Structural Investigation on Fuel Leakage of Cryogenic Fuel Tanks

碳纤维增强塑料（CFRP）等复合材料的广泛应用，使可重复使用运载器（RLV）的研制成功依赖于其重量的大幅度减轻。对结构重量减轻的最大贡献可通过使用复合材料贮箱来实现，该复合材料贮箱用于低温燃料，该低温燃料占总发射重量的90%以上。在本研究中，燃料泄漏通过叶栅的损伤，如横向裂纹层压板从结构力学的角度进行了深入的研究。实验和分析结果表明：（1）氦泄漏主要发生在层合板各层均含横向裂纹的情况下，且载荷与泄漏率之间存在较强的相关性。对于具有完整层的层压板，泄漏在可忽略的水平之下。(2)泄漏被证明是定量预测的结构参数，包括裂纹张开位移和施加的载荷。(3)提出了一种简单的泄漏路径构造模型，并开发了一种在机械和热载荷下准确预测泄漏的方案。通过与双轴十字形层合板试件和氦气实验结果的比较，验证了预测方法的正确性。(4)指出了利用温度相关材料特性预测力学或泄漏行为的重要性，并强调了本文所得到的结果，表明新引入的结构模型可以预测通过含损伤层合板的燃料泄漏。

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.