Conference Programme

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Overview
Session
M-04: Symp M
Time:
Tuesday, 20/Jun/2017:
1:30pm - 3:30pm

Session Chair: An-Chou Yeh, National Tsing Hua University
Session Chair: Erwin Peng, National University of Singapore
Location: Rm 327

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Presentations
1:30pm - 2:00pm
Invited

Architectured Designer Metamaterials with Tunable Thermal Expansion and Shape Memory Effects

Nicholas X. FANG, Qiming WANG, Qi GE

Massachusetts Institute of Technology, United States

Three-dimensional lightweight material building blocks, through the combination of molecular design of material behavior and microscale geometric patterning, show promise to revolutionize the ability to dissipate energy and manipulate wave propagation. Such materials are desirable for a broad array of applications such as structural components, catalysts supports and energy efficient materials.

In this invited talk, I will present our development of three dimensional micro/nanofabrication technique, projection microstereolithography (PuSL), to enable design and exploration of digitally coded multifunctional and multimaterial lightweight metastructures at unprecedented dimensions. As an example, we show that our designed lightweight multimaterial lattices can exhibit significant negative thermal expansion (NTE) in three directions and over a temperature range of 170 degrees. Such NTE is induced by the structural interaction of material components with distinct thermal expansion coefficients. The NTE can be tuned over a large range by varying the thermal expansion coefficient difference between constituent beams and geometrical arrangements. Our experimental results match qualitatively with a simple scaling law and quantitatively with computational models. In a second example, I will also show our effort to design and construct metastructures with constituents and compositions that exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior.


2:00pm - 2:15pm
Oral

Collective Durotaxis on 3D Printed Mechanotactic Hybrids

Pingqiang CAI1, Michael LAYANI2, Wan Ru LEOW1, Shahrouz AMINI1, Ali MISEREZ1, Shlomo MAGDASSI2, Xiaodong CHEN1

1Nanyang Technological University, Singapore; 2The Hebrew University of Jerusalem, Israel

Various physiological and pathological processes are reliant on collective cell migration, such as embryo development, wound healing, immune surveillance and cancer metastasis. During these processes, living cells migrate in a physically complex physiological microenvironment, constantly subject to a plethora of mechanical cues such as topographical cues, physical confinement and ECM stiffness. The migrating cells sense and respond to these mechanical cues via the process of mechanotransduction, such as haptotaxis and durotaxis of single cells. Given the prevalence of varying stiffness in the physiological environment, systems have been developed in an attempt to mimic in vivo stiffness variations. However, the cell migration behaviours in these systems might not be accurately ascribed to varying stiffness before excluding the topographical and compositional cues, which have also been reported to impact cell migration. Thus it remains a challenge to develop a system that represents varying ECM stiffness independently of the topographical and compositional cues over a wide lateral span. Therefore, we have established a platform of mechanotactic hybrids, projecting lateral gradients of apparent interfacial stiffness onto the planar surface of a compliant hydrogel layer by an underlying rigid substrate with microstructures inherited from 3D printed moulds, to establish the mechanistic coupling of epithelial migration with the ECM stiffness independently of interfacial compositional and topographical cues. Our strategy has clearly demonstrated the collective durotaxis of epithelial migration, which is greatly dependent on the long-range intercellular forces transmission.


2:15pm - 2:30pm
Oral

Design of Functionally Graded Lattices for Optimised Light-weight Structures

Stephen DAYNES1, Stefanie FEIH1, Wen Feng LU2, Jun WEI1

1Singapore Institute of Manufacturing Technology (SIMTech), Agency for Science, Technology and Research (A*STAR), Singapore; 2Department of Mechanical Engineering, National University of Singapore, Singapore

One of the great advantages of additive manufacturing is the ability to produce extremely complicated three-dimensional designs with relatively few manufacturing constraints. Lattice structures are an example of such complexity, where an assembly of cells can be printed to form a load bearing, yet lightweight, core. Additively manufactured lattice structures typically take the form of slender truss members arranged in an array of unit cells. Many unit cell designs have already been proposed along with characterised stiffness and strength behaviour. However, little attention has been given regarding the optimal arrangement of these cells with a view to structural optimisation. A related issue is how to appropriately combine solid and lattice regions in a structure for an optimal trade-off between stiffness, strength and low mass.

To address these issues, we propose new numerical approaches to functionally grade lattice structures with respect to optimal stiffness, strength and density properties. In this work, topology optimisation is used to find optimal density and stress distributions within an idealised core volume. These data sets are then used as a basis for generating optimal graded lattice cell arrangement. Our methods are experimentally validated with a selection of sandwich structure designs to show how we can tailor both stiffness and strength.


