Residual Stress Evaluation in Vitreous Enameled Steel Sheets by Digital Images Analysis of Microstructures - Visual Computing: Scientific Visualization and Imaging Systems - page 174

Fig. 9.10 The interface between the coating and substrate

Consequently, it is difficult to obtain a discretization of this zone of the material
on which a representative finite element mesh should be generated. The finite
element meshes directly obtained from the binarized images were not satisfactory,
in particular because a dense discretization was obtained and was difficult to
associate the proper mechanical and thermal properties in the interface zone.
To further investigate on this zone of the material, energy dispersive X-ray
(EDX) analysis was used to study the composition and microstructural changes
occurring near the coating-substrate interface. The results are reported in Fig. 9.11 .
The diagrams show the reciprocal interaction between the coating and the steel
substrate. In fact, starting from the inner substrate, steel slowly degrade into the
coating components, while the percentage of silicate, basic component of the
coating, asymptotically grows from the surface of the substrate.
Finally, a simplified discretization was adopted. The graded layer was simu-
lated by introducing graded interlayers, as reported in literature for the numerical
simulation of two dissimilar materials joined by a graded layer [ 16 ], with inter-
mediate mechanical and thermal properties between those of the coating and the
substrate. This discretization also gives the capability to separately evaluate
the influence on the residual stress of the bubbles in the coating and the presence of
the graded layer.

9.5 Results and Discussion

The vectorized images were imported in a commercial finite element code to
perform the analysis of the residual stress. The finite element simulations were
performed by means of ANSYS F.E.M. software. The images of the coating
microstructures were discretized with quadrilateral plane elements to create a
finite-element mesh adapted to fit within material boundaries. The bubbles in the
microstructure were considered to be empty cells whose interstices are free to
move.