Multiscale physics-based modeling of friction

Friction;partial slip;multiscale modeling;roughness;fretting;bolted joints

Eriten, Melih

关键词: Friction;    partial slip;    multiscale modeling;    roughness;    fretting;    bolted joints;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/31078/Eriten_Melih.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Frictional contacts between solids exist in nature and in a wide range of engineering applications. Friction causes energy loss, and it is the main source of wear and surface degradation which limits the lifetime of mechanical systems. Yet, friction is needed to walk, run, accelerate, slow down or stop moving systems. Whether desirable or not, friction is a very complex physical phenomenon. The behavior of systems with friction is nonlinear, and the physical mechanisms governing friction behavior span a wide range of spatial and temporal scales. A thorough study of friction should employ experimentalists and theoreticians in chemistry, materials science, tribology, mechanics, dynamics, and structural engineering. High spatial and temporal resolutions are required to capture and model essential physics of a frictional contact. However, such a detailed model is impractical in large-scale structural dynamics simulations; especially since frictional contacts can be numerous in a given application. Reduced-order models (ROMs) achieve broader applicability by compromising several aspects and accounting for the important physics. Hence, rather simple Coulomb friction is still the most ubiquitous model in the modeling and simulation literature. As an alternative, a reduced-order friction model built-up from micromechanics of surfaces is proposed in this work. Continuum-scale formulation of pre-sliding friction behavior is combined with material-strength-based friction coefficients to develop a physics-based friction model at asperity-scale. Then, the statistical summation technique is utilized to build a multiscale modeling framework. A novel joint fretting setup is designed for friction experiments in a practical setting, and the developed models are tested. Both asperity and rough surface friction models show good agreement with experimental data. The influences of materials, surface roughness and contact contamination on the friction are also studied. Finally, the developed models are incorporated in to a simple dynamical system to illustrate broader applicability. The models proposed in this work account for loading-history dependence, partial slip, gross slip, nonlinear stiffness and energy dissipation characteristics of frictional contacts. In doing so, the models require no curve-fit or look-up parameters. Instead, the formulations are developed from continuum mechanics, and the required parameters can be determined from simple tension/compression and surface roughness tests. In this sense, the developed models are physics-based and predictive. The parameters employed in the models depend on the contact conditions, surface roughness and material properties. For instance, the developed models use a dry-contact formulation at asperity-scale, and the macroscale friction predictions are tested only for dry contacts. However, the multiscale modeling approach can be applied to model the effect of lubrication provided that asperity-scale contact accounts for it. Besides, frictional contacts of certain materials exhibit severe adhesion, cold welding and galling behavior as demonstrated experimentally in this work. If these behaviors are modeled at asperity-scale, then the friction at rough contact scale can be obtained by the same procedure presented in this work. This flexibility is another significant advantage of the proposed modeling approach.