Analysis of the Fracture of a Turbine Blade

The cause of crack initiation turbine blade had initially cracked by a fatigue mechanism over a period of time and then fractured by the overload at the last moment. Experimental procedure consists of macroscopic inspection, material verification, microscopic examination, and metallographic analysis and finally FE. And for these procedures, some specimens were prepared from a fractured blade. Using ICP and energy dispersive X-ray fluorescence, the chemical composition of the blade was carefully analyzed. The segregated area of Ti and Mo, caused generally by inappropriate manufacturing process, is found by the microstructure and EDX analysis of the blade. The fracture blade which installed on the third stage rotor of the turbojet was fractured at about 6 cm distance from the hub of proposed blade. The non-linear finite element method (FEM) was utilized in order to define the stress state of the disc or blade segment under operating conditions. High stress zones were found at the region of the lower fir-tree slot, where the failure occurred. A computation were also achieved with excessive rotational speed. The aim of this study is devoted to the mechanisms of damage of the turbine disc, and furthermore the critical high stress areas.