Prediction of Erosion Characteristics for Ablative Throat Insert Liners Using Ultrasonic Velocity Measurements

Launch vehicles use ablative nozzle liners to function under very high thermal and erosive environments. In solid motor nozzle throats, graphite or carbon phenolic materials are used because of their high heat of ablation and erosion resistance. Ultrasonic testing is implemented as the primary NDT technique for throat insert liners by almost replacing radiography testing. Though introduced for defect detection, it is found that the ultrasonic velocity measurements can be used in the prediction of erosion characteristics of throat insert liners. A model is developed for erosion prediction based on solid motor ballistic laws and equations of material density with ultrasonic velocity correlation. Erosion in solid motor throat depends on motor design, propellant, nozzle and throat material. Assuming other parameters to be constant, the erosion is related to the density of the throat. Also correlation is established between density and ultrasonic velocity in the graphite. Hence, erosion of graphite and carbon phenolic throat insert liner is predicted using ultrasonic velocity measurements. The predicted erosion values are compared with post-flight values.