Theoretical modelling of digital radiographs of composite rocket nozzles for the analysis of defects

X-ray radiography techniques are widely used for the non-destructive evaluation of composite nozzle liners of rocket motors. In conventional radiography it is difficult to distinguish the images corresponding to excess resin and resin lean regions in the composite, since the variation in the optical density is very small. Also, porous layers and minor delaminations will cast similar images in the radiographic projection. In this work, theoretical modelling is carried out for various defect conditions to study their effects on the X-ray images. The results are useful for characterisation of the defects in the nozzle liners by radiographic nondestructive evaluation. The observations provide very good input for the interpretation of radiographs in silicaphenolic and carbon-phenolic rocket nozzles. The details of the software developed and its application to solve specific problems are discussed. The changes in optical density with respect to the width of the defect, location of the defect and circumferential extension are investigated.