Abstract
The term “Foreign Object Damage (FOD)” refers to the damage associated with the impact of particles on aircraft engine components that causes changes in fatigue strength as a result of induced stress concentrations, residual stresses and microstructural changes. This paper presents the Finite Element (FE) models created to study the stress field induced by the impacts of a steel sphere on a 7075-T6 hourglass specimen. The impacts occur at the minimum cross section, in the normal and oblique directions. The results reveal that in the event of an oblique impact the axial tensile stresses are greater and closer to the crater created by the impact. The superposition of the residual axial stresses to the bending stresses by fatigue test allows to identify the areas in which the maximum stresses are reached and therefore crack initiation is expected.
Highlights
FOD is the damage induced by the impact of particles on the components of the aircraft engine ingested during take-off, taxiing and landing
This paper presents the Finite Element (FE) models created to study the stress field induced by the impacts of a steel sphere on a 7075-T6 hourglass specimen
The superposition of the residual stresses induced by FOD with the bending stresses made it possible to identify the areas subjected to the highest tensile stresses, which are unfavorable from a fatigue point of view
Summary
FOD is the damage induced by the impact of particles on the components of the aircraft engine ingested during take-off, taxiing and landing. Peters and Ritchie [3] simulated FOD by firing hardened steel spheres in the normal direction to the surface of a specimen using compressed air-gun setup and observed the induced microstructural effects. From their analysis, they drew the important consideration that the nature of the microstructural damage is a function of the impact speed. Plastic flow of material generated micro-notches and micro-cracks that affected fatigue life For this reason, impacts simulated in quasi-static conditions can provide useful information on the fatigue strength only for low impact speeds, i.e. when the induced microstructural effects are less evident. At high speeds, a dynamic model is strictly necessary
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