A novel test rig for in situ and real time optical measurement of the contact area evolution during pre-sliding of a spherical contact

Abstract

An experimental test rig was developed in order to investigate elastic-plastic single micro-spherical contact under combined normal and tangential loading. This novel apparatus allows in situ and real time direct optical measurement of the real contact area (RCA) evolution in pre-sliding. It also allows relative displacement measurements under very low rates of tangential loading (down to 0.01 N/s) to capture accurately the fine details at sliding inception. This is achieved by piezoelectric actuation in closed loop feedback control in addition to synchronization with data and image acquisition to obtain real time measurement. The RCA measurement is realized by direct optical observation technique, whereas two different image processing algorithms were implemented for the elastic and the elastic-plastic contact regimes. The various features and capabilities of the test rig are presented along with some preliminary experimental results of RCA and friction behavior to assess its performance.

Development of a Lap Joint Fretting Apparatus

“…Contrary to indirect methods mentioned above, direct measurements of forces and relative displacements were performed in fretting experiments by Varenberg et al [18] and Ovcharenko et al [19]. The experimental apparatus described in [19] utilizes a piezoactuator to impose controlled displacements on the flat sample and measures the relative displacements between the sphere and flat samples by a proximity sensor.…”

“…The experimental apparatus described in [19] utilizes a piezoactuator to impose controlled displacements on the flat sample and measures the relative displacements between the sphere and flat samples by a proximity sensor. The friction force is measured directly by a load cell whereas the normal force is imposed by dead weights.…”

In situ investigation of the contact area in elastic–plastic spherical contact during loading–unloading

“…details in Ref. [20]. The white dashed line in figures 4 and 5 marks the border of the contact area.…”

“…This will be done for different materials and sphere diameters by accurate image processing techniques. The test rig allows direct and in situ measurements of the evolution of RCA between a rigid flat and a deformable sphere under combined normal and tangential loading in both elastic and elastic-plastic contact modes [20]. For the current study only the normal loading mechanism (module III, see figure 2) was used.…”

In-situ Observations of a Multi-Asperity Real Contact Area on a Submicron Scale

“…For an accurate investigation of the real contact area and understanding the actual contact, an experimental approach must be adopted that makes it possible to facilitate theoretical approaches with the actual measurements. In the literature [22] to [31] several experimental techniques are described for real-contact-area measurements. Probably the most practical in-situ methods for real-contact-area measurements are based on the electrical [24] and thermal [25] contact resistance, as well as ultrasonic [26] and [27] and optical [28] and [29] principles.…”