Apparatus for measuring the limit of strain of materials subjected to alternating stress

摘要

600,501. Testing physical qualities. COR, P. April 18, 1940, No. 7036. [A Specification was laid open to inspection under Sect 91 of the Acts, Oct. 21, 1941.] [Class 106 (ii)] Apparatus for the testing of materials under alternating stress comprises a fixed vice for holding the test-piece, a movable vice for clamping the test-piece at an adjustable position, means for adjusting the clamping pressure, oscillatory exciting means operative on the unsupported part of the test-piece, and means for giving an indication of increase of amplitude of the oscillation of the test-piece. The specimen strip 7, Fig. 2, is gripped at one end by a vice 2 fixed to the main frame 1. A second vice 3 frictionally engages the strip 7 and is movable along the latter guided by fixed rods 4, so that the length of the specimen extending to the left beyond the vice 3 is varied. The free end of the specimen is subjected to the action of an electromagnet 8 adjustably mounted on the frame and supplied with alternating current so as to vibrate it in the direction indicated in dotted lines in the frequency of the alternating current or some multiple thereof. In use, the magnet is connected up and the specimen vibrated, the vice 3 being moved to a position in which the amplitude is a maximum, this point indicating resonance. This frequency may be found by means of a stroboscope. The amplitude of the vibration may be measured by a contact device 18, Fig. 3, in circuit with a lamp 25 and which is adjustable on the machine bed relatively to a scale 21 by screws so that it is moved up towards' the end of the vibrating strip until the latter is touched whereupon contact is broken and the lamp goes out.