纖維纏繞複材壓力容器於液壓試驗的音洩研究

Abstract

纖維纏繞壓力容器於液壓試驗時，以音洩技術監測材料破壞瞬間釋放的聲波訊號，有助於了解結構的破壞強度。本文研究的複材壓力容器係依據ASTM D-2585規範製作，纖維纏繞角度由內而外為[±15.92°]2，直筒段外圍增設4層周向纏繞的纖維。音洩量測以首次出現明顯能量及累計振盪計數曲線斜率轉折點設為壓力容器的指標性破壞，兩者的指標破壞壓力平均值為1,239及1,038psi。當壓力超過1,000psi，反覆加壓的壓力未達前次最大壓力，累計振盪計數曲線即出現斜率轉折點。證實複材結構破損的音洩具有費樂希帝效應，費樂希帝比值介於0.825~0.935之間。 本文以有限元素分析計算首層破壞發生時的壓力及破壞位置，首層破壞壓力比較接近累計振盪計數曲線斜率轉折獲得的指標性破壞壓力，惟破壞位置有差異。八具爆破的複材壓力容器中，有四具發生貫穿壁厚的破壞，一具發生45o斜角破壞，三具於第4、5層間發生脫層，直筒段周向排列纖維斷裂，推測脫層肇因於基材裂縫的延伸。數值模擬結果顯示，直筒段第4、5層間之脫層會造成周向纏繞纖維的應力大幅增加，與實驗觀察吻合。

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.