Stability analysis of a solid rocket motor's composite case under external pressure

Paper number

IAC-06-C2.7.02

Author

Mr. Yuan Li, Academy of Aerospace Propulsion Technology, CASC, China

Year

2006

Abstract

Some Solid Rocket Motors (SRMs) must endure definite external loads during the missle’s working process. Especially to those composite cases with thin walls will possibly become invalid. So it is necessary to study the stability behavior of composite cases under external pressure.
Classical stability analyzing methods that based on the linear buckling theory always ignore the influence of the nonlinear factors. These analyzing methods consider that the case’s structure has no geometrical defects, the external loads imposed on the case are not partiality, and the analysis of the distortion is restricted in course of small displacement. These assumptions are not consistent with the case’s actual structure. The essence of stability analysis is nonlinear, any linear supposes will bring definite errors and designation of the SRM according to these calculated results will be dangerous. Analyzing of the case with nonlinear theories must consider the nonlinear factors. Nonlinear factors include lots of aspects, such as geometrical structure, material and boundary conditions, etc. Geometrical nonlinear is the foremost factor in analysis of the stability of composite case under external pressure. 
Stability behavior of a SRM’s laminated cylindrical composite case under external compression is studied by using the finite element method in this research. The main body of the case studied is made of high strength organic fiber reinforced epoxy resin composite material. The wall of the case is only 9 millimeter. The nonlinear critical buckling loads are considered by introducing the linear buckling modes to simulate the initial geometrical defects of the case’s structure. Comparing the calculation results with the testing results, it shows that the linear critical buckling load is higher than the nonlinear critical buckling load. The nonlinear critical buckling loads decrease with the increase of the initial defects. As to the case studied in the research, the critical buckling load calculated by linear analyzing method is 0.4143MPa, the critical buckling load calculated by nonlinear analyzing method with the introduced defect’s size of 1 millimeter is 0.31MPa, the actual load tested by experiment is 0.26MPa. So the calculated result of the imperfect structure by introducing proper initial geometrical defects is much closer to the actual value. 
Only the influence of the initial defects on the critical load under external pressure is discussed in this paper. The more reliable results will be achieved if more nonlinear factors can be considered. The nonlinear analyzing method used in this research can provide a more perfect reference to the stability design of solid rocket motors’ composite cases.

Abstract document

IAC-06-C2.7.02.pdf

Manuscript document

IAC-06-C2.7.02.pdf (🔒 authorized access only).

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