Coulomb's Theory Of Friction

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Friction is a crucial phenomenon in metal cutting which is very complex to model. It has a significant effect on the amount of power required for removing a given volume of metal, surface quality of the finished product, and the extent of tool wear. However, many studies assume no friction in the metal cutting process due to lack of experimental techniques to directly measure the coefficient of friction.
Sticking and sliding regions are the two contact regions along the tool-chip interface. A critical friction stress τ_c and coefficient of friction µ are assumed to exist in the sticking and sliding regions, respectively[42]. Most analyses have applied classical friction situation following Coulomb’s laws which is based on coefficient of friction [e.g., [55], [62]]. Frictional sliding force F is proportional to the force N normal to the interface at which sliding is taking place. This model can be expressed by:
However, the above equation fails to give accurate prediction in high normal stress conditions. Several studies applied modified Coulomb friction law [e.g., [42], [40], [63],[41]] in which critical friction stress depends on pressure normal to the tool-chip interface, coefficient of friction, and threshold value for the conventional Coulomb friction stress. In this model the contact point is in the sticking
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In the previous method, when tool tip was close enough or certain level of some physical data was reached, the immediate nodes ahead of the tool tip would be separated. Although the initial method was simple and had advantages, it was not capable of surface roughness prediction and account for fracture. The method predicted different types of chip morphology, such as continuous chip, shear localized chip with and without complete chip

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