A model to predict the ultrasonic field radiated by magnetostrictive effects induced by EMAT in ferromagnetic parts
Résumé
An Electro-Magnetic Acoustic Transducer (EMAT) is a non-contact source used in Ultrasonic Testing (UT) which generates three types of dynamic excitations into a ferromagnetic part: Lorentz force, magnetisation force, and magnetostrictive effect. This latter excitation is a strain resulting from a magnetoelastic interaction between the external magnetic field and the mechanical part. Here, a tensor model is developed to transform this effect into an equivalent body force. It assumes weak magnetoelastic coupling and a dynamic magnetic field much smaller than the static one. This approach rigorously formulates the longitudinal Joule's magnetostriction, and makes it possible to deal with arbitrary material geometries and EMAT configurations. Transduction processes induced by an EMAT in ferromagnetic media are then modelled as equivalent body forces. But many models developed for efficiently predicting ultrasonic field radiation in solids assume source terms given as surface distributions of stress. To use these models, a mathematical method able to accurately transform these body forces into equivalent surface stresses has been developed. By combining these formalisms, the magnetostrictive strain is transformed into equivalent surface stresses, and the ultrasonic field radiated by magnetostrictive effects induced by an EMAT can be both accurately and efficiently predicted. Numerical examples are given for illustration.
Mots clés
Dynamics
Ferromagnetic materials
Ferromagnetism
Magnetic fields
Magnetism
Magnetostrictive devices
Mathematical transformations
Surface properties
Dynamic magnetic fields
Electromagnetic acoustic transducers
External magnetic field
Magnetoelastic couplings
Magnetoelastic interactions
Magnetostrictive effect
Magnetostrictive strain
Surface distributions
Ultrasonic testing