Slip Motion and Stability of a Single Degree of Freedom Elastic System with Rate and State Dependent Friction

WE CONSIDER quasistatic motion and stability of a single degree of freedom elastic system undergoing frictional slip. The system is represented by a block (slider) slipping at speed V and connected by a spring of stillness k to a point at which motion is enforced at speed V,. We adopt rate and state dependent frictional constitutive relations for the slider which describe approximately experimental results of Dieterich and Ruina over a range of slip speeds % In the simplest relation the friction stress depends additively on a term A In V and a state variable 0; the state variable B evolves, with a characteristic slip distance, to the value -B In K where the constants A, Bare assumed to satisfy B > A > 0. Limited results are presented based on a similar friction Iaw using two state variables. Linearized stability analysis predicts constant slip rate motjon at V0 to change from stable to unstable with a decrease in the spring stiffness k below a critical value k,,. At neutral stability oscillations in slip rate are predicted. A nonhnear analysis of shp motions given here uses the Hopf bifurcation technique, direct determination of phase plane trajectories, Liapunov methods and numerical integration of the equations of motion. Small but finite amplitude limit cycles exist for one value of k, if one state variable is used. With two state variables oscillations exist for a small range of k which undergo period doubling and then lead to apparently chaotic motions as k is decreased. Perturbations from steady sliding are imposed by step changes in the imposed load point motion. Three cases are considered : (1) the load point speed V0 is suddenly increased; (2) the load point is stopped for some time and then moved again at a constant rate; and (3) the load point displacement suddenly jumps and then stops. In all cases, for all values of k, sufficiently large perturbations lead to instability. Primary conclusions are: (I) “stick-slip” instability is possible in systems for which steady sliding is stable, and (2) physical manifestation of quasistatic oscillations is sensitive to material properties, stiffness, and the nature and magnitude of toad perturbations. t Visiting, Division of Applied Sciences, Harvard University, 1981-3.