Structural Investigation on Fuel Leakage of Cryogenic Fuel Tanks

基于碳纤维增强塑料（CFRP）等复合材料的广泛应用，可重复使用运载火箭（RLV）的成功发展取决于运载火箭重量的大幅减轻。对结构重量减少的最大贡献可能是利用复合燃料箱来储存低温燃料，这种燃料占发射总重量的90%以上。本文从结构力学的角度深入研究了层压板横向裂纹等损伤的级联泄漏问题。实验和分析结果表明：(1)氦气泄漏与层合板各层均含有横向裂纹有关，且加载载荷与泄漏率有较强的相关性。泄漏在可忽略的水平下，层合板与完整的层。(2)采用包括裂缝张开位移和施加荷载在内的结构参数可以定量预测渗漏。(3)提出了泄漏通道施工的简单结构模型，并提出了机械和热载荷下泄漏的精确预测方案。通过与双轴十字形层压试样和氦气实验结果的对比，验证了预测方法的正确性。(4)强调了利用温度相关的材料特性来预测力学或泄漏行为的重要性。研究结果表明，所建立的结构模型可预测含损伤层合板的燃油泄漏。

The successful development of the Reusable Launch Vehicles (RLV) depends on the drastic weight reduction of the vehicle based on the wide application of composite materials such as Carbon Fiber Reinforced Plastics (CFRP). The largest contribution to the structural weight reduction may be achieved by the utilization of composite tanks for cryogenic fuel that makes up more than 90 % of the gross launch weight. In the present study, the fuel leakage through the cascades of damages such as transverse cracks in the laminate is thoroughly investigated from the structural mechanics point of view. The experimental and analytical studies revealed the followings :(1) The gas helium leakage was identified with the laminates containing transverse cracks in all of their layers, showing strong correlation between the applied load and leakage rate. The leakage was under negligible level with laminates with intact layers.(2) Leakage was shown to be quantitatively predictable by employing the structural parameters including crack opening displacements and applied loads.(3) Simple structural model for leakage paths construction was proposed and a scheme for accurate prediction of leakage under both mechanical and thermal loads was developed. The prediction method was then verified through the comparison with the experimental results employing biaxial cruciform laminate specimens and gas helium.(4) The importance of using temperature dependent material properties for the predictions of mechanical or leakage behaviors was shown and emphasized.With the results obtained herein, the fuel leakage through the laminates containing damages was shown to be predictable by the newly introduced structural model.