A two-dimensional model of the transversal cross section of a bonded rocket propellant grain was subjected to uniform and steady thermal loading and, alternatively, to mechanically applied uniform radial displacements on the outer boundary. The optimization of perforation contours (attained in previous research programs by applying uniform pressure on the outer boundary of the grain model) was confirmed for both types of thermal loading. The concentration factor at the fillets of the inner contour was determined. An attempt was made to predict the maximum strain in the actual propellant subjected to the same thermal conditions. The material used for the model was a urethane rubber. The thermoelastic properties of the model material were determined.