A critical review of the biomechanical stress analysis of the human femur.

The objective of this paper is to present a critical review of the mechanical behaviour of the human femur with particular emphasis on the determination of the internal stress distribution under the action of a variety of forces resulting from daily living activities. For attaining such a goal, knowledge of the applied forces in combination with the internal structure and the mechanical properties of the material of the femur is needed. The whole work is divided into four parts. In the first two parts a brief description of the structure and the mechanical properties of the cortical and cancellous bones of the femur determined from the tension, compression, shear, bending, torsion and impact tests takes place. The third part deals with the analysis of the joint and muscle forces acting on the femur. In the fourth part the mathematical and experimental methods for the determination of the stress distribution in the femur are presented in detail. The mathematical methods include use of the beam theory and finite elements, while the experimental methods incorporate the brittle and photoelastic coatings, the strain gauges and the two- and three-dimensional photoelasticity. Finally, an analysis of the strength characteristics of the femur from the point of view of fracture mechanics is undertaken.

Distance measuring based on caustics.

A distance measuring technique based on caustics formed by illuminating an ellipsoid reflector with a point light source was developed. A study of the influence of the ellipticity of the mirror and the relative positions of the screen where the caustic is formed, the point source, and the mirror on the limits and accuracy of the range measured was undertaken. It was found that the accuracy in measuring a distance may be greater than the accuracy obtained by a direct measurement of the same distance by any conventional method used in measuring the diameter of the caustic on the screen.

Surface topography by caustics.

The optical method of caustics, initially developed for recording abrupt plate slopes created by singularities in elastic stress fields, was extended to incorporate the study of the general case of any type of surface. A universal technique, based on the general theory of caustics developed in this paper, was formulated to study the topography of any surface from its corresponding caustics obtained by illuminating the surface by a parallel, convergent, or divergent light beam. The special case of an axisymmetric mirror with elliptical cross section, whose ellipticity varies from zero to infinity, was studied extensively to show the potentialities of the technique developed. It was shown that the caustics obtained are very sensitive to the particular form of the surface considered. From the procedure developed in this paper it was concluded that the method of caustics can be successfully used to record the topography of any surface with large or infinitesimal slopes.