Use of an X-Ray Process Model to Determine Crack Detectability in a Multi-Layer Geometry

Abstract

Inspection of a multi-layer geometry is of particular interest to the aircraft industry in which areas repaired with doublers must be continually inspected for further crack growth in the underlying structure. In some muti-layer geometries, x-ray inspection is the modality of choice due to the inaccessibility and limitations of other techniques. Because x-ray inspectability is extremely dependent upon crack opening and orientation, a need exists to quantitatively assess the detectability of cracks for various crack geometry parameters and x-ray generator parameters. X-ray simulation models for different generator types, generator settings, inspection geometries and crack parameters can be used to make these quantitative assessments [1]. The long term goal of this work is to contribute to an inspection standard for certain aircraft geometries which will account for variabilities in generator characteristics such as output spectrum, filtration, voltage and current. In this paper, we target a specific aircraft inspection problem and apply the x-ray simulation model to crack detectability in terms of contrast. In addition, some model validation is performed to support the results of the inspection simulations. Finally, a preliminary quantitative measure of crack detectability in terms of both size and contrast is derived and applied to the simulation results.