7Underhill W R L,Dokainis M A, Oravas G E. A method for contact problems usingvirtual elements[J]. Comput Meth Appl Mech Engng,1997,143: 229～247.
8Simo J C,Wrigger P,Tayor R L. A perturbed Lagrangian formulation for the finiteelement solution of contact problems[J]. Comput Meth Appl Mech Engng, 1985,50:163～180.
9Haug D,Saxce G. Frictionless contact of elastic bodies by finite element methodand mathematical programming technique. Comput Struct, 1980,11: 55～67.
10Klarbring A. General contact boundary conditions and the analysis of frictionalsystems[J]. Int J Solids Struct,1986,22: 1377～1398.
