3.2.13 Slider mechanism with slip-rate-dependent friction

Product: ABAQUS/Standard  

This example is intended to provide basic verification of the slip-rate-dependent friction models in ABAQUS for static and dynamic analysis. Two slip-rate-dependent friction models are implemented. One is an extended form of the classical Coulomb friction model in which the friction coefficient can be defined in terms of slip rate, contact pressure, surface temperature, and field variables. In the second model the user provides a static friction coefficient, a kinetic friction coefficient, and a decay parameter. The static friction coefficient decays exponentially to the kinetic friction coefficient. This model is referred to as the exponential decay friction model and is selected with the EXPONENTIAL DECAY parameter on the *FRICTION option.

This problem also illustrates the use of the *CONTACT INTERFERENCE and *CHANGE FRICTION options.

Problem description

Material

All parts of the model are elastic. The Young's modulus, Poisson's ratio, and density for the rod and the cylinder are 207 GPa (30.0 × 106 psi), 0.3, and 7800 kg/m3 (0.73 × 10–3 lbf s2/ in4), respectively. The compound has a Young's modulus of 6.9 GPa (1.0 × 106 psi), a Poisson's ratio of 0.2, and a density of 1069 kg/m3 (0.1 × 10–3 lbf s2/ in4).

It is assumed that the interface between the slider and the compound is rough; i.e., no slip can occur when contact is established. The rough surface interface is modeled with the Lagrange friction model and a high friction coefficient. It is assumed that the interface between the rod and the compound is polished and has a static friction coefficient . Experimental tests show that the dynamic friction coefficient, , is 0.1 for a slip rate equal to 2.5 inches per second. Furthermore, the static coefficient decays exponentially to the kinetic friction coefficient, , according to , where is the decay coefficient. The dynamic coefficient at higher slip rates is not known; hence, the default ABAQUS assumption that the ratio to is 5% is used. The idealized friction model is illustrated in Figure 3.2.13–3 and is specified with the TEST DATA parameter on the *FRICTION option. ABAQUS calculates the kinetic friction coefficient and the decay parameter. For the cases that use the Coulomb friction model, the data for the friction coefficient and the corresponding slip rate have been provided in tabular form.

Loading

The compound material is tightly fit between the rod and the slider in the first step of the analysis. The initial overclosure is resolved with the *CONTACT INTERFERENCE option.

Friction is introduced in the second step with the *CHANGE FRICTION option. The contact interference option is removed. No loads are specified in this step to ensure that contact and equilibrium are established.

A harmonic sliding motion of the form is applied to the cylinder. The amplitude, A, is equal to 101.6 mm (4.0 inches), and the frequency, , is equal to rad/second. This form of harmonic motion is selected since it produces a zero velocity and avoids an intantaneous acceleration jump at the beginning of the dynamic step. A dynamic analysis is performed for 10 seconds to complete one full cycle of harmonic load in Step 3. Another harmonic cycle is completed using a static analysis in Step 4.

Results and discussion

Input files

Figures

Figure 3.2.13–1 Axisymmetric model of the slider mechanism.

Figure 3.2.13–2 Detail of the compound between the rod and the sliding cylinder.

Figure 3.2.13–3 Idealized friction model for the rod–compound surface interface.

Figure 3.2.13–4 Mises stresses.

Figure 3.2.13–5 Normal contact forces across the rod–compound surface interface.

Figure 3.2.13–6 Shear forces across the rod–compound surface interface.