Date of Award

Summer 2001

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering - (M.S.)

Department

Mechanical Engineering

First Advisor

Avraham Harnoy

Second Advisor

E. S. Geskin

Third Advisor

Edward L. Dreyzin

Abstract

The feasibility of a unique design of orthopedic- joint implant is investigated. The work focuses on the dynamic friction characteristics of a new joint. This unique design can be also useful in machinery involving oscillating motion similar to that of the hip joint during walking. An elastomeric layer bonded behind the rigid acetubular cup can be beneficial in improving the durability of prosthetic implants. Angular compliance offered by the elastomeric layer reduces relative sliding between the surfaces, lowers contact stresses by distributing pressure more evenly, and reduces the possibility of incongruent loading conditions caused by misalignment. The application of a compliant bearing is not limited to prosthetic implants. Like a working biological joint, machinery operating with frequent start-stop sinusoidal motion is characterized by high friction at the start-up and point of velocity reversal. Contact between the surfaces, which results in wear, is most likely to occur when the velocity passes through the zero velocity region. In the presence of lubrication, angular compliance allows a hydrodynamic film to build up before there is a sliding motion with direct contact between surfaces. A short sliding motion at the start of the cycle is replaced by rolling motion.

A friction measuring apparatus was constructed to study the dynamic friction properties of both the current and proposed bearing in order to establish the feasibility of such a design. Dynamic friction measurements were conducted without lubrication and with LW 104, 5W, and 1 OW viscosity oils. In addition, tests were conducted with varied loading, frequency of oscillations, and sinusoidal velocity for both the rigid and compliant design. Although only a small amount of angular compliance was introduced to the bearing, the results indicated a significant improvement in performance. It was found that when lubricated, use of the compliant bearing resulted in reduced start-up friction. Increasing load, viscosity, and frequency of oscillation resulted in a more significant reduction of the start-up friction.

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