The paper addresses experimental characterization of instant shape of paraffin grain with predefined structural discontinuity in process of combustion and its possible influence on structural integrity of hybrid propellant motor. The one-port paraffin grains with and without artificial crack were subjected to combustion in a hybrid propellant test-motor and considerable discrepancies of temperature on external surface of the non-cracked and the cracked grains were detected. Elevated temperature on the external surface of cracked grain was caused by fast evolution of the crack in direction of motor’s casing during combustion process. Thus, it was shown that crack formation causes a local overheating of structural casing that may subsequently jeopardize structural integrity of the motor
