Apparatus for initiating fatigue related damage on a member

Abstract

Apparatus is disclosed for initiating fatigue related damage on a circumferential surface of a rotatable member resultant from application of a tensile stress condition and a superimposed contact stress condition. The apparatus includes structure for supporting the member for axial rotation, structure for applying a load to the member during the rotation thereof to create a bending moment at a predetermined axial location along the member and a resultant tensile stress condition on a circumferential surface thereof at a corresponding location. The apparatus further includes structure for creating a contact stress on the circumferential surface of the member at the predetermined location.

We claim: 
     
       1. Apparatus for initiating fatigue related damage on a circumferential surface of a member, the circumferential surface extending around an axis of the member, the apparatus comprising: structure for supporting the member for rotation about the axis;   structure for applying a load to the member during the rotation thereof to create a bending moment at a predetermined axial location on the member and a resultant tensile stress condition at a predetermined location on the circumferential surface thereof;   structure for creating a contact stress at the predetermined location on the circumferential surface of the member, including a member having a circumferential surface positioned for rotating contact with the circumferential surface of the first named member at the predetermined location, and means biasing the second named member against the first named member during the rotating contact.   
     
     
       2. Apparatus, as set forth in claim 1, wherein the structure for supporting the first named member comprises a plurality of aligned bearings. 
     
     
       3. Apparatus, as set forth in claim 1, wherein the structure for applying the load to the first named member comprises a load cell to allow determining the magnitude of the load applied. 
     
     
       4. Apparatus, as set forth in claim 3, wherein the structure for applying the load to the first named member further comprises a mechanism allowing varying the load. 
     
     
       5. Apparatus, as set forth in claim 1, further comprising a rotating power source for rotating the first named member. 
     
     
       6. Apparatus, as set forth in claim 1, wherein the means biasing the second named member against the first named member comprises a fluid under pressure in fluid communication with the second named member. 
     
     
       7. Apparatus, as set forth in claim 6, further comprising a pressure transducer in communications with the fluid under pressure operable for sensing pressure changes in the fluid resulting from pitting on the circumferential surface of at least one of the first named member and the second named member. 
     
     
       8. Apparatus, as set forth in claim 1, further comprising an accelerometer for detecting movements of the second named member indicative of pitting on the circumferential surface of at least one of the first named member and the second named member. 
     
     
       9. Apparatus, as set forth in claim 1, wherein the first named member comprises an elongated shaft having a first end, an opposite second end, and an intermediate portion located therebetween, the structure for supporting the first named member comprises a plurality of aligned bearings supporting the shaft adjacent the first end thereof, and the structure for applying the load comprises a load attached to the shaft adjacent the second end thereof. 
     
     
       10. Apparatus, as set forth in claim 1, wherein the second named member comprises a ball.