The influence of nonlinear pre-stress on wave propagation through viscoelastic composites.

不均匀的粘弹（VE）材料（即，它们的材料性质是空间依赖的）被用于工业部门内的许多应用中，例如机械和汽车以及航空航天工业中的噪声和振动隔离器、土木工程应用中的桥梁轴承和地震减震器以及水下航行器上使用的声学瓦，后者是该项目中特别感兴趣的例子。它们也作为身体中的软生物组织自然产生。在这些情况下，材料经常受到压力，导致材料的大变形（即非线性预应力）。在水下航行器的情况下，粘弹性声学瓦片在航行器潜水时受到巨大的压缩力，导致材料的大变形。在软组织背景下，预应力可能由于一些现有的残余应力而存在，或者它可能由生理或机械机制引起，例如用于医疗目的，以便在扫描之前增加组织对比度。VE材料的后续增量（线性）响应对于稳定性、增量本构行为或简单地适用于所讨论的材料的目的可能非常有用。在这些非线性预应力状态下，可以使用无损评估（NDE）技术评估复合材料的性能，例如通过介质发送超声波并测量响应。在软组织的情况下，增量波将是诊断的成像工具。预应力在均匀材料和简单的不均匀材料的各个方面已经评估以前，但更困难的问题，一般不均匀的材料还没有被充分描述在文献中。曼彻斯特数学学院和Thales Underwater Systems Ltd（TUSL）之间的这个合作项目旨在开发一个通用理论，以描述非线性预应力对非均匀介质中波传播的影响。这个理论将被应用，以预测本构响应的颗粒复合材料感兴趣的TUSL，虽然一般的理论将适用于许多非均匀结构。

Visco-elastomeric (VE) materials which are inhomogeneous (i.e. their material properties are spatially dependent) are employed in numerous applications within the industrial sector, e.g. noise and vibration isolators in machinery and the automotive and aerospace industry, bridge bearings and seismic shock absorbers in civil engineering applications and acoustic tiles used on underwater vehicles, the latter being the example of specific interest in this project. They also arise naturally as soft biological tissues in the body. In these contexts the materials are frequently subjected to pressures which lead to large deformations (i.e. a nonlinear pre-stress) of the material. In the underwater vehicle context, viscoelastic acoustic tiles are subjected to massive compressional forces as the vehicle dives leading to a large deformation of the material. In the soft tissue context, a pre-stress may exist due to some existing residual stress or it could be induced by physiological or mechanical mechanisms, e.g. for medical purposes, in order to increase tissue contrast before scans. The subsequent incremental (linear) response of VE materials can be of great use with regard to the stability, incremental constitutive behaviour or simply the fitness-for-purpose of the materials in question. The behaviour of composite materials can be assessed in these nonlinear pre-stressed states by using non-destructive evaluation (NDE) techniques, e.g. sending ultrasonic waves through the media and measuring the response. In the soft-tissue context the incremental wave would be the imaging tool for diagnosis.Various aspects of pre-stress in homogeneous materials and simple inhomogeneous materials have been assessed previously but the more difficult problem of generally inhomogeneous materials has not been described fully in the literature. This collaborative project, between the School of Mathematics in Manchester and Thales Underwater Systems Ltd (TUSL), aims to develop a general theory in order to describe the influence of nonlinear pre-stress on wave propagation through inhomogeneous media. This theory will then be applied in order to predict the constitutive response of particulate composites of interest to TUSL, although the general theory will be applicable to many inhomogeneous structures.