Residual Stress Evaluation in Vitreous Enameled Steel Sheets by Digital Images Analysis of Microstructures - Visual Computing: Scientific Visualization and Imaging Systems - page 179

40 20

(b)

(a)

15

30

10

20

5

10

0

0

-5

-10

-10

-15

-20

-20

-30

without g.l.
with g. l.

without g.l.
with g.l.

-25

-40

-30

-50 -35

0,0 0,2 0,4 0,6 0,8 1,0 1,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2

y [mm] y [mm]

Fig. 9.18 The residual stress along with a transversal section. a Wet enameling technique and
b dry enameling technique

magnification and the values were found similar for the coatings manufactured
with the different technologies.
Figure 9.17 shows the gray-scale map of the longitudinal stress obtained in
these simulations.
In particular, Fig. 9.17 a is relative to the coating manufactured with the wet
enameling technique, while Fig. 9.17 b is relative to the coating manufactured with
the dry enameling technique.
The results show that the presence of the graded layer gives a contribute to the
reduction of the maximum values of the thermal stress in the coating, as compared
with the previous simulations.
Figure 9.18 shows the trend of the residual stress along with a transversal
section, corresponding to X/l = 0.5, relative respectively to the coatings manu-
factured with the two manufacturing technologies.
From the diagrams it can be observed, in particular, that the steep discontinuity
in stress at the coating-substrate interface is slightly attenuated when the graded
layer is introduced in the models. However, differently from the functionally
graded materials where, typically, the graded interlayers are used to mitigate the
thermal stresses [ 17 ], this occurrence is not particularly evidenced in the coatings
analyzed. Among the different factors that contribute to this circumstance, such as
geometry and composition, probably, the presence of the bubbles masks the effect
on the residual stress of the graded interface between the coating and the substrate.

9.6 Conclusions

In this chapter, a method based on digital images of cross-section micrographs has
been applied to the analysis of residual stress in enameled coatings. The results,
relative to coatings manufactured with different technologies, highlight the