During the stretching of the film, its deformation (% elongation) is measured and the surface topography of the coating is imaged simultaneously using the PO3D profilometer.
In figure 1, images acquired at 0%, 2% and 8% elongation are shown. The tension is applied vertically. From 2% elongation, cracks start to appear in the coating. At 8 % elongation, very marked striations are clearly observable in the direction perpendicular to the elongation. The cracking threshold of the coating is therefore around 2% elongation. In figure 2, the plot of the crack density as a function of the percentage of elongation applied to the film is presented. Stretches around the cracking threshold (visible in the inset) were then performed with a step of 0.25% elongation, the cracking then appearing around 2.4% elongation.