Thermal Loading Effect on the Bore Deformation of Viscoelastic Solid Propellant Grain

What is it about?

The aim of this study is to perform thermostructural analysis of a composite solid propellant grain by using experimental approach and finite element method to determine the effect of environmental temperature changes from curing temperature to low firing temperature conditions on the hoop and axial strains on the grain bore surface of a multilayered solid rocket motor. Linear elastic and nonlinear viscoelastic material models were generated and implemented in ANSYS finite element code for two-dimensional axisymmetric grain. In order to simulate the nonlinear behavior of the propellant grain exactly, the viscoelastic material model data were obtained experimentally from uniaxial stress relaxation tests at different temperatures and strain load levels based on propellant specimen, then the concept of the shift factor and the time-temperature superposition principle (TTSP) were used to obtain the relaxation modulus master curve. The verification of the finite element models was accomplished by comparing the numerical result with the hoop and axial strain data obtained experimentally at different times and temperatures from the homogeneous shrinkage of a three layered thick-walled solid propellant cylindrical tube grain bonded to a rigid case motor with different material proprieties for each layer. The experimental data show the great effect of the temperature change on the grain profile and the nonlinear viscoelastic results are found to be in a good agreement with the experimental results than the linear elastic results.

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Why is it important?

Conclusively, this research can be used as a reference for grain design and structural integrity of solid propellant grains, such as more realistic prediction with high accuracy can be obtained in cases of transient thermal loads.