Ultrasonic Properties of Propellant Ingredients

• Published in: Journal of propulsion and power 2004-01, Vol.20 (1), p.135-140
• Main Authors: Kohga, Makota, Frederick, Robert A, Moser, Marlow D
• Format: Article
• Language: English
• ISSN: 0748-4658; 1533-3876
• DOI: 10.2514/1.9240

Ultrasonic, pulse-echo transducers send acoustic waves through a solid propellant to determine the web thickness and the burning rate. The acoustic speed in the propellant increases with increasing pressure and must be quantified to make accurate burning-rate calculations. This experimental work determined the speed of sound as a function of pressure for cured and uncured binder materials hydroxyl-terminated polybutadiene (HTPB) and polytetrahydrofuran (PTHF) and epoxy. A nitrogen system pressurized the 3-cm-diam, 2-47-mm-thick, cylindrical samples to pressures of 15 MPa at pressurization rates of 2 or 14 MPa/s. The results show that the acoustic velocity of cured HTPB, PTHF, and epoxy are 1510, 1650, and 2600 m/s, respectively, at 6.9 MPa. Velocities for uncured HTPB and PTHF range from 1560 to 1610 m/s. The uncertainty is estimated at 1 percent for a 15-mm sample thickness. The pressure sensitivity is linear above 3 MPa at 1.4 to 4.3 m/s. MPa. A study of cured and uncured HTPB sample~, having lengths from 2 to 47 mm revealed a 20 percent variation in the sound speed at sample lengths below 10 mm. This effect could be the result of a measurement bias for the cured samples and surface tension for the uncured samples. (Author)