Glossary F-K
Fatigue - Is a process by which a material is weakened by cyclic loading. The resulting stress may be below the ultimate tensile stress
Flat Springs - These are made from flat strips and may come in a wide variety of forms.
Fracture - Is the separation of a body into two, or more, pieces under the action of stress.
Free length - The overall length of a spring in the unloaded position.
Ground ends - Ends of springs are ground to provide a flat plane.
Heat setting - Fixturing a spring at elevated temperature to minimize loss of load at operating temperature.
Helical Torsion Springs - Similar to the helical compression springs, these are loaded by a torque about the helix axis. To transmit this torque special ends are normally required.
Hole - This is the minimum diameter of the hole in which spring can work
Hooks - Open loops or ends of extension springs.
Hot-wound springs - Having large bar diameters > 16mm and above. They are widely used in automotive and railroad equipment. For smaller bar sizes: 9mm to 16mm can be either hot- or cold-wound
Hydrogen embrittlement - Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure.
Hysteresis - The mechanical energy loss that always occurs under cyclical loading and unloading of a spring, proportional to the are between the loading and unloading load-deflection curves within the elastic range of a spring.
Initial tension - The force that tends to keep the coils of an extension spring closed and which must be overcome before the coil starts to open.