Background:
A full understanding of the mechanism of sample destruction during strength loads requires the necessary detailed microscopic analyzes. They enable the assessment of the structure of materials and defects invisible to the naked eye.

Aim:
Structural assessment of samples and their fractures using a digital microscope and a scanning electron microscope.

Material and methods:
The research material consisted of a total of 30 samples subjected to the three-point bending test. Observations were made using a Keyence VHX-900F digital microscope. Then, the selected and representative fractures of the samples and their sections were observed using the Hitachi TM 3000 Scanning Electron Microscope.

Results:
The phenomena visible in the graphs showing the relationship between the generated force and deformation for each of the tests carried out during the three-point bending test were confirmed in microscopic images of damaged samples. Imperfections in the bonding of the glass fibers with the composite have been observed.

Conclusions:
In samples reinforced with a single glass fiber band debonding was the most common. In samples reinforced with two single bands of glass fibers, so-called first ply failure was observed. The most common structural defect of the samples were air bubbles formed during the sample preparation stage.