Ultrasonic Attenuation Method for the Evaluation of Damage

这项研究的结果总结如下三个阶段。弹性动力散射能量的计算公式引入弹性动力散射截面来计算紧凑型散射体的弹性动力散射能量。弹性动力散射截面的近似表达式分三步建立。(1)用散射幅度表示散射场。(2)散射幅度与散射截面的关系。(3)考虑入射波和散射波的干涉效应，近似计算散射截面。通过数值计算，证实了该近似表达式(弹性动力学光学定理)对弹性动力学散射截面的计算具有较好的精度。散射截面、衰减和损伤的关系用散射体的稀疏分布来模拟损伤。从考虑散射衰减的角度出发，将损伤分布与散射截面联系起来，建立了散射截面、衰减与损伤之间的关系式。一种损伤评估方法提出了一种损伤评估方法。在该方法中，衰减由实验测量，散射截面由数值方法计算。然后根据第二阶段推导出的关系进行损伤评估。为了使该方法得到实际应用，需要澄清以下两点。(1)给出了计算任意形状散射截面的方法。(2)假定损伤为稀疏分布，则可忽略多次散射效应的距离。利用边界元方法对第一点进行了数值求解。第二点是通过求解多次散射问题来阐明的。

The results of the study are summarized in the following three stages.1. Formulation to calculate the elastodynamic scattering energyThe elastodynamic scattering cross sectin was introduced to evaluate the elastodynamic scattering energy from a compact scatterer. The approximate expression of the elastodynamic scattering cross section was formulated in the following three steps. (1) Expression of the scattered field by the scattering amplitude. (2) Relation between scattering amplitude and scattering cross section. (3) Approximate calculation of the scattering cross section by considering the interference effect of the incident wave and the scattered waves. From the numerical calculation, it was confirmed that the approximate expression (Elastodynamic optical theorem) has good accuracy to evaluate the elastodynamic scattering cross section.2. A relation for scattering cross section, attenuation, and damageThe damage was modeled by the dilute distribution of scatterers. From the consideration of attenuation induced by the scattering, the distribution of damage was connected to the scattering cross section and a relation among scattering cross section, attenuation, and damage was formulated.3. A method to evaluate the damageA method to evaluate the damage was proposed. In this method, the attenuation is measured from the experiment and the scattering cross section is calculated by the numerical procedure. Then the damage is evaluated from the relation derived in stage 2. For the practical use of the method, the following two points should be clarified. (1) The method to calculate the scattering cross section for arbitrary shape is available. (2) The negligible distance of the multi-scattering effect is known for the assumption of the dilute distribution of the damage. The first point was clarified numerically by using the boundary element method. The second point was clarified by solving the multiple scattering problem.