According to the classic friction
forces laws postulated by Leonardo da Vinci and Amonton, friction force does
not depend on the contact area created between the planes coming into contact. An additional prevalent claim assumes that the
magnitude of the friction coefficient between two elements is constant and does
not depend on the contact geometry or on the normal load. However, later
experimental and theoretical research works, from the first half of last
century, show that new discoveries contradict old rules of classical friction
theory. The experimental and theoretical works dealing with research of static
friction coefficients showed significant contradictions between experimental
results and the known laws of classic friction theory. This research intends to
focus on comparison between the models lately developed and the experimental
results that were published on the subject of prediction of friction force and
static friction coefficient. For this purpose we chose to check through a
series of experiments the elastically perfectly plastic contact model developed
by L. Kogut and I. Etsion of the Technion Mechanical Engineering Faculty. The
model provides a prediction of the real contact area between spherical surface
and rigid flat. The model also predicts the static friction force and friction
coefficient that will be developed. An experimental measurement system was
constructed in order to make it possible to measure friction forces under
normal load in several geometrical conditions. The
results obtained indicate the creation of a real contact area, similar to the
prediction by the model analyzed, as well as a reduction of 66% in the static
friction coefficient with the increasing of the normal load
