An Assessment of Laboratory Techniques for Simulating Foreign Object Damage on a Leading Edge Geometry
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS AND MANUFACTURING DIRECTORATE
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Foreign object damage FOD from particles ingested into jet engines can have a detrimental effect on the fatigue strength of fan and compressor airfoils. The damage caused by these particles often is in the form of a geometric discontinuity like a notch. However the presence of residual stresses and substructural damage in regions adjacent to the notch prohibit the use of simple notch analyses. In this investigation, three different quasi-static, pendulum, and ballistic techniques of imparting damage are studied with respect to the damage they create and the resultant high cycle fatigue HCF strength of a titanium simulated airfoil geometry. The ballistic technique is used as a baseline as it most closely simulates an object being ingested into an aircraft engine. In this case, steel spheres having diameters ranging from 0.5 to 2.0 mm are used as the impacting objects at velocities over a range from 40 to 520 ms. For the quasi-static and pendulum cases, hardened steel indentors with radii similar to those used for the ballistic impacting were used. Step loading tests in tension at a frequency of 350 Hz are used to establish the fatigue limit stress corresponding to 10exp 7 cycles. The role of residual stresses is identified through the use of samples subjected to stress relief annealing after impact. Simple notch analysis is used to estimate the effect of the geometry of the notch. Comparisons between as-impacted and stress relieved specimens were used to help identify the affect of residual stresses.
- Properties of Metals and Alloys
- Jet and Gas Turbine Engines