Friction law for hydrostatic mixed lubrication regime

The accuracy of the finite element simulation of bulk forming processes is connected to the interface friction law. For quasi-static processing operations, the well-known plastic wave friction model, applied to unlubricated contacting interfaces of metallic workpieces with rigid tools, is a versatile link between the Coulomb–Amonton and the constant friction laws. An improvement of the plastic wave friction model is proposed for mixed lubricating conditions when the load is carried by the asperities in direct contact and by the lubricant. The main assumption of this new constitutive relation uses the compressibility of the trapped lubricant in the pockets created inside the tool asperity with the rising plastic wave. This new friction law is used for the simulation of different ring-compression tests carried out by Tan et al. [J. Mater. Proc. Technol. 80–81 (1998) 292].