Analysis Procedure for Frictional Contact Problems Using Interface Finite Elements

摘要

An important class of structural mechanics problems deals with thestress analysis of bodies in contact. The primary objective of this studywas to develop a system capable of solving large and complex frictionalcontact problems with special emphasis on truss-type bolted connectionsin three dimensions.Isoparametric finite elements were used in this study to alloweffective modeling of irregular geometries. A variational principle wasdeveloped which provided a convenient means for carrying out the finiteelement discretization and for arriving at a symmetrical system ofsimultaneous equations.An important feature of this study is the incorporation of theinterbody tractions on the contact surface as primary variables, thusavoiding the need to return to the element level to compute and averagethe contact stress after each load step. This was accomplished withoutmodification of the standard finite element method by the developmentof special interface elements which are used along the interbody surfaces.These elements contain "stress nodes" whose unknowns are the interfacetractions.The numerical procedure presented allows either incremental loadingor iteration with total loads for those problems in which the solutionis independent of applied load level. It accounts for frictionless aswell as frictional contact. For the incremental procedure, the load pattern is applied at eachstep and a load factor is computed for each IIstress node". Each factorrepresents the lowest fraction of the load which will cause that node tochange IImode ll• The minimum load factor determines the size of the loadstep.The procedure was implemented in a general-purpose finite elementprogram called FINITE, which features user-oriented input, and reaccess,substructuring and static condensation capabilities. Use of staticcondensation allows the incremental or iterative solution to be carriedout on a relatively small number of nodes.The procedure presented here applies to surfaces which are initiallyin contact. However, it can be easily extended to include interferencesor initial clearances.The results for several examples were presented and compared withexperimental and analytical solutions. The comparisons indicate thatgeometrically more complex bolted connections can be handled with goodaccuracy.