The reflected caustics formed from cross-sections of twisted prismatic bars

Summary If a prismatic bar made of a homogeneous isotropic and elastic material is submitted to torsion, cross sections of the bar are twisted and warped. In this paper the shape and size of the caustics and pseudocaustics formed from reflections of light rays on these cross sections were analytically and experimentally studied. This study is concerned with cross sections of circular, elliptic, triagular, and rectangular shapes of different ratios between their characteristic dimensions. It was proved that the experimentally derived caustics are in good agreement with the theoretical curves. Then this method of reflected caustics is a sensitive device for the detection and the accurate measurement of the torsional loading of such elements of structures. With 15 Figures