Dynamic response of multi scale periodic materials and structures

现代结构材料被设计成以最小的重量实现高刚度、强度、韧性和阻尼，以构建用于制造（移动机床结构）和运输（海军、航空航天和汽车工业中的夹层板）的高效结构部件。 将两种或更多种材料组合，通过创建具有上级其母体材料的性能的新混合材料来满足相互冲突的材料性能要求。在背景基质介质中使用颗粒或纤维的复合材料说明了材料水平上的杂化。这些轻质材料的工程应用可以在结构水平上进一步增强，通过扩展混合的相同思想，体现在使用在两个面板材料之间粘合的芯材料的夹层结构中。上述两种工程实践引出了一个问题：能否通过借用结构建筑的例子，利用尺寸、尺度和形状来设计混合材料？为了回答这个问题，首先开发了金属和聚合物泡沫，最近又开发了晶格材料。正在开发这些新的周期性材料类别，以不仅满足高比刚度和强度的结构效率要求，而且满足其他功能要求，例如有利的热响应和振动声学响应。近年来，快速成型技术、3D打印技术、软光刻技术等制造技术的发展促进了多功能结构材料的研究。由于泡沫材料的随机微结构导致其刚度不足，现在人们的注意力已经转向具有周期性微结构的材料。新兴制造技术不仅提供了联合收割机两种材料的能力，而且还控制形状（微结构）和长度尺度，从而创造出创新材料、结构和设备。 通过设计周期性微结构来控制波和声响应的能力导致了一类新的周期性复合材料的出现，其具有有前途的振动声学和动态响应特性。尽管周期性在介观周期性材料中被设计，但周期性是纳米材料如单层石墨烯（SLG）和碳纳米管（CNT）固有的，其中碳原子以六方晶格排列。在这两个尺度上，缺陷和非线性源的存在是不可避免的。虽然原子间势是SLG和CNT中的非线性的来源，但几何和材料非线性与微桁架晶格材料相关。该研究将研究微纳米周期性材料的线性和非线性动态响应，特别是在缺陷和耗散机制的存在下。 本文研究多尺度周期性材料和结构的动力响应问题。本研究的长期目标，理论和实验相结合，是了解微结构的规模，形状和尺寸对有效的机械性能，振动声学，和周期性材料的波传播响应的影响。短期内将集中研究中尺度的周期性材料。产生的基础知识将被利用来设计多功能结构和设备，用于制造业，航空航天和生物医学行业。由于采用了基本的积木式方法，这种广泛的应用是可能的。 该研究项目将在未来五年内在全球研究界和加拿大航空航天和制造业感兴趣的这一新兴领域培养四名研究生（2名博士和2名硕士）。

Modern structural materials are designed to achieve high stiffness, strength, toughness and damping with minimum weight to build efficient structural components used in manufacturing (moving machine tool structures) and transportation (sandwich panels in naval, aerospace and automotive industries). Combining two or more materials fulfils the conflicting material property requirements by creating a new hybrid material with properties superior to those of its parent materials. Composite materials using particles or fibres in a background matrix medium are illustrative of hybridization at the material level. Engineering application of these lightweight materials can be further enhanced, at the structural level, by extending the same idea of hybridization, embodied in sandwich construction using a core material bonded between two face sheet materials. The above two engineering practices lead to the question: can one design hybrid materials by borrowing examples from structural construction utilizing size, scale, and shape? The quest to answer this question has first lead to the development of metal and polymeric foams and more recently lattice materials. These new class of periodic materials are being developed to fulfil not only the structural efficiency requirements of high specific stiffness and strength, but also other functional requirements such as favourable thermal and vibro-acoustic response. Recent developments in manufacturing technologies such as rapid prototyping, 3-D printing, soft lithography have invigorated research to design multifunctional structural materials. Given the lack of stiffness of foams due to their random micro-architecture, attention has now turned onto materials with periodic microstructure. Emerging manufacturing techniques not only offer the ability to combine two materials but also control the shape (micro-architecture) and length scale leading to the creation of innovative materials, structures, and devices. The ability to control wave and acoustic response by designing periodic microarchitecture has led to the emergence a new class of periodic composite materials with promising vibroacoustic and dynamic response characteristics. Whereas periodicity is engineered in mesoscale periodic materials, periodicity is intrinsic to nanomaterials such as Single Layer Graphene (SLG) and Carbon Nanotubes (CNT), wherein carbon atoms are arranged in a hexagonal lattice. At both scales the presence of defects and sources of nonlienarity are unavoidable. While interatomic potentials are the sources of nonlinearity in SLGs and CNTs, geometric and material nonlinearities are relevant to micro truss lattice materials. The proposed research will study linear and nonlinear dynamic response of micro and nanoscale periodic materials particularly in the presence of defects and dissipation mechanisms. The proposed research is concerned with dynamic response of multiscale periodic materials and structures. The long-term goal of this research, combining theory and experiments, is to understand the influence of microstructural scale, shape, and size on effective mechanical properties, vibro-acoustic, and wave propagation response of periodic materials. The research will focus on periodic materials at mesoscale in the short-term. Fundamental knowledge generated will be exploited to design multifunctional structures and devices for applications in manufacturing, aerospace, and biomedical industries. Such wide-ranging applications are possible due to the basic building-blocks approach pursued. This research program will train four graduate students (2 PhDs and 2 MAScs) over the next five years in this emerging area of interest to global research community and Canadian aerospace and manufacturing industries.