BIEM-BASED VARIATIONAL-PRINCIPLES FOR ELASTOPLASTICITY WITH UNILATERAL CONTACT BOUNDARY-CONDITIONS

The structural step problem for elastic-plastic internal-variable mate rials is addressed in the presence of frictionless unilateral contact conditions. Basing on the BIEM (boundary integral equation method) and making use of deformation-theory plasticity (through the backward-dif ference method of computational plasticity), two variational principle s are shown to characterize the solution to the step problem: one is a stationarity principle having as unknowns all the problem variables, the other is a saddle-point principle having as unknowns the increment s of the boundary tractions and displacements, along with the plastic strain increments in the domain. The discretization by boundary and in terior elements transforms the above principles into well-posed mathem atical programming formulations belonging to the symmetric Galerkin BE M formulations (with features such as a symmetric sign-definite coeffi cient matrix, double integrations, and hypersingular integrals). (C) 1 998 Published by Elsevier Science Ltd. All rights reserved.