Cheol-Ung Kim

Analysis of filament wound composite structures considering the change of winding angles through the thickness direction

In this study, filament winding patterns were calculated using a semi-geodesic fiber path equation for an arbitrary surface. Because the fiber path depends on the surface where fibers are wound, the winding angle varies in the longitudinal and thickness directions of a wound structure. The fiber angle difference through the thickness was calculated for several design parameters, such as helical winding thickness and angle. Finite element analyses were performed considering the change of winding angles through the thickness by a commercial FEA code, ABAQUS. A user subroutine, ORIENT, was coded to impose the change of winding angles to each solid element. Water-pressuring tests were performed for an advanced standard test evaluation bottle (ASTEB). The results of the finite element analysis considering geometrical nonlinearities were verified with the experimental data.

Strain monitoring of a filament wound composite tank using fiber Bragg grating sensors

In this paper, we present strain monitoring of a filament wound composite tank using fiber Bragg grating (FBG) sensors during hydrostatic pressurization. 20 FBG sensors and 20 strain gages were attached to the domes and cylinder of the composite tank. A wavelength-swept fiber laser was used as a light source to supply high signal power. From the experimental results, it was successfully demonstrated that the FBG sensor system is useful for large structures that require a large number of sensor arrays.

Structural Analysis and Strain Monitoring of the Filament Wound Motor Case

Filament wound structures such as pressure tanks, pipes and motor cases of rockets are widely used in aerospace applications. The determination of a proper winding angle and thickness is very important to decrease manufacturing difficulties and to increase structural efficiency. In this study, possible winding angles considering the slippage between a fiber and a mandrel surface are calculated using the semi-geodesic path equation. In addition, finite element analyses using ABAQUS are performed to predict the behavior of filament wound structures considering continuous change of the winding angle and thickness at the dome part due to fiber built-up near the metallic boss. Water-pressuring tests of a third stage motor case are performed to verify the analysis procedure. The strain gages are attached on the surface in the fiber direction. Progressive failure analysis predicted the burst pressure a little bit higher than the experiment and the weakest region of the motor case very well. The effect of reinforcement is also studied to increase its performance.

In-situ Health Monitoring of Filament Wound Pressure Tanks using Embedded FBG Sensors

ABSTRACT In this research, in-situ structural health monitoring of filament wound pressure tanks were conducted during water-pressurizing test using embedded fiber Bragg grating (FBG) sensors. We need to monitor inner strains during working in order to verity the health condition of pressure tanks more accurately because finite element analyses on filament wound pressure tanks usually show large differences between inner and outer strains. Fiber optic sensors, especially FBG sensors can be easily embedded into the composite structures contrary to conventional electric strain gages (ESGs). In addition, many FBG sensors can be multiplexed in single optical fiber using wavelength division multiplexing (WDM) techniques. We fabricated a standard testing and evaluation bottle (STEB) with embedded FBG sensors and performed water-pressurizing test. In order to increase the survivability of FBG sensor during cure, we suggested a novel fabrication process for embedding FBG sensors into a filament wound pressure tank, which includes a new protecting technique of sensor heads, the grating parts. From the experimental results, it was demonstrated that FBG sensors can be successfully adapted to filament wound pressure tanks by embedding.

Optimal Design of Filament Wound Structures Based on the Semi-geodesic Path Algorithm

This research aims to establish an optimal design method of filament wound structures. Filament winding is one of the most reliable and affordable production techniques for high performance composite structures such as pressure tanks, pipes and motor cases of rockets which are widely used in the aerospace application. However, the problem with filament winding is that the trajectory of the fiber path and the corresponding fiber angles cannot be chosen freely because of the stability requirement of fiber path. Most design and manufacturing of filament wound structures are based on manufacturing experiences, and there is no established design rule. In this research, possible winding patterns considering the windability and the slippage between fiber and mandrel surface were calculated using the semi-geodesic path algorithm. In additiori, finite element analyses using commercial code, ABAQUS, were performed to predict the behavior of filament wound structures. On the basis of the semi-geodesic path algorithm and the verified finite element analysis method, an optimal design algorithm for filament wound structures was suggested using the genetic algorithm.