Thesis PhD Gianluca Chiappini

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14 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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Thesis PhD
Gianluca Chiappini


Abstract

In the last years, the techniques of optical measurement of sizes and deformations

have had an incredible
development and growth; various methods of acquisition, processing and correction of measurements
algorithms have been proposed.

Without doubts
s
hape acquisition

is one of the most topical issues in i
ndustry engineering, with a wide

range of possible applications

(i.e. modeling corpses and environments in virtual reality, restoring or
rehabilitating manufactures, etc)

as well as the ability to map a
full
-
field

deformation by optical methods is
a goal whose
achievement has always stim
ulated the research and study of new techniques of
measurement
.

At the present time there isn’t
a unique direction of development

which allows to include

accuracy, speed,
versatility and ease of use

in a single

instrument: for this reason, the scientific community try to propose
new approaches to this problem and, above all, to develop measurement devices based on well
-
known
technologies, but
supplemented

with
software and innovative methods
.

The
present work

co
nsisted in
processing

an algorithm that allows to acquire

the shape of an object
characterized by complex geometry

in a short time

and with accuracy.

This system is a combination of a DIC
technique with wh
ite
-
light speckle and the
phase
shift

technique. The

DIC is used to compute the in
-
pla
ne
displacement while the
phase
shift

is used to compute displacement along the thickness.

The first part of this dissertation, after a brief description of main optical
s
hape acquisition

technologies,
describes
phaseshift

technique

and the developed
multiprojection

algorithm.

The second part analyses
the required concepts to use
full
-
field

deformation

measurement method, the
developed code and some examples of different geometry and material objects (metals and rubber
-
like
materials).

The third part presents a novel method to measure the 3D strain field of a sheet metal specimen at large
strain. This s
ystem is a combination of a DIC technique with white
-
light speckle and the phase shift
technique. The DIC is used to compute the in
-
plane displacement while the phase shift is used to compute
displacement along the thickness.
To demonstrate

the effectivene
ss of the method, an experimental test
was conducted using a thick sheet of alumin
i
um and a suitable experimental setup was developed. At the
end of the work, a 3D mesh of the specimen was obtained from which it is possible to follow the 3D strain
history
of the specimen during the whole test, beyond the occurrence of the localized necking that is one
limit of the 2D applications. The developed technique shows good potentiality and it could be used, in
future works, to have a direct characterization of the
mechanical properties of sheet metals.