Tofeldt Oskar, Ryden Nils
Division of Engineering Geology, Lund University, P.O. Box 118, SE-22100, Lund, Sweden.
J Acoust Soc Am. 2017 May;141(5):3302. doi: 10.1121/1.4983296.
Lamb modes with zero group velocity at nonzero wave numbers correspond to local and stationary resonances in isotropic plates. Lamb modes can be utilized for nondestructive evaluation of the elastic properties and thickness. One example of an application is the testing of plate-like concrete structures. In this example, continuous variation in the material velocity through the thickness may occur. This is usually not accounted for in analyses, and with this as starting point, two inhomogeneous and nonsymmetric cases with continuous material variations are investigated using a semi-analytical finite element technique and a simulated measurement application. In a numerical study limited to the lowest zero-group velocity mode, results show that these modes for the inhomogeneous cases are generated with similar behavior and the same detectability as in the case of an isotropic plate. However, a complex relationship between mode frequency and material velocity exists for the inhomogeneous cases. This hinders the evaluation and interpretation of representative estimations such as those for a cross-sectional mean value of the plate properties. This may lead to errors or uncertainties in practical applications.
在非零波数下具有零群速度的兰姆波模式对应于各向同性板中的局部和驻波共振。兰姆波可用于无损评估弹性特性和厚度。一个应用实例是对板状混凝土结构进行检测。在这个例子中，材料速度可能会在整个厚度上连续变化。在分析中通常不会考虑这一点，以此为出发点，使用半解析有限元技术和模拟测量应用研究了两种具有连续材料变化的非均匀和非对称情况。在一项仅限于最低零群速度模式的数值研究中，结果表明，非均匀情况下的这些模式与各向同性板的情况具有相似的行为和相同的可检测性。然而，非均匀情况下模式频率与材料速度之间存在复杂的关系。这阻碍了对代表性估计值（如板特性的横截面平均值）的评估和解释。这可能会在实际应用中导致误差或不确定性。
