Mat-1.3656 Numeerisen
analyysin ja laskennallisen tieteen seminaari.
Ma 8.10. 2007, sali U356
Sven Bossuyt
Mixed
numerical-experimental characterization of deformation behaviour
involving discontinuous displacement
fields
The inelastic deformation behaviour of many materials is non-uniform on
a mesoscopic scale. Models assuming uniform deformations at the
macroscopic scale, using homogenized properties, are often good enough
for practical applications. But in some cases, the uniform deformation
is unstable with respect to non-uniform perturbations, and highly
localized deformation is observed on the macroscopic scale. Three
examples of such behaviour will be presented: shear banding in bulk
metallic glasses, multiple cracking in textile-reinforced cement-matrix
composites, and delamination in polymer-matrix composites. For each of
these materials, optimal use of their capabilities in engineering
applications requires predictions of the non-uniform deformation
behaviour, so this is a problem of practical interest.
A solution may be found in recent advances in optical measurement
techniques for experimental mechanics, enabled by continuing evolution
of computers and digital cameras. "Full-field" optical measurement
techniques are of particular interest: optical imaging is then used to
do measurements simultaneously at each point in the image. As a result,
localized deformation can be observed even if it is not a priori known
where in the image it will occur. In principle, at least, full-field
measurements could be combined with a numerical model of non-uniform
deformation behaviour, to determine appropriate material parameters via
an inverse method.
This seminar will focus on ongoing research, using displacement fields
measured by "digital image correlation", to quantitatively characterise
localised deformation behaviour of materials. In digital image
correlation, displacement fields are obtained from the coordinates of
corresponding subsets in sequences of images. Digital image processing
algorithms are used to match subsets of the image of the deformed
material, to corresponding subsets in an image of the material before
deformation. Shortcomings of existing implementations of this technique
will be highlighted, especially with regard to highly localised
deformations, and possible improvements building on ideas from other
fields will be discussed.