Multiscale Architectured Materials (MAM II): Tailoring Mechanical Incompatibility for Superior Properties: Materials with Architectured Structures
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Yuntian Zhu, North Carolina State University; Irene Beyerlein, University of California, Santa Barbara; Yves Brechet, Grenoble Institute of Technology; Huajian Gao, Brown University; Ke Lu, Institute of Metal Research, Chinese Academy of Science; Xiaolei Wu, Institute of Mechanics, Chinese Academy of Science

Wednesday 8:30 AM
March 1, 2017
Room: 24B
Location: San Diego Convention Ctr

Session Chair: Yves Brechet , Grenoble Institute of Technology; Ruth Schwaiger, Karlsruhe Institute of Technology

8:30 AM  Invited
Materials by Design: 3-Dimensional Nano-Architected Meta-Materials: Julia Greer1; Lucas Meza1; Alessandro Maggi1; Victoria Chernow1; Xiaoxing Xia1; 1California Institute of Technology
    Creation of extremely strong yet ultra-light materials can be achieved by capitalizing on hierarchical design of 3-dimensional nano-architectures. These nanolattices exhibit superior thermomechanical properties at extremely low mass densities because the constituent size (nanometers to microns) is comparable to characteristic microstructural material length scale. We developed a process to fabricate 3-dimensional nanolattices whose relevant dimensions span from nanometers to microns, with overall dimensions of ~1cm. We discuss deformation, mechanical properties, and energy absorption in nanolattices made from different materials and deformed in an in-situ nanomechanical instrument. Attention is focused on interplay between internal microstructural length scale of materials and external limitations, where competing material- and structure-induced size effects drive overall properties. We focus on metallic, ceramic, and glassy nanolattices and discuss their properties in the framework of mechanics and physics of defects. Specific applications include biomedical devices, ultra lightweight batteries, photonics, damage tolerance, and flaw (in)sensitivity in fracture.

8:55 AM  
Mechanics of Single-wire Entangled Architected Materials: David Rodney1; Sabine Rolland du Roscoat2; Laurent Orgéas2; 1Université de Lyon; 2Université Grenoble Alpes - CNRS
    We study the mechanics of an architected material made of the disordered entanglement of a single long fiber, using a combination of experiments and simulations. We produced samples from single fibers of a superelastic shape-memory alloy, a viscoelastic polymer or a ductile metal. The samples were subjected to deformation cycles, tracking local deformations with x-ray tomography. Numerically, we employed Kirchhoff’s elastic rod theory to simulate the same cycles on both numerical substitutes of the experimental samples and on idealized periodic structures. This architecture exhibits surprising mechanical properties, in part because of its topology in-between a discrete and a continuum medium. In particular, we find large and reversible extensions of its volume, both in tension and compression. This material is thus reversiby dilatant in both directions, with a Poisson's function varying from above 1/2 in compression to less than 0 in tension (Rodney et al., Nature Materials 15 (2016) 72-77)

9:15 AM  
Designing Lightweight Composite Cellular Architectures: Glenn Hibbard1; 1University of Toronto
    This presentation will discuss design strategies undertaken in the development of lightweight composite cellular architectures. By combining the design of the underlying cellular architecture and the composited material that makes up that architecture, new domains of material property space can be accessed. However, the design approach undertaken depends significantly upon the depth of mechanistic understanding that is held for the relevant failure mechanisms. Several case studies will be examined including those of metal-metal, metal-ceramic, and metal-polymer micro-truss architectures.

9:35 AM  
Development and Compressive Deformation of Polymer-metallic Microcellular Structures: Theresa Juarez1; Almut Schroer2; Ruth Schwaiger2; Andrea Hodge1; 1University of Southern California; 2Karlsruhe Institute of Technology
    Cellular materials with designed architecture, especially those with micro and nanosized features, have demonstrated superior strength-to-density ratios when compared to other cellular materials. These types of structures have been realized by combining multiple synthesis methods, such as 3D printing and coating techniques, to expand their achievable properties. This study aims to enhance the mechanical properties of polymer microlattices by coating printed microstructures with metal films using sputtering to generate a metal-polymer composite. The mechanical behavior of the structures is evaluated through uniaxial compression testing and subsequent imaging for the observation of failure mechanisms. Using sputtering as a coating technique will expand the combination of composites and layer thicknesses that can be achieved, and also make these type of structures viable for a variety of applications.

