| Summary: | 碩士 === 中華工學院 === 航空太空工程研究所 === 85 === Using the advantage of reconstructing the surface of a bodyt,
the stereo vision is used to measure the three-dimensional
deformation field of a curved surface and study the strain. The
specimens used in the experiment are round tension specimens
made of 2024 aluminum alloy. A displacement controlled
loading was applied to the specimen until the specimen was
subjected to a strain of 1.5%. Under the world coordinate X-
Y-Z erected by the stereo vision,the position coordinate of each
point on the surface of the undeformed round tension specimen
was determined. By the use of nonlinear optimization
technique, both the position of the centerline and the radius of
the cylinder were obtained. Using coordinate transformation, the
position coordinate determined relative to the world
coordinate system can be expressed in the cylindrical
coordinate. By measuring the position coordinate of each point
on the surface of the deformed round tension specimen, the
displacement fields u,v and w were determined relative to the
world coordinate system and converted through coordinate
transformations, to the displacement fields Ur, UTheta and Uz
expressed in the cylindrical coordinate. Using least square fit
of a polynomial, the displacements UTheta and Uz were
smoothed in the direction of Theta and z to determine the strain
fields ?zz, ???and ??z which were expressed in the
cylindrical coordinates. Results indicate that the measured
mean value of ?zz by the stereo vision is in a good agreement
with the value measured by the Instron extensometer and the
strain gage. The mean value of ??z approaches zero as
expected. In the experiment, it is hard to determine ???since
there is a difficultly in eliminating the effect of rigid body
motion on the displacement Ur which is enclosed in the terms of
???. Experimental results indicate that the stereo
vision system may erect a cylindrical coordinate system to
measure the deformation field of a cylindrical surface
and analyze the strain field. Hence, the analysis method
established in the paper may be applied to study the deformation
probelms such as piping under pressure, and fracture
problems such as piping with cracks.
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