LOW DENSITY MATERIALS 18 March 2011

JOYCELYN HARRISON

Program Manager

AFOSR/RSA

Air Force Office of Scientific Research

AFOSR

Distribution A: Approved for public release; distribution is unlimited. 88ABW-2011-0806

2

2011 AFOSR SPRING REVIEW2306C PORTFOLIO OVERVIEW

NAME: Joycelyn Harrison

BRIEF DESCRIPTION OF PORTFOLIO:

Fundamental advances in the discovery, understanding

and processing of materials that can enable substantial

reductions in system weight with enhancements in

performance and function for AF aerospace systems

LIST SUB-AREAS IN PORTFOLIO:

Structural Lightweighting

Multifunctional Materials

Engineered Hybrid Materials

3

Why Low Density Materials?

Aerospace and cyber platforms can

not afford parasitic weight or volume….

• Miniaturization

• Payload

• Duration

• Cost

Materials must provide structural

integrity with other attributes…

• Adaptability

• Self awareness

• Environmental resistance

4

Transformative research targeting advanced materials that

enable substantial reductions in system weight with

enhancements in performance and function

Enhanced Specific Capabilities

(performance / pound)

Capability * r -1

Low Density Materials

5

Taking the Weight Out of Traditional Composites

- Increasing specific properties of composites

- Molecular modeling to improve life prediction capability

- Integration of nanoporosity into composites

Designing Materials to Couple

Structure + Function

- Novel actuation materials

- Novel multifunctional structures

Bottom-up Hybrid Materials Design

– Computational tools to guide

material synthesis

Increasing Specific Capabilityin Aerospace Platforms

6

7

The Promise of Carbon Nanotubes for

Lightweight, High Strength Structures

10

100

1000

1 10 1000.1

Specific

Modulus

GPa/(g/cm3)

Specific Strength, GPa/(g/cm3)

0.2 0.5 2 5 20 50

20

50

200

500

Al 2219

Al Foam

M46J CFRP

Ti Foam Sand

Al2O3/Al

BeAl

SiC/Be

M46J

IM7

SWNT

IM7 CFRP (TRL=4-9)

TiAl

Charlie E. Harris, M. J. Shuart, H. Gray, NASA/TM-2002-211664

8

A Path To Transformative Multifunctional Structures

Nanotailoring Processing Self-Reinforced

Composites Neat Nanotubes Nanotube Structures

Nanotailoring

traditional

composites can

only lead to

incremental

improvements

Macroscopic

Nanotube Structures

which approach the

mechanical and

transport properties

of CNTs

Among the scientific

challenges that must be

overcome in order to achieve

the next generation of

lightweight, multifunctional

structures:

- Efficient alignment and

densification of bulk volumes

of nanotubes

- Discovering mechanisms for

efficient cross-linking or

welding of nanotubes

* Plans are underway

to establish an MOA

with NASA in this area.

Richard Liang et.al, FSU.

9

Ben Wang, et.al. Florida State Univ.

Nanotube Reinforced

Composite without

Carbon Fiber

10

Processing Towards

Neat Nanotube Structures

Highly Aligned

Nanotube Sheets

Polygonization for

maximum packing

density and contact area

Richard Liang, et.al. Florida State Univ.

Radiation-induced

crosslinking of CNTs

Preliminary results show

increases in tensile

strength, modulus and

electrical conductivity

11

MURI 11 Topic: Nanofabrication of 3D Nanotube Architectures

Nanotube networks will enable the

translation of exceptional 1D and 2D

properties of tube and sheets into

three dimensions

Objective: Provide fundamental understanding of principles behind

the assembly of 3D, tunable nanotube architectures and investigation

of mechanical and transport properties of these novel structures

Among the Scientific Challenges for

Fabrication of 3D Nanotube

Architectures are:

- Atomistic assembly of nanotube

nodal joints

- Control of nodal geometry

connectivity, rigidity and durability

- Understanding the influence of node

configuration on mechanical and

transport properties

12

Atomistic Modeling Guides

Fabrication of 3D Nanotube Networks

Ajit Roy, et.al, AFRL/RX

Molecular dynamics (MD)

modeling of nanotube networks

offers critical insights and can

inform fabrication on:

- Most stable nodal

connectivity

- Effects of residual catalyst

- Most durable network

geometry

- Electron and phonon

transport throughout network

Nanotube-graphene geometry (pillar length and inter-pillar

spacing) significantly influences network properties

13

Structural Stability of CNT Pillared

Graphene Network – Preliminary Results

1st mode

For applied loads the CNTs do not deform

but single layer graphene experiences

severe buckling. Single graphene layer

will not impart structural rigidity.

Buckling Behavior

1.21

3.25 2.36

3.940

40

80

120

160

200

Yo

un

g’s

mo

du

lus

, E

1[G

Pa

]

II

I

IV

III

Effective Mechanical Properties

Effective in-plane modulus is

highest with short CNT pillars and

broader spacing between pillars.

Very important implications for fabrication!

