Gas Leakage Evaluation of CFRP Cross-ply Laminates under Biaxial Loadings

Abstract

In this study, leak characteristics of CFRP (carbon fiber reinforced plastic) cross-ply laminates are experimentally investigated under biaxial loadings using a specially prepared in-plane biaxial testing system. Permeability through the damaged laminate under biaxial stresses was measured with a leak detection system. In order to evaluate the effect of damage on leakage, ultrasonic C-scan was used to inspect the matrix cracking in the specimens. Experimental results reveal that leakage through the damaged laminate is in correlation with the amount of damage and depends not only on load level but also on biaxial load ratio. Leak analysis, which had been previously developed, was employed and calculations of permeability were in good agreement with the experimental data. The results indicate the validity of the assumption of domination of crack openings on permeability, and the dependency of constants of leak conductance on damage susceptibility in the leak analysis.

Influence of stacking sequence on leakage characteristics through CFRP composite laminates

“…In previous study [13], biaxial load with load ratio 1:1 could not make matrix cracks in all layers in a carbon fiber/toughened epoxy laminate, which specimen configuration was identical with the specimen configuration in this paper, due to lower strain induced at the gauge area than biaxial load with other load ratio such as 1:0. However gauge area of the cruciform specimen was buckled under biaxial load with load ratio 1:0.…”

“…Generally, the permeation due to diffusion is much smaller than that due to leak through leakage paths. In our previous study [13], the effect of diffusion was confirmed to be negligible compared to leakage through cracks in the laminate. In this study, permeability through the laminate was presumed to be caused only by the leaks.…”

“…The system consisted of the cruciform type biaxial testing machine, leak measurement cell and a helium leak detector [13].…”

“…The leakage through composite laminates under mechanical loads and cryogenic condition was experimentally investigated [8,9], and permeability through the damaged laminate changes with not only temperature variation but also with applied loads. Leakage analysis scheme was also developed in consideration of the relationships between damage and gas permeation, and good agreement with experimental data were shown [10][11][12][13].…”

Finite Element Based Method to Predict Gas Permeability in Cross-ply Laminates

“…Different lay-ups are tested in experiments such as cross-ply [2][3][4][5]8] and multi-directional ply composites [6][7][8], and textile composites [9]. Even though hydrogen is the working gas in the propellant tank, due to safety considerations, most researchers use helium gas instead in their experiments [2][3][4][5]8,9].…”