Nanocomposite Strain SensorsChristopher J. Tzanavaris

Motivation

•To introduce a lighter, lower cost strain sensor.

•Versatility – a wide range of applications from aerospace to structural

•To take a fresh look at strain sensors and see where there is opportunity for alteration.

Measuring Strain

•Measure conductivity•Apply strain•Conductivity decreases•Strain can be interpreted as a function of

conductivity

Outline

•Introduction▫Literature review and comparative analysis

•Materials overview▫Fabrication process

•Data & Results▫Examination of past and recent data

Issues and trends•Conclusions

Introduction

The research is on strain sensors that are:•Lighter•Less expensive

▫Carbon Nanotubes (CNTs) vs. Vapor-grown Carbon Fibers (VGCFs) SWCNTs cost ~$80/gram vs. $5-6/gram1

1. http://www.cheaptubes.com/carbon-nanotubes-prices.htm#Multi_Walled_Nanotubes_Prices

Carbon nanotubes (CNTs) vs. Vapor Grown Carbon Fibers (VGCFs)• Similar mechanical and electrical properties• Sizes of VGCFs can vary from a few nm (similar

to CNTs) to about ten microns.2

• Comparable geometry▫High aspect ratio▫‘Nanofiber’ designation for VGCFs (diameter is

between 10 and 100 nm) and the presence of a central hollow core.2

2. Endo, Morinobu, and M. S. Dresselhaus. "Nanostructures Seminar Series at MIT." MIT Nanostructures Lab, 2003. Web. 11 Mar 2010. <http://web.mit.edu/tinytech/Nanostructures/Spring2003/MDresselhaus/i789.pdf>.

Materials Overview•Vapor-grown carbon fibers (VGCF)•Polydimethylsiloxane (PDMS)•Curing agent Source: Simpson, Brian, David Hill, and

Kyriaki Kalaitzidou. "Manufacturing and Characterization of Nano-Composite Linear Strain Sensors." ANTEC Conference 2009. (2009): Print.

Effect of Strain on Conductivity for10:1, 4% VGCF

Source: Simpson, Brian, David Hill, and Kyriaki Kalaitzidou. "Manufacturing and Characterization of Nano-Composite Linear Strain Sensors." ANTEC

Conference 2009. (2009): Print.

Possible Solutions

•Change the ratio of base to curing agent•Past research was with 10:1, with varying

percentages of VGCF from 1.5 – 4 wt. %. ▫10:1▫10:1.5▫10:2

3 and 4 wt. % VGCF

Testing

•Tensile testing (Dynamic mechanical analysis)▫Dimensions: 20 mm x 6 mm x 1.75 mm▫Samples strained at 1%/min▫Max 25%

•Conductivity testing▫Strain applied and conductivity is

measured

Tensile Modulus Data

10/1, 3% 10/1, 4% 10/1.5, 3% 10/1.5, 4%2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

Effect of Curing Agent and VGCF concentrations on Tensile Modulus

(E)

Ratio, %VGCF

E (

MP

a)

0 1 2 3 4 51.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

Effect of VGCF concentration on Electrical Resistance For 10:1 Monomer:Curing Agent Ratio

3% VGCF, Load-ing

3% VGCF, Unload-ing

4% VGCF, Load-ing

Strain (%)

Resis

tan

ce (

Oh

ms)

0 1 2 3 4 51.00E+03

1.00E+04

1.00E+05

1.00E+06

Effect of Curing Agent Ratio on Electrical Resistance for 3%

VGCF

10:1, Loading

10:1, Unloading

10:1.5, Loading

10:1.5, Unloading

10:2, Loading

10:2, Unloading

Strain (%)

Resis

tan

ce (

Oh

ms)

Conclusions

•Higher ratios show better recovery of conductivity upon unloading

•Long term trends need to be tested▫Initial stain may cause a fundamental

change in fiber alignment.▫Fatigue tests will be performed

•Compare fiber alignment hypothesis with SEM images.

•Formulate a quantifiable calibration curve

Special Thanks

•Professor Kyriaki Kalaitzidou•Brian Simpson•Professor Gleb Yushin and his research

team for use of their equipment•Md. “Atiq” Bhuiyan

Questions???