It is proposed to use rotational rheometer with various fixtures for development of test methodologies for rheological characterization of composite propellant under high shear and extension. Following three different techniques will be used to characterize the rheological properties of composite propellant suspensions.
a. Thin Gap Rheology: For measurement of rheological properties under high shear rate
b. Squeeze Gap Rheology: For measurement of rheological properties under extensional flow
c. Hyperbolic Contraction Technique: For measurement of Extensional flow property; the feasibility of this method for rheological characterization of propellant is to be studied.
Following methodology will be used for development of test:
a. High shear rate rheology
Initial trials will be conducted with model systems consisting of suspensions based on binder and filler with volumetric loading simulated with actual composite propellant. It is proposed to carry out Couette flow rheology using several gaps/lengths. The overall analysis will involve the following steps:
• Preliminary characterization of suspensions response at large gaps
• Systematic investigation of the dependence of gaps on raw signals (torque, position and rotation/oscillation rates) from the rheometer
• Measurement of normal force difference and its relation with strain rate
• Calibrate the gap errors at narrower gaps
• Development of fluid mechanical solutions of linear momentum balances with example constitutive models
• Comparison of experimental and theoretical raw signals for a given set of experiments
• Modification of constitutive models
• Coarse-grained simulations to understand the microstructure and effect of shear at different gaps
• Exploration of microstructures at different gaps using optical rheological techniques; which would involve optical microscopy, atomic force microscopy and light scattering.
b. Squeeze flow rheology
• Development of appropriate lubrication for achieving extensional flow in a rheometer
• Squeeze flow rheology of propellant dispersions
• Quantification of extensional viscosity at different squeeze rates
c. Hyperbolic contraction technique
Propellant suspensions being visco-elastic in nature, both shear and extensional behavior need to be characterized. One of the techniques for characterization of extensional properties for thick suspensions is Hyperbolic Contraction Technique involving contraction flow of suspensions through hyperbolic nozzle at specified displacement and measurement of exerted forces using load cells. A hyperbolic geometry is used to generate extensional properties based on pressure drop measurement using numerical methods.
A feasibility study of this method is to be carried out for rheological characterization of propellant and related numerical simulation code is to be formulated for measurement of extensional viscosity and dependence of extensional viscosity in extension rate.
d. Constitutive modeling
In the present proposal, some of the models will be identified based on preliminary rheology analysis. The selected models then will be used for simulating high shear rate, squeeze flow and hyperbolic contraction technique.

Rheology of Composite Propellant Suspension under high Shear and Extension
HEMRL is involved in development of composite propellant for various applications. Mixing of propellant suspension is one of the most critical steps in processing of composite propellant. Various batch types of mixers viz., vertical planetary mixers and sigma are being used for mixing of propellant suspensions. Further, HEMRL is developing a continuous mixing system based on twin screw mixer for such applications.
The mixing of composite propellant is a complex phenomenon involving various types of actions viz., shear, extension, compression, cutting, folding, pumping, etc. The extensional flow and shear flows are reported to govern the mixing and dispersive mixing index is proposed in the literature based on the strength of extensional and shear flow during the mixing. To understand these flows, it is necessary to determine the flow properties of propellant suspension under the shear and extension rates prevalent during the propellant mixing.
Presently, the rheological properties of propellant suspensions are measured under low shear rate < 1s-1 using the torsion rheometer. However, for studying mixing in twin screw mixers, the rheological data is required under high shear and extension rate. These data will be very useful for comparing various configurations of mixers, design of screw elements and numerical simulation of propellant mixing. Hence, it is proposed to develop test methodology for determination of rheological properties of composite propellant suspensions under high shear and extension.