2D-DIC for the quantitative validation of FE simulations and non-destructive inspection of aft end debonds in solid propellant grains

This paper presents the application of 2D full-field optical displacement measurements for quantitative validation of Finite Element (FE) simulations in solid propellant grains. The experimental validation is done using an instrumented small-scale Structural Test Motor (STM) subjected to thermal load. Displacement field at the aft end of STM has been computed using two-dimensional Digital Image Correlation (2D-DIC) and compared with FE simulation results. The current research aims towards highlighting two important aspects in the application of 2D field measurements with solid propellants. Firstly, the effect of out-of-plane deformation of the propellant face, due to thermal shrinkage, on the experimentally measured displacement field is studied and a compensation is applied to correct for the resulting displacement bias. Secondly, the potential of using full-field displacements for non-destructive testing is demonstrated; from the analysis of observed displacement profile at the aft end, a small debond near the propellant–insulation–metal triple interface is identified and the FE model is then updated based on this information to complete the validation. It is also shown that the complete profile of the debond can be approximated in this manner.