  The load-area relation of rough surfaces is of great interest in tribology.
For elastic-plastic solids with strain hardening, an incremental model is
adopted to analyze the contact of rough surfaces, in which the contact is
modeled by accumulation of equivalent circular contacts with varying radius.
For three typical rough surfaces with various material properties, comparisons
with direct finite element calculations demonstrate the efficiency of this
incremental contact model. An approximate linear relation between load and
contact area is predicted by both methods up to a contact fraction of 15%. The
influence of yield stress and strain hardening index on the load-area
proportionality is presented. This work gives a simple while effective method
to calculate the load-area relation for rough contact of strain hardening
materials.
