Improvements in and relating to devices adapted for use in determining, registering or recording stresses in structural and other members or as stremmatographs, extensometers and dilatometers

摘要

443,738. Extensometers. JENSEN, R., P.O. Box 1361, Johannesburg, South Africa. Sept. 8, 1934, No. 25896. [Class 106 (ii)] Comprises a construction in which the movable member of the two members engaging the object under stress causes tilting of a concave mirror to reflect a beam of light which has travelled lengthwise of a casing back to a fixed mirror at the same end as the source of light, the beam being again reflected through the chamber to a light sensitive surface. A chamber 1 in which a light sensitive surface may be supported has a lamp 2 mounted in a tube 3 with an extension 4 through which the light is projected on to a concave mirror 5, the mounting of which is provided with pivots. The mounting is provided with a recess in which engages one pointed end of a rod 12, the other pointed end of which engages a recess in a rod 13. The chamber 1 is secured on the member to be tested by a screw clamp 26 which is provided with a point 27 to engage a centre punch mark, and a screw 28 to receive the clamp. The rod 13 is provided with a detachable point 25 to engage the other centre punch mark in the member under test. Between a shoulder 17 on the rod 13 and a sliding cover 19 is located a spring 18. The end 23 of the rod 13 passes freely through a hole in the cover, a pin 24 securing the rod when the device is not in use. A spring surrounding the pointed rod and fastened at the ends to the mounting of the mirror 5 and to the rod 13 respectively keeps the rod 12 in engagement. Expansion of the member to which the device is connected will cause displacement of the mirror 5 and hence displacement of the beam reflected from the mirror 29 which beam passes through a slot 30 in a diaphragm 31 on to a photographic film extending through the channel 32 from a spool in a chamber 33 to a take-up spool in a, chamber 34. The spools are arranged in a film box, the top of which is secured by a screw and nut 36, 37. The spindle of one bobbin upon which a spool is mounted may be turned through toothed gear from outside. A sighting mirror carrier on a rod 44 may be moved to intercept the beam from the mirror 29 and viewed through an opening 41 in order to observe the position of the image. A second source of illumination may be arranged in a tube 46 to form an under or base line on the sensitive surface. This source may be a device to give an electric spark at predetermined intervals. The device is small, the overall length being rather less than three inches.