Experimental observation of ordered stress patterns in iron films deposited on silicone oil surfaces

We report the observations of large ordered stress patterns, namely bands, in iron films deposited on silicone oil surfaces. The bands grow from the sample edges and then extend into the central regions of the films after deposition. The total length of one band may be more than 5 mm. If two bands meet on their ways, they may cross each other without interference or coalesce harmoniously. The inverse situation that one band bifurcate into two bands is also observed. The X-ray diffraction experiment shows that the nearly free sustained iron films still exhibit polycrystalline structures and our further experiment indicates that the bands result from the ordered aggregation of the iron crystal grains