Impact Response of Graphite-Epoxy Flat Laminates Using Projectiles that Simulate Aircraft Engine Encounters

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Abstract
An investigation of the response of a graphite-epoxy material to foreign object impact was made by impacting spherical projectiles of gelatin, ice, and steel normally on Modmor II/PR-286 flat panels. The observed damage was classified as transverse (stress wave delamination and cracking), penetrative, or structural (gross failure): the minimum, or threshold, velocity to cause each class of damage was established as a function of projectile characteristics. Steel projectiles had the lowest transverse damage threshold (30 m/s), followed by gelatin (170 m/s) and ice (215 m/s). Making use of the threshold velocities and assuming that the normal component of velocity produces the damage in non-normal impacts, a set of impact angles and velocities was established for each projectile material which would result in damage to composite fan blades. Analysis of the operating parameters of a typical turbine fan blade shows that small steel projectiles are most likely to cause delamination and penetration damage to unprotected graphite-epoxy composite fan blades.

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