Measuring Angle of Twist in a Torsion Experiment

Measuring Angle of Twist in a Torsion Experiment AbstractAt our university, every mechanical engineering student must take asophomore level one-credit hour course titled “Mechanics of Materials Lab”.One of the five experiments in the course focuses on the study of elastic andplastic deformation behavior of a circular cross-section metallic rod intorsion. The shear strain on the surface of the rod is determined bymeasuring the angle of twist over a gage length. Until recently, the angle oftwist was measured using a troptometer that was designed and fabricatedin-house more than thirty years ago. There have been several difficulties inusing this troptometer: (i) mounting it on the specimen; (ii) easily readingthe angle of twist; and (iii) taking it off after the plastic deformation begins.Last year, we designed and fabricated several sets of specimen clamps towhich we can attach a pair of commercially available digital inclinometers.This new way of measuring the angle of twist eliminates all the threedifficulties mentioned above.This paper will describe the new experimental setup, include engineeringdrawing of specimen clamp, present typical experimental results, andsummarize its benefits over the old troptometer. We believe that this paperwill of significant interest to all instructors who teach a lab course inmechanical properties of materials.