*5.2. Assessment of Crack Width*

Optical measurements and DIC were also used to analyze the development of cracks visible on the surface of the beam and to measure their width. It is also possible to determine the moment the crack starts to develop. In Figure 13 shows the numbering of the analyzed cracks.

**Figure 12.** Deformation fields on the surface of the beam in X and Y direction during loading phases measured by DIC.

**Figure 13.** Numbering of the analyzed cracks [40].

As can be seen in Figure 14, the main vertical crack (Crack 01) formed exactly in the middle of the beam span and appeared in the first phase of the loading. Then the load was reduced to zero and the crack was almost completely closed. It appeared again during the second phase of the experiment.

**Figure 14.** The crack width development during the loading phases.