2:30pm - 2:45pm
Oral

Design Optimization of Cellular Materials with Shellular Cores Fabricated by Selective Laser Melting

Lei ZHANG1, Stefanie FEIH2, Stephen DAYNES2, Wen Feng LU1, Michael Yu WANG3, Jun WEI2

1Department of Mechanical Engineering, National University of Singapore, Singapore; 2Joining Technology Group, Singapore Institute of Manufacturing Technology (SIMTech), Agency for Science, Technology and Research (A*STAR), Singapore; 3Robotics Institute, Department of Mechanical and Aerospace Engineering, and Department of Electronic and Computer Engineering of Hong Kong University of Science and Technology, Hong Kong S.A.R. (China)

Designing metallic cellular materials with shellular cores composed of continuous and smooth shells is a novel approach for lightweight and multi-functional applications. A typical group of geometries to form such structures are triply periodic minimal surfaces are with zero mean curvature at every point, e.g. Schwarz’ P, D and Schoen’s Gyroid surfaces. Compared to the current widely used lightweight porous materials such as metallic foams and lattices, shellular-cored materials have a significantly larger surface area while maintaining high load bearing capacity. This indicates their application potential for ultra-light and mechanically efficient structural components, components with enhanced heat dissipation or battery electrodes. The development on selective laser melting allows the fabrication of shellular structures composed of complex geometries and thin wall features. In this paper, the 3D models of shellular structures with various types of triply periodic minimal surfaces are created using implicit surfaces, resulting in surface models which are well suited for additive manufacture. We investigate the mechanical behaviors of shellular structures using numerical and experimental approaches. The mechanical properties are predicted using finite element method. Numerical optimization is performed to identify the most efficient surface geometry parameters to maximize the relevant design objectives such as stiffness or surface area. Selective laser melting is employed to fabricate the shellular structures and compression tests are preformed to validate the numerical simulation results.


2:45pm - 3:00pm
Oral

Gigahertz Electromagnetic Structures via Direct Ink Writing for Radio Frequency Oscillator and Transmitter Applications

Nanjia ZHOU, Chengye LIU, Donhee HAM, Jennifer A. LEWIS

Harvard University, United States

Wireless technology has undergone a profound transformation from cellular voice communications to pervasive networks that connect humans, machines, and “things” with ever increasing data content and capacity. Central to this wireless revolution are chip-scale radio-frequency (RF) electronics that combine passive electromagnetic devices and active transistors to generate and process gigahertz (GHz) signals. Here we produce a broad array of 2D and 3D RF passives that operate at GHz frequencies via direct ink writing conductive silver nanoparticle inks both in-plane and out-of-plane, including lumped devices (e.g., inductors and capacitors) and wave-based devices (e.g., transmission lines, their resonant networks, and antennas), whose maximum quality factors (Q) and operational frequencies exceed 40 and 45 GHz, respectively. We further combine them with discrete transistors to fabricate self-sustained oscillators, synchronized oscillator arrays, and wireless transmitters clocked by the oscillators. Our direct ink writing approach would also enable RF passives to be printed directly on CMOS chips for rapid prototyping and testing of new device designs. We ultimately envision creating more complex passive electromagnetic structures, by coprinting multiple functional materials of varying magnetic, dielectric, and conductive properties. Diverse RF functionalities with improved passive performance should be realized by exploiting their 3D structure–function relation coupled with tailoring their composition locally.


3:00pm - 3:15pm
Oral

Porous Structure Design Effect on Mechanical Properties

Che-Nan KUO1, Marie-Salomé DUVAL-CHANEAC2, Yu-Lun SU1, Yao-Cheng WU3, Jacob Chih-Ching HUANG3

1Casting Technology Section, Metal Processing R&D Department, Metal Industries Research & Development Centre, Taiwan; 2cole Nationale d'Ingénieurs de Saint-Étienne, France; 3Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Taiwan

Nowadays, some medical devices such like spine cage, hip cup, or reconstruction mandible are introduced porous structure to promote the integration between bone cell and porous medical device. However, porous structure is to fabricate by traditional process, such as machining or casting. Electron beam additive manufacturing technology is one of the metal 3D printing methods and is able to fabricate such porous structure. In this study, electron beam additive manufacturing technology is introduced to fabricate porous structure with different design. This study explores the design effect of the porous structure on mechanical properties. The results of biocompatibilities, mechanical properties, and microstructure of the EBAM samples are examined and discussed. Meanwhile, medical devices were fabricated by this technology, and gradient porous structure was introduced to improve the function of the medical devices as well.


3:15pm - 3:30pm
Oral

The Effect of Uni-and Binary Solvent Additives in PTB7:PC61BM Based Solar Cells

Genene Tessema MOLA

University of KwaZulu-Natal, South Africa

The effect of uni-and binary solvent additives on the performance of organic solar cells based on poly{4,6-(2-ethylhexyl-3-fluorothieno [3,4-b]thiophene-2-carboxylate)alt-2,6(4,8-bis(2-ethylhexyloxy)benzo [1,2-b:4,5-b]dithiophene) (PTB7) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was investigated using chloroform host solvent. The use of binary solvents additive was found to be more effective in improving the collection of photo-generated current in thin film organic solar cells (TFOSC). The boiling points of the solvents and their degree of ability to dissolve the fullerene molecules are some of the factors that determines the effect of binary solvents additive. The inclusion of solvent additives in device processing improved the power conversion efficiency of TFOSC which can be attributed to the polymer crystallinity and the formation of favorable phase separated domains for the percolation of free charge carriers. Moreover, the investigations on the charge transport properties suggest that a little reduction in the non-germinate recombination was realized leading to the improved charge extraction in the devices with binary solvents additive compared to those processed without additive solvents.



 
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