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Abstract: This research aims to perform the optimal design of filament wound type 3 tanks under internal pressure. So far, most designs have not been optimized to account for the requirements of filament wound structures, and no design method exists for general filament wound structures under internal pressure, satisfying given design requirements. In this research, a new design algorithm which had been proposed in our previous research was utilized. The optimal design algorithm includes the semi-geodesic path algorithm, progressive failure analysis and genetic algorithms. In addition, a modified sub-string genetic operator that improves the genetic algorithm was newly suggested and verified through a basic design. Finally, the optimal design algorithm was applied to a representative filament wound type 3 tank—high pressure hydrogen storage tank. [Copyright &y& Elsevier]

In this study; probabilistic analysis and experimental tests are conducted to predict the probabilistic deformation and strength of composite pressure vessels subjected to inner pressure loading. A computer code was utilized for the progressive failure analysis and probabilistic strength analysis with the Edgeworth expansion method and the Monte-Carlo method. The effects of design random variables on the structural behavior of the composite pressure vessel were quantified by probabilistic analysis. Three design random variables with uncertainties were selected: (1) composite elastic constants; (2) lamina strength; and (3) the thickness of the helical and hoop layer. The accuracy of probabilistic analysis was verified by comparing the predicted results with the experimental hoop strain or with the burst pressure obtained by a hydro-test with ten composite pressure vessels. The improvement of the structural design based on the probabilistic analysis is also discussed. The sensitivities of each response to the design random variables were evaluated and conclusions are drawn concerning the relative importance of these variables in the design problem. [Copyright &y& Elsevier]

In this study, experimental tests and an analytical approach are conducted to verify the size effect on the fiber strength of a composite pressure vessel. As an analytical method, the Weibull weakest link model and the sequential multi-step failure model are considered and mutually compared. In the case of carbon fiber tensile strength, there is no large difference between the analytical methods for the volumetric size effect. To verify the validity of the analytical approach, experimental tests were performed using fiber strand specimens, unidirectional laminate specimens and composite pressure vessels. Good agreement for fiber strength distribution was shown between the test data and predicted results. The volumetric size effect shows the clearly observed tendency towards fiber strength degradation with increasing stressed volume. Because the volumetric size effect depends on material and processing factors, the reduction of fiber strength due to the stressed volume shows different values according to the variation of material and processing conditions. [Copyright &y& Elsevier]

This research aims to establish an optimal design method of filament wound structures under internal pressure. So far, most design and manufacturing of filament wound structures have been based on manufacturing experiences, and there is no established design rule. In this research, the semi-geodesic path algorithm was used to calculate possible winding patterns taking into account the windability and slippage between the fiber and the mandrel surface. In addition, 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 finite element analysis method, a filament wound structure was designed using the genetic algorithm. [Copyright &y& Elsevier]

Low-velocity impact damage is a major concern in the design of structures made of advanced laminated composites, because such damage is mostly hidden inside and cannot be detected by visual inspection. It is found that the acoustic emission (AE) waves generated by impact loads are undistinguishable from each mode and amount of damage by the conventional analysis methods in time or frequency domain. The wavelet transform (WT) can decompose the AE signals in time and wavelet scale domains, and catch the differences in these waves. It enables to distinguish the damage modes and size. This paper presents the application of the WT to detect the impact damage. As a fundamental approach, the characteristics of the AE signals due to matrix cracks and the evolution of free-edge delamination in [±452/02/902]S Gr/Ep laminates under tensile load were analyzed by the WT. Then the characteristics of impact damages of quasi-isotropic laminates were studied using the WT. [Copyright &y& Elsevier]

Abstract: Advanced composites are being extensively used for aerospace structures due to their high stiffness–weight and strength–weight ratios. A built-in structural diagnostic system is being developed to continuously monitor the integrity and reliability of the composite structures. Such structures are substantially large, and hence require a large number of sensors. The fiber Bragg grating (FBG) sensor system is a useful tool for health monitoring of such a large structure because it has multiplexing and multi-channeling capabilities. In this paper, an FBG strain sensing system using a wavelength-swept fiber laser (WSFL) was applied for the realization of a smart composite wing box. This system was connected with 24 FBGs, which were embedded into the structural components of the single wing cell. The wing box was tested under bending load, which simulated the lift-induced bending of an airplane wing. Three fiber optic sensor lines were embedded into the top skin and one fiber optic sensor line was embedded into the front spar of the wing box. Experimental results were discussed in comparison with finite element analysis result. All strain data were visualized in real time under the scheme of passive in-situ diagnostics. [Copyright &y& Elsevier]

It is an important issue not only for military purposes but also from commercial point of view, whether or not the reflective wave from an incident electromagnetic wave can be nullified. In this research, by blending conductive carbon black with the binder matrix of glass/epoxy composite, a radar absorbing structure (RAS) which can support loads and absorb the electromagnetic wave has been designed. The RAS was specially designed so as to exhibit the optimum absorptivity for X-band of (8.2–12 GHz) frequency ranges, centered at 10 GHz. Its absorbing characteristics were also investigated. Unlike other existing measurements of reflection loss using a waveguide, the reflection loss within an anechoic chamber simulating the radar cross section method of measurement was used with a plane-wave shaped incident wave. An optimized multi-layer design of RAS using the adopted material system is described in this research. [Copyright &y& Elsevier]