On The Design And Application Of High-precision Stability Experimental System For Thin-walled Aerospace Shell Structures

Thin-walled cylindrical shells are widely used in launch vehicle structures?and their buckling loads have a great influnce on the achievement of the load-carrying capacity of launch vehicles.As is well known,buckling loads of thin-walled cylindrical shells would have a significant reduction caused by the disturbance of initial geometric imperfections,and its numerical prediction of buckling loads is achieved by preforming complex nonlinear stability analysis.Therefore,the accurate prediction of buckling loads is a recognized problem in the field of structural mechanics.In recent years,for a growing demand of deep space exploration and other scientific activities,countries in the world are competing to develop heavy carrier rocket technology.A series of prediction methods of buckling loads for thin-walled shells are renewed.Among these methods,the high-precision stability experimental method causes lots of attention.Aerospace industry in our country has been developing over the decades,and a large progress has been achieved about the high-precision stability experimental methods.However,the accuracy of stability experiments is still hard to satisfy the requirement of fast development in aerospace industry.The main challenges are as follows:1)It is difficult to accurately consider the effects of initial imperfections in existing stability experiments owing to lack of initial imperfection data.There is still a large discrepancy between numerical prediction results and test results.2)Non-uniform loading capacity is insufficient in existing stability experiments.The buckling loads of thin-walled shells is underestimated by the empirical evaluation strategy of the worst loading condition.3)When the prediction of shell buckling experiments is not accurate,the traditional methods neglect the effect of geometric imperfection at the preliminary design stage,thus they have an inadequate ability to resist the disturbance of geometric imperfections of thin-walled shells and could not satisfy the requirement of high buckling loads.With respect to above problems,the research of observation-representation-prefabrication experimental system design and high-precision non-uniform loading system design are firstly carried out in this study.The high-precision stability experimental system is built based on the above research for improving the accuracy of stability experiment.Further,by means of this experimental system,a series of shell buckling experiments are carried out.With the test results,the accuracy ofbuckling loads for thin-walled shells has been improved by combining the experimental method with the numerical method.Finally,the optimization performance of buckling loads for thin-walled shells is carried out based on the high-precision prediction method.The innovative design with high buckling loads is proposed to improve the load-carrying capacity of thin-walled shells.The main content of this thesis is as follows:(1)A high-precision observation-representation-prefabrication experimental system is established.For thin-walled cylindrical shells,non-contact full-field optical observation system has been established and numerical prediction method of buckling loads based on 3D point clouds data has been developed.With the above system and method,observation and characterization for initial imperfection of thin-walled shell is accurately obtained.High-precision loading control process of multi-lateral perturbation loads based on stepping waiting type has been proposed for prefabricating of dimple-type imperfections.(2)A high-precision non-uniform loading system design is established,and the over-loading condition could be avoided.This system consists of a flexible tooling with variable trusses for non-uniform axial compression and a loading system for non-uniforrm external pressure.An optimization method for non-uniform elastic boundary of thin-walled shells is proposed.The optimization problem takes the equivalent stiffness index as the design objective and a flexible tooling with variable trusses for non-uniform axial compression is obtained.The flexible tooling could efficiently reduce the loading error caused by uniform elastic boundary in space segment experiment.A distributed external pressure loading system based on the airbag loading is proposed for accurate loading around the 3600°circumferential direction.(3)Based on the established experimental system,a series of shell buckling experiments are carried out to obtain buckling loads with different approaches,including the approach based on measured imperfection,Single Perturbation Load Approach(SPLA)and Worst Multiple Perturbation Load Approach(WMPLA).By comparison of the prediction results by these approaches,WMPLA is proved to be the most high-precision approach,which could cover the effect of initial imperfections.(4)Optimization method is proposed for double-skin stiffened cylindrical shells based on the high-precision prediction method of load-carrying capacity.By comparison of buckling loads between double-skin stiffened cylindrical shells and traditional stiffened cylindrical shells,the strong abjitiy to resist imperfections of double-skin cylindrical shells is revealed.By means of the optimization method based on the high-precision prediction method of load-carrying capacity for double-skin stiffened cylindrical shells,the load-carrying capacity of double-skin cylindrical shells has been remarkably improved.