There are fundamental differences in the mechanical contact algorithms in Abaqus/Standard and Abaqus/Explicit. These differences are reflected in how contact conditions are defined. The main differences are the following:
For contact pairs Abaqus/Standard typically uses a pure master-slave relationship for the contact constraints by default (see “Defining contact pairs in Abaqus/Standard,” Section 36.3.1 of the Abaqus Analysis User's Guide); the nodes of the slave surface are constrained not to penetrate into the master surface. The nodes of the master surface can, in principle, penetrate into the slave surface. Abaqus/Explicit includes this formulation but typically uses a balanced master-slave weighting by default (see “Contact formulations for contact pairs in Abaqus/Explicit,” Section 38.2.2 of the Abaqus Analysis User's Guide).
The contact formulations in Abaqus/Standard and Abaqus/Explicit differ in many respects. For example, Abaqus/Standard provides a surface-to-surface formulation, while Abaqus/Explicit provides an edge-to-edge formulation.
The constraint enforcement methods in Abaqus/Standard and Abaqus/Explicit differ in some respects. For example, both Abaqus/Standard and Abaqus/Explicit provide penalty constraint methods, but the default penalty stiffnesses differ.
Abaqus/Standard and Abaqus/Explicit both provide a small-sliding contact formulation (see “Contact formulations in Abaqus/Standard,” Section 38.1.1 of the Abaqus Analysis User's Guide, and “Contact formulations for contact pairs in Abaqus/Explicit,” Section 38.2.2 of the Abaqus Analysis User's Guide). However, the small-sliding contact formulation in Abaqus/Standard transfers the load to the master nodes according to the current position of the slave node. Abaqus/Explicit always transfers the load through the anchor point.