Analysis of turbo impeller rotor failure

• A partially drilled hole was machined in a turbo impeller rotor.
• Fracture analysis, alloy's characterization and numerical simulation were performed.
• Fracture was attributed unbalance caused by the partially drilled hole.

The aim of the current study is to analyze the failure of a turbo impeller rotor made of AA 7075 aluminum alloy. We found a drilled hole partially out of position, and it might have been the possible cause of failure. The aim of the analysis is to check the influence of the machining mistake on the failure. Fracture analysis techniques were performed through scanning electron microscopy and low-magnification optical microscopy. The alloy was characterized through chemical, microhardness and microstructural analyses. The numerical simulation was performed to check the stress level generated in the impeller depending on the size of the hole chamfer and on the introduction of the machining mistake. We concluded that the failure in the rotor began in a hole adjacent to the partially drilled one and attributed the fracture onset to the stress concentration caused by the chamfer burrs and by the unbalance caused by the partially drilled hole.