2.1 Bracket material of the RRJ-95 aircraft (No. 89051) and its
fracture zone
The bracket was failed over four lug sections at the holes with a
diameter of 8 mm for a bolt (Fig. 1). Mechanical and corrosion damages
in the zones of bracket fracture were not observed. The bracket surfaces
were typical for shot peening.
The origins of fatigue cracks were located at the inner edges of holes
without chamfer (see Fig. 1b). The lug fracture surfaces were numbered
in accordance with the sequence of studies.
Material researches had shown that the structural material is aluminium
alloy 1933T3 (Al-Zn-Mg-Cu) with a standard chemical composition (Table
1) and the microstructure (Fig. 2a) recommended for the manufacturing
bracket with the ultimate tensile stress of 500 MPa.