ELVIS: A Custom Tribology System

AJ Almaguer University of California, Berkeley

Mechanical Engineering '10

5/16/11

A Custom Tribology System Medical Polymers Group @ UC Berkeley

ELVIS

Operate Maintain

Program

Motivation: Increase Implant Life

UHMWPE

CoCr Alloy

¨ WEAR and Fatigue/Fracture

Motivation: Decrease Wear

What is ELVIS?

Three testing stations

1 2 3

What is ELVIS?

Converted Vertical

Knee Mill

Vertical Mill

Table

1 2 3

Load cells

Pneumatics

What is ELVIS?

Load cells

Pneumatics

PID Controller

Can do Pin on Disk tests too

Pin

Disk

Elvis Software: LabView

Elvis Software: LabView

While loops control each

feature

Advantages

¨  Custom path ¨  Custom loads ¨  Friction Measurements

Load

µ

Figure 8 vs. Line Wear path

Cross shearing increases wear by two orders of

magnitude1,2

[1] Bragdon C. R., O’Connor D. O., Lowenstein J. D., Jasty M., and Syniuta W. D., 1996, “The importance of multidirectional motion on the wear of polyethylene.,” Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 210(3), pp. 157-65. [2] Wang A., Polineni V. K., Essner A. P., Sokol M., Sun D. C., Stark C., and Dumbleton J. H., 1997, “The Significance of Nonlinear Motion in the Wear Screening of Orthopaedic Implant Materials,” Journal of Testing and Evaluation, 25(2), p. 239.

Figure 8 Path

initialize variables & read user controls

Figure 8 Path

Configure buffer & start path

Generate figure 8 points

Figure 8 Path: Generating points

Figure 8 Path

Pause motion and count elapsed cycles

Measured Coefficient of Friction

Measured Stribeck Curve

Boundary Lubrictiaon

Mixed Lubrication

Hydrodynamic Lubrication

A Custom Tribology System Medical Polymers Group @ UC Berkeley

ELVIS

Acknowledgements

¨ Professor Lisa Pruitt ¨ Eli Patten ¨ Farzana Ansari ¨ Fellow Research Assistants of

the MPG Group