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Structural Analysis Procedure for a Case Bonded Solid Rocket Propellant Grain
During the service life, a case-bonded solid propellant rocket grain is subjected to many stress-inducing environments. The viscoelastic nature of the propellant causes a strong load-rate and temperature dependence of mechanical properties. Besides a natural decrease of physical propellant parameters in unloaded conditions, called chemical aging, there is also a mechanical properties degradation, reffered to as cumulative damage. Temperature variations are found to be the main reason for the propellant strain and stress capacity decreasing during the storage. Various mathematical models for a structural solid propellant grain integrity analysis have been made, but they are not of the same validity as the more common models for elastic analysis. They have to be followed by appropriate three-dimensional tests. Unfortunately, it is almost impossible to make reproductive failure tests that would verify the quality of the analysis. In the case of an antihail rocket propellant grain, the repeated appearance of cracks in the star pointed grain channel has given a useful statistical sample for mathematical model verification and further analysis. Key words: rocket motor, propellant grain, solid rocket propellant, structural analysis, mechanical characteristics, temperature influence, cumulative damage, service life.
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