Initial contact stress

This problem contains basic test cases for one or more Abaqus elements and features.

This page discusses:

Elements tested
Problem description
Results and discussion
Input files

Elements tested

C3D8

C3D8R

C3D10

C3D20R

CPE4

CPE4P

CPE8RP

CPS4

Problem description

Initial contact stresses are computed automatically from user-specified underlying element initial stresses. This capability is tested for both finite- and small-sliding contact, the node-to-surface and surface-to-surface contact formulations, and general contact. Representative element types (including XFEM elements with an initial crack) are incorporated in these tests. The enhanced geostatic procedure is used to obtain an equilibrium state of stress while minimizing displacements to be within a specified tolerance. These tests also verify enhanced geostatic procedures that involve contact interactions.

Results and discussion

In all cases the tests verify the initial contact stress capability. The initial contact stresses are reported correctly at the zero increment. In the enhanced geostatic procedure, the final displacements satisfy the prescribed tolerance.

Input files

inicstr_block_pen_both.inp: Contact initial stresses are computed approximately at a contact interface between two rows of elements with uniform differing element stresses. Penalty contact enforcement is used with the surface-to-surface formulation. The enhanced geostatic procedure (invoked with the UTOL parameter) is specified for the first and only step.

inicstr_block_pen_c0_both.inp: Same as inicstr_block_pen_both.inp except using penalty contact enforcement with a nonzero clearance at zero pressure.

inicstr_block_augm_both.inp: Same as inicstr_block_pen_c0_both.inp except using augmented Lagrange contact enforcement.

inicstr_block_direct_both.inp: Same as inicstr_block_augm_both.inp except using direct contact enforcement with Lagrange multipliers.

inicstr_block_presover_both.inp: Same as inicstr_block_direct_both.inp except the exponential pressure-overclosure relation is used.

inicstr_wet_block.inp: Initial effective contact stresses are derived from initial effective stresses in the underlying deformable elements for a block model with pore pressure degrees of freedom and linear two-dimensional elements.

inicstr_quadcdp2d.inp: Initial effective contact stresses are derived from initial effective stresses in the underlying deformable elements for a block model with pore pressure degrees of freedom and quadratic plane strain elements.

inicstr_block_slide_xcont.inp: Initial contact stresses on an initial stationary crack are derived from initial stresses in the underlying XFEM elements for a block model. The analysis involves a push down step followed by finite sliding between crack surfaces modeled with general contact.

inicstr_block_normal_ics_both.inp: Initial contact stresses are calculated for a block model with linear three-dimensional hexahedral elements, and the enhanced geostatic procedure (invoked with the UTOL parameter) is used to minimize displacements.

inicstr_wet_blockrig.inp: Initial effective contact stresses are derived from initial effective stresses in the underlying deformable elements on one side of a deformable to rigid contact with pore pressure degrees of freedom and linear three-dimensional elements.

inicstr_blocksuppl.inp: Initial contact stresses are calculated for a block model meshed using quadratic tetrahedral elements with a node-to-surface contact pair with active supplementary constraints.

inicstr_fault2d_flat_dry_alone.inp: Initial contact normal and shear stresses are derived in a two-dimensional fault slip with a linearly varying initial stress field in the underlying CPE4 elements. These initial contact stresses serve as a better starting point for establishing an overall equilibrium state.

inicstr_fault2d_flat_dry.inp: Same as inicstr_fault2d_flat_dry_alone.inp except using the enhanced geostatic procedure (invoked with the UTOL parameter).

inicstr_fault2d_flat_wet_alone.inp: Initial contact normal and shear effective stresses are derived in a two-dimensional fault slip with a linearly varying initial stress field in the underlying CPE4P elements. These initial contact stresses serve as a better starting point for establishing an overall geostatic equilibrium state.

inicstr_fault2d_flat_wet.inp: Same as inicstr_fault2d_flat_wet_alone.inp except using the enhanced geostatic procedure (invoked with the UTOL parameter).

The following input files test initial element stresses being read from a prior analysis:

inicstr_ics_alone_patch_orig.inp: A block of quadratic elements are pushed down against a flat rigid surface resulting in uniform element stresses.

inicstr_ics_alone_patch_init_sim.inp: Initial element stresses are read in through the SIM database generated from inicstr_ics_alone_patch_orig.inp. Initial contact stresses derived from the element stresses bring the initial state to an equilibrium state.

inicstr_interf_orig.inp: Cylindrical shrink fit analysis followed by an axial twist to establish element stresses.

inicstr_interf_initfromstep2.inp: Read initial element stresses from the output database of inicstr_interf_orig.inp, and derive initial contact normal and shear contact stresses. The derived initial contact stresses bring the initial state to a nearly equilibrium state.