GB205972A - A new or improved proportionality indicator for use in testing and indicating tensile strains - Google Patents

Abstract

205,972. Hummerston, J. Oct. 2, 1922. Testing physical qualities of materials. -A testing-apparatus is arranged to indicate when the limit of elasticity has been reached in a tensile test piece by one reading only. The test piece, Fig. 1, has two portions A, B, of different cross-section, and the apparatus indicates when the relation between the rates of strain in the two portions alters as it does when the weaker portion B has reached its limit of elasticity. Figs. 4 and 5 show one form of apparatus. The frame 1 is attached to . the test piece by a single setscrew 4, and carries two levers 15, 22, the ends -of which are forked and fitted with pegs or discs 19, 23 adapted to engage the shoulders F, H at the upper and lower ends of the weaker portion B of the test piece. An adjustable pivot 12, 14 is provided on the part 2 of the frame 1 for the upper lever 15, and a .pivot 20 is arranged for the lower lever 22. On the lever 22 is pivoted at 2;') a lever 24 which is connected with the upper lever 15 by a spring 29 and a pointed rod 26: The end of the lever 24 engages the actuating plunger 30 of a micrometer indicator or dial gauge 31. When the test piece is subjected to stress, the forked ends of the levers 15, 22 follow the elongation, but only a differential movement is communicated by the lever 24 to the indicator plunger 30. The levers are so proportioned that no movement, or only a slight movement, is shown on the indicator 31. until the elastic limit is reached in the portion B. At this stage the strain in the portion increases rapidly compared with that in the portion A, and the deferential lever 24 is displaced to produce a large movement on the indicator 31, thus showing that the elastic limit has been reached in the weaker portion of the test piece. The arrangement of the lever 24 may be varied. The part 2 of the frame 1 bears against the test piece at 7, and it also carries positioning jugs 8. To hold the levers rigid when the apparatus is not in use, or when being attached to a test piece, a cam 36 is provided, adapted. when rotated by the lever 38, to engage and lock the levers 15, 22. A pin 9 supports the apparatus when laid on its side out of use. Fig. 11 shows a modification in which the differential lever 24 is dispensed with, the indicator 31 being mounted on the upper lever 15. The plunger 30 of the indicator 31 is actuated by the lower lever 22 through a pin 43, and the pivots 12, 20, 27 are so positioned that no substantial movement is shown on the indicator until the elastic limit is reached in the portion B. A set screw 44 enables the indicator pointer to be adjusted. The lever 51 for locking the levers 15, 22 when the apparatus is not in use, has a cam 58 and a roller 56. Fig. 15 shows a modified arrangement suitable for use when it is desired to keep the apparatus clear of the shackles of the stress-applying machine. The frame 2 of the apparatus is secured to the test piece by a set screw at the junction of the portions A, B, and the forked ends of the upper and lower levers 15, 22 engage'the test piece at the shoulders F, H. The upper lever is adjustably pivoted at 12 and is connected to the lower lever by a pivot rod 26 which has a sliding bearing 60 that permits of rocking in the frame 2. The indicator 31 is mounted on a bracket 49 on the frame 2 and its plunger 30 contacts with the lower lever 22. Springs 63, 64 draw the levers together, and a locking ]ever 51 having a cam 58 and a roller 56 is provided. If the shoulders on the test piece have a gradual slope, the levers may be arranged to contact with it by centre points instead of by the pegs and discs. 19, 23. The framework is preferably formed of aluminium alloy. When applied to long test pieces, a connecting rod may be arranged between. the locking lever 51 and one of the levers to be locked. The levers may be adjusted so that theindicator pointer moves slightly in one direction before the. elastic limit is reached, and moves in the :other .direction when the limit has been' reached in the weaker position.