Variations of In-Plane Mechanical Properties of Cellular Structures With Different Hierarchical Organizations

2020 ◽  
Author(s):  
Souvik Chakraborty ◽  
Dylan Hebert ◽  
Tanvir Rahman Faisal
Keyword(s):  
Mechanical Properties ◽  
Cell Wall ◽  
Hierarchical Structure ◽  
Unit Cell ◽  
Cellular Structures ◽  
Initial Shape ◽  
Unit Cells ◽  
Cell Topology ◽  
Homogeneous Cell ◽  
Hierarchical Organizations

Abstract Inspired by the nature, this study analyzes in-plane compressive responses of different modes of hierarchical architected structures with varying topologies. Architected cellular structures with two different unit cell topologies — square and kagome are considered, both having a relative density of 0.25. Each unit cell topology is designed with three different configurations. The base structure is the primitive one with solid homogeneous cell wall. The nested hierarchical structure is derived from the primitive one with cellular structuring in the cell wall. The third and final one is the fractal-like hierarchical structure, where same unit cells appear on different length scales. 3D printed structures were subjected to uniaxial compression to characterize their in-plane mechanical properties. The compressive stress-strain behaviors reveal that all the structures demonstrate the classical behavior of cellular structures followed by significant recovery of their initial shape upon load withdrawal. The energy absorptions demonstrated by the plateau regions before densification are not only governed by their structural topologies, but also largely governed by the configurations of hierarchical organizations. Hence, this study suggests the application specific design of hierarchical architected structures for defined loading conditions.

Developing Design Guidelines for Meso-Scaled Periodic Cellular Material Structures Under Shear Loading

2016 ◽  
Author(s):  
Mohammad Fazelpour ◽  
Prabhu Shankar ◽  
Joshua D. Summers
Keyword(s):  
Design Process ◽  
Effective Property ◽  
Design Guidelines ◽  
Shear Loading ◽  
Unit Cell ◽  
Cellular Material ◽  
Plane Shear ◽  
Unit Cells ◽  
Cell Topology ◽  
Shape Characteristics

Much research has been conducted on effective elastic properties of meso-scaled periodic cellular material (MPCM) structures; however, limited research is found in the literature for design guidelines to develop a unit cell (UC) topology and shape for multiple loading conditions. The current methods to design topology of unit cells has experienced limitations including numerical modeling challenges and trial-and-error associated with topology optimization and intuitive methods, respectively. To address this limitation this paper aims to develop guidelines for redesign of unit cell topology and shape under in-plane shear loading. The guidelines are intended to use design knowledge for helping engineers by providing recommendations at any stage of the design process. In this paper, the guidelines are developed by changing topology characteristics to achieve a desired effective property of a MPCM structure. The effect of individual members such as side connection and transverse connection of MPCM structure when subjected to in-plane shear loading are investigated through conducting a set of numerical simulation on UCs with similar topology and shape characteristics. Based on the simulation results, the unit cell design guidelines are developed to provide recommendations to engineers on improving shear flexure of MPCM during the design process.

scholarly journals Design and Mechanical Testing of 3D Printed Hierarchical Lattices Using Biocompatible Stereolithography

Designs ◽  
2020 ◽  
Vol 4 (3) ◽  
pp. 22 ◽  
Author(s):  
Md Moniruzzaman ◽  
Christopher O'Neal ◽  
Ariful Bhuiyan ◽  
Paul F. Egan
Keyword(s):  
Mechanical Testing ◽  
Elastic Moduli ◽  
Cost Effective ◽  
Building Blocks ◽  
Cell Number ◽  
Unit Cell ◽  
Tissue Scaffold ◽  
Unit Cells ◽  
Cell Topology ◽  
3D Printed

Emerging 3D printing technologies are enabling the rapid fabrication of complex designs with favorable properties such as mechanically efficient lattices for biomedical applications. However, there is a lack of biocompatible materials suitable for printing complex lattices constructed from beam-based unit cells. Here, we investigate the design and mechanics of biocompatible lattices fabricated with cost-effective stereolithography. Mechanical testing experiments include material characterization, lattices rescaled with differing unit cell numbers, topology alterations, and hierarchy. Lattices were consistently printed with 5% to 10% lower porosity than intended. Elastic moduli for 70% porous body-centered cube topologies ranged from 360 MPa to 135 MPa, with lattices having decreased elastic moduli as unit cell number increased. Elastic moduli ranged from 101 MPa to 260 MPa based on unit cell topology, with increased elastic moduli when a greater proportion of beams were aligned with the loading direction. Hierarchy provided large pores for improved nutrient transport and minimally decreased lattice elastic moduli for a fabricated tissue scaffold lattice with 7.72 kN/mm stiffness that is suitable for bone fusion. Results demonstrate the mechanical feasibility of biocompatible stereolithography and provide a basis for future investigations of lattice building blocks for diverse 3D printed designs.

scholarly journals Dual Graded Lattice Structures: Generation Framework and Mechanical Properties Characterization

