Carbon Nanotube-based Sensing Layers Applied to Structural Steel Tension Members

quartzaardvarkUrban and Civil

Nov 29, 2013 (3 years and 8 months ago)

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RESULTS

FUTURE WORK













ACKNOWLEDGEMENTS

New

tests

are

already

being

carried

out

and

others

are

in

the

stage

of

definition
.

The

interest

with

these

new

sets

is

on

exploring
:



Source

of

baseline

drift
.


Effects

of

inelastic

deformation
.


Repeatability

of

the

finally

selected

technique

(method

A)

and

its

results
.


Quantitative

correlation

of

initial

resistance

and

resistance

change

with

the

sensing

surface

area

and

the

concentration

of

CNTs
.


Response

of

the

sensor

when

applied

to

rebars

(rather

than

smooth

rods)
.

© 2012, University of Delaware, all rights reserved

BACKGROUND





EXPERIMENTAL METHODOLOGY

INTRODUCTION

Carbon Nanotube
-
based Sensing Layers Applied to Structural Steel Tension Members


Jose Fernando Rave Arango
1)
, Hongbo Dai
1)
, Thomas Schumacher
1)
, and Erik T. Thostenson
2)


University of Delaware


Center for Composite Materials


Civil and Environmental Engineering
1)
/Mechanical Engineering
2)


As

structures

age,

they

begin

showing

distress

and

thus

become

more

vulnerable

to

failure

and

hazards
.


About

¼

of

the

bridges

in

the

U
.
S
.

are

either

structurally

deficient

or

functionally

obsolete

[ASCE,

2009
]
.


Need
:

Structural

health

monitoring

(SHM)

techniques

that

allow

owners

to

make

informed

decisions

for

maintenance,

so

as

to

improve

safety

and

reliability

of

infrastructure
.


Objective
:

Develop

carbon

nanotube

(CNT)
-
based

sensing

layers

that

can

be

applied

to

critical

structural

members

for

quantitative

real
-
time

performance

and

condition

monitoring
.

Source: www.flickr.com

This project was jointly supported by the
University of Delaware and the CMMI
-
NSF
Grant # 1234830.

CONCLUSIONS


In

the

present

work

preliminary

tests

were

carried

out

on

the

application

of

innovative

CNT
-
based

sensing

layers

to

structural

steel

tension

members

for

structural

health

monitoring
.


Results

show

that

the

manufacturing

methodology

proposed

leads

to

a

sensing

layer

whose

overall

resistance

is

remarkably

sensitive

to

deformation

changes
.


Resistance

change

tends

to

follow

load

and

strain

change

very

tightly

and

with

immediate

response
.


There

seems

to

be

a

moving

baseline

for

the

resistance
.

However,

it

tends

to

be

asymptotic

with

increasing

time,

which

could

point

out

the

necessity

to

let

the

system

undergo

a

“warm

up”

time

prior

to

measurements
.


It

is

demonstrated

that

when

data

post
-
processing

and

baseline

correction

are

applied,

resistance

response

very

closely

fits

the

loading

profile
.


In

synthesis,

with

the

results

gathered

to

this

point,

the

proposed

SHM

technique

is

deemed

very

promising

for

actual

industrial

implementation
.

Test #1 (specimens A & B)
. Above: original data for extension and change
in resistance. Below: results after post
-
processing (noise reduction,
smoothing, baseline correction and normalization).


Two

7
-
in

sections

of

a

0
.
5

in
-
dia
.

steel

rod

(with

smooth

surface)

were

prepared

as

specimens
.


Preparation

included

three

parts
:

an

insulating

layer

to

break

electrical

continuity

between

the

sensor

and

the

bar,

the

actual

sensing

layer

corresponding

to

the

network

of

CNTs

and

a

final

insulation

of

the

network

from

the

environment

to

avoid

interference

from

any

external

source
.

A

different

manufacturing

method

was

carried

out

for

each

specimen
:




One

important

type

of

such

critical

members

are

steel

tension

members

(
rebars
,

cables,

etc
.
),

which

constituted

the

focus

of

these

summer

2012

research

activities
.


CNTs

have

unique

multifunctional

properties,

including

exceptional

electrical

conductivity

and

extremely

high

aspect

ratios

(length/diameter)
.


It

has

been

observed

that

if

the

high

aspect

ratio

is

preserved

during

dispersion,

an

electrically

conductive

network

of

CNTs

can

be

formed,

which

in

addition

exhibits

strain/resistance

coupling

behavior
.












This

piezoresistive

behavior

is

the

principle

underlying

the

sensing

capability

of

the

network
:

as

the

material

is

strained

in

tension,

tunneling

gaps

between

tube/tube

contacts

appear,

thus

increasing

the

overall

network

electrical

resistance
.

METHOD

BAR INSULATION

SENSING LAYER

ENV.

INSULATION

A

Epoxy coating (Epon862

+ Epikure9553)

Sonicated

sizing agent
containing CNTs

Epoxy coating (Epon862

+ Epikure9553)

B

Epoxy coating (Epon862

+ Epikure9553)

Sonicated

sizing agent containing CNTs added to
epoxy resin (Epon862

+ Epikure9553)


Wires

were

attached

to

each

end

to

act

as

electrodes

and

then

the

bar

was

set

up

in

a

material

testing

machine

and

subjected

to

repeated

and

increasing

tension

loading,

while

applying

a

constant

voltage

of

20

V

through

the

specimens

and

measuring

the

DC

current

with

a

digital

multimeter

so

as

to

calculate

resistance
.



Several

reasons

pointed

specimen

A

as

preferred
;

a

2
nd

test

was

performed

on

it
.

Test #2 (specimen A only)
. Above: original data for load and change in
resistance. Below: results after post
-
processing (noise reduction,
smoothing, baseline correction and normalization).