Acoustic Emission in Filament Wound Composite Pressure Vessels under Hydraulic Test
|關鍵字:||纖維纏繞壓力容器;音洩;液壓試驗;首層破壞;filament wound composite pressure vessels;acoustic emission;hydraulic test;first-ply failure|
Monitoring acoustic emission (AE) suddenly released from fractures in filament wound composite pressure vessels (FWCPV) under hydraulic proof test benefits understanding structural failure strength. The specimens studied are carbon/epoxy FWCPV manufactured in accordance with ASTM D-2585 standard. Four inner layers of the pressure vessel were helically wound at □15.92° helix angles and then reinforced by four hoop wound filaments in the cylindrical hollow portion. The first significant AE energy and slope variation in the cumulative AE count curves are set to be an indication for failure of the pressure vessel. Both average indicative failure pressures are 1,239 and 1,038 psi, respectively. Beyond 1,000 psi in the cyclic pressurization, the cumulative AE count curve had a steep slope variation in the range of internal pressure inferior to the previous maximum value. The Felicity effect for composite structures was discovered, and the average Felicity ratio was between 0.825 and 0.935. Finite element analysis was used to determine the first-ply failure pressure and its position. The value of calculated first-ply failure pressure is close to the indicative failure pressure based on steep slope variation of cumulative AE counts. However, there remains an inconsistency between the real failure location and prediction. In the eight exploded FWCPV specimens, four were exploded with a penetration through the thickness; one had a clear cutting with the edge 45o inclined to the axis; three failed in fiber breakages in hoop wound filaments and delamination. The latter is suspected to be caused by matrix crack extension. Simulated results manifest that the normal stress along the fiber orientation increases if delamination occurs between the fourth and fifth ply. Both numerical results and experimental evidence are in good agreement.
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