Direct ultrasonic measurement of solid propellant ballistics

This article illustrates the application of an ultrasonic pulse-echo techni que to determine the burning rate of a composite solid propellant as a func tion of pressure. An evaluation of the measurement uncertainty of the metho d is also presented. Unlike the more traditional strand burner techniques, where dozens of constant pressure tests are necessary, the ultrasonic techn ique measures the burn surface position thousands of times per second as th e pressure varies. This reduces the number of tests necessary to determine the ballistic characteristics of the propellant by an order of magnitude. T his work presents new methods to characterize the changing speed of sound i n the propellant and quantitative estimates of the measurement uncertainty in the burning rate measurement. The results of the uncertainty analysis sh owed that the measurement is accurate to around 4%. The propellant samples were tested in a closed-combustion vessel, under pressurization rates of up to 15.8 MPa/s. The data obtained with the closed-combustion-vessel tests u sing the ultrasonic method are experimentally congruent with tests conducte d in strand burners in steady-state conditions. (C) 1999 American Institute of Physics. [S0034-6748(99)01611-1].