14

Intercalated CVD growth of vertically-

aligned CNTs in thermally-expanded

graphite sheets

Pillared CNT/Graphene FabricationClose Collaboration with Modeling

Liming Dai, Case Western Reserve U.

Modeling suggests CNTs grown on

multiple interconnected graphene

sheets similar to these graphite sheets

might yield better structural rigidity

Proposed Pillared CNT/Graphene

Fabrication Method

15

Nodal Connectivity

Impacts Transport Properties

Effect of Nodal Connectivity on Phonon Transmission at CNT Interface

For optimum phonon transmission, self-similar atoms, carbon-

carbon junctions, and no residual catalyst are needed

Clean CNT-Graphite interface with no

residual catalyst as verified by EDX

elemental analysis

Varshney, et al, submitted to J. Applied Physics, 2010

Maximum Transmission12 CH2 linkers6 CH2 linkers3 CH2 linkers

3 CH2 linkersO

vera

llTr

ansm

issi

on

16

Carbon Nanotube Truss ArchitectureNolan Nicolas, Mid-Atlantic Research & Innovation Center

Challenging Chemical

Synthesis

Nanotube truss performance may be maximized by bearing

mechanical loads and conduction along their axis

Tailored Functionalization:

Must distinguish between

end-groups and sidewalls to

enable self-assembly.

Node Conversion:

Solvophilic sidewall

functionalization stabilizes

the sidewalls in solution.

Solvophobic end groups

precipitate together to form

end-to-end spaceframe

networks.

Nanotube Truss

Network

17

Recent Research Transition

Nanotailored Carbon Fibers

Satish Kumar, Georgia Institute of Technology

Significant Enhancement in Carbon Fiber Properties

• Structural analysis (SEM,

TEM, WAXD, Raman)

suggests CNT facilitates

graphitic structure formation

in its vicinity

• Carbonized PAN/CNT

exhibited significantly

improved tensile strength

and modulus, 64% and

49%, respectively

G-band evolution:

graphitic structure

formation

PAN PAN/CNT

Successful Technology Transition

- DARPA Advanced Structural Fiber Program - $10.5 M for

Phase I and Phase II

- Program Property Goals: Tensile Strength 12.5 GPa,

Modulus 420 GPa, Strain to Failure 1.5%

18

19

- Understand molecular

level response to effects

of physical aging,

environment (oxidation,

temperature, etc) and

damage events

- Understand how to

translate molecular level

response to bulk material

attributes

- Employ this fundamental

understanding to design

novel hybrid materials for

optimum performance

Epoxy

Graphite

Efficient Approaches to Incorporating

Physical Aging in a Crosslinked Epoxy,

Odegard, Michigan Tech Univ.

Fracture Parameters from

Atomistic to Micro, Brietzman, et.al,

AFRL/RX

Molecular Modeling of

Polymer Matrix Composites

Oxidation Tolerant Composites,

Pochiraju, et,al, Univ. Alabama

EPON-862

DETDA

Time & Temperature

Dependent Debonding

in Composites, Roy,

et,al, Univ. Alabama

Modeling Elastic & Failure Behavior,

Mukhopadhyay, et.al, Wright State U.

100 nm 1 m m 100 m m 1 mmÅ 10 nm

Bottom-Up Design of Multifunctional Hybrid Materials

Prior focus is on modeling PMCs, future increased

emphasis will be on Hybrid Materials Design

20

molecular

precursors

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

10

20

30

40

50

60

70

Fra

ctu

re E

nerg

y, G

C(J

/m2)

Zr:Si Ratio

Sol-Gel

SiO2

Epoxy

Sol-Gel

SiO2

Epoxy

failure path

(graph theory)

molecular structure (NMR, FTIR)

Molecular Structure Modeling and Design Tools

Molecular Structure (MD)

network

stiffness0.6 0.8 1.0 1.2 1.4 1.6

0

5

10

15

20

25

Young's

Modulu

s (

GP

a)

Density (g/cc)

Elastic

Fracture

MechanicalProperties

Reinhardt Dauskardt, Stanford U.

21

Engaging the Research Community

AFOSR

Low Density

Materials

Principal Member of

Reliance 21 Board

Materials and Processing

Community of Interest

NSF

CMMI – *Adaptive

Systems EFRI topic

DoD liaison for

National Academies

Lightweighting Study

DOD CommunityAFRL TDs

LRIRs, STTRs, MURIs,

Workshops, Reviews

RX

RV

RW

Key Interfaces for Other Services

ARO – David Stepp

ONR – Ignacio Perez

DARPA – Brian Holloway

NASA

*MOA on Lightweight

Structures

DOE

Oak Ridge National

Lab - Composites

Processing

Other Governmental

Agencies

* Denotes ongoing plans for formal collaboration.

22

Program Trends

Structural lightweighting via nanotailoring

resins and fibers for traditional composites

Improved life prediction capability in traditional composites

Innovative use of porosity

Structural lightweighting targeting macroscopic nanotube

structures

Nanofabrication of 3D nanotube architectures (MURI)

Multifunctional materials to couple structure and function

Development of modeling capability to guide

Bottom-Up Design of Hybrid Materials

TR