Defining Initially Bonded Crack Surfaces in Abaqus/Standard
Potential crack surfaces are modeled as secondary and main contact surfaces (see About Contact Pairs in Abaqus/Standard). Any contact formulation except the finite-sliding, surface-to-surface formulation can be used. The predetermined crack surfaces are assumed to be initially partially bonded so that the crack tips can be identified explicitly by Abaqus/Standard. Initially bonded crack surfaces cannot be used with self-contact.
Define an initial condition to identify which part of the crack is initially bonded. You specify the secondary surface, the main surface, and a node set that identifies the initially bonded part of the secondary surface. The unbonded portion of the secondary surface will behave as a regular contact surface. Either the secondary surface or the main surface must be specified; if only the main surface is given, all of the secondary surfaces associated with this main surface that have nodes in the node set will be bonded at these nodes.
If a node set is not specified, the initial contact conditions will apply to the entire contact pair; in this case, no crack tips can be identified, and the bonded surfaces cannot separate.
If a node set is specified, the initial conditions apply only to the secondary nodes in the node set. Abaqus/Standard checks to ensure that the node set defined includes only secondary nodes belonging to the contact pair specified.
By default, the nodes in the node set are considered to be initially bonded in all directions.
Input File Usage
INITIAL CONDITIONS, TYPE=CONTACT
Abaqus/CAE Usage
Interaction module: Create Interaction: Surface-to-surface contact (Standard)
Bonding Only in the Normal Direction
For fracture criteria based on the critical stress, critical crack opening displacement, or crack length versus time, it is possible to bond the nodes in the node set (or the contact pair if a node set is not defined) only in the normal direction. In this case the nodes are allowed to move freely tangential to the contact surfaces. Friction (Frictional Behavior) cannot be specified if the nodes are bonded only in the normal direction.
Bonding only in the normal direction is typically used to model bonded contact conditions in Mode I crack problems where the shear stress ahead of the crack along the crack plane is zero.
Input File Usage
INITIAL CONDITIONS, TYPE=CONTACT, NORMAL
Abaqus/CAE Usage
Bonding only in the normal direction is not supported in Abaqus/CAE.