Seong-Kyun Cheong

Utilization of Finite Element Analysis in Design and Performance Evaluation of CFRP Bicycle Frames

With the continuing demand for lightweight bicycles, carbon fiber composite materials have been widely used in manufacturing bicycle frames and components. Unlike general isotropic materials, the structural characteristics of composite materials are strongly influenced by the staking directions and sequences of composite laminates. Thus, to verify the design process of bicycles manufactured using composites, structural analysis is considered essential. In this study, a carbon-fiber-reinforced plastic (CFRP) bicycle frame was designed and its structural behavior was investigated using finite element analysis (FEA). By measuring the failure indices of the fiber and matrix under various stacking sequences and loading conditions, the effect of the stacking condition of composite laminates on the strength of the bicycle structure was examined. In addition, the structural safety of the bicycle frame can be enhanced by reinforcing weak regions prone to failure using additional composite laminates.

Strain and damage monitoring in solar-powered aircraft composite wing using fiber Bragg grating sensors

A solar powered aircraft is operated by converting solar energy into electrical energy. The wing of the solar powered aircraft requires a wide area to attach a number of solar cells in order to collect a large amount of solar energy. But the structural deformation and damage of the aircraft wing may occur because of bending and torsional loads induced by aerodynamic force during the operation. Therefore, the structural health monitoring of the wing is needed for increasing the operating time of the aircraft. In this study, the strain and damage of a composite wing of a solar powered aircraft were monitored by using fiber optic sensors until failure occurrence. In detail, a static loading experiment was performed on the composite wing with a length of 3.465m under a solar simulation environment, and the strain and acoustic emission (AE) of fracture signal were monitored by using fiber Bragg grating (FBG) sensors. In the results of the structural experiment, the damage occurred at a stringer when 4.5G load was applied to the composite wing, and the strain variations and AE signals were successfully measured by using FBG sensors. As a result, it is verified that the damage occurrence and location could be estimated by analyzing the strain variations and AE signals, and the fiber optic sensor would be a good transducer to monitor the structural status of a solar powered aircraft.

A Study on the Accelerated Life Test of Rubber Specimens by using Stress Relaxation

Rubber parts are widely used in many applications such as dampers, shock absorbers, and seals used in railway and automotive industries. Much research has thus far been conducted on property estimation and life prediction of rubber parts. To predict the service life of rubber parts at room temperature, most prior work adopts the well-known Arrhenius model that needs the accelerated life test in high-temperature conditions. However, they may not reflect the actual conditions of use that rubber parts are usually used under a specific strain condition during long period of time. In this context, we propose a method for the life prediction of rubber parts in actual conditions of use. The proposed method is based on the accelerated life test using stress relaxation during which three relatively high elongation percentages (100%, 200%, and 300%) are applied to the rubber specimens. Rubber specimens were prepared in accordance with KS M 6518 standard and three stress relaxation testers were fabricated for actual experiments. Finally, a inverse power model for life prediction was derived from experimental results. The predicted life was compared with the actual test life for validation.

Interlaminar Fracture Toughness of Hybrid Composites Inserted with Different Kinds of Non-Woven Tissues : Part I-Mode I

In this study, the interlaminar fracture toughness in mode I of a hybrid composite inserted with different types of non-woven tissues was determined. The interlaminar fracture toughness in mode I is obtained by a double cantilever beam test. The experiment is performed using three types of non-woven tissues: 8 g/m 2 of carbon tissue, 10 g/m 2 of glass tissue, and 8 g/m 2 of polyester tissue. Considering a specimen with no non-woven tissue as a reference, the interlaminar fracture toughness in mode I of specimens inserted with non-woven carbon and glass tissues decreases by as much as 6.3% and 11.4%, respectively. However, the fracture toughness of a hybrid composite specimen inserted with non-woven polyester tissue increases by as much as 69.4%. It is considered that the specimen inserted with non-woven polyester tissue becomes cheaper, and lighter, and the value of the fracture toughness becomes much greater than that of the non-woven carbon tissue.