Our customer is involved in user trials of solid propellant rocket motors towards acceptance of production lots. During static firing, cracking and scooping of throat material is sometimes reported. It was felt that phenomena might be due to incompatibility of material with stress and thermal loading existing inside the nozzle. Customer sought to study this problem using Design of Experiment (DOE) approach to identify best material composition.
Zeus Numerix first obtained pressure and heat flux distribution inside the nozzle using viscous compressible CFD simulation on proprietary package. Transient thermal analysis and structural analysis of nozzle section was conducted using FEM approach. Stresses so obtained were compared against shock resistance criteria to predict cracking phenomena. Finally, the material properties were varied to identify the most sensitive parameter.
For the available candidate materials, Zeus Numerix reported Crack Initiation Factor. Their relative values matched with the trends observed during static trials. Of various techniques of DoE, ‘one at a time’ technique was used. Optimum material properties have been identified and based on them the customer started development of new material.