Reduced order models for characterizing friction interfaces have been investigated for the last 75 years. Recent work has been focused on microslip formulation of the interface behavior, where continuous contact is approximated with a multi-point contact model. A novel multi-point contact model is presented in this work, which is entirely derived from a shear lag approach to resolve the kinematic state of the friction interface under the presence of tangential loading. Both static and dynamic loading conditions are analyzed and comparisons are drawn between the continuous and discrete models. The series Iwan model presented in this work differentiates between the elastic and friction components of the interface displacement, both parameters being calibrated using material properties and model geometry. Convergence behavior of such models with increasing model order is demonstrated. The response characteristics of the series Iwan model under dynamic loading conditions is also investigated. The series Iwan model is in good agreement with the shear lag approach for results such as propagation of the slip zone with increasing pullout force. The transient response of the the structural mass and the kinematic states of the damping elements are convergent with increasing model order.
Numerical models to simulate interface behavior of friction connections under cyclic loading are investigated. The question of validity of lower-order models in successfully capturing response of friction joints under cyclic loading is addressed. Single-element macroslip models are not capable of capturing localized interface behavior prior to gross interfacial slip. This paper focuses on the convergence behavior of a multipoint contact microslip model comprised of Iwan-type elements for different physical parameters such as system response amplitude and kinematic state of the friction joint. System dynamics play a significant role in determining the convergence of structural behavior, especially for tuned damper sets in the nonzero damper mass case. This behavior is explored using simple linearized models that explain the response sensitivity in terms of the overall modal density near the forcing frequency. Convergence of the interface response kinematics is also considered, with a focus on the number of damping elements operating in the stick, stick-slip, and slip regimes at steady state. Energy dissipation scaling under light forcing is also examined, with the class of models considered here yielding scaling exponents consistent with experimental observations and analytical predictions from the literature. We show that the interface kinematic behavior converges at a slower rate than the structural response and therefore requires a higher-order interface model. These results suggest that extremely low-order models (i.e., <5 damping elements) provide predictions that are model order dependent, while higher-order models (i.e., >50 damping elements) are not. This result impacts model development and calibration approaches, as well as providing clues for appropriate model reduction strategies.
We have studied dynamic friction phenomena using a variety of experimental measurement approaches. We have combined thermoelastic stress analysis (TSA) and optical microscopy to measure both the stress field and the interface slip displacement in a model frictional contact. We use a plane stress, fiber pullout-type geometry to produce a line contact interface. The interface operated in the partial slip regime with no gross sliding. The stress field and slip displacement information allow us to construct a friction constitutive relationship directly from experimental data. We also use complementary interface modeling to physically interpret the experimental observations. The results suggest that the interface slip zone size is a nominally linear function of pullout force, while the interface slip displacement responds as a second-order function of distance along the interface. When combined, these observations suggest a scaling law for per-cycle energy dissipation of the form E ∼ Fo3, where Fo is the forcing amplitude. Experimental and modeling results are presented to support this conclusion.
Numerical models to simulate interface behavior of friction connections under cyclic loading are investigated. The question of validity of lower order models in successfully capturing response of friction joints under cyclic loading is addressed. Single-element macroslip models are not capable of capturing localized interface behavior prior to gross interfacial slip. This paper focuses the convergence behavior of a multi-point contact microslip model comprised of Iwan-type elements for different physical parameters such as system response amplitude and kinematic state of the friction joint. It is observed that system dynamics play a significant role in determining the convergence of frictional behavior, especially for tuned damper sets. This behavior is explored using simple linearized models. In addition, the interface kinematic behavior converges at a slower rate than the structural response and therefore requires a higher-order interface model.
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