Mechanical testing of the external fixator by holographic interferometry

Tests carried out on the Hoffmann- Vidal external fixator by means of holographic interferometry are reported. These tests refer exclusively to the quality of functioning of the joints connecting transfixing pins and side bars. It is a question of 1) evaluating the behavior of the ball joint subjected to realistic loads, 2) verifying the rigidity of a lightened joint bowl as compared to a heavier one, and 3) comparing the respective resistance of two similar joint models to a rotation of the bar around its axis. The main findings are the remarkable elastic behavior of the ball joint, the effectiveness of the lightened bowl, and the fact that two cousin models may behave quite differently with respect to their resistance to axial slipping rotation of the bar. The interferometric technique is thus expected to have further applications in similar evaluations.