In laboratory acoustoelastic tests the load direction is known, and usually the employed ultrasonic waves are propagated along the direction of one of the principal stresses. Completely different is the situation for “in situ” acoustoelastic tests, where the principal stress directions are not known in advance: therefore, in principle, it is needed to examine the material acoustic response along different directions to effectively characterize the actual stress state.The above considerations suggest deepening the study of the sensitivity of the acoustoelastic effect on the propagation direction of ultrasonic waves. Here, this issue is experimentally investigated regarding a uniaxially prestressed isotropic material and by using the results of laser ultrasonic tests.In particular a Nd:Yag laser with 1064 nm wavelength was used as the pump laser for acoustic wave excitation; an optical path equipped with a cylindrical lens handled by a goniometric device allows for the rotation of the laser beam, thus varying the direction of the ultrasonic beam generated into the sample. A laser interferometer Quartet system was used for acoustic wave detection.In this way, it is studied how the acoustoelastic effect is affected by the variation of the propagation direction for both bulk and surface waves. The polar diagrams of the slowness for each kind of propagating wave are experimentally reconstructed for each considered prestress level.

Directional Sensitivity of the Acoustoelastic Effect in Uniaxially Prestressed Materials

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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