Civil & Environmental Engineering

beepedblacksmithUrban and Civil

Nov 29, 2013 (3 years and 4 months ago)

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Experimental
Methodology


The

test

setup

is

illustrated

in

Figure

3
.

This

setup

is

often

referred

to

as

‘pitch
-
catch’

where

a

piezoelectric

transmitter

creates

a

ultrasonic

stress

wave

on

one

side

of

the

specimen

that

is

measured

on

the

opposite

face

by

a

piezoelectric

receiver
.

The

fastest

stress

wave

type

that

exists

in

a

solid

is

the

so
-
called

compression

or

p
-
(primary)

wave

mode
.

For

this

study,

a

wave

signal

as

shown

in

Figure

4

(black

line)

with

a

peak

frequency

of

150

kHz

was

used

as

input

signal

and

repeated

several

times

so

that

statistical

variations

of

the

measurement

and

material

could

be

established
.














Figure 3.

Experimental setup


Results


Two

parameters

were

determined

from

the

recorded

data

using

Matlab
:


The

p
-
wave

amplitudes

A
p

of

the

received

signals

(see

Figure

4
.
a)


The

p
-
wave

velocity

c
p

using

the

time

difference

D
t

and

thickness

d

between

the

transmitted

and

the

received

signal

(see

Figure

4
.
a)












(a)




(b)

Figure 4.

Example of transmitted (black) and received (red) signal
waveforms from (a) an integer area and (b) an area having a ‘blow
-
out’.


It

was

found

that

the

p
-
wave

amplitudes

from

the

OSB

(Figure

2
.
b)

had

a

lower

amplitude

and

a

slower

velocity

than

the

plywood

(Figure

2
.
a)
.

This

can

be

attributed

to

a

lower

density

(more

voids)

of

the

OSB
.

Non
-
Destructive
Testing
of Wood
-
Based Composites Using Ultrasonic Stress Waves

Table

1
.

Estimated

p
-
wave

velocities

for

all

specimens








Figure

5

shows

an

example

of

how

the

data

can

be

represented

using

a

contour

plot

for

the

p
-
wave

velocities

for

specimens

3
)

and

4
)
:















(a)




(b)


Figure 5.
Contour plots for p
-
wave velocities in (a) low density panel
and (b) panel with a blow
-
out board


Conclusions


The

different

specimens

could

be

distinguished

by

the

different

p
-
wave

velocities
.

Using

ultrasonic

NDT,

flaws

in

wood
-
based

composites

such

as

‘blow
-
outs’

can

be

quantified

and

localized
.


Future

Work


Continued

evaluation

of

wood
-
based

composites

using

ultrasonic

stress

wave

propagation

and

correlation

with

mechanical

properties

such

as

density,

glue

line

content

and

quality,

and

tensile

and

shear

strength
.



Acknowledgments


This

research

work

was

sponsored

by

the

University

of

Delaware

Research

Foundation

(UDRF)

Research

Experience

for

Undergraduates

(REU)

Summer

Internship

Program
.

Wood

composite

specimens

were

provided

by

Arijit

Sinha
,

Assistant

Professor

in

Wood

Science

at

Oregon

State

University
.

The

support

is

greatly

appreciated
.

Jean Carlo
Vilalta
, Undergraduate Research Assistant & Thomas Schumacher, Assistant Professor (Adviser)

Civil & Environmental Engineering

Objectives:
T
o detect (using ultrasonic NDT)
any flaws or
irregularities within the wood specimens otherwise
undetectable by visual
means.

Introduction and Background



W
ood

and

wood
-
based

composites

are

more

likely

than

other

materials

to

decay

under

certain

environmental

conditions

and

exposure
.


Non
-
destructive

testing

(NDT)

is

commonly

used

to

determine

the

properties

of

different

materials

such

as

metals,

polymers,

and

concrete,

without

varying

their

end
-
use

capabilities
.


NDT

may

be

used

to

analyze

physical

and

mechanical

properties

of

wood
-
based

composites
.


Specifically,

ultrasonic

NDT

may

be

useful

in

the

evaluation

of

wood
-
based

composites

during

the

manufacturing

process

to

estimate

glue

line

quality

and

to

detect

flaws

(see

Figure

1
)

to

accomplish

quality

control
.






Figure 1.
Example of a ‘blow
-
out’ (large crack parallel to the surface
of the specimen) in a wood
-
based
composite.







Test Specimens


Four

engineered
-
wood
-
type

specimens

were

tested

and

are

shown

in

Figure

2
:

1)
0
.
75


thick,

16


x

3
”,

plywood

(Figure

2
.
a)

2)
0
.
75


thick,

16


x

3
”,

oriented

strand

board

(OSB)

(Figure

2
.
b)

3)
0
.
75


thick,

16


x

16
”,

low
-
density

particle

board

with

a

‘blow
-
out’

(Figure

2
.
c)

4)
0
.
75


thick,

16


x

16
”,

low
-
density

particle

board

(Figure

2
.
d)












(a) (b) (c) (d)


Figure 2.

Test specimens





















Waveform

Generator

Data
Acquisition
System

Signal
Preamplifier

Waveform
Amplifier

Computer using
wave recording
software

Specimen

Transmitter

Receiver

The

objective

of

this

study

is

to

evaluate

ultrasonic

NDT

methods

for

the

detection

and

visualization

of

flaws

in

wood
-
based

composites

such

as

‘blow
-
outs’

and

the

distribution

and

quality

of

the

glue

line
.




Change in time

(s)

of
wave
arrival

A
p

D
t


D
p
d
c
t