International Journal of Energetic Materials and Chemical Propulsion

THE PRESSURE SENSITIVITY OF THE ULTRASONIC WAVES VELOCITY: A CONTRIBUTION TO A BETTER DETERMINATION OF THE ENERGETIC MATERIAL REGRESSION RATE

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Experimental methods based on ultrasound waves propagation have been applied to the determination of either the burning or the degradation rate of the energetic materials used in solid or hybrid propulsion systems. These techniques are non-intrusive and can be used under realistic conditions. Their working principle relies on the measurement of the Time Of Flight (TOF) of the mechanical waves travelling through the tested material(s), which is influenced by both pressure and temperature effect on the wave velocity. The goal of this paper is to focus on the pressure effect only, by comparing the published data and the relative analyses, presenting the authors point of view and, possibly, suggesting the most acceptable approach to account for this effect. This aspect represents an important challenge because the confidence level in the energetic material regression rate value, deduced from the TOF measurement, is directly related to the values of the pressure sensitivity of the wave velocity. The mechanical behavior of the energetic material is, then, the key point. Examples of applications, such as those to a classical composite solid propellant and to a Hydroxyl Terminated PolyButadiene (HTPB) fuel grain in hybrid motors, illustrate and feed the discussion.