ROTATION MOULDING OF A HOLLOW FEMUR FOR 3-D PHOTOELASTIC STRESS ANALYSIS

Abstract

Rotation moulding techniques were evaluated in the fabrication of whole, hollow femur models for the expressed purpose of three-dimensional photoelastic stress analysis. The moulding process required the characterisation and assessment of three essential parameters; the speed ratio, resin viscosity-time profile and rotation mode. Flow visualisation experiments, which were undertaken to assess the optimum speed ratio, yielded a value of 5.6. The finalised moulding sequence was then generated based on the speed ratio, taking into account the variations in the resin viscosity over time and the incorporation of a bidirectional rotation mode about the minor axis. The loads applied onto the models simulated single-legged stance and took into consideration the appropriate anatomical and biomechanical relationships of the femur. In addition, a stiffness ratio was developed and incorporated into the formulation of the applied loads to account for the disparity between the moduli of bone and the resin used. The photoelastic experiments displayed the development and progression of the stress fringes. Stress concentrations were observed at the superior head-neck junction, greater trochanters as well as the medial and lateral surfaces of the femoral shaft. Results derived from the finite element studies of a hollow femur were consistent with those from the photoelastic experiments. Likewise, the data obtained from other related research were comparable as well. The physiologic resemblance of the models permitted an investigation into the effects of prosthetic implants on stress profiles. A Swiss AO Dynamic Hip Screw (OHS) implant has been demonstrated to significantly alter the stresses manifested at the proximal regions.