HW5 Problem 2
Problem:
When performing complex finite element analysis in Abaqus, there are often problems that we
assign a friction coefficient between two bodies that come into contact. While often a book
value for the friction coefficient is used, there has not been verification that the friction value is
mimicking real life correctly.
Background:
The standard friction formulation used in Abaqus is the classical isotropic Coulomb friction
model. This model assumes that no motion occurs unless the equivalent frictional stress is
greater than the critical stress. The critical stress is defined as the friction coefficient multiplied
by the contact pressure normal to the surface. This friction model is expected to perform very
closely to a real life state.
Project:
For my project I would like to mimic real life 'friction tests' using finite elements to see if the
results would match the theoretical solutions. One example would be to have a block on a flat
surface that is tilted to an incline. Then, the friction value is measured based on the angle at
which the block begins to slide. I have found that performing this analysis would be very
similar to representing the ‘inclined plane test’ from www.worldoftest.com
Different coefficients of friction could be tested. Each one would represent different types of
materials such as metal on metal, metal on plastic, and plastic on plastic. Another factor that
could be tested is the effect of mesh density on the results. It would be good to know if you
need a certain quality mesh to have accurate friction results, or if any mesh will do.
Another friction test that could compare finite element analysis to real life is by dragging one
surface compared to the other and measuring the force it takes to drag. This test would be
based off of ‘the Coefficient of Friction Machine’ created by Chemsultants. The same variables
can be tested as in the incline test. It can be seen whether both tests can be modeled
accurately or if one is preferred. Both use different methods of loading and the results will be
able to be used to have a greater understanding of how friction works using Abaqus.
References:
Abaqus 6.12 Theory Manual – 5.2.3 Coulomb Friction
Abaqus 6.12 User’s Manual – 36.1.5 Frictional Behavior
http://www.worldoftest.com/pdf/Qualitest_COF_PO1.pdf - Inclined plane tester
http://www.chemsultants.com/testing-equipment-products/testing-devices/coefficient-offriction.aspx - Dragging friction tester
Friction testing standard - ASTM D1894