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About this book

This book deals with a group of architectured materials. These are hybrid materials in which the constituents (even strongly dissimilar ones) are combined in a given topology and geometry to provide otherwise conflicting properties. The hybridization presented in the book occurs at various levels - from the molecular to the macroscopic (say, sub-centimeter) ones. This monograph represents a collection of programmatic chapters, defining archimats and summarizing the results obtained by using the geometry-inspired materials design.

The area of architectured or geometry-inspired materials has reached a certain level of maturity and visibility for a comprehensive presentation in book form. It is written by a group of authors who are active researchers working on various aspects of architectured materials. Through its 14 chapters, the book provides definitions and descriptions of the archetypes of architectured materials and addresses the various techniques in which they can be designed, optimized, and manufactured. It covers a broad realm of archimats, from the ones occurring in nature to those that have been engineered, and discusses a range of their possible applications. The book provides inspiring and scientifically profound, yet entertaining, reading for the materials science community and beyond.

Table of Contents

Frontmatter

Chapter 1. Microtruss Composites

Abstract
This chapter provides a framework for predicting buckling instabilities (global and local) in composite struts using a discretizing approach to divide the cross-section into finite regions or blocks (elements) with distinctive composition and material properties. This framework is applied to two compositing approaches: (1) an additive process, e.g. electrodeposition of nanocrystalline nickel (n-Ni) on steel or aluminum substrates creating a discrete interface, and (2) mass transport phenomena, e.g. gas carburization of steel microtrusses creating a continuous and gradual change in composition. The individual composite struts are prone to failure through inelastic/elastic global/local buckling instabilities due to their typically high slenderness ratio (for lightweight requirements). An optimal architecture is defined as the lightest architecture in the defined architectural space that can support a given load before failing; mathematically equivalent to satisfying the Kuhn-Tucker condition. For the electrodeposition example, the optimal trajectory was found to be dependent on the substrate material as well as the level of adhesion of the sleeve to the substrate. However, in the carburizing example, optimal architectures cannot be found using the same optimization approach due to the negligible weight penalty associated with the addition of carbon atoms (i.e. no trade-off between strength and mass). Other factors such as ductility and fracture toughness need to be addressed to find the optimal architectures.
Khaled Abu Samk, Glenn D. Hibbard

Chapter 2. Topological Interlocking Materials

Abstract
In this chapter, we present a materials design principle which is based on the use of segmented, rather than monolithic, structures consisting of identical blocks locked within the assembly by virtue of their special geometry and mutual arrangement. First, a brief history of the concept of topological interlocking materials and structures is presented and current trends in research are outlined. Recent work of the authors and colleagues directed at the variation of the shape of interlockable building blocks and the mechanical performance of structures—either assembled from them or 3D printed—are overviewed. Special emphasis is put on materials responsive to external stimuli. Finally, an outlook to possible new designs of topological interlocking materials and their engineering applications is given.
A. V. Dyskin, Yuri Estrin, E. Pasternak

Chapter 3. Architectured Materials with Inclusions Having Negative Poisson’s Ratio or Negative Stiffness

Abstract
Architectured materials with negative Poisson’s ratio (auxetic materials) have been subject of interest for quite some time. The effect of negative Poisson’s ratio is achieved macroscopically through various types of microstructure made of conventional materials. There also exist (unstable) microstructures that, under certain boundary conditions, exhibit negative stiffness. In this chapter we review the microstructures that which generate macroscopic negative Poisson’s ratio and negative stiffness, determine their effective moduli and discuss general properties of the materials with such microstructures. We then consider hybrid materials consisting of conventional (positive Poisson’s ratio and positive moduli) matrix and randomly positioned inclusions having either negative Poisson’s ratio or a negative stiffness (one of the moduli being negative). We use the differential scheme of the self-consisting method to derive the effective moduli of such hybrids keeping in the framework of linear time-independent theory. We demonstrate that the inclusions of both types can, depending on their properties, either increase or decrease the effective moduli.
E. Pasternak, A. V. Dyskin

Chapter 4. Computational Homogenization of Architectured Materials

Abstract
Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials.
Justin Dirrenberger, Samuel Forest, Dominique Jeulin

Chapter 5. Design Methods for Architectured Materials

Abstract
Architectured materials offer a great potential of performance for various applications, but they have to be tailored to fulfil each set of requirements. Designing an architectured material implies determining all its attributes: components, architecture, volume fractions, interfaces…Numerous methods have been developed for product design or for single material selection, but few deal with architectured materials. Because of the difficulty to determine all the parameters at the same time, studies have been carried out about specific tasks in architecture materials design. In this chapter, after having presented material selection methods and design or creativity methods that can be useful in this context, some results are detailed about methods for analysing the set of requirements, identify some incompatibilities between the functions, and select the components in the case where the architecture is defined.
F. X. Kromm, H. Wargnier

