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Dry frictional contact between two metallic surfaces, one cast iron and the other steel, is analyzed. The experiments were conducted using a pin-on-disk setup instrumented with force and acceleration transducers. The interactions between friction, wear, and vibrations and their dependence on normal load and system stiffness are investigated. The results indicate that stiffness has a significant effect on the normal load at which transition takes place from mild to severe friction and wear. The variation of surface roughness with normal load for different stiffnesses is also examined. The different regimes of friction are observed, as the normal load is increased. They are characterized as steady state friction region, nonlinear friction region, region of transient friction with disturbances and region of self-excited vibrations. It is shown that the transition from the steady-state friction can be characterized by a sudden increase in the coefficient of friction and amplitude of slider oscillations.

The barreling of cylindrical specimens during upsetting is a common example of free deformation. However, there is no analytical solution to predict the extent of barreling and even experimental work is scarce. In this study tests were conducted on 7075–0 aluminum with specimens of three height-to-diameter ratios. Some specimens were upset dry, others were lubricated. A suitable parameter was chosen to characterize the extent of barreling. The influence of various process variables on this parameter was studied. A simple analysis is given to relate this parameter to other geometrical factors. The possibility of analytical prediction of barreling is considered, but appears to be as yet remote.

This paper presents experimental data and a physical model of the effects of normal load and system rigidity on the friction and wear processes with water lubrication. The transition from mild to severe friction and wear was found to be independent of the system rigidity, but dependent on the normal load. As the normal load is increased further, it reaches another critical value, which depends on the system rigidity, at which high frequency self-excited vibrations are generated. These oscillations exhibit a coupling between the frictional and normal degrees of freedom. It is shown that mild wear rate increases with the normal load and also with the system rigidity.

Different types of vibrations induced by dry friction are investigated by means of a model apparatus described in Part 1. The structural model is obtained from the measurement of the modal frequencies and damping ratios of three degrees of freedom. The oscillations in the normal and frictional forces, as well as the slider vibrations, have been measured and analyzed. As the normal load is increased, four different regions of vibrations are observed corresponding to the four friction regimes discussed in a companion paper. Small oscillations are encountered at low values of the normal load and they are possibly caused by random surface irregularities. The vibration characteristics are changed when transition occurs from steady state friction. When the normal load is further increased, self-excited periodic vibrations are produced. The spectra of the oscillations are related to the modal frequencies. Self-excited vibrations are analyzed on the basis of the experimental data.

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It is shown that wear is an increasing function of system stiffness. The increase in the frequency of the applied load oscillations in normal direction causes increase of number of loading cycles per unit time that, in turn, causes increased rate of wear particles formation due to fatigue. A wear model has been developed which accounts for slider oscillation in the normal direction. Experimental data correlate very well with the theoretical analysis.