The effects of AP particle size and concentration on ap/htpb composite propellant burning rates
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2017 by Gordon R. Morrow and Eric L. Petersen. The burning rates of IPDI-cured AP/HTPB propellants with a standard curing ratio of 10.44:1 were analyzed. It is well known that the particle size of AP greatly affects the burning rate, yet there exists a lack of archival databases for a wide range of particle sizes and pressures. Testing conditions for this study included an AP average size range of 20 m 200 m with two intermediate steps, a pressure range of 500 - 2,250 psi with multiple intermediate steps, and lastly a concentration range of 70% to 85% AP by mass with three intermediate steps. As expected, decreasing the AP size increased the burning rate for sizes above about 45 m. The results for the smaller sizes (20 and 45 m) converged to similar burning rates, indicating that the mixture is nearing a premixed burning limit. Power law burning rate expressions were obtained for each mixture. Most importantly, an empirical model describing the burning rates over the entire range of propellants tested was created that is easy to use and mirrors the power law. In the future, these same formulations should be tested between the 2,250 to 5,000 psi ranges where the role of AP becomes crucially important.
