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.