Thickness measurement of individual layers in sandwich structures with unknown ultrasound velocity

Abstract

This work focuses on the investigation of method for material thickness measurement, when there is no necessity to know in advance what the speed of ultrasonic in the material investigated is. The reason, why the use of speed of ultrasonic in material thickness measurement should be eliminated is, that the measurement of speed of ultrasonic takes some time and requires additional expenses, beside the speed measured will be exact only under the same circumstances, which were on the time of measuring.

Most of methods for thickness measurement apply only to single-layer structures with the known speed of ultrasonic in them. Nowadays the amount of industry products with the sandwich structure (one of the most developing areas is the production of tubes with the variety in diameters and in thickness of walls; another one is the industry of aviation and astronautics), which are made out of several different materials, increases. That is why the use of ultrasonic applying it to sandwich structures becomes of the great importance. However, the effective and practical use of ultrasonic for measurement of sandwich structures is still problematic; the investigation of sandwich structures is not very prevalent, and the methods, when there is no necessity to know in advance what the speed of ultrasonic in the material is, still are not fully investigated. Promotion of investigation and measurement of sandwich structures indicates the need of new methods, which would help to measure the thickness of different layers of sandwich structures without knowledge about the ultrasonic speed in them. This work presents the model of sandwich structure, suggests the algorithm for measurement of thickness of different layers and presents experiments performed. The work is based on the material [9], describing the method of ultrasonic measurement, intended for measurement of thickness of object and ultrasonic speed in it. For this purpose two transducers – transmitter and receiver - from the same side of object were used. According to the distance between transducers and flight-of-time between transmitted and received impulses, there can be the thickness of layers of the object investigated and the speed of ultrasound in them calculated.

The theoretical modeling was carried out with the help of the mathematical packet "MATLAB". Through modeling and experiment rather good adequacy of results was reached.