Three-Dimensional Stress-Strain State Analysis of the Bimetallic Launch Vehicle Propellant Tank Shell

A high competition level in modern space-rocket technology requires continuous improvement of structural elements and enhancement of their reliability, on the other hand, reduction in production costs and lead times. One of the pressing problems of national rocket engineering is to hold down the number of physical tests (especially destructive) of the samples and replace them with computational methods. The first consideration in efficiently designing space-rocket power structures, such as propellant tanks, high-pressure cylinders, etc., is to increase the net volume of the structure and cut down its materials consumption without losing strength properties. Various engineering designs are employed to enhance the reliability and strength of such structures: end and intermediate rib stiffening, variable shell thickness, etc. The new model of a bimetallic waffle-skin shell of a launch vehicle propellant tank, made of an aluminum alloy and strengthened with a titanium skin, is advanced. The finite element method-based software was used to perform its 3D stress-strain state computations. The results for bimetallic shell computations showed that a titanium skin was liable to elastic strains that do not exceed 0.54 %, and maximum equivalent strains of an aluminum alloy reached about 0.7 %, while equivalent elastic strains were approximately half as much. Computational studies confirmed that the bimetallic shell of a lower weight exhibited insignificant plastic strains compared to the conventional waffle-skin design. Moreover, the thickness of an aluminum alloy sheet for shell fabrication is reduced by more than half; thus, the shell alternative as a double-layer structure can be employed to advantage. The computational results can be used to design new space-rocket structural elements and assess their stress-strain state.