Viscoelastic Modelling of Solid Rocket Propellants using Maxwell Fluid Model

  • Himanshu Shekhar High Energy Materials Research Laboratory, Pune
  • A.D. Sahasrabudhe College of Engineering, Pune
Keywords: Solid rocket propellants, mechanical properties, viscoelasticity, Maxwell fluid, spring constant, damping coefficient

Abstract

Maxwell fluid model consisting of a spring and a dashpot in series is applied for viscoelastic characterisation of solid rocket propellants. Suitable values of spring constant and damping coefficient wereemployed by least square variation of errors for generation of complete stress-strain curve in uniaxial tensile mode for case-bonded solid propellant formulations. Propellants from the same lot were tested at different strain rates. It was observed that change in spring constant, representing elastic part was very small with strain rate but damping constant varies significantly with variation in strain rate. For a typical propellant formulation, when strain rate was raised from 0.00037/s to 0.185/s, spring constant K changed from 5.5 MPato 7.9 MPa, but damping coefficient D was reduced from 1400 MPa-s to 4 MPa-s. For all strain rates, stress-strain curve was generated using Maxwell model and close matching with actual test curve was observed.This indicates validity of Maxwell fluid model for uniaxial tensile testing curves of case-bonded solid propellant formulations. It was established that at higher strain rate, damping coefficient becomes negligible as compared to spring constant. It was also observed that variation of spring constant is logarithmic with strain rate and that of damping coefficient follows power law. The correlation coefficients were introduced to ascertain spring constants and damping coefficients at any strain rate from that at a reference strain rate. Correlationfor spring constant needs a coefficient H, which is function of propellant formulation alone and not of test conditions and the equation developeds K2 = K1 + H ´ ln{(de2/dt)/(de1/dt)}. Similarly for damping coefficient D also another constant S is introduced and prediction formula is given by D2 = D1 ´ {(de2/dt)/(de1/dt)}S.Evaluating constants H and S at different strain rates validate this mathematical formulation for differentpropellant formulations. Stress-strain curves for solid propellants can be generated at those strain rates atwhich actual testing is not possible. Close matching of test and predicted stress-strain curve indicates propellantbehavior as visco-elastic Maxwell fluid.

Defence Science Journal, 2010, 60(4), pp.423-427, DOI:http://dx.doi.org/10.14429/dsj.60.488

Author Biographies

Himanshu Shekhar, High Energy Materials Research Laboratory, Pune
Done MTech in Mechanical Engineering from IIT, Kanpur, and is working as Deputy Director at High Energy Materials Research Laboratory (HEMRL), Pune. He has developed infrastructure for processing large size casebonded solid propellant rocket motors and has processed several motors, which have been fired successfully. He is working as Head, Ballistics group, HEMRL, and has designed propellant grains for various applications.
A.D. Sahasrabudhe, College of Engineering, Pune
Obtained PhD in Mechnical engineering from IISc, Bangalore and is Director and professor in Mechanical engineering at College of Engineering, Pune. He is gold medalist and recipient of cash prize for standing first in all ten semesters during BE. He has guided 40 BTech students and 5 PhD students. He has 34 publications to his credit, organised9 seminars and handled 9 consultancy projects.
Published
2010-07-09
How to Cite
ShekharH., & SahasrabudheA. (2010). Viscoelastic Modelling of Solid Rocket Propellants using Maxwell Fluid Model. Defence Science Journal, 60(4), 423-427. https://doi.org/10.14429/dsj.60.488