Small Strain Limit Research Articles

New Techniques for Measuring Forces and Wear in Telephone Switching Apparatus

One of the main problems in obtaining long life in telephone switching equipment is the wear caused by large momentary forces. In order to investigate this problem several new techniques have been devised for measuring normal and tangential forces and for producing and controlling normal and tangential motions for wear studies. The forces are measured by inserting small barium titanate ceramics between the points of application of the forces and observing the voltages generated on a cathode ray oscillograph. Barium titanate ceramic is about fifty times as sensitive as quartz and has a high enough dielectric constant so that with conventional amplifiers time intervals as long as a tenth second can be measured. Both normal and tangential forces can be measured by using properly poled ceramics. By using weights on top of the crystals, normal and tangential accelerations can be measured. With these ceramics, forces have been measured for relays and for frictional sliding of a wire over a plastic. By employing a barium titanate transducer capable of a large amplitude at 18,000 cycles it has been shown that no wear occurs for normal forces, and that all the wear observed in a relay is due to tangential sliding. Quantitative measurements of wear have been made for a variety of materials, and it has been shown that materials with a large elastic strain limit will wear better than materials with a small elastic strain limit even though the latter have a higher yield stress; materials such as plastics and rubber will outwear materials such as metals or glasses. As the length of slide is reduced there is a threshold of motion for which there is no gross slide and very little wear. This region is determined by the condition that the tangential force is smaller than the normal force times the coefficient of friction. Theoretical and experimental results are obtained for this region and an equation is derived which determines the possible displacement without gross slide. The stress strain curve occurs in the