Fretting Wear Testing Machine
Figure 1 shows the layout of the fretting wear test rig. In this set up two stationary cylindrical specimens mounted on a rotary table, clamp the reciprocating specimen on both sides. The two stationary cylindrical specimens are installed on the rotary table at 90 degrees to the moving specimen. This forms a crossed cylinder geometry which provides a well-defined point contact without suffering any alignment problems. An elliptical contact of varying aspect ratio can be obtained by varying the angle between the fixed and the moving specimens. Figure 2a and 2b show the test setup in circular and elliptical point contact modes. The point contact geometry is run without lubrication, but it can be lubricated if required. Dead weights placed on top of the upper stationary specimen provide the normal load to the contact. This simple arrangement allows the maximum contact pressure to be varied from 0.5 to 2 GPa. A piezoelectric force sensor is situated inside the connection between the actuator and the moving specimen. This force sensor measures the tangential force applied by the actuator. The output of the force sensor is routed to the same data acquisition card driving the actuator.
The test rig has been designed to be modular. The test rig accepts a ball on flat specimen module instead of the crossed cylinders when required. Figure 3 shows the ball on cylinder module inserted in the test rig. A sapphire window can replace the flat specimen. A microscope head is inserted into a slot machined above the sapphire window. This enables easy observation of the fretting contact as it undergoes wear.
|View of FWTM installed at METL||
Wear Scar for a circular contact note the stick zone in the center and slip on the periphery