Identification of Viscoelastic Parameters for Composite Propellant by Indentation Technique

A method for identifying the relaxation modulus or creep compliance of composite propellant based on indentation technique is proposed, which can rapidly and nondestructively measure the mechanical properties of solid rocket motor grain in storage. According to viscoelastic indentation theories, a constitutive model for conical indentation is derived to predict the mechanical parameters of composite propellants. The indentation test with different loading rates and the traditional tensile stress relaxation test for a certain PBT composite propellant were carried out to verify the feasibility of the proposed method. The results show that the prediction results calculated by the constitutive model are in good agreement with the load‐displacement curves of the indentation test, and the mechanical parameters identified by the constitutive model are similar to those parameters fitted by the tensile stress relaxation test. Relevant methods and conclusions can provide a reference for structural analysis and storage life prediction of solid rocket motors.