A considerable number of brake discs of fire fighting vehicles used in supporting to the aeronautical activities were
found cracked during NDT. Macrofractography of the discs, manufactured in gray iron, showed several cracks running
along the radius of the friction surfaces having length approximately in the range 1–7.5 cm. Further cracks examination by
using optical microscope and field emission scanning electron microscope (FESEM) revealed the cracks were propagated
in semi elliptical shape through the thickness of the friction surfaces in accordance with a thermal fatigue mechanism. Two
zones that exhibited defined signs of heating were also observed. In addition, no sign of defects that could have originated
the cracks were found. The discs were found to be confirmed to the chemical, microstructural and hardness measurements
requirements for the selected material. The finite element analysis (FEA) performed to determine the temperatures profile
in the disc as well as to estimate the stresses distribution during the braking also confirmed the relatively high temperatures
reached during the braking actions and attributed to the residual tensile stress due to the repetition of the thermal stress
cycles the cause of the cracks, respectively. It was recommended all fire fighting vehicles used be examined, the brake discs
replaced and an improvement in terms of material choice eventually be developed