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1528
Author(s):  
Khaled G. Mostafa ◽  
Guilherme A. Momesso ◽  
Xiuhui Li ◽  
David S. Nobes ◽  
Ahmed J. Qureshi
Keyword(s):  
Mechanical Properties ◽  
Relative Density ◽  
Lattice Structure ◽  
Cell Types ◽  
Functionally Graded ◽  
Unit Cell ◽  
Lattice Structures ◽  
Unit Cells ◽  
Mechanical Properties Characterization ◽  
Graded Lattice

Additive manufacturing (AM) enables the production of complex structured parts with tailored properties. Instead of manufacturing parts as fully solid, they can be infilled with lattice structures to optimize mechanical, thermal, and other functional properties. A lattice structure is formed by the repetition of a particular unit cell based on a defined pattern. The unit cell’s geometry, relative density, and size dictate the lattice structure’s properties. Where certain domains of the part require denser infill compared to other domains, the functionally graded lattice structure allows for further part optimization. This manuscript consists of two main sections. In the first section, we discussed the dual graded lattice structure (DGLS) generation framework. This framework can grade both the size and the relative density or porosity of standard and custom unit cells simultaneously as a function of the structure spatial coordinates. Popular benchmark parts from different fields were used to test the framework’s efficiency against different unit cell types and grading equations. In the second part, we investigated the effect of lattice structure dual grading on mechanical properties. It was found that combining both relative density and size grading fine-tunes the compressive strength, modulus of elasticity, absorbed energy, and fracture behavior of the lattice structure.

Cellular Honeycomb-Like Structures With Internal Buckling and Viscous Elements for Simultaneous Load-Bearing and Dissipative Capability

2012 ◽  
Author(s):  
Silvestro Barbarino ◽  
Michael E. Pontecorvo ◽  
Farhan S. Gandhi
Keyword(s):  
Companion Paper ◽  
Unit Cell ◽  
Cellular Structures ◽  
Initial Stiffness ◽  
Analysis And Design ◽  
Design Load ◽  
Softening Behavior ◽  
Linear Behavior ◽  
Buckling Beam ◽  
Unit Cells

Cellular structures with hexagonal unit cells show a high degree of flexibility in design. Based on the geometry of the unit cells, highly orthotropic structures, structures with negative Poisson’s ratios, structures with high strain capability in a particular direction, or other desirable characteristics may be designed. Much of the prior work on cellular structures is based on hexagonal honeycomb-like unit cells, without any inclusions. A companion paper to the current paper presented a vision of cellular honeycomb-like structures with diverse inclusions or internal features within the unit cells (such as contact elements resulting in stiffening behavior, buckling beams resulting in softening behavior, bi-stable elements producing negative stiffness or viscous dashpots producing dissipative behavior). That paper further went into details on linear springs as the most fundamental of inclusions. In the present paper, a buckling beam and viscous dashpots are used as inclusions in the basic pin-jointed rigid-walled hexagonal unit cell. The buckling beam provides the cell with a high initial stiffness and load carrying capability. At loads beyond the critical buckling load, the unit cell softens (while still retaining the ability to carry a “design” load), and undergoes large deformation under incremental load. The viscous dampers undergo a correspondingly large stroke resulting in high dissipative capability and loss factor under harmonic or transient disturbance beyond the design load. In the paper, an analysis and design study of the cell behavior with variation in unit cell geometric parameters, buckling beam parameters and viscous dashpot parameters is presented. The analytical results in the paper are validated against ANSYS Finite Element results. Further, a prototype unit cell with an aluminum internal buckling beam and viscous dashpots is fabricated and tested under static and dynamic loads in an Instron machine. Good correlation is observed between the tests, the FE results and the analytical simulations when accounting for the non-linear behavior of the viscous dashpot used in the tests.

Study on Cellular Structures as the Core Architectures of Parts Based on Selective Laser Melting

2012 ◽  
Vol 538-541 ◽  
pp. 1904-1907 ◽  
Author(s):  
Dong Ming Xiao ◽  
Yong Qiang Yang ◽  
Xu Bin Su ◽  
Man Hui Zhang ◽  
Di Wang
Keyword(s):  
Mechanical Properties ◽  
Relative Density ◽  
Selective Laser Melting ◽  
High Heat ◽  
Unit Cell ◽  
Cellular Structures ◽  
Compression Tests ◽  
Laser Melting ◽  
The Core ◽  
Cell Architecture

Cellular structures exhibit favorable properties for multifunctional applications, such as light weight, high load-bearing combined with high heat exchange capability. This paper is to seek optimal cellular structures as the core architectures of parts manufactured by selective laser melting (SLM) technology, which provides required mechanical properties. Design features for characterizing optimal structural performance are discussed. Some preliminary design rules are developed to improve the manufacturability and the quality of cellular structures, the orientation of strut is designed as ±45° or 90°. Compression tests are also carried out to seek cellular structures of synthetically optimal mechanical properties. Comparing the effects of the unit cell architecture and the relative density on mechanical properties, it reveals that unit cell architecture is dominant rather than the relative density, and the truss lattice with [90°,±45°] structure is the overall best performing among the selected cellular structures.

