An experimental study on mechanical and ballistic characteristics of different HTPB composite propellant formulations

Abstract

The main goal of this paper is to investigate the changing in the tensile behavior and the burning rate characteristics of hydroxyl-terminated polybutadiene (HTPB) propellantunder the variations of the crosslinking density, which was predominantly determined by the equivalent ratio of diisocyanate to total hydroxyl (NCO/OH ratio), which known as the curing ratio. Four variousbatches with different curing ratios (NCO/OH) percentage were produced in which the production processes were fixed. Uniaxial tensile tests were conducted at different temperatures (-40, 20 and 55°C), and different strain rates (0.000656 1/s, 0.0328 1/s) using a Zwick universal test machine. In order to measure the burning rate, cured solid propellant strands were tested using the acoustic wave emission method under different pressure ranging from 4 to 10 MPa. The experimental results indicate that the tensile behavior of HTPB propellant is remarkably influenced by curing ratio, strain rate, and temperature. It was observed that a great change on stress-strain curves affected various curing ratios and temperatures on the mechanical behavior of propellant composition. The results showed that high curing ratio leads to increase theultimatestress and decrease the strainat maximum stress, but higher temperatures lead to decrease theultimate stress and the strain at maximum stress.The curing ratios (NCO/OH) have an intense impact on mechanical characteristics, but slightly impact on ballistic characteristics for propellant. Furthermore, careful measurements of these parameters are important to control the production quality and to provide a reliable comparison between different propellant batches.