2.2 Components of the RRJ-95 aircraft (No. 95075) wing airframe
In the process of bench testing of the RRJ-95 aircraft (No. 95075) wing
airframe, after operating of 19950 laboratory flights, a crack was found
that spread to the face plane of the stiffened panel from under the
middle bracket of the engine pylon mount, Fig. 3. When 20019 laboratory
flights were generated, the crack appeared from under the plane of the
middle bracket of engine pylon mount in the aft direction.
The tests were continued, and during the inspection for likely defects
of the lower stiffened panel after the operating time of 20487
laboratory flights, a crack was found that appeared from under the root
bracket of the engine pylon mount. This crack developed from the hole
with a diameter of 12 mm for the bolt connecting the bracket with the
stiffened panel. The crack length was 96 mm in the forward direction and
21 mm in the aft direction.
When disassembling the middle bracket, it was found that the crack
developed to the face plane of the stiffened panel from the hole with a
diameter of 14 mm for the bolt connecting the bracket with the stiffened
panel. The crack length was 23 mm in the flight direction and 74 mm in
the opposite flight direction.
Material researches had shown that the structural material is aluminium
alloy 1163 (Al-Cu-Mg) with standard chemical composition (Table 1) and
the microstructure (Fig. 2b) recommended for the manufacturing bracket
with the ultimate tensile stress of 460 MPa.
Fracture surfaces of all structures were analysed by the well-known
method [2] on the scanning electron microscope Carl Zeiss EVO40.