Experimental investigation on multi-material gap measurements by computed tomography using a dedicated reference standard

Geometrical measurement of multi-material assemblies can be a challenging task. This is particularly important considering that an assembly of parts that individually passed through quality control does not necessarily result in a defect-free product. More specifically, the geometrical verification of multi-material assemblies should be performed by a non-destructive method, as invasive techniques can cause distortion of parts, relaxing of materials and other unwanted effects. In this context, computed tomography (CT) emerges as a promising technology. However, there are still challenges in achieving full traceability of CT measurements. Moreover, measurements of parts with multi-material interfaces generate even more complex measurement scenarios. In this study, multi-material effects on CT measurements are addressed. More specifically, the measurands defined as a gap between two different materials are investigated, as this is the typical application in industry (e.g. verification of fitting tolerances). The errors of gap measurements are evaluated on a series of dedicated reference standards. Several critical aspects of multi-material measurements are addressed in this study and preliminary results of CT performance in multi-material gap measurements are presented