Kubrusly Alan C, Tovar Pedro, von der Weid Jean Pierre, Dixon Steve
Centre for Telecommunication Studies, Pontifical Catholic University of Rio de Janeiro, Rio de Janeiro, Brazil.
Centre for Telecommunication Studies, Pontifical Catholic University of Rio de Janeiro, Rio de Janeiro, Brazil.
Ultrasonics. 2021 Apr;112:106334. doi: 10.1016/j.ultras.2020.106334. Epub 2020 Dec 24.
When shear horizontal ultrasonic guided waves interact with thickness discontinuities in plates, the reflected and transmitted wavefields can be composed of several modes due to mode conversion. It is known that in a plate with a symmetric discontinuity, with respect to the plate's mid-plane, mode conversion is restricted to modes that share the same symmetry as the incident mode. In this paper, we use an analytical model based on the reciprocity principle and finite element analysis to investigate mode conversion due to the interaction with different types of discontinuity, namely, non-symmetric, symmetric and geometrically symmetric but with opposite boundary conditions, that is one side of the discontinuity free and the other rigidly fixed. We show that the reflected field due to interaction with the latter is virtually restricted to modes with the opposite symmetry of the incident one, acting as a symmetry inverter discontinuity. Unlike fully symmetric discontinuities, the effectiveness of a symmetry inverter discontinuity depends on the frequency. This was proved with aid of the analytical model for a full-depth discontinuity and verified for partial depth discontinuities. Finally, symmetry inversion of SH waves was experimentally verified in acrylic plates which were symmetrically machined and filled with steel in one side to mimic a fixed boundary condition.
当水平剪切超声导波与板中的厚度不连续处相互作用时，由于模式转换，反射和透射波场可能由几种模式组成。众所周知，在具有对称不连续的板中，相对于板的中平面，模式转换仅限于与入射模式具有相同对称性的模式。在本文中，我们使用基于互易原理的解析模型和有限元分析来研究与不同类型不连续处相互作用引起的模式转换，即非对称、对称以及几何对称但具有相反边界条件的情况，也就是不连续处一侧自由而另一侧刚性固定。我们表明，与后者相互作用产生的反射场实际上仅限于与入射模式具有相反对称性的模式，起到了对称反转不连续的作用。与完全对称的不连续不同，对称反转不连续的有效性取决于频率。这通过全深度不连续的解析模型得到了证明，并针对部分深度不连续进行了验证。最后，在经过对称加工且一侧填充钢以模拟固定边界条件的丙烯酸板中，通过实验验证了SH波的对称反转。
