behavior of ultrasonic wave propagation...

BEHAVIOR OF ULTRASONIC WAVE PROPAGATION IN PRESENCE OF HOLES ON PEQUIÁ (Aspidosperma

desmanthum) WOOD

• Authors: Drª Raquel Gonçalves;

• Drº. Domingos G. P. Cerri;

• Msc. Chiara B. Secco;

• Fernando A. F. Batista,

•

17th International Nondestructive Testing and Evaluation of

Wood Symposium

September 14th-16th, 2011

Even within the Brazilian context, in which the oldest university is 90 years old,

Unicamp can be considered a young institution (only 43 years old) but has

already a strong tradition in education, in research and services to society.

School of

Agricultural

Engineering

(FEAGRI)

-31 thousand

undergraduate students

(66 courses)

-16 thousand graduate

students (135 Programs)

- 10% of the master’s

and doctoral thesis in

the country.

-1.733 faculty members

-15 % of all research

done in Brazilian

universities

NDT Research Group

Researches and Students Group

• 1 associated professor,

• 1 assistant professor,

• 2 postdoctoral,

• 2 PhD students,

• 2 master students,

• 1 technique

• 12 undergraduate students.

INTRODUCTION

One of reasons for the low yield of a tree is the presence of hole. Some

species of commercial or strategic value present holes caused by the

action of fungi and bacteria or by natural causes. If this hollow is large it is

economically unfeasible to extract timber for the timber sector.

INTRODUCTION

One the other hand some companies in the business of furniture

designs are interested in the use of parts of trunk that have the

hollow

OBJECTIVE

Evaluate the change in velocity of ultrasound wave propagation in the presence of holes of known size and

determining a model describing this behavior to generate images.

• Wood piece - Pequiá (Aspidosperma desmanthum);

MATERIAL


MATERIAL

Density is approximately:

•790 kg m-3 in the air dry condition (humidity around 13%)

•1210 kg m-3 in the saturated condition.


MATERIAL

Evaluate the change in velocity

of ultrasound wave propagation

in the presence of holes and

determining a model describing

this behavior.

390 mm x 390 mm x 50 mm

Healthy and massive


• Ultrasound equipment (USLab, AGRICEF, Brasil);

• Exponential Transducer of 45 kHz;

MATERIAL

Scheme of the production of artificial circular hole with the percentage increase in size as compared to the healthy and massive part

METHODOLOGY

30 mm

• CNC machine – SENAI - Itatiba-SP;

• Circular holes: 5%, 10%, 15%, 20%, 25%, 35%, ande 55%

METHODOLOGY

RESULTS AND DISCUSSION

0,0

100,0

200,0

300,0

400,0

500,0

600,0

0 10 20 30 40 50 60

Tim

e o

f w

ave

pro

pag

atio

n

(s)

Hole percentages (%)

X6

X5

X7

X4

X8

Time behavior as a function of the position of measurement in X direction for the hole.


0,0

100,0

200,0

300,0

400,0

500,0

600,0

0 10 20 30 40 50 60

Tim

e o

f w

ave

pro

pag

atio

n

(s)

Hole percentages (%)

X6

X5

X7

X4

X8

The more displaced from the center of the hollow, the smaller the increased of wave

travel, because there is a shorter way to deviate from the hollow


In order to verify if the wave changes in its course when faced with the presence of hollow, for each strip of the grid and for each percentage increase in the hole, it was measured the expected length path wave, which corresponds to the smallest perimeter around the produced hollow. This calculation was performed using photos taken at the time of the test, which were reproduced in the AutoCad, and using this software, the lengths path around the hollow could be determined accurately.

Expected wave path length (X6)

In order to verify if the wave changes in its

course when faced with the presence of hollow,

for each strip of the grid and for each percentage

increase in the hole, it was measured the

expected length path wave, which corresponds to

the smallest perimeter around the produced

hollow. This calculation was performed using

photos taken at the time of the test, which were

reproduced in the AutoCad, and using this

software, the lengths path around the hollow

could be determined accurately.

Hollow


Hole (%) Velocity (m.s-1) Path Length (mm)

0 1670 390

5 1604 426

10 1600 427

15 1480 447

20 1470 449

25 1470 449

35 1240 486

55 762 563

Velocity and path length calculated for the center strip of the grid (X6, Y6).

120% 70%

The velocity variations were 120% and path length 70%


Hole (%) Velocity (m.s-1) Path Length (mm)

0 1670 390

5 1604 426

10 1600 427

15 1480 447

20 1470 449

25 1470 449

35 1240 486

55 762 563

The increase of the time wave propagation in the presence of the hollow in

the piece were caused by the change of wave path and not by its passage

through the inner void produced


Correlations between the variation of velocity of ultrasonic wave propagation

and the path of ultrasonic wave for the wood of Pequiá

Path = -0.1619*Vel + 686.52 R = 0.89

300

350

400

450

500

550

600

650

500 1000 1500 2000

Pat

h o

f u

ltra

son

ic w

ave

s p

rop

agat

ion

(m

m)

Velocity of ultrasonic waves propagation (m.s-1)


Based a model generate

images

Ø 670 mm and 100 mm thickness



30 mm

• CNC machine – SENAI - Itatiba-SP;

• Circular holes: 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%

and 90%.


METHODOLOGY


0 %

5 %

Pequiá Photo Generated image



15 %

25 %




35 %

45 %




55 %

65 %




75 %

85 %




2 1


90 %

Despite some distortion in the hollow shape represented by the image, and

also in the case of the pieces with 85% and 90% of hollow the image

indicate the advancing of hollow to the edges, in general the image

represents adequately the existence, size and positioning the hollow.

NEXT STEPS

In the continuity of this research the diffraction grid also was used

(not focused in this presentation), which presented better results,

showing more accuracy to detect the small holes, and less

interferences distortions in the hollow shape and in the edges.

• The results showed that the velocity of ultrasound wave

propagation is affected by the presence of hollow and, the

velocity reduction is caused by the change of the wave path,

which tends to shift the void and go to the material.

• The variation of velocity with the increase of the dimension

of the hollow can be represented by a linear model.

• Although the generated images present some failures,

caused by interference of the method used by the adopted

software, the actual condition of the piece was adequately

represented. This result indicating the possibility of using the

Brazilian equipment and the simple methodology of

ultrasound wave propagation in this kind of evaluation.

CONCLUSIONS

ACKNOWLEDGMENTS

behavior of ultrasonic wave propagation...

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