title: Measurement of material nonlinearity using surface acoustic wave parametric interaction and laser ultrasonics.
abstract: A dual frequency mixing technique has been developed for measuring velocity changes caused by material nonlinearity. The technique is based on the parametric interaction between two surface acoustic waves (SAWs): The low frequency pump SAW generated by a transducer and the high frequency probe SAW generated and detected using laser ultrasonics. The pump SAW stresses the material under the probe SAW. The stress (typically <5 MPa) is controlled by varying the timing between the pump and probe waves. The nonlinear interaction is measured as a phase modulation of the probe SAW and equated to a velocity change. The velocity-stress relationship is used as a measure of material nonlinearity. Experiments were conducted to observe the pump-probe interaction by changing the pump frequency and compare the nonlinear response of aluminum and fused silica. Experiments showed these two materials had opposite nonlinear responses, consistent with previously published data. The technique could be applied to life-time predictions of engineered components by measuring changes in nonlinear response caused by fatigue.
authors.affiliation: Division of Electrical Systems and Optics, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, United Kingdom. T.stratoudaki@nottingham.ac.uk
authors.forename: Theodosia
authors.initials: T
authors.lastname: Stratoudaki
authors.forename: Robert
authors.initials: R
authors.lastname: Ellwood
authors.forename: Steve
authors.initials: S
authors.lastname: Sharples
authors.forename: Matthew
authors.initials: M
authors.lastname: Clark
authors.forename: Michael G
authors.initials: MG
authors.lastname: Somekh
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Collison
mesh_terms: D000162:Acoustics; D003252:Construction Materials; D004581:Electronics; D007834:Lasers; D008962:Models, Theoretical; D017711:Nonlinear Dynamics; D012449:Safety; D017603:Signal Detection, Psychological; D013499:Surface Properties; D014465:Ultrasonics / Q000379:methods*