Cellular Honeycomb-Like Structures With Internal Inclusions in the Unit-Cell

2012 ◽  
Author(s):  
Michael E. Pontecorvo ◽  
Silvestro Barbarino ◽  
Farhan S. Gandhi
Keyword(s):  
Cell Wall ◽  
System Level ◽  
Cellular Structures ◽  
Specific Element ◽  
Unit Cells ◽  
Rigid Cell Wall ◽  
A Cell ◽  
Element Type ◽  
High Degree ◽  
Analytical Expressions

Cellular structures with hexagonal unit cells show a high degree of flexibility in design. Based on the geometry of the unit cells, highly orthotropic structures, structures with negative Poisson’s ratios, structures with high strain capability in a particular direction, or other desirable characteristics may be designed. Much of the prior work on cellular structures is based on hexagonal honeycomb-like unit cells, without any inclusions. The present paper envisages extending conventional cellular honeycomb-like structures to have inclusions or internal features within the unit cells. Various types of internal features such as contact elements, buckling beams, bi-stable/snap-through elements or viscous dashpots can result in unit cells which display stiffening, softening, negative stiffness, or dissipative behavior. A structure can be assembled using a specific element type, or different types of elements in specific arrangements, to provide desired system level behavior. The ability to so optimally and flexibly design cellular structures could potentially lead to their replacing conventional structures made from bulk materials. As a first step, this paper presents work on hexagonal unit cells with linear springs as the simplest of inclusions. The hexagonal cell itself is comprised of rigid links and pin-joints. Since such a cell has no stiffness of its own, the behavior of any internal feature is emphasized. However, for kinematic stability purposes, three springs are required, and the significance of these constraints within the cell will be discussed. For different spring arrangements, closed-form analytical expressions are derived for the in-plane modulus and Poisson’s ratio. The analytical expressions are validated using NASTRAN finite element simulations, as well as against experimental tensile/compressive tests of fabricated unit cells with internal springs. When the spring stiffness exceeds certain values, the rigid cell wall assumption is no longer valid, and these bounds are established. The validated analysis is used to conduct design studies on how the cell modulus would vary with geometric parameters such as cell angle and cell wall length ratio.

Rapid Manufacturing of Cellular Structures of Steel or Titaniumalumide

2011 ◽  
Vol 690 ◽  
pp. 103-106 ◽  
Author(s):  
Lukas Löber ◽  
Denis Klemm ◽  
Uta Kühn ◽  
Jürgen Eckert
Keyword(s):  
Mechanical Properties ◽  
Mechanical Performance ◽  
Steel Powder ◽  
Cellular Structures ◽  
Rapid Manufacturing ◽  
Lattice Structures ◽  
Experimental Conditions ◽  
X Ray ◽  
Whole Process ◽  
Unit Cells

The Selective Laser Melting (SLM) technique is used to produce different cellular structures. Regular unit cells are placed in tensile bars to determine the mechanical performance of different lattice structures. The mechanical properties of the tensile bars with lattice structures are compared to fully dense tensile bars. Tensile bars are produced by conventional casting to compare the mechanical properties between SLM and casting. To exclude other influences, the whole process chain starting from the powder to the finished part is characterized. The different powders, namely 1.4404 steel powder and a titaniumaluminde (Ti-48Al-2Cr-2Nb [TiAl]) powder are characterized via scanning electron microscopy (SEM), energy disperse x-ray spectroscopy (EDS), chemical analysis and light microscopy (LM). In addition measurements of the particle size distribution are conducted. Detailed experimental conditions of the SLM-process are given.

scholarly journals MODELING OF PLASTIC DEFORMATION OF POROUS POWDER MATERIALS

2003 ◽  
Vol 8 (4) ◽  
pp. 351-360
Author(s):  
G. Zayats ◽  
R. Kusin ◽  
V. Kapcevich
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Unit Cell ◽  
Powder Materials ◽  
Porous Powder ◽  
Technological Parameters ◽  
Technological Characteristics ◽  
Unit Cells ◽  
Powder Particles ◽  
Good Agreement

In the present study the model of plastic deformation of porous powder materials (PPM) is described and numerically simulated. This model enables prediction of change of fundamental technological parameters of PPM in plastic deformation conditions, i.e. porosity, pore size, specific surface and mechanical properties. Porous media is described by unit cells consisting of eight powder particles. The parameters of unit cell (the distance between the centers of particles, the angles of the array and the dimensions of interparticle connections) form the model of porous material and define its technological characteristics. The model takes into account the effect of deforming anisotropy on PPM properties. Calculations are performed in nonorthogonal coordinates connected with unit cell. In the case of uniaxial straining obtained numerical results have shown good agreement with the experimental results.

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