Chapter 6. Topological Optimization with Interfaces

Abstract
Design of architectured materials and structures, whether in nature or in engineering, often relies on forms of optimization. In nature, controlling architecture or spatial heterogeneity is usually adaptive and incremental. Naturally occuring architectured materials exploit heterogeneity with typically graded interfaces, smoothly transitioning across properties and scales in the pursuit of performance and longevity. This chapter explores an engineering tool, topology optimization, that is at the frontier of designing architectured materials and structures. Topology optimization offers a mathematical framework to determine the most efficient material layout for prescribed constraints and loading conditions. In engineering, topology optimization is identifying designs with interfaces, materials, manufacturing methods, and functionalities unavailable to the natural world. The particular focus is on the variety of roles that interfaces may play in advancing architectured materials and structures with topology optimization.
N. Vermaak, G. Michailidis, A. Faure, G. Parry, R. Estevez, F. Jouve, G. Allaire, Y. Bréchet

Chapter 7. Friction Stir Processing for Architectured Materials

Abstract
Friction Stir Processing (FSP) is a solid-state process derived from Friction Stir Welding (FSW). FSP may be applied for the efficient manufacturing of metallic alloys based architectured materials. Indeed, the FSP tools allow locally modifying the microstructure of alloys or assembling dissimilar materials. The architectured materials that were or may be manufactured by friction stir processing will be discussed in this chapter. FSP may improve the mechanical performances of cast alloys, process metal matrix composites (MMC), make sandwiches, foams or additively manufactured structures. The aim is to process materials with improved lightweight performances, static or fatigue properties, crack resistance, toughness or wear resistance.
Aude Simar, Marie-Noëlle Avettand-Fènoël

Chapter 8. Severe Plastic Deformation as a Way to Produce Architectured Materials

Abstract
In this chapter, a group of processing techniques leading to desired materials architectures is discussed. They are based on severe plastic deformation (SPD) by shear combined with high hydrostatic pressure. Originally, these techniques were developed for imparting to the material an ultrafine grained (UFG) microstructure thus improving its mechanical performance characteristics. An added benefit of SPD processing in the context of architectured materials is its ability to tune the inner makeup of a hybrid material at a macroscopic scale. After a brief introduction to the available SPD processing techniques, we provide an analysis of architectured multiscale structures with UFG constituents they can produce. A target of this research is development of materials with a high specific strength and low overload sensitivity. Specific designs enabling a favourable combination of these properties are considered. An emphasis is put on structures that include soft layers whose presence delays strain localisation and failure of the hybrid material.
Yan Beygelzimer, Roman Kulagin, Yuri Estrin

Chapter 9. Architectured Polymeric Materials Produced by Additive Manufacturing

Abstract
Polymers play an important role in our everyday life. With the advent of additive manufacturing (AM) technologies, the design and manufacture of new polymer-based composite materials has experienced a significant boost. AM enables precise deposition of printable material(s) with micro scale accuracy to build up a desired structure in three dimensions in a layer-by-layer fashion. In this chapter, recent advances in the use of additive manufacturing for the design of architectured polymer-based materials is discussed. A compendium of the existing AM methods is presented, followed by an overview of applications of AM technology to fabrication of polymer-based materials with engineered inner architecture.
Andrey Molotnikov, George P. Simon, Yuri Estrin

Chapter 10. Mechanics of Arthropod Cuticle-Versatility by Structural and Compositional Variation

Abstract
The arthropod cuticle may be seen as a multifunctional material displaying a wide range of physical properties. The materials properties of the cuticle are brought about by compositional and structural gradients at multiple hierarchical levels. In the following chapter we first discuss the main components of the cuticle, namely, chitin, proteins, water, mineral and tanning agents and their relevance in determining the mechanical properties of the cuticle. We then describe the hierarchical organization of the cuticle and how it contributes to tuning the mechanical properties of the material. Finally we show several examples of cuticular structures with increasing structural complexity to exemplify the discussed principles.
Yael Politi, Benny Bar-On, Helge-Otto Fabritius

Chapter 11. The Multiscale Architectures of Fish Bone and Tessellated Cartilage and Their Relation to Function

Abstract
When describing the architecture and ultrastructure of animal skeletons, introductory biology, anatomy and histology textbooks typically focus on the few bone and cartilage types prevalent in humans. In reality, cartilage and bone are far more diverse in the animal kingdom, particularly within fishes, where cartilage and bone types exist that are characterized by features that are anomalous or even pathological in human skeletons. Here, we discuss the curious and complex architectures of fish bone and shark and ray cartilage, highlighting similarities and differences with their mammalian skeletal tissue counterparts. By synthesizing older anatomical literature with recent high-resolution structural and materials characterization work, we frame emerging pictures of form-function relationships in these tissues and of the evolution and true diversity of cartilage and bone.
Ronald Seidel, Aravind K. Jayasankar, Ron Shahar, Mason N. Dean

