GB190828412A - Measuring and Recording Small Strains or Movements, applicable to Extensometers and the like. - Google Patents

Abstract

28,412. Kirkaldy, W. G. Dec. 30. Testing strength of materials; indicating small movements.-Relates to apparatus for measuring the alteration in length of bodies when subjected to forces, especially to means for indicating the strain at a distance. A pair of clamps attached to a distance bar 1, Fig. 1, are attached to the specimen by clamping-screws 3 ; one of the clamps has an upright frame from which hang links 6 to carry a lever 5 for measuring the extension. The lever 5 bears at one end with a knife-edge against a distance-piece 15 and at an intermediate point against a fulcrum 8 adjustable by a screw 10, and at the upper end bears against a bent lever 12, the other arm of which comprises a chamber 13 of a fluid-transmitting system connected by a tube 14 to the indicating-apparatus. This consists of a glass tube 23, Fig. 5, open to the tube 14, to a chamber 25 with a regulating-screw, and to a collapsible chamber which carries a knife-edge bearing against a spring-controlled lever 21. Alteration of length of the specimen thus disturbs the level of liquid in the tube 23 and this must be restored to position, as seen in the reading microscope 24, by turning the micrometer screw 22, on the head of which the reading of the strain is made. The apparatus is calibrated by taking a reading for a standard gaugepiece 17, Fig. 1, the necessary adjustment being made by moving the fulcrum 8, which can be clamped, and the gearing of the measuriug-screw 22. The chamber 25 enables the level in the tube 23 to be adjusted. A simpler form of indicator may be employed, such as a pointer attached to a lever operated by the collapsible chamber or a graduated tube, instead of the tube 23. For cylindrical specimens, four clamping-screws 3 are arranged, each in a pair of rings 18 supported by distancepieces 1 and having distance-pieces 20 between the transmission apparatus 13 and the other clamp. Four chambers 13 are symmetrically arranged around the clamp and are connected by one pipe so as to communicate the mean extension to the indicating-apparatus. Where the alteration of the specimen is comparatively large, a lazy-tongs may be employed instead of the distance-piece 15, Fig. 1, so as to reduce the reading to convenient limits..