Microstructure-Based Multi-Physics Characterisation and Modelling of Magnetorheological Elastomers

磁流变弹性体（MREs）是一种多相、多功能的复合材料，其磁性颗粒悬浮在非磁性弹性体固体中。通过改变外加磁场，磁流变磁体的机械性能几乎可以在瞬间可逆地改变和控制。因此，MREs被视为一类智能材料，在许多工业应用（例如，自适应调谐减振器，刚度可调支架和人造肌肉）中具有前景。然而，由于难以精确地模拟MRE的非线性和各向异性行为（包括颗粒的非线性铁电特性，基体的非线性力学响应以及材料微观结构和外磁场引起的各向异性），目前缺乏MRE的广义本构模型，这使得目前难以在虚拟环境中模拟和优化MRE应用的设计。考虑到计算机辅助工程在当今设计方法中的重要性，这显然是阻碍MREs广泛利用的一个重大障碍。此外，在为特定应用改进和定制MREs之前，对MREs中微观结构和宏观尺度行为之间关系的基本理解是必不可少的。该项目关注的是有限变形状态下MREs的磁力学行为的建模和表征，以便最终了解MREs的结构-性能关系。目标是通过在微观尺度上对代表性体积元（RVE）模型的多物理场模拟均质化，开发第一个基于微观结构的MREs宏观磁力学本构模型。在本研究中，MicroCT将获得各种MRE材料的真实三维微观结构，以建立MRE的计算磁力学RVE模型。宏观尺度完整的磁力学本构模型将通过RVE模型的均质化推导和校准。将实施综合实验，并采用测量的微观尺度变形（通过MicroCT）和宏观尺度（均匀化）变形（通过数字图像相关（DIC）系统）分别验证开发的基于微观结构的RVE模型和宏观尺度模型。然后，这些模型将被应用于一个实际的工程问题，即MRE橡胶空气弹簧的设计优化。该项目以分析、数值和实验工作的独特结合为基础，它将提供(1)MRE材料的磁力学实验方案；（ii）基于微观结构的MRE材料RVE模型；（iii）磁力学问题的多物理场非线性有限元求解器；（iv）适用于任何多物理现象的一般宏观尺度本构建模框架。该项目的成功成果将对工业界和学术界产生重大的直接影响。

Magnetorheological elastomers (MREs) are multi-phase, multi-functional composite materials with magnetisable particles suspended in a non-magnetic elastomer solid. The mechanical properties of MREs can be reversibly changed and controlled almost instantaneously by altering an externally applied magnetic field. For this reason MREs are regarded as a class of smart materials and hold promise in many industrial applications (e.g., adaptive tuned vibration absorbers, stiffness tuneable mounts, and artificial muscles). However, a generalised constitutive model for MREs is lacking due to the difficulties to model precisely MREs' nonlinear and anisotropic behaviour (including the nonlinear ferroelectric properties of the particles, the nonlinear mechanical response of the matrix, and the anisotropy caused by the material microstructure and the external magnetic field), making it currently difficult to simulate and optimise the design of MRE applications in a virtual environment. Given the importance of computer aided engineering in today's design methodology, this is clearly a significant obstacle preventing widespread exploitation of MREs. Furthermore, a fundamental understanding of the relationship between microstructure and macroscale behaviour in MREs is essential before improving and tailoring MREs for a specific application can be achieved. This project is concerned with modelling and characterisation of the magnetomechanical behaviour of MREs in the finite deformation regime in order to ultimately understand the structure-property relation of MREs. The goal is to develop the first realistic microstructure-based macroscale magnetomechanical constitutive model for MREs via homogenisation of the multi-physics simulation of representative volume element (RVE) model at the microscale.In the proposed research, true 3D microstructures of various MRE materials will be obtained by MicroCT to develop computational magnetomechanical RVE models of MREs. Macroscale complete magnetomechanical constitutive models will be derived and calibrated through homogenisation of the RVE models. Comprehensive experiments will be implemented and the measured microscale deformation (via MicroCT) and macroscale (homogenised) deformation (via Digital Image Correlation (DIC) system) will be employed to verify the developed microstructure-based RVE models and macroscale models respectively. The models will then be applied to a real engineering problem, the design optimisation of the MRE rubber air springs.This project hinges upon a unique combination of analytical, numerical and experimental work and it will deliver (i) magnetomechanical experimental protocols for MRE materials; (ii) microstructure-based RVE models for MRE materials; (iii) a multi-physics nonlinear FEM solver for magnetomechanical problems; and (iv) a general macroscale constitutive modelling framework applicable to any multi-physics phenomena. The successful outcome of this project will have significant direct impact on both industrial and academic communities.