Metallic composites and foams are prospective materials for use in the aerospace and automotive industry for crash energy absorption safety parts or lightweight constructions. During manufacturing, artifacts in the foamable precursor material or material quality variations can influence the foam structure after the foaming process; thus, such a process requires quality control. The advantage of ultrasonic techniques is the possibility to perform noncontact and one-sided access measurements online. A three-layer system consisting of a layer of aluminum foam precursor sandwiched between two aluminum sheets has been investigated.
The problems of ultrasonic nondestructive characterisation of such materials are due to the very similar density and ultrasound velocity of the adjacent layers, which produce very weak reflections of ultrasonic waves, and the thin layers also give overlapped reflections in the time domain.
The objective was to develop an ultrasonic technique that is suitable for measurement of the total thickness and the thickness of individual layers of metal composite (foam).
The proposed technique is based on the identification of object parameters. The numerical iterative deconvolution technique was investigated, analysed, and adapted to measure the thickness of individual layers with similar density and ultrasound velocity of the multilayered aluminum foam precursor material. Theoretical analysis and experimental investigations have shown that application of the proposed numerical iterative deconvolution enables the thickness measurement of individual layers with the expanded uncertainty of less than +-10 micrometers.
The developed technique, which is based on pseudorealtime data processing embedded into the hardware digital signal processing systems, is a prospective method to use in the automotive and aerospace industry for online quality control.