Structural Investigation on Fuel Leakage of Cryogenic Fuel Tanks

可重复使用运载火箭(RLV)的成功研制依赖于基于碳纤维增强塑料(CFRP)等复合材料的广泛应用而大幅减轻运载火箭的重量。对结构重量减轻的最大贡献可能是使用占总发射重量90%以上的低温燃料复合材料油箱。本文从结构力学的角度对层合板中横向裂纹等损伤级联的燃料泄漏问题进行了深入的研究。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，载荷与泄漏率之间有很强的相关性。(2)利用裂纹张开位移和外加载荷等结构参数，可以定量地预测渗漏。(3)提出了渗漏路径构造的简单结构模型，提出了机械荷载和热荷载作用下渗漏的精确预报方案。通过与采用双轴十字形层板试件和气体氦的实验结果的比较，验证了该预测方法的有效性。(4)指出并强调了利用材料性能随温度变化来预测力学或渗漏行为的重要性。根据本文的结果，通过新引入的结构模型可以预测通过含损伤层板的燃料泄漏。

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.