EMAT generation of bulk forces in a ferromagnetic plate and their equivalent surface stresses

C. Rouge (1) , A. Lhémery (1) , C. Aristégui (2)

1 DISC (CEA, LIST) - Département Imagerie et Simulation pour le Contrôle (CEA, LIST)
2 I2M - Institut de Mécanique et d'Ingénierie de Bordeaux

Electro-magnetic acoustic transducers (EMAT) are successfully used in many NDE applications, despite their low efficiency: they do not require a coupling medium and can easily generate elastic waves that standard piezoelectric transducers cannot, such as shear horizontal guided waves. There are all sorts of EMAT designs, so much so that dedicated simulation tools are necessary to optimally conceive an EMAT for a given application. EMAT performances also strongly depend on material properties of the piece under test. Here, ferromagnetic materials are considered. In such a material, an EMAT is the source of three forces resulting from three distinct and generally nonlinear phenomena: in addition to the Lorentz's force generated in all conductive media, the magnetization and magnetostriction forces take place. All these forces are modelled as vector fields in the volume of the specimen. However, wave generation is more efficiently predicted by considering sources of surface stress than sources of body force. Thus, a general model is derived for transforming body forces into surface stresses; this approach is used to express the 2D modal amplitudes of Lamb waves generated by an EMAT in a ferromagnetic plate as quasi-closed form solutions.

Mots clés: Elastic waves; Ferromagnetic materials; Ferromagnetism; Guided electromagnetic wave propagation; Nondestructive examination; Shear flow; Surface properties; Surface waves; Conductive media; Coupling medium; Electromagnetic acoustic transducers; Ferromagnetic plate; Non-linear phenomena; Quasi-closed-form solutions; Shear horizontal guided waves; Wave generation; Acoustic transducers

Domaines: Physique [physics]

C. Rouge, A. Lhémery, C. Aristégui. EMAT generation of bulk forces in a ferromagnetic plate and their equivalent surface stresses. Journal of Physics: Conference Series, 2014, 498 (1), ⟨10.1088/1742-6596/498/1/012013⟩. ⟨cea-01820755⟩