An optical load-extension indicator, together with some diagrams obtained therewith

Abstract

The object of this paper is to describe an instrument by means of which load-extension diagrams of different materials may be obtained with precision, and to show some of the diagrams obtained therewith. The majority of machines for testing the strength of materials are fitted with apparatus for the purpose of obtaining automatically load-extension diagrams of the specimens tested. In a common form of the instrument the diagram is drawn by a pencil or tracing point on a sheet of paper wrapped round a drum. The pencil is constrained so that it is only free to move in a direction parallel to the axis of the drum. The instrument can be attached to the frame of the machine, or to a support external to the frame. The pencil receives a motion proportional to the extension of the specimen through the agency of a fine wire carried over guide pullers to clips fixed at a definite distance apart on the specimen, whilst simultaneously the drum receives an angular displacement proportional to the load applied to the specimen by means of a wire led over guide pullers and fastened to the jockey weight.