THE EFFECT OF NONLINEARITIES ON THE STRAIN CONCENTRATION FACTORS IN SOLID-PROPELLANT GRAINS

Maximum induced strains in slotted and star grains are obtained from t he inner bore hoop strain of a simple hollow cylindrical grain, by app lying strain concentration factors (SCF), during preliminary grain con figuration design. Here, the effect of certain inherent material and g eometric nonlinearities on the SCF is studied through a step-by-step n onlinear finite element analysis of grains, for ignition pressurizatio n load. The material nonlinearity considered here is due to the presen ce of internal voids in the grain material which induce nonlinearity i n the behaviour of bulk modulus with respect to the magnitude of hydro static pressure. Under geometric nonlinearity, grain deformations are taken into account at each load step of the step-by-step finite elemen t analysis. Results show that the effect of nonlinearities on the SCF is quite considerable.