Friction in Forming: An Experimental-Numerical Method to Quantify Contact Behavior

摘要

Phenomelological models for mechanical interactions: the friction model of Coulomb, the Von Mises model, and elastoplastic analogies were studied. A thermodynamical continuum framework for the contact behavior in forming processes is presented. The mechanical contact models fit within this framework under quite general conditions. It is shown that measurement of the normal stress and, if possible, the shear stress in the contact area between tool and workpiece is necessary to obtain reliable values for contact quantities suitable to evaluate the contact behavior. The accuracy of the contact quantities can be increased by also taking the displacements of the unloaded surface into account, provided these are measured accurately enough. A contactless photogrammetric displacement measuring method is presented. The theoretically predicted accuracy is not reached, due to deficiencies in the modelling. A contact stress measuring tool for upsetting experiments was developed. Measurement of the elastic strains within the tool combined with a numerical model, delivers the values of the contact stresses between tool and workpiece. The strains are measured with thin film strain transducers.