a loading-unloading contact mechanics model of rough surfaces is established. The existence conditions of elastic deformation
elastoplastic deformation and fully plastic deformation of single asperity are deduced. And the mechanical expressions of single asperity under loading and unloading are obtained for different deformation conditions. The traditional area density distribution function of asperities is modified according to a rule that the real contact area and total contact load at the end of loading equal the real contact area and total contact load in the inception of unloading. And the
area and density distribution function of asperity's frequency index is deduced under loading and unloading conditions. Eventually
the relationship between total contact load and real contact area is obtained. The results show that the contact mechanical properties of the rough surface depend on the asperity's frequency index in a loading-unloading cycle. When asperity's frequency index n
min
+5 is less than critical elastic frequency index n
ec
the rough surface shows an elastic deformation behavior in a loading-unloading cycle. When the asperity's frequency index n
min
is greater than the critical elastic frequency index and the deformation is greater than the critical deformation
and the real contact area in unloading process is greater than that in loading process. As the deformation increases
the non-dimensional difference between the real areas of loading and unloading is proportional to the deformation
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