Evaluation of the Volumetric Erosion
of a Nominally Spherical Surface.

John W. McBride
http://sciencelinks.jp/j-east/article/200313/000020031303A0408895.php

TaiCaan Technologies Ltd.
Southampton, United Kingdom
J.W.McBride@taicaan.com

The surface shown in Fig.1 is an electrical contact surface that has been eroded by an arc discharge (this is the default data set, used in BODDIES DEMO software package that can be supplied on request). The surface was originally nominally spherical.

Fig.1 Data Set of an Eroded Electrical Contact Surface.

The surface shows an eroded area at the top of the surface. BODDIES can be used to edit the surface, rotate the surface and present the surface in a number of different ways. To remove the nominal surface a best fit non-linear least squares method is applied to the data, to generate the surface shown below in Fig.2

Fig.2 Data Set after Form Removal.

After the spherical surface has been removed a flat datum surface remains which can then be used to evaluate the volumetric erosion both above and below this datum surface. The sphere fitting method used shows the radius of the surface before form removal to be 2.43 mm. To process the data for volume, first a contour map of the surface is produced. This is shown in Fig 3.

Fig.3 Contour Map.

The contour map of the surface shown in Fig.3 can be used interactively with a cursor to find specific height values on the surface. Three data points are then selected by the user to define a plane that is set as the datum. The volume of the surface both above and below the datum plane is then calculated. For the case shown, the volume above the datum is 0.0516 mm3  and the volume below the surface 0.032 mm3.

Further Information

McBride, J.W., "Volumetric erosion measurements of contacts tested in DC automotive relays". Forty-Seventh IEEE Holm Conference on Electrical Contacts, Montreal, 2001, 73-81

McBride, J.W., The volumetric erosion of electrical contacts. IEEE Transactions on Components and Packaging Technology, 23(2), 2000, 211-21

McBride, J.W., "A review of volumetric erosion studies in low voltage electrical contacts". Technical Report of IEICE EMD2001-45 (2001-09). The Institute of Electronics, Information and Communication Engineers, 2001, 1-8

McBride, J.W., Cross, K.J. and Abu Sharkh, S.M., The evaluation of arc erosion on electrical contacts using three-dimensional surface profiles. IEEE Transactions on Components, Packaging, and Manufacturing Technology, 19(A), 1996, 87-97