1.7.4 Friction models in ABAQUS/Standard

Product: ABAQUS/Standard

Elements tested

B21 B31

Features tested

Problem description

The model consists of two rods perpendicular to a fixed rigid surface forced into contact with the rigid surface by a concentrated load applied in the axial direction at the top of each rod. Subsequently, shear forces are applied, such that , to verify the “stick” condition. Afterward, prescribed displacements are applied to the rods to force them to slide around the surface.

The contact between the bottom end of the rod and the rigid surface is modeled by specifying a master-slave contact pair. The bottom end of the rod constitutes the slave surface created with the *SURFACE, TYPE=NODE option and has a contact area of unity; hence, the normal force applied on the rod is equal to the contact pressure. Each rod has its separate surface interaction created with the *SURFACE INTERACTION option and the *FRICTION option. During the analysis the friction models are modified with the *CHANGE FRICTION option.

Model:

Average length of all contact elements

0.5

Material:

Young's modulus	30 × 10⁶
Poisson's ratio	0.3

Coulomb friction model

The first two steps of the analysis establish contact between each rod and the rigid surface and set up an equilibrium solution in which each beam element is compressed by a force of 300. The temperature of the slave node is specified as 20° and that of the rigid surface, as 0°; therefore, the average surface temperature is 10° when contact is established. In Step 3 the normal force is increased to 400, and a shear force is applied to the first rod such that and the rod remains sticking. The shear force is removed in Step 4. In Step 5 the friction model for rod 1 is modified. The normal force is increased to 550, and a shear force is applied such that and the rod still remains sticking. The shear forces are removed in Step 6. In Step 7 the original friction model is specified with the RESET parameter on the *CHANGE FRICTION option. The pressure on rod 1 is increased to 850, and a slip is applied. In Step 8 a slip velocity–dependent friction model is introduced for rod 2. In Step 9 a slip is applied to rod 2 in which the slip rate is varied by prescribing the displacement with an amplitude curve during the static step.

Surface interaction for rod 1:

Step 1

0.005 + 2.5 × 10^–4( – 100).

0.005 + 3.3 × 10^–4( – 100). (Anisotropic model only for case with 2 slip directions.)

Step 5

0.002 + 3.3 × 10^–4 for 100 500.

0.1650 + 0.002 + 5.5 × 10^–4( – 500) for 500 900.

Step 7

Same as specified in Step 1.

Step 8

0.0 for the elastic slip formulation.

Rough friction model for the Lagrange multiplier formulation.

Surface interaction for rod 2:

Step 1

0.0 for the elastic slip formulation.

Rough friction model for the Lagrange multiplier formulation.

Step 8

for 0;

2.0 for 0 2.0;

for 2.0, where

0.2 and 0.0 for 100.0 and

0.4 and 0.2 for 500.0.

Exponential decay model

The first two steps of the analysis establish contact between each rod and the rigid surface and set up an equilibrium solution in which each beam element is compressed by a force of 300. The pressure is kept constant throughout the analysis. In Step 3 a shear force is applied to rod 1 such that and the rod remains sticking. The shear force is removed in Step 4. In Step 5 the friction model for rod 1 is modified by providing test data. A shear force is applied such that and the rod remains sticking. The shear forces are removed in Step 6. In Step 7 the original friction model is specified with the RESET parameter on the *CHANGE FRICTION option. A slip is applied to rod 1. In Step 8 a new friction model is introduced for rod 2. In Step 9 a slip is applied to rod 2 in which the slip rate is varied by prescribing the displacement with an amplitude curve during the static step.

Surface interaction for rod 1:

Step 1

0.3;