Assessment and Optimization of CFRP Liquid Hydrogen Tanks

Kurzfassung

Liquid hydrogen (LH2) tanks made from composite materials (CFRP) promise the mass savings in skin mass by a factor of 3 compared to metal tanks. In contrast to wound CFRP vessels, tanks made from Automated Fiber Placement (AFP) enable a much higher degree of freedom of the stacking sequence, high tape placement precision, a higher deviation from the geodesic path (steering) and allow the manufacturing of segments. This way composite layers can be tailored to local mechanical and leakage allowables. On the other hand, the steering curvature must be limited in order to prevent buckling of the tape laid (steering constraints). Another feature introduced with AFP is the cutting of single tows within a tape to maintain a uniform layer thickness on the double curved tank domes. This leads to the formation of triangle gaps and hence a local stiffness and strength knockdown. To account for the huge design space, steering constraints and triangle gaps, the software tankoh2 was developed. It automatically creates FEM tank models taking gaps into account by means of homogenization approaches. Additionally, layer angles can be defined by location variable angle settings or by selecting a certain layup strategy such as constant angles or geodesic layup. In the future tankoh2 will be extended with an optimizer to close the design loop. The optimizer will adapt the layup according to the results of the structural and leakage assessment to reduce weight while being constrained by the steering and other manufacturing limits.