Determination of all acoustic material parameters of polymers II

如今，聚合物越来越多地用于广泛的应用领域。一个典型的例子是在复杂的基于超声的测量系统和设备中使用聚合物。这种装置的开发通常需要数值模拟。正确的数值预测，但是，只有当适当的材料模型和参数是可用的。传统上，聚合物的粘弹性和温度依赖性材料特性是使用准静态测试程序来确定的，该测试程序仅对低频有效。然而，基于超声波的应用需要在高频范围内的材料参数的知识，因此需要开发适当的非破坏性方法来以高精度确定后者。因此，申请人先前的合作工作一直致力于开发用于材料表征的基于波的方法。这些都是基于使用优化技术最大限度地减少测量和模拟信号的差异。这里，使用了挤出的圆柱形样品。这种样品的相应材料行为可以理想化为横向各向同性。所提出的算法相对于剪切参数的灵敏度的显着增加已获得通过使用非均匀激励通过修改后的，分段的换能器设置。一个特定的数值工具的比例边界有限元法（SBFEM）的基础上，已开发，以尽量减少模拟时间。该方法不仅利用了SBFEM的半解析性质，而且利用了圆柱形样品的对称几何形状。此外，通过使用所提出的算法的微分，在计算效率上已经实现了显着的增益。然而，分段的换能器设置与额外的挑战相关联。特别是，需要发射器和接收器的精确对准，以保证与数值模拟的可比性。为了减少不确定性，我们的目标是开发一种新的设置，其中只有一个传感器连接到样品的一面，作为发射器和接收器。这种修改后的设置将反过来导致对信号处理和系统特性的更高要求。本项目的另一个目的是进一步改进材料表征的优化算法。在这里，我们计划使用在以前的项目中确定的更强大的成本函数来系统地优化样品的中空圆柱形几何形状，以便找到独特的材料参数。将在不同的温度下进行测量和评估，以评估和验证所提出的方法。在这种情况下，新的理论概念建模阻尼将比较经典的方法和评估的适用性。

Today, polymers are increasingly used in a wide field of applications. A typical example is the use of polymers in complex ultrasound-based measurement systems and devices. The development of such devices typically requires numerical simulations. Correct numerical predictions, however, can only be obtained if appropriate material models and parameters are available. Traditionally, the viscoelastic and temperature-dependent material properties of polymers are determined using quasi-static testing procedures, which are valid for low frequencies only. Ultrasound-based applications, however, require the knowledge of material parameters in the high-frequency range and thus the development of appropriate non-destructive methods for the determination of the latter with high precision.Previous collaborative work of the applicants has therefore been directed at the development of wave-based methods for material characterization. These are based on minimizing the discrepancy in measured and simulated signals using optimization techniques. Here, extruded cylindrical samples have been used. The corresponding material behavior of such samples can be idealized as transversally-isotropic. A significant increase in the sensitivity of the proposed algorithm with respect to the shear parameters has been obtained by using non-uniform excitations through a modified, segmented transducer setup. A specific numerical tool based on the scaled boundary finite element method (SBFEM) has been developed to minimize simulation time. The approach exploits not only the semi-analytical nature of the SBFEM but also the symmetric geometry of cylindrical samples. In addition, a significant gain in computational efficiency has been achieved by using differentiation of the proposed algorithm.The segmented transducer setup, however, is associated with additional challenges. In particular, precise alignment of transmitter and receiver is required to guarantee comparability with the numerical simulation. To reduce uncertainty, we aim to develop a new setup where only one transducer is attached to one face of the sample, acting as the transmitter and receiver. This modified setup will, in turn, result in higher requirements concerning signal processing and system characterization. Another aim of this project is to further improve the optimization algorithm for material characterization. Here, we plan to use the more robust cost function identified in the previous project to systematically optimize the hollow cylindrical geometry of samples such that unique material parameters are found. Measurements will be conducted and evaluated at varying temperatures in order to assess and validate the proposed methods. In this context, novel theoretical concepts of modeling damping will be compared to classical approaches and evaluated in terms of applicability.