Abstract
Friction models are proposed for anisotropic and heterogeneous dry friction on boundaries of polymer solids. Unit vectors and oriented angles of sliding velocities, radii of curvature and unit normal vectors of sliding trajectories are taken as independent variables in constitutive equations of anisotropic and heterogeneous friction. Heterogeneous dry friction of a polymer pin in pin-on-disc tests is illustrated in the case of Archimedean spiral trajectory. Individual molecular chains composing polymer materials can move inside the material with a high degree of friction anisotropy. The resistance of macromolecule motion is considered with respect to micromechanical models of macromolecules, their kinematics, and friction laws. Two approaches are applied for modeling of anisotropic friction inside polymer materials: continuum-based models (anisotropic viscous friction) and micromechanical models (anisotropic dry friction). Examples of macromolecule dry friction are considered under conditions of spinning and sliding of a disc-like macromolecule and snake-like sliding of a long macromolecule.
Highlights
This study is an extension of the research presented at 14th World Congress on Computational Mechanics (WCCM) and European Community on Computational Methods in Applied Sciences (ECCOMAS) Congress 2020, virtual congress: 11–15 January 2021 [1]
The material parameters used in the friction equations can be determined directly from experiments, since proposed dry friction models on boundaries of polymer solids are based on the phenomenological approach
Main advantages of the proposed friction models are as follows: they are simple enough and they have a finite number of parameters, and they can be extended to other types of frictional anisotropy and nonhomogeneity important in polymers
Summary
This study is an extension of the research presented at 14th World Congress on Computational Mechanics (WCCM) and European Community on Computational Methods in Applied Sciences (ECCOMAS) Congress 2020, virtual congress: 11–15 January 2021 [1]. The macromolecules are randomly oriented, but under sliding and friction the molecular chains can be aligned in one direction [10], so that the microstructure may be highly anisotropic (Figure 1). This is responsible for significant changes of friction [3,11]. The purpose of this study is to include microstructure evolution effects in friction equations for polymers on external boundaries of solids and inside materials This is realized with the aid of anisotropic and nonhomogeneous friction models including useful additional independent variables. The application examples show how author’s friction models can be used to derive equations for friction forces in the given cases
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