Influence Of Texture Anisotropy On Acoustoelastic Birefringence In Materials

In view of some materials is anisotropy before unstressed, study on the acoustoelasticeffect has a direct significance to our life and production. This experiment studied theacoustoelastic birefringence of strong anisotropic medium (birch and elmwood sample).This paper mainly uses the birch and elmwood as samples, they are mainly presentedorthogonal anisotropic characteristics.In order to compare with the isotropic materials, andwe have measured the nylon sample. We use the transmission method, the experimentunder uniaxial stressed and unstressed states, and the direction of ultrasonic wavepropagation is perpendicular to loading direction.For birch elmwood and nylon samples under unstressed state，the oscillation directionof the shear waves was varied by rotating an ultrasonic sensor, and the relationshipbetween the shear wave velocity and the oscillation direction was examined. The resultsindicated that when the oscillation direction of the shear wave corresponded to one of theanisotropic directions of the wood plate specimen, the shear wave velocity decreasedsharply and the relationship between shear wave velocity and rotation angle tended tobecome discontinuous，the shear wave velocity showed fan-shaped. For nylon sample，therelationship between shear wave velocity and rotation angle tended to a ring, regardless ofthe oscillation direction.We investigated the velocities of ultrasonic shear waves propagating transversely tothe applied stress direction in specimen to study the effect of anisotropy on acoustoelasticbirefringence for birch and elmwood specimens under stress state. The experimentalresults of elmwood and birch were similar to unstess state. When the oscillation directionof the shear wave corresponded to one of the texture anisotropic directions of the woodplate specimen, the shear wave velocity decreased sharply and the relationship betweenshear wave velocity and rotation angle tended to become discontinuous. Compared withunstessed condition, the shear wave value of the azimuth angles nearly no change. Theshear wave velocities slightly increased with compressive stress at almost rotated angles,which is different from acoustoelastic effect of Japanese magnolia. On the contrary, forisotropic material (nylon specimen), when the shear wave oscillated along the stressdirection, the shear wave velocity peaks regardless of the plate axis direction of thespecimen, the value of shear wave velocity is similar to an elliptic ring instead of circular ring, major axis of the ellipse corresponds to loading direction. Stress-inducedacoustoelastic birefringence was obvious. The azimuth angles of extremum value mainlydepended on stress-induced anisotropy and were almost not influenced by the textureanisotropy, in contrast with the strong anisotropy of birch and elmwood samples.The above results show that the strong anisotropy of birch and elmwood samples，stress-induced acoustoelastic birefringence was not obvious. The azimuth angles ofextremum value mainly depended on the texture anisotropy and were almost notinfluenced by stress-induced anisotropy. Both birch and elmwood specimens exhibit slightacoustoelastic birefringence effects. The ultrasonic shear wave propagated in wood understress was confirmed to be polarized in the anisotropic axis of the wood. This study ishelpful for us to carry out ultrasonic measurement in wood specimens based onacoustoelastic method. It’s provides preliminary experience and basis for theacoustoelastic effect of strong anisotropic medium.