GB706627A - Improvements in and relating to fatigue testing machines - Google Patents

Abstract

706,627. Fatigue testing of materials. NATIONAL RESEARCH DEVELOPMENT CORPORATION. April 4, 1952 [April 4, 1951], No. 7855/51. Class 106 (2) A fatigue testing machine for simultaneously testing a plurality of specimens comprises specimen loading heads disposed in a circle about the principal axis of the machine, each having a loading spring system which is cyclically deflected by a swash-plate universally pivoted on, but not rotatable relatively to that axis and rocked by a rolling member rotated about the principal axis. A base chamber 10 houses a vertical shaft 14 driven through a flexible coupling 15 by an electric motor 16. Secured to the upper end of the shaft 14 is a disc 19 carrying two rollers 21, 22 at its rim on angularly spaced axes 23, 24 extending radially to the shaft 14. Opposite the rollers 21, 22 the disc 19 carries a balance weight 25. The base-chamber 10 has a cover-plate 26 incorporating a sleeve 27 coaxial with the shaft 14. A stem 28 is slidable but not rotatable in a bushing 29 in the sleeve 27, and to the lower end of the stem 28 is universally jointed a swash-plate 32 contacting the rollers 21, 22. Spring spiders 33, 34 are secured to the top and bottom of the sleeve 27 and secured to the outer ends of the arms thereof are loading rods 35, the spiders allowing the rods 35 to have axial movement only. The rods 35 pass through the cover-plate 26 and the swash-plate 32. Near their lower ends are collars 42 (retained, for instance, by nuts 43) and between these collars and the swash-plate 32 loading springs 44 are compressed. The extreme lower ends of the rods 35 may move in guide holes 45. At their upper ends the rods 35 carry chucks 47 for the lower ends of the test specimens 48. Chucks 52 for the upper ends of the test specimens are carried by a chuck-plate 53 rigidly secured to the bushing 29. A nut 56 secures to the bushing 29 a long upwardly extending hollow-cantilever 58 to the upper end of which a second hollow-cantilever 61 is secured extending downwardly outside the first cantilever and carrying at its lower end a substantial weight in the form of a disc 64. The stiffness of the cantilevers and the mass of the weight are calculated to constitute a vibrating system which balances the rocking of the swashplate at the running frequency. In operation rotation of the rollers 21, 22 causes the swashplate 32 to tilt in such a manner that each spring 44 is compressed in turn, the forces set up in the springs being conveyed to their associated test specimens 48 by the rods 35. The magnitude of these forces may be regulated as a whole for the test specimens 48 by adjusting the vertical setting of the swash plate 32 through screw and nut means 65, 28 or individually by adjusting the nuts 43 or by changing the springs 44. When a specimen fractures, each succeeding compressive action on its associated spring 44 causes the corresponding spider arm 33 to move downwards and contact a stop 49 thus limiting respective specimens break. Each stop 49 may the movement of the loading heads when the be an electrical contact associated with an individual counter and be adapted to stop the counter when the specimen 48 fails. The machine is run until all the counters have stopped, such a state indicating that all the specimens have fractured. A second contact may be provided at each head whereby a signal is given or the machine is stopped when the last specimen breaks. The number of loading rods depends on the size of the specimens. If small screws are to be tested, there may be as many as twentyfour and the speed may be as high as 3000 r.p.m. Every head of the machine need not be used and the specimens need not be evenly distributed, as the unused loading heads still react directly on the frame of the machine through the stops 49. Changes may be made to load the test specimens in compression, bending, or torsion.