the combined maximum stress and Yamada-Sun criteria most accurately predicts the failure loads of the composite laminated joints.

Experimental and Finite Element Characterization of the Crippling Failure of Composite Stiffeners

Progressive failure analysis based on the complete unloading method was conducted to investigate the crippling failure of carbon/epoxy composite stiffeners under axial compression. A modified arc-length algorithm was incorporated into a nonlinear finite element method to trace the equilibrium path after local buckling. For the validation of the finite element method, several carbon/epoxy Z-section stiffeners were tested in compression. The finite element results on the buckling and crippling stresses showed good agreement with the experimental results.

Strength of Composite Laminated Bolted Joint Subjected to a Clamping Force

As these composites have become more popular, composite joint design has become a very important research area, as these joints are often the weakest parts of composite structures. In this paper, the strength of a composite laminated bolted joint being subjected to a clamping force was tested and predicted using the FAI (Failure Area Index) method. The strengths of composite joints subjected to clamping forces on different geometric shapes and dimensions were predicted using the FAI method, and the results were compared with experimental results. From the tests and analyses, the strength of a given composite laminated bolted joint subjected to a clamping force could be predicted within 22.5% via the FAI method.