Chapter 12. Insect-Inspired Distributed Flow-Sensing: Fluid-Mediated Coupling Between Sensors

Abstract
Crickets and other arthropods are evolved with numerous flow-sensitive hairs on their body. These sensory hairs have garnered interest among scientists resulting in the development of bio-inspired artificial hair-shaped flow sensors. Flow-sensitive hairs are arranged in dense arrays, both in natural and bio-inspired cases. Do the hair-sensors which occur in closely-packed settings affect each other’s performance by so-called viscous coupling? Answering this question is key to the optimal arrangement of hair-sensors for future applications. In this work viscous coupling is investigated from two angles. First, what does the existence of many hairs at close mutual distance mean for the flow profiles? How is the air-flow around a hair changed by it’s neighbours proximity? Secondly, in what way do the incurred differences in air-flow profile alter the drag-torque on the hairs and their subsequent rotations? The first question is attacked both from a theoretical approach as well as by experimental investigations using particle image velocimetry to observe air flow profiles around regular arrays of millimeter sized micro-machined pillar structures. Both approaches confirm significant reductions in flow-velocity for high density hair arrays in dependence of air-flow frequency. For the second set of questions we used dedicated micro-fabricated chips consisting of artificial hair-sensors to controllably and reliably investigate viscous coupling effects between hair-sensors. The experimental results confirm the presence of coupling effects (including secondary) between hair-sensors when placed at inter-hair distances of less than 10 hair diameters (d). Moreover, these results give a thorough insight into viscous coupling effects. Insight which can be used equally well to further our understanding of the biological implications of high density arrays as well as have a better base for the design of biomimetic artificial hair-sensor arrays where spatial resolution needs to be balanced by sufficiently mutually decoupled hair-sensor responses.
Gijs J. M. Krijnen, Thomas Steinmann, Ram K. Jaganatharaja, Jérôme Casas

Chapter 13. Architectured Materials in Building Energy Efficiency

Abstract
The term “architecture” included in the “architectured material” approach receives a particular echo in the building sector. It inevitably evokes the technical and artistic discipline of adapting the building to its use. In a similar way the architecturation of materials approach in response to complex and antagonistic expectations for energy efficiency in building is promising although it is less developed in this sector than in others. However the engines for its development are indeed more present than ever: reduce the total emissions of greenhouse gases, demands for multifunctionality, and requests for inaccessible properties by a single bulk material. If mechanics has long been the central concern, the end of the 20th century marked a turning point towards energy and that is the reason why this chapter deals to this aspect and especially with the building envelope. Many properties come to complicate the game of simple thermic and mix the cards: mechanical (compression, tensile, creep), hydric (water sealing and absorption), hygric (water sorption and permeation), acoustics, aesthetics, cost, optical (visible and infrared), embodied energy and environmental impact, etc. Examples are given in this chapter. This approach started very late, only sixty-seventy years ago with the foaming of polymers and with the manufacturing of mineral wool. In parallel other material where designed at a scale closer to the product scale like hollow bricks, lightweight concretes. It is only very recently that a final improvement is done on traditional insulation materials polymeric foams and glass wool by achieving a very efficient infrared opacification. It is also in the same time that the breakthrough of the super insulation comes based on a specific architecture of the material involving more matter but dealing with the nanometer scale in order to confine the molecules of the gas in pores smaller than their mean free path. Two families of material/products are exemplified: the vacuum insulation panels and the super insulation at atmospheric pressure. For each, several optimisation problems are ongoing or on the table and the architecture of the material and product is the key for success in reaching antagonist attempts. The strongly moving context around the renewables energies is also bringing new playground for architectured materials. One first theme is the heat storage where the difficulty for reaching the wanted power could be addressed by this approach. The very wide and new second theme is the field of active walls and specific collectors where the aimed properties ask for filling some gaps in the materials spaces. Finally the approach of architectured materials is slowly irrigating the developments for energy efficiency in building with the knowledge diffusion and thanks to the education students are more and more aware of the possibilities of this approach especially to solve difficulties and then to innovate.
Bernard Yrieix

Chapter 14. Topological Interlocking Blocks for Architecture: From Flat to Curved Morphologies

Abstract
The paper concerns the theme of topological interlocking blocks for architecture and the relationship between flat stereotomic assemblies and curved morphologies. After a brief history of the subject, theoretical foundations and speculative research are presented. The research includes several built full-scale prototypes and architectural elements. The last part of the chapter describes the didactic experiences concerning the theme, during the third year Architectural Design Studio held by the authors, at Politecnico di Bari, Italy.
Giuseppe Fallacara, Maurizio Barberio, Micaela Colella

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