9:55 AM Break

10:15 AM  Invited
High-strength, Light-weight Hierarchical Materials Based on 3D Direct Laser Writing: Ruth Schwaiger1; 1Karlsruhe Institute of Technology (KIT)
    Cellular materials with designed architectures having characteristic features in the micro-to-nanometer range exhibit superior strength-to-density ratios. In our approach, polymeric truss structures are fabricated by 3D direct laser writing and coated using thin film deposition techniques with the goal to expand their achievable properties. For example, coating with ceramic films 10 - 100 nm thick using atomic layer deposition, exploits mechanical size effects as the strength of thin films exceeds the strength of the corresponding bulk material. However, the method is limited to ceramics and thin layers. Coating the structures with metallic films represents another approach to expand the properties and applicability of microarchitected materials. The truss structures are characterized using nanomechanical testing methods. Elastic deformation and failure depend sensitively on details of the architecture. We demonstrate that the specific strength of these designed cellular materials is significantly improved compared to all other engineering foams with density below 1 g/cm³.

10:40 AM  
Toughening of Meso-structured Materials in Additive Manufacturing: Hang Yu1; 1Virginia Tech
    With the capability of precisely locating chemical compositions, elastic properties, and interfaces in a material, additive manufacturing provides new avenues to designing tough materials by controlling the crack path, which is predominately influenced by meso-scale material features. Here, we explore the problem of mesostructure toughening, that is, to optimize the fracture toughness for a given loading condition through meso-scale materials design in additive manufacturing. From compact tension test, we show that the fracture toughness of meso-structured nylon and fiber-reinforced composites is significantly improved as compared to their monolithic counterparts. By introducing interfaces as crack arrestors, the crack tip is blunted and the driving force for crack propagation is decreased; by forming Bouligand structures as crack dividers, the crack path is deviated from a direct route and the energy cost for crack propagation is significantly increased. Implementation of mesostructure design in metallic materials will also be discussed for toughness optimization.

11:00 AM  
Chemical Etching of Ti Lattice Structures Manufactured by Electron Beam Melting: Influence on the Stiffness of the Octet-Truss Structures and Modeling of the Dissolution Kinetics at the Scale of Individual Struts: Pierre Lhuissier1; Charlotte De Formanoir2; Guilhem Martin1; Rémy Dendievel1; Stephane Godet2; 1Université Grenoble Alpes; 2Université Libre de Bruxelles
    In the present work, titanium octet-truss lattice structures of various densities were produced by electron beam melting (EBM). The as-built struts exhibit an important roughness level. Consequently, a chemical etching procedure was developed and was shown to significantly reduce the roughness throughout the entire lattice structure. The decrease in roughness comes along with an increase in stiffness to density ratio. This is attributed to the increased mechanical efficiency of the struts associated with the removal of powder particles stuck to the surface and with the global decrease in roughness. Individual struts were characterized experimentally while submitted to a chemical etching treatment by high resolution X-ray tomography. A cellular automaton based model was also developed in order to predict the evolution of the as-built strut under etching. The model enables to predict the overall and local etching rates as well as the evolution of the decrease in roughness.

11:20 AM  
Surface Gradient Architectured Materials Processed by Severe Plastic Deformation via Surface Abrasion Torsion: Ji Hyun Moon1; Ho Yong Um1; See Am Lee1; Jae Ik Yoon1; Jaimyun Jung1; Hyoung Seop Kim1; 1POSTECH
     Surface gradient architecturing of metallic materials is a potential solution for recovering less ductility of ultrafine grained materials. Bulk ultrafine grained materials are usually produced using severe plastic deformation (SPD). There are various SPD methods, such as equal-channel angular pressing, accumulative roll bonding, high-pressure torsion, and twist extrusion with high imposed strain for grain refinement. Simple torsion can be a SPD process, but stress concentration in the surface of specimens restricts high number of rotation. Therefore, in order to impose high strain in simple torsion, surface abrasion torsion is developed. It is demonstrated that surface gradient architectures can be produced using the proposed surface abrasion torsion. In addition, the mechanical properties of the processed material are systematically analyzed.