A METHOD OF NONLINEAR VISCOELASTIC ANALYSIS OF SOLID-PROPELLANT GRAINS FOR PRESSURE LOAD

For structural integrity evaluation of solid propellant grains under i gnition pressurization load, an accurate estimation of the maximum ten sile strain and the corresponding rate of strain at the port surface i s essential, because of the viscoelastic nature of the material. Here, a method of non-linear viscoelastic stress analysis for ignition pres surization load is developed following step-by-step finite element met hod considering the material and geometric non-linearities. The materi al non-linearity considered here is due to the non-linear bulk modulus which depends on the magnitude of the hydrostatic pressure. The geome tric non-linearity is considered here by computing the element stiffne ss matrix and load vector at each time step, based on the deformed con figuration. The method of analysis developed is applied to solve two p ractical grain problems. Results show that the maximum tensile strain and the rate of strain decrease considerably when the non-linearities are considered and the maximum tensile strain and the maximum rate of strain do not occur at the same burning time.