Constitutive response and damage in solid propellants

Solid propellants are composite materials with complex microstructure. In a generic form, the material consists of polymeric binder, ceramic oxidizer, and fuel particles (e.g. aluminum). Damage induced by severe stress and extreme temperatures is manifested in particle cracking, decohesion along particle/polymer interfaces, and void opening. In this work, the effect of damage due to particle dewetting on the material macroscopic response is investigated by accounting for large deformations. First, issues pertaining to the constitutive behavior of the individual components in the absence of damage are reviewed. Next, with the use of rigorous composite homogenization theory, a macroscopic constitutive law is devised that accounts for continuous void nucleation and growth upon straining. The standard relaxation and uniaxial tension tests are used to calibrate the model parameters. The model is implemented in our Center's finite element code Rocsolid to study damage evolution in the propellant grain of the Titan IV SRMU PQM-1 rocket motor.