Helical spring lock washers have been in use for well over 100
years. They are still used on many applications in the belief
that they will will "lock" the nut/bolt to the joint
and prevent loosening. The body of evidence, based upon both
experience and experimental results, is that they do not prevent
loosening and can be shown to actually speed up the rate of
loosening in many cases. Junker originally showed in his work
published in 1969 that these washers are ineffective in preventing
loosening. Joints containing these washers have come loose resulting
in structural failure leading to both material and human loss.
A series of tests were performed by Bolt Science to illustrate
the performance of this type of washer compared to a plain
nut by itself. The results are shown in the videos and in
the preload decay curve below. The preload decay curve is
from the tests shown in the video. The tests were performed
on M8 fasteners.