A Belleville washer, also known as a coned-disc spring, conical spring washer, disc spring, Belleville spring or cupped spring 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 or flexible quality to a bolted joint or bearing. They may also be used as locking devices, but only in applications with low dynamic loads. what is the expected life of the typical belleville washer? how long until it will loose tension? loosen up?