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SOFTWARE VISUALIZATION OF DEFORMATION FIELDS

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SOFTWARE VISUALIZATION OF DEFORMATION FIELDS Powered By Docstoc
					                      9th International Research/Expert Conference
          „Trends in the Development of Machinery and Associated Technology“
                   TMT 2005, Antalya, Turkey, 26-30 September, 2005


        SOFTWARE VISUALIZATION OF DEFORMATION FIELDS

           L. W. Meyer 1+3), T. Jirka2+3), T. Halle 1), H. Staňková1+2), B. Mašek1+2)

   1 - University of                   2 - University of West                3 – Nordmetall GmbH,
 Technology, Chemnitz                    Bohemia in Pilsen                       Burkhardtsdorf
 Faculty of Mechanical                 Universitní 22, Pilsen                 Einsiedler Straße 18
     Engineering                           Czech Republic                          Germany
  Chemnitz, Germany


ABSTRACT
The analysis and development of technological processes, which are based on plastic deformation of
materials, is a complex problem because large amounts of data must be handled. A lot of information
obtained from investigated deformed bodies takes on a global form of an optical perception.
Therefore, for an exact description and data evaluation it is necessary to convert the optical
perception to a digitized form. Yet, the problem does not consist in the digitization itself only. It also
includes the evaluation of the deformation information being represented by the change of the optical
information. This can concern the microvisioplasticity or deformation grids. The necessity to compare
FEM results to experimental findings frequently arises. This is why a software tool has been
developed, which allows the real deformation results to be converted to color fields, as it is commonly
known from FEM simulation postprocessors.
Key words: deformation field, FEM simulation, deformation visualization

1. INTRODUCTION
The development of technological processes, which employ plastic deformation to produce semi-
products or final components, tends towards higher intensities and higher manufacture precision.
These trends can only be implemented with sufficient knowledge of the process from both the
technical as well as the material point of view. The design of contemporary processes is often aided by
a computer simulation, which introduces a concept about local material flow based on its behavior
within a model. Each model describes the behavior of the real object more or less precisely and it is
therefore necessary to verify the results of the computations and compare them to practical outcomes.
There is a large amount of verification methods. In common practical applications selected defined
sizes or contour shapes are compared most often. Sometimes a more complex examination of a
deformation field is necessary for some special purposes or for a more detailed analysis. FEM
simulation software postprocessors are often equipped with visualization algorithms capable of
converting numerical results to color fields. This form is much more acceptable for human eyes as it
allows easier and more thorough perception and understanding of the computed values.
On the other hand, many methods have been used in practice for a long time, which are able to more
or less demonstrate the resulting deformation in the formed body. These methods, generally called
visioplastic, include for instance the surface deformation mesh method at metal sheet formation or the
method of spatial deformation mesh obtained either by the semi-product composition or by embedding
alternative or contrast materials into the formed body. The evaluation is then often made through a
standard metallographic method based on macro or micro cuts or by optical or some other computer
aided techniques as for example computer tomography.
The so called microvisioplasticity can be utilized for small volumes. In this case deformation changes
of defined elements included in the structure are observed. Comparison of their initial and final state
then allows to evaluate the deformation field.
Despite the development of these methods, visualization compatible with the results of computational
simulations remains to be the weak point in the comparison sequence. To supplement this missing
piece, the bellow described software has been developed. This software can be used for the analysis of
not only the forming processes but also other treatments based on the principle of plastic deformation.
The deformation taking place during metallic chip formation when cutting can serve as a good
example. The output of the program is compared to the FEM simulation results in Fig. 1.




    Fig. 1: Comparison of the FEM simulation output with the Deformation Evaluator results [1]
2. DESCRIPTION OF THE PROGRAM FUNCTIONALITY AND CONTROLS
The program is called Deformation Evaluator and its environment can be seen in Fig. 2. It takes a
special, preferably grayscale, image as its input. This image can be acquired during some
technological process and contains information about how the material in question was deformed in
different locations. Such information is encoded within the image in the form of quasi-elliptical shapes
on the surface of the material. As the image is displayed, the user can mark these shapes using a
mouse. For each shape to be considered, the user clicks four spots, which represent the end points of
the two axes of an ellipse approximating the quasi-elliptical shape. The important advantage is the
manmade identification of visible grains and the combination with a subsequent software evaluation.
That means that only the clearly detectable grain shapes are taken into account. Smeared or lost grain
boundaries are not used and cannot disturb the accuracy. The order of the point insertion does not
matter since the program detects the major and minor axes as well as the center of the ellipse. The
center is considered to be a reference point to which the computed deformation ϕv will be assigned.
However, this deformation must first be calculated using the following von Mises relation [2]:


                  ϕv =
                          2
                          3
                              (
                            * ϕ12 + ϕ 2
                                      2
                                          )        with ϕ1 = ln (a / r ) , ϕ 2 = ln (b / r ) ,


                                                                     S        π ⋅a ⋅b
where a and b are the major and the minor semi-axes and r =              =            = a ⋅ b is the radius
                                                                     π           π
of a circle with the same area S as the approximating ellipse. The deformation is then extrapolated
from the ellipse center over the user defined range in the picture. The user can also adjust a scale in a
HSV color system, through which the deformation is mapped into color thus obtaining a color field.




                    Fig. 2: The environment of the Deformation Evaluator program
Finally, this color field is blended with the original grayscale image to reveal the areas of high and low
von Mises deformation. The blending procedure allows the user to specify the opacity of the color
field thus making the underlying image more or less visible. If the analyzed material does not cover
the whole image, the background is supposed to be darker. In that case, setting up an appropriate
threshold allows to black out this area and to have the deformation evaluated only where really
needed.
The resulting colored image may be exported with the color scale being included or not. A section of
such image can be seen in Fig. 3. Similarly, the user inserted points can be saved at any time into a
data file and loaded back again later for additional editing.




        Fig. 3: An example section of a processed image with the user inserted points displayed
As mentioned above, the program is optimized for using grayscale images. Though, color images may
technically also be used. In that case, however, opacity should be set to maximum, as the program
blends the colors of the original picture with the colors obtained by evaluating the deformation.
Otherwise, the resulting color field might be misleading.
The Deformation Evaluator program currently works with bitmap as well as jpeg images, which is
sufficient for most purposes. However, extension to other graphical formats is possible.

3. CONCLUSION
The Deformation Evaluator program fills in the gap between the real vision of deformation fields and
the deformation field visualized by the FEM simulation program postprocessor. Its high flexibility
arises from a wide range of available individual settings for deformation field evaluation, choice of
parameters describing the deformation and other visualization possibilities as documented on
presented images. The manmade decision of identifying grain boundaries and geometries avoids
uncertainties by software routines.


REFERENCES
[1] Halle, Th.: Zusammenhänge zwischen Spanvorgängen und dem mechanischen Werkstoffverhalten bei
    hohen Dehnungsgeschwindigkeiten, Dissertation TU Chemnitz, Prof. Werkstoffe des Maschinenbaus, 2005.
[2] Mises, R. V.: Mechanik der Festen Körper im plastisch deformablen Zustand, Math.-phys. Kl., p. 582 – 592,
    1913.

				
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