Volume 3, Issue 4 (July 1975)
An Extensometer for Circumferential Strains
An instrument is described for measuring circumferential strains in plastic specimens of circular cross section. It consists of four direct-current differential transformers (DCDTs) suitably mounted on an invar ring. The DCDTs probe the position of the surface of the specimen at opposite ends of two mutually perpendicular diameters. Examples of performance are given for creep of a thin-walled tube of polyurethane.