Experimental definition of dynamic friction

Abstract

A simple and effective method is offered for defining the dynamic factor of friction based on a modification of the Kolsky method. The numerical analysis of this technique has shown that this experimental method allows for an adequate determination of a coefficient of kinetic friction while a calculation correction of the measured effort is necessary for defining the coefficient of static friction. For the adequate simulation of high-speed processes in designs subjected to dynamic influence, knowledge of both the dynamic properties of the materials and characteristics of friction between interactive surfaces is necessary. Friction and wear processes are the essential factors influencing the work of a cutting tool. Knowledge of the characteristics of friction is necessary for the development of the technological processes for high-speed machining of metals, such as rolling, deep-drawing, molding, etc. Taking this into consideration, friction is extremely important in the modeling of processes of a ballistic penetration. For a complete characterization of friction phenomena, it is necessary to carry out numerous experiments which influence various factors that must be investigated: contact pressure, speed of relative movement and a roughness of surfaces, and temperature. In static conditions, many effective methods for defining friction characteristics are developed. As for the dynamic charac- teristics of friction, they are virtually not investigated due to the absence of reliable techniques for their definition. Currently, there are some experimental techniques that are known for investigating dynamic friction. They can be divided into the following basic groups: � experiments using the slanting impact of plates at speeds of impact up to several hundred meters per second with registration of shock-wave loading parameters by means of laser interferometer (VISAR) (1-3); � use of an updated split Hopkinson pressure bar (SHPB) (4, 5). This technique assumes applying axial dynamic force to a turning system specimen-bar, a technique that is in the early stages of development. The typical speeds of relative movement of the contacting surfaces used in this type of experiment were 1-5 m/s; � updating of a torsional variant of the SHPB with the static application of axial loading (6); � using the method of molded specimens, developed for low speeds of sliding, which allows investigations of the phenomenon of friction in a steady state (7-9); � quasi-static tests (10, 11); and, � using the method of mathematical identification for the definition of the law of friction (12), (13). The parameters describing friction were matched with mathematical modeling by comparing the results of natural and numerical tests. An analysis of the current state of experimental investigations of dynamic friction show that existing methods and schemes demand either complex devices and methods for parameter