The National Key Basic Research and Development Program of China (973 Program), No. 2014CB049000, 2014-2018
Aiming at implementing the tasks of future manned missions to the moon and deep space exploration, the argument about the development of heavy-lift launch vehicle with the diameter of 8.5 m and the carrying capacity of hundreds of tons is now in progress. It has been determined that the grid stiffened shells would be widely adopted in the fuel tanks, which influence the structural weight, as well as the load-carrying capacity of a launch vehicle. However, the rapidly increased thrust of the heavy-lift launch vehicle leads to the requirement of high service performance under large axial compressive load, and increases the imperfection sensitivity of load-carrying capacity, which implies that the actual load-carrying capacity of a stiffened shell is significantly lower than that of a perfect shell model. In the traditional design of stiffened shells, the allowable load is multiplied by a knockdown factor (much less than 1.0), which is derived based on a large amount of experimental data. Nevertheless, it is practically impossible to carry out numerous experiments for the large-diameter stiffened shells. Thus, the knockdown factors are derived by the extrapolation method based on the available experimental data from the medium and small-diameter structures or even experiences, which increases the design risk and makes it difficult to reduce the structural weight. Therefore, a reliable method to determine the knockdown factors is urgently needed. Furthermore, it is crucial to develop an active imperfection-resisted design approach as well as the effective design theory and method taking account of the imperfection sensitivity. From the point of view of increasing the values of knockdown factors, the innovative concept of the stiffened shells with low imperfection sensitivity will be proposed for weight reduction of the launch vehicles. The weakness of fundamental research in the field is restricting the development of fuel tank design of launch vehicle in China.
This project focuses on a key fundamental scientific problem, lightweight design theory and method of grid stiffened cylinder shell allowing for imperfection sensitivity, by multiple utilizations of the analytical, numerical and optimization methods as well as the principal experiments. Three scientific difficulties including “prediction theory and validation of knockdown factors for stiffened shells under axial compression”, “mechanical mechanism of load-carrying capacity and low imperfection sensitivity of hierarchical stiffened shells” and “optimization theory and method of stiffened shells allowing for imperfection sensitivity” will be analyzed and investigated respectively to settle the key scientific problem.