Fatigue indicator for repeatedly stressed member - has circular central shearing sliver between to rigid members propagating cracks from ends of slit

摘要

The tell-tale consists of two thick elements (1a,1b) joined by a thin circular sliver which is provided with a slit and pref. a central hole. The elements are secured to or incorporated in the stressed member so that they undergo relative displacement in a plane parallel to that of the sliver. When the member is strained the sliver is subjected to shear in its own plane, and the slit extends in the direction of relative displacement so that two cracks appear at its ends and are propagated towards each other or towards the opposite edge of the sliver, whose central area thus becomes detached. The sliver may have a thickness of 1mm and its central hole a radius of 3.5mm; the slit may be 1.6mm thick and extend to a point 1.5mm from the central hole. The device provides immediate warning of fatigue.