Experimental study on the porosity of HTPB propellant: characterization of damage evolution

To characterize the damage evolution mechanism of HTPB composite solid propellant,
the porosity as well as the sphericity will be analyzed using micro-CT. Under normal
temperature and pressure, the damage mechanisms include voids, "dewetting" damage
at the AP particle-matrix interface, cracks within the matrix, and cavities formed from
the aggregation of “dewetting” and crack damage. In this paper, two models were
established based on strain and depth for both the damage evolution mechanism model
and the sphericity model related to the proportion of porosity of HTPB propellant. The
results showed that in the initial state, the porosity was about 0.4%, with roundish pores
having high sphericity (0.61-1) accounting for the majority. With the damage evolution,
the ratio of crack-like pores to roundish pores increased from 20% to 90%. Along with
different types of damage mechanisms, the growth of porosity exhibited linear behavior
under low-strain conditions and followed a power-law relationship under high-strain
conditions. These parameters and formulas can be utilized in subsequent numerical
simulation models. This study contributes to designing and practical applications of solid
rocket motors according to the damage evolution of HTPB propellant.