VUINTERACTION

In the purely mechanical analyses the interaction of the two elastic bodies is introduced through boundary conditions on the nodes away from the interface. Three separate loading conditions are applied to generate the following stress states in the interface: uniform normal stress without yielding, uniform shear stress, and nonuniform normal stress causing significant yielding at one end of the interface. For the first two cases the solution is compared with that of a reference model that uses a linear softening interface behavior available in Abaqus. For the last case with plasticity, the solution is compared with that of a reference model that uses subroutine VUINTER for defining the interface response. In addition, for the last case a gap is introduced between the two elastic bodies to account for the thickness of the interface material.

In the thermomechanical analyses the two elastic bodies are held fixed with a gap between them. An initial temperature of 100° is given to one body; an initial temperature of 0° is given to the other body. The temperature differential causes heat flow between the bodies, resulting in a steady-state temperature of 50° in both bodies. The solution is compared to that obtained with the interface thermal conductance.

The two surfaces, identified for interaction, are tracked to identify those segments of these surfaces that are within a fixed distance, called tracking thickness, and those segments are made available in the user subroutine VUINTERACTION for defining their interaction. Hence, the tracking thickness must be set greater or equal to the maximum anticipated interface material thickness.

The state variables are associated with secondary nodes and can be passed to user subroutine VUINTERACTION multiple times within an increment as a given secondary node may be within tracking distance to multiple main facets. In the elastic-plastic analysis using VUINTERACTION, two state variables are used to keep track of the current yield stress. During the solution the previous yield stress is read from state variable 1 and the new yield stress is written to state variable 2 for time increments that are odd; the previous yield stress is read from state variable 2, and the new yield stress is written to state variable 1 for time increments that are even. This setup is incorporated to avoid using a state variable that has already been updated in the current time increment.

When thermal interaction is active between the surfaces, the heat fluxes are calculated by multiplying the thermal conductivity of the interface material with the temperature difference between the secondary node and main contact point and dividing by the initial interface thickness. Effects such as heat generation due to friction are not taken into account.