An ultrasound method for the acoustoelastic evaluation of simple bending stresses

Ultrasonic waves constitute a privileged tool for investigation in the anal ysis and characterisation of mechanical stress states. Ultrasonic wave velo cities depend on many physical properties of the propagation medium such as the second-, third- and higher-order elastic constants, the volume density and the strain. They also depend on whether the wave is longitudinal or tr ansversal. In this last case, they also depend on the wave polarisation dir ection. The present paper deals with the classical acoustoelasticity in stressed an d elastically deformed media when they are submitted to bending stresses. A numerical and an experimental evaluation of the resulting change in the ul trasound velocities as a function of bending loads are described. Some resu lts have been obtained on the variation of propagation velocities of the lo ngitudinal and transversal polarised waves as a function of mechanical bend ing loads applied on samples made of S 185 steel. The acoustoelastic evalua tions have been achieved in three zones under bending stress (compressed, c entral and extended fibres) in the case where the path of probing, longitud inal and linearly polarised shear waves are parallel to the sample axis. As additional investigation on acoustoelastic behaviour on bending load, we p ropose some acoustoelastic responses simulated numerically on materials of known macroscopic properties. The experimental study was achieved by means of a measurement set-up compos ed of an ultrasound bench and a mechanical test machine. In order to measur e the variations of the propagation velocity, a correlation technique has b een used to obtain an accurate estimation of the propagation time. The velo city measurements have taken into account the elastic deformation of the sa mples made of carbon steel (C 35). (C) 2001 Elsevier Science Ltd. All right s reserved.