Biomedical Engineering Reference
In-Depth Information
The study tested four typical articulations as shown in Fig. 2.24. It should be
noted that the "area" contact device is not fully congruent. There is a difference in
radii of about 1.5%. These equations are not valid for full congruency which may
be computed simply by P/A where A is a known contact area.
Fig. 2.24
Contact Types Evaluated
The results for both computed and measured stresses are shown in Fig. 2.25.
It may be seen from Fig. 2.25 that at acceptable levels of stress (about 10MPa
[26]), agreement of theory and experiment yields similar results. Thus the
elasticity solution is tractable at acceptable stress levels and degree of incongruity.
The effect of metal backing is not significant at such incongruity and stress.
The equations appear to provide a reasonable estimate of stress in the "point"
contact device. This result is, however, misleading. It is likely that the
underestimation due to the metal backing is compensated by the overestimation
associated with the use of elastic equations in the plastic stress range. The
overestimation appears greater at the higher stress levels near the yield strength
since the actual stress cannot be substantially greater than yield.
