1.6.3 Small-sliding contact between coupled pore pressure-displacement elements

Product: ABAQUS/Standard  

Elements tested

CAX8P    CPE8P   

Feature tested

*CONTACT PAIR, SMALL SLIDING

Problem description

Figure 1.6.3–1 Element topology for all tests.

Model:

The out-of-plane thickness for all elements is 0.5.

Material:

The elastic properties of the soil are Young's modulus = 1 × 108 and Poisson's ratio = 0.0. The permeability of the soil = 1 × 10–4. The initial void ratio = 1.0 for all tests.

Boundary conditions:

In all tests, nodes are restrained in the 1-direction.

Analysis tests

There are four different tests.

Initial conditions test

This test verifies that the *INITIAL CONDITIONS, TYPE=PORE PRESSURE option works with the *CONTACT PAIR option. All nodes in the model are initialized to a pore pressure of –50.0.

Consolidation test

The consolidation test verifies that the *CONTACT PAIR option works properly with the *SOILS, CONSOLIDATION procedure. The test is essentially a one-dimensional problem where two surfaces are brought together at a constant rate, as shown in Figure 1.6.3–2.

Point A in the figure corresponds to nodes 1, 5, and 2; point B corresponds to nodes 4, 7, and 3; and so on. As points C and B move toward each other, fluid rushes out through points A and D. This gives rise to a compressive stress state in the soil segments AB and CD. A pore pressure field develops to balance out the effective stresses.

Steady-state test

The steady-state test verifies that the *CONTACT PAIR option works properly with the *SOILS procedure. The problem is the same one that is modeled in the consolidation test. There is zero stress and zero pore pressure at steady state; therefore, the use of the *CONTROLS option is necessary to avoid convergence difficulties as a result of the fact that both the time average force and the force residuals are practically zero.

Interference test

The interference test verifies that a combination of interface overclosure and pore pressure gradient is handled correctly by the *CONTACT PAIR option. The test is essentially a one-dimensional problem where two surfaces start with an interference fit and a pore pressure gradient exists across the two bodies. The steady-state equilibrium is sought.

Results and discussion

Most of the input files used for these tests include the UNSYMM=YES parameter on the *STEP option. Using the unsymmetric solver improves convergence in steady-state analyses.

Initial conditions test

The pore pressure at every node should be –50.0.

Consolidation test

From Darcy's law we find that during the first step of the analysis the effective stress profile is as shown in Figure 1.6.3–4.

From equilibrium of tractions we find that the pore pressure distribution is as shown in Figure 1.6.3–5. After the surfaces have stopped moving toward each other, the stresses and pore pressure quickly drop to zero. This is modeled in the second step of the analysis.

Steady-state test

The steady-state result is zero stress and zero pore pressure.

Interference test

This problem can be analyzed as a linear superposition of two states, as shown in Figure 1.6.3–6.

Input files

ei13psi1.inp

Initial conditions test, CPE8P elements.

ei13psi1_surf.inp

Initial conditions test, CPE8P elements, surface-to-surface constraint enforcement method.

ei13psi1_auglagr.inp

Initial conditions test, CPE8P elements.

ei13psi1_auglagr_surf.inp

Initial conditions test, CPE8P elements, surface-to-surface constraint enforcement method.

eia3psi1.inp

Initial conditions test, CAX8P elements.

eia3psi1_surf.inp

Initial conditions test, CAX8P elements, surface-to-surface constraint enforcement method.

ei13psnc.inp

Consolidation test, CPE8P elements.

ei13psnc_surf.inp

Consolidation test, CPE8P elements, surface-to-surface constraint enforcement method.

ei13psnc_auglagr.inp

Consolidation test, CPE8P elements.

ei13psnc_auglagr_surf.inp

Consolidation test, CPE8P elements, surface-to-surface constraint enforcement method.

eia3psnc.inp

Consolidation test, CAX8P elements.

eia3psnc_surf.inp

Consolidation test, CAX8P elements, surface-to-surface constraint enforcement method.

ei13psns.inp

Steady-state test, CPE8P elements.

ei13psns_surf.inp

Steady-state test, CPE8P elements, surface-to-surface constraint enforcement method.

ei13psns.inp

Steady-state test, CPE8P elements.

ei13psns_surf.inp

Steady-state test, CPE8P elements, surface-to-surface constraint enforcement method.

ei13psni.inp

Interference test, CPE8P elements.

ei13psni_surf.inp

Interference test, CPE8P elements, surface-to-surface constraint enforcement method.

ei13psni_auglagr.inp

Interference test, CPE8P elements.

ei13psni_auglagr_surf.inp

Interference test, CPE8P elements, surface-to-surface constraint enforcement method.

eia3psni.inp

Interference test, CAX8P elements.

eia3psni_surf.inp

Interference test, CAX8P elements, surface-to-surface constraint enforcement method.

Figures

Figure 1.6.3–2 One-dimensional consolidation test.

Figure 1.6.3–3 Interference test.

Figure 1.6.3–4 Effective stress profile for the first step of the consolidation test.

Figure 1.6.3–5 Pore pressure distribution for the consolidation test.

Figure 1.6.3–6 Linear superposition of two states used to solve the interference test problem.