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.