Foreign object damage (FOD) is an aerospace term for damage caused to aircraft by collision or ingestion of uncontrolled items such as debris, litter, birds or ice. FOD is often considered to be a problem with composite structures, not because they are more easily damaged, but because they tend to spring back rather than dent causing hidden or barely visible impact damage (BVID). One of the prime causes of impact damage is ice; large hailstones or accretions shed from elsewhere on the airframe.
Damage to helicopter rotor blades
Horsfall I & Turnock W (2003) Impact damage behaviour of composite rotorblade structures. In: 48th Int. SAMPE Technical Conference, Dayton, 28 September 2003.
Damage from ballistic threats
Higher velocity impact damage can be caused by pebbles from a road, bullets or bomb fragmentation. These produce a more concentrated damage pattern that may or may not penetrate the composite. If the composite is providing a structural function then the loss in strength can be significant and is at a maximum at impact velocities which are just stopped or just perforate the panel.
Horsfall I, Watson CH & Boswell C (2007) Residual strength of composites after ballistic impact. In: 23rd International Symposium on Ballistics, Tarragona, 16 April 2007.