Fatigue - The phenomenon of the progressive fracture of a metal by means of a crack which spreads under repeated cycles of stress.

Ferrous - Metals or alloys that contain appreciable amounts of iron.

File Hardness - Hardness as determined by the use of a file of standardized hardness on the assumption that a material which cannot be cut with the file is as hard as, or harder than, the file. Files covering a range of hardness’s may be employed.

Finish Coat - The topcoat or exposed prime side paint film.

Flatness - Flatness is a measure of a cut length sheet's ability to conform to a flat horizontal surface. Maximum deviation from that surface is the degree to which the sheet is out of flat. Flatness is often expressed quantitatively in either Steepness or I-Units.

Flexibility - The degree to which a paint film can withstand deformation without significant change in color and appearance.

Fractu Re testing - Breaking a specimen and examining the fractured surface with the unaided eye or with a low-power microscope to determine such things as composition, grain size, case depth, soundness, or presence of defects.