Experimental detection by magnetoelastic sensors and computational analysis with finite elements, of the bending modes of a cantilever beam with minor damage

This work introduces for first time the use of the magnetoelastic sensors as vibration probes for damage detection in mechanical structures such as cantilever beams. The purpose is to show some of the advantages of these materials as vibration detectors, as well as the accuracy of them in detecting the natural frequencies of mechanical structures. The sensor used is a ribbon which is composed of an amorphous metallic alloy known as “Metglas 2826MB3”. Various long aluminum alloy beams of the same dimensions but with a single transverse crack at different positions and depths were tested, fixed at one end by using a hydraulic press so as to have consistent boundary conditions. The beams were excited by a single short and intense mechanical contact pulse and then left free to vibrate. The vibrations were forcing the magnetoelastic sensors to change their magnetic state dynamically and thus produce a voltage signal at a close-by external coil. The Fourier analysis reveals seven dominant peaks which lay very close (most of the error values are between 0.5-1.5 %) to the first seven bending mode peaks predicted by the finite-element-method (FEM) commercial software “ANSYS”. Thus the current work is a proof-of-principle that the magnetoelastic sensors can be used for damage detection of mechanical structures.