Abstract

A Model for the Interaction of Plane Waves with Nonlinear Interfaces

C.Pecorari (Marcus Wallenberg Laboratory, Department of Vehicle Engineering, Royal Institute of Technology, Stockholm, Sweden)

e-mail: claudio@fkt.kth.se

Cracks generated by fatigue or stress corrosion processes tend to have faces which conform to each other at the scale defined by the grain size. Thus, even a small compressive stress suffices to bring the surfaces in close contact, and dramatically changes the linear response of the defect to an incident ultrasonic wave. Methods that exploit the nonlinear response of a crack with faces in close contact have been developed during the past years, and have shown promising results. However, a satisfactory theoretical description of the interaction between such a defect and a probing wave is still lacking. Towards this goal, a new set of boundary conditions to be enforced at an interface formed by two surfaces in partial contact is proposed. Three mechanisms responsible for the nonlinear behaviour of the interface are discussed. Two of them stem from the dependence of the interfacial elastic properties on the applied stress, and are of "classical" type. The third mechanism is of hysteretic nature, and is caused by the partial slipping of the contacts when they are subjected to a tangential load. Numerical results are presented which refer to the simple cases of bulk waves at normal and oblique incidence.

Section : 3