Investigation of Frictional Sliding Behavior: Experimental and Numerical Studies

Date

2023-12-08

Author

Özcan, Tutku Ilgın

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Stability of frictional sliding in terms of stick-slip and steady sliding behavior and the mechanisms that drive these behaviors is a topic of interest in the fields of tribology, geomechanics, and control engineering. In this thesis, stability of frictional sliding is investigated both experimentally and numerically. The experiments are carried out by side-driven direct shear experiments of two plates under compressive loading. The numerical method uses Maxwell-slip model and Burridge-Knopoff model consisting of mass-spring units pulled by a slider on top, i.e., top-driven, representing an interface of a sliding plate on top of a rigid substrate. In the experiments, the effects of surface roughness and initial compressive (normal) stress are investigated using three material pairs: PMMA/PMMA, TPU/PMMA, and PLA/PLA. The roughnesses on PMMA were created by polishing the samples with different grit sandpapers, on PLA by changing the printing orientation in a 3D printer. We found that for PMMA material, higher initial normal stress causes the sliding mode to change from steady sliding to stick-slip behavior. The same behavior change is observed also for higher roughness at high normal compressive stresses. On the other hand, TPU material transitions from stick-slip behavior to steady sliding behavior with increasing initial normal stress. Additionally, we found that for PLA material, sinusoidal behavior is observed for different sinusoidal patterns. For PLA material a more complicated relationship is observed. In the numerical simulations, a quasi-static solution to the Maxwell-slip model with Coulomb friction law is used to investigate the effect of roughness on the sliding behavior by representing higher roughness with higher randomness of the initial block positions. The static model is used for the first time to relate the microscopic level feature (roughness) is related to the macroscopic sliding behavior of the interface. We found that increasing the roughness changes the global sliding behavior from stick-slip to steady sliding. Additionally, a dynamic solution to the Maxwell-slip model with Coulomb friction law, is used to investigate the initial normal load effects on the frictional sliding behavior and sliding dynamics. In the dynamic model, we found that increasing the initial normal load also changes the global behavior from stick-slip to steady sliding. At the local level, with increasing initial normal load, the local frictional sliding region changes in a continuum from crack-like expanding sliding region to travelling slip pulse type sliding region and further to travelling train of slip pulses. Finally, the Burridge-Knopoff model is used to investigate the effect of the linear distribution slope, reflecting the compression load level, on the sequence of the block slippages, i.e., the evolution of slip on the interface. The results of the BK model show that during the friction force drop, slip propagates along the interface as pulses, either as a single pulse in one direction or as a crack that splits into two oppositely moving pulses.

Subject Keywords

Tribology, modelling, experiments, sliding friction, stick-slip, roughness

URI

https://hdl.handle.net/11511/107791

Collections

Graduate School of Natural and Applied Sciences, Thesis