An aircraft turbine engine fan casing is required to contain released fan blades in the event of blade failure. Fiber reinforced polymer composite materials have been used in fan casings because of their high strength to density ratio when compared to metal alloys.
When fiber reinforced polymer composite material is subjected to a high energy impact, such as in a fan casing during blade release, the impact energy is generally absorbed by fiber breaking, fiber pull out, resin cracks, and ply delamination. A fan casing usually has to absorb impact energy, resist puncture, and maintain structural integrity for safe engine shutdown.
A known theory to improve the energy absorption capability of fiber reinforced polymer composite materials is to promote fiber pull out. Fiber pull out generally absorbs energy via the creation of new surfaces between the fibers and the resin due to the frictional force that pulls and separates the fibers from the resin. However, fiber pull out usually reduces the post impact carrying load capability and structural integrity of the composite material, as pulled out fibers can no longer transfer loads to other fibers through the resin.
Accordingly, improvements are desirable.