Determination of all acoustic material parameters of polymers II

今天，聚合物在广泛的应用领域得到了越来越广泛的应用。一个典型的例子是在复杂的基于超声波的测量系统和设备中使用聚合物。这类装置的开发通常需要数值模拟。然而，只有在有合适的材料模型和参数的情况下，才能获得正确的数值预测。传统上，聚合物的粘弹性和温度相关的材料特性是通过准静态测试程序来确定的，这种测试程序仅在低频下有效。然而，基于超声波的应用需要了解高频范围内的材料参数，因此需要开发合适的非破坏性方法来高精度地确定后者。因此，申请人以前的合作工作是针对基于波的材料表征方法的开发。这些都是基于使用优化技术最小化测量信号和模拟信号之间的差异。这里使用的是挤压的圆柱形样品。相应的材料行为可以理想化为横观各向同性。通过一种改进的分段换能器设置，采用非均匀激励，显著提高了算法对剪切参数的灵敏度。为了最大限度地缩短模拟时间，开发了一种基于尺度边界有限元法的专用数值工具。该方法不仅利用了SBFEM的半解析性质，而且还利用了圆柱体试件的对称几何。此外，通过使用所提出的算法的差分法，计算效率获得了显著的提高。然而，分段换能器的设置伴随着额外的挑战。特别是，为了保证与数值模拟的可比性，需要发射机和接收机的精确对准。为了减少不确定度，我们的目标是开发一种新的装置，其中只有一个换能器连接到样品的一面，充当发射器和接收器。这种修改的设置反过来将导致对信号处理和系统特性的更高要求。本项目的另一个目标是进一步完善材料表征的优化算法。在这里，我们计划使用上一个项目中确定的更稳健的成本函数来系统地优化样品的中空圆柱几何形状，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，以评估和验证拟议的方法。在此背景下，新的理论概念的建模阻尼将与经典的方法进行比较，并评估其适用性。

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.