Static Friction Measurement of Steels Under Dry and Lubricated Conditions Using An Oscillating Tribometer

For the dimensioning of press fits and screw connections, knowledge around the static friction coefficient between two surfaces is essential. Variation of the surface and the state of lubrication can change this parameter. The research in this publication presents a novel screening method for the static coefficient of friction, using an oscillating tribometer with electromagentic drive. The materials which were investigated, were two types of steels (stainless steel 1.4313 and heat-treatable steel 1.6511), combined in different ways, in dry or lubricated and also in nitrided condition.The novel test method can be used at application-near contact pressures, up to 120 MPa as used in this research. I particular the test method works with a linear increase of the stroke setpoint, starting from almost zero. As the actuator stroke increases, so do the shear forces due to elastic deformation of the components. These shear forces are perfectly measurable with the tribometer's piezo friction force transducer. Finally, the shear force exceeds the static friction and sliding occurs. High-resolution data acquisition provides insight into braking loss events and reveals the fundamental friction effects of common engineering materials at relevant loading levels.The reproducible results for the static friction coefficient enabled the authors to draw some correlations between surface hardness conditions and the static friction. The presented method and the final findings hopefully provide engineers with a better understand of this important parameter in the future.