In Situ Optical Observation of Nanoscale Contact Spots Evolution Under Normal Loading

The mechanical contact and electrical contact performance of metal electrode materials are mainly determined by fine details of contact spots for rough surfaces. In this article, an in situ optical observation test rig is designed to obtain the real-time image of contact interface with nanoscale resolution for the cambered electrode sample and flat sapphire plate under the normal load force. Then, a specified image processing algorithm is presented to visualize the real contact area, and further extract the size and shape features and distributions of contact spots. It is found that contact spots with oval shape are the main part for the real contact region. In addition, the evolution progress of the real contact area is analyzed in combination with the piecewise variation in the number of contact spots. The results show that the coalescence extension of neighboring contact spots and formation of newly produced contact spots would make the real contact area increase linearly, and the sharp number increment of contact spots is the main reason under low contact force.