Lecture 12, 2008. Design of Composites / Hybrid Materials, or Filling Holes in Material Property Space (2/2) - PowerPoint PPT Presentation

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Lecture 12, 2008. Design of Composites / Hybrid Materials, or Filling Holes in Material Property Space (2/2)

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Title: MECH4301 L12 Hybrids (2/2) Author: Carlos Caceres Last modified by: Carlos H. Caceres Created Date: 7/24/2000 2:53:39 PM Document presentation format – PowerPoint PPT presentation

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Title: Lecture 12, 2008. Design of Composites / Hybrid Materials, or Filling Holes in Material Property Space (2/2)


1
Lecture 12, 2008. Design of Composites /
Hybrid Materials, or Filling Holes in Material
Property Space (2/2)
  • Textbook Chapter 13, Tutorial 6
  • Papers (light reading)
  • Microtruss core 1
  • Microtruss core 2

2
Hybrid Materials four families of configurations
Composite Sandwich Lattice Segment
3
Review Fibre and particulate composites the math
  • Rule of mixtures for density
  • (exact value)
  • Rule of mixtures for stiffness
  • Along the fibres
  • (upper bound, Voigt)
  • Across the fibres
  • (lower bound, Reuss)

Same sort of equations for strength, heat
capacity, thermal and electrical conductivity,
etc.
4
Hybrid Materials four families of configurations
Composite Sandwich Lattice Segment
5
Hybrid Materials of Type 2 Sandwich Panels
6
A Sandwich Panel as a Single Material the math
  • Rule of mixtures for
    density
  • Fibre composites
    Sandwich panels
  • Rule of mixtures for stiffness
  • Fibre composites (tension) Sandwich
    panels (bending)

  • equivalent


  • flexural


  • modulus

7
Hybrid Materials four families of configurations
Composite Sandwich Lattice Segment
8
Lattices Bending dominated vs. Stretch dominated
structures
Bending dominated structures
Cable
Leaf spring
We use Shaping to give the sections a LOWER
flexural stiffness per kg than the solid sections
from which they are made.
9
Bending dominated structures Foams
Prove this
Very flexible structure low effective E
Prove Proportionality constant of order 1
10
Compressive deformation behaviour of foams
11
Collapse of foams
metallic foam (plastic hinges)
elastomeric foam (elastic buckling)
ceramic foam (hinges crack)
12
Stretch dominated structures
over-constrained
rigid
flexible
bending-dominated (mechanism)
stretch-dominated structures
13
Stretch dominated structures
A micro-truss structure
14
Micro-truss core designs for panels
Periodic cellular material cores are based on a
regularly repeating geometric unit, or cell, like
a cube (square honeycomb) or pyramid. This
technology allows for consistently spaced
open-cells, which facilitate the addition of
materials like magnets, cables, or ceramics, for
example and therefore increase functionality. The
open cells also permit fluid flow that can
achieve more efficient thermal management.
http//www.cellularmaterials.com/coredesigns.asp
15
http//etd.gatech.edu/theses/available/etd-1122200
5-162952/unrestricted/wang_hongqing_v_200512_phd.p
df
Bone Foam (bending dominated) or micro-truss
(stretch dominated)?
A foam in a panels core behaves like a
micro-truss structure, only with slightly less
efficiency
http//www.srl.gatech.edu/publications/2005/DETC20
05-85366.pdf
16
Bending dominated vs. Stretch dominated structures
micro-truss hybrids ultraligth, high flexural
stiffness
Foams ultraligth solids
1/3 of the bars are loaded in tension
Foams power law relationships (involve the
second moment I) Loaded in compression
Micro-truss linear relationships Flexural loading
Panels with foamed cores linear relationship as
well E(flex) (?/ ?
s)Eface3f Ef (the foam as panel core behaves
like a micro-truss structure)
17
Stiffness vs density for foams and micro-truss
structures
18
http//www.cellularmaterials.com/advantages.asp
19
Hybrid Materials four families of configurations
Composite Sandwich Lattice Segment
20
Unbonded structures that carry load
Examples of topological interlocking
21
Damage tolerance of segmented structures Weibull
statistics
Max slope Weibull modulus m
Design ? for single large element
segmented body fails at ? , D
Vt volume of whole body Vs volume of one
element n Vt/Vs number of elements P
critical failure probability D, D fraction
/critical fraction/ of elements that failed ?t
?s design stress, damage and of solid body
and segmented body Vo, ?o, m Weibull
parameters Kc stress concentration factor
Effect of segmentation on available stress
22
Scale effects on the strength of micro-truss
structures
Ashby Brechet, 2003
Weibull modulus m
metals
ceramics
23
The strength of ceramic foams of different cell
sizes
Compressive strength
fine cells
For given density, foams with fine cells are some
5 times stronger than foams with coarse cells
coarse cells
density
Colombo and Bernardo, Composites Sci. Tech.,
2003, 63, 2353-2359.
24
Hybrids The main points
  • Combining properties may help filling holes and
    empty areas in material property-space maps.
  • Appropriate Hybrid materials can be created by
    combining material properties and shape, the
    latter at either micro or macro scale.
  • Properties of hybrid materials can be easily
    bracketed by simple mathematical relationships
    which allow straight forward description of
    behavior .
  • These functional relationships allow exploring
    new possibilities.

25
The End Lecture 12 (Hybrids, 2/2)
26
Schematic illustrations of microtruss lattice
structures with tetrahedral, pyramidal, Kagome
and woven textile truss topologies
doi10.1016/j.actamat.2004.09.024    
                 Acta Materialia Cellular metal
lattices with hollow trusses Douglas T.
Queheillalt and Haydn N.G. Wadley
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