A Belleville washer is a type of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic. Belleville washers are typically used as springs, or to apply a pre-load of flexible quality to a bolted joint or bearing. Some properties of Belleville washers include: high fatigue life, better use of space, low creep tendency, high load capacity with a small spring deflection. and possibility for high hysteresis (damping) by stacking several belleville washers on top of each other in the same direction.
Belleville springs are also used in a number of landmines e.g. the American M19, M15, M14, M1 and the Swedish Tret-Mi.59. The target (a person or vehicle) exerts pressure on the belleville spring, causing it to exceed a trigger threshold and flip the adjacent firing pin downwards into a stab detonator, firing both it and the surrounding booster charge and main explosive filling. Some makers of bolt-action target rifles use Belleville washer stacks in the bolt instead of a more traditional spring to release the firing pin, as they reduce the time between trigger actuation and firing pin impact on the cartridge.
They may also be used as locking devices, but only in applications with low dynamic loads, such as down-tube shifters for bicycles. Belleville washers are seen on Formula One cars, as they provide extremely detailed tuning ability. The World War II-vintage German Junkers Ju 88 aircraft's single strut, "twisting"-through 90° during retraction/extension main gear made primary use of belleville washers as its main shock absorption mechanism. At least one modern aircraft design, the Cirrus SR2x series, uses a Belleville washer setup to damp out nose gear oscillations (or "shimmy").
Belleville washers have been used as return springs in artillery pieces, one example being the French Canet range of marine/coastal cannon from the late 1800s (75 mm, 120mm, 152 mm). Another example where they aid locking is a joint that experiences a large amount of thermal expansion and contraction. They will supply the required pre-load, but the bolt may have an additional locking mechanism (like Thread-locking fluid) that would fail without the Belleville.
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