GB434509A - Improvements in extensometers and strain gauges - Google Patents

Abstract

434,509. Extensometers. DAVEY, N., Building Research Station, Bucknall's Lane, Garston, Hertfordshire. June 13, 1934, Nos. 17455/34 and 644/35. [Class 106 (ii)] In instruments of the kind in which a wire is stretched between two knife edges mounted on a body with provision for relative movement, and means are provided for vibrating the wire, such means are so arranged that the tension in the wire is not transmitted to the knife edges or gauge points. The instrument comprises a bifurcated member 1 between the sides of which fits a member 2, the knife edges 3, 4 being arranged one on each member. The wire 5 is connected at one end to the front end of the member 2, the other end of the wire being connected to an adjusting screw 7, 8 passing through a cross-piece 6 of the member 1. The members 1, 2 are provided with registering notches 9, 10 at top and bottom. In these, leaf springs 11, 12 are placed and locked by wedge-shaped keys 13, 14 secured by screws 15. The wire is vibrated by electromagnets carried by the member 1. In another form the leaf springs are arranged within the length of the wire providing a shorter instrument. In still another form, the springs are arranged outside the length of gauge wire and are connected directly to the members 1, 2. A calibrating device, Fig. 10, has two anvils 30, 31 between which the standard wire 46 is clamped. The anvil 30 is adjustable by a screw 33, while the anvil 31 is connected to a spring 34 and is connected to the frame 35 by leaf springs 36. The spring 34 is a calibrated spiral spring initially under slight tension. It is connected to a sliding block 37 through which passes a micrometer screw 38, the head 39 of which co-operates with the scale 40. The standard wire is energized by electromagnets 41.