Patent GB-216266-A (GB)
Title: A new or improved combined strain stress proportionality indicator and extensometer
IPC: G01N3/06
Filed: 1923-03-24
Abstract: 216,266. Hummerston, J. March 24, 1923. Testing physical qualities of materials.-In a testing machine for detecting the stage at which alterations occur in the relation between stress and strain in a test piece, an extensometer is arranged to actuate the plunger of an indicator dial, and the casing of the dial is simultaneously moved by a device geared to the stress-applying mechanism in such a. way that no indication is given on the dial until the elastic limit is reached. The modulus of elasticity may be determined by a single reading. A microscope may be used instead of a dial, and the method may be applied to tension, compression, bending, and torsion tests. Figs. 1, 2, and 3 show the application to a test piece 1 under tension tests. Extensometer levers 13, 19 are connected to the test piece by centrepoints 10, 20, and are held in position by springs 24, 25 and a pivot rod 21 bearing on the levers at 22, 23. The upper lever 13 is connected to the frame 6 by a universal joint at 14, and is fitted with a weight 41 for the purpose of balancing this part of the mechanism. The joint 14 is supported by a flanged collar 18 which has rotary freedom in the frame. The collar may be supported by a bracket 86<1>. An adjustable bearing 26 on the lower lever 19 takes the end of a rod 27, which passes through an opening in the collar 18 and engages the spindle 28 of the dial indicator 29. A spring-pressed bolt 33 is provided for supporting the lower end of the lever 19 when the extensometer is being set or is not in use. The extensometer may be adapted for test pieces of different length by moving the brackets on the frame 6 and altering the rods 21, 27 and springs 24, 25. The casing of the indicator 29 is mounted on a lever 56 pivoted to the frame at 57, and having a ball 61 at the other end engaging an adjustable inclined plane 45. This plane is moved horizontally during the progress of a test in order to raise the gauge casing as the stress is applied to the test piece. It is pivoted at 53 to a sliding frame 43, and its angle of inclination is adjusted by a micrometer 46 until, when a load well below the elastic limit is applied, no indication is given on the gauge. The application of further load will then produce an indication when the elastic limit is reached. Knowing the dimensions of the levers, &c., the modulus of elasticity may be determined from the reading of the micrometer 46. The sliding frame 43 is driven from the stressapplying mechanism of the testing machine by a screw and nut 76, 77, bevel gears 74. 75, shaft 70, gear 69, and gear 68 meshing with a gear 66 on the boss of the control handle 67. The gear 69 may be replaced by a gear of different size, the gear 68 being mounted on a movable stud 83. The shaft 70 is divided into two parts connected by a clutch 71, so that the slide 43 may be set initially by turning a handle on a cross shaft 79. In the starting position the ball 61 is vertically above the pivots 53 of the inclined plane 45, and is in line with the pivots 57 and the bearing ball 49 of the micrometer 46. This position is indicated by marks 63, 64 on the slide and frame respectively. The driving gear of the sliding frame 43 may be modified to suit the type of machine to which the device is applied, and the drive may be imparted through the shaft 79 instead of the shaft 70. The frame 6 supporting the apparatus is mounted in trunnion bearings 7 concentric with the shaft 70, so that it may be moved away from the test piece in the direction of arrow 11, Fig. 1, without disturbing the gearing. Multiplying levers may be arranged between the gauge casing 29 and the lever 56. Fig. 10 shows a modification, in which a microscope is used instead of a dial gauge. The extensometer levers are inverted, the lower lever 13 being supported by an adjustable pivot 89. A pivoted rod 21 separates the levers, which are connected by a pair of springs 25. To the end of the upper lever 19 is adjustably secured a thin plate 95 having an opening with a cross-wire for observation by the microscope 87. The microscope, which is carried by the lever 56 actuated by the inclined plane 45, is mounted at a point beyond the pivots 53, so that its movement due to the action of the inclined plane is in the same direction as that of the end of the lever 19. In use, the carriage of the inclined plane is set to zero, as described above, and the extensometer levers are adjusted by the milled head 103 carrying the pivot 89 until the cross-wire on the plate 95 is observed in the microscope. A small load is then applied to the test piece, and the angle of the inclined plane is adjusted until the cross-wire is again observed at the same place in the microscope. During the application of further stress, the cross-wire will appear stationary until the elastic limit is reached. A spring-pressed bolt 33 supports the levers when the extensometer is being set, and an electric lamp 102 is arranged to illuminate an inclined mirror 101 set behind the cross-wire. The apparatus may be .adapted for compression tests by arranging the inclined plane 45 to transmit movement in an opposite direction to the gauge or microscope. Figs. 16 and 17 show an adaptation of the device for bending tests. The test piece 1 is supported horizontally, and beneath it are arrranged pegs 114, 116, the load being applied centrally. The centre peg 116 is mounted on the extensometer lever 19, and the side pegs 114 are carried by a. cross-member 112 on the lever 13 which is attached, to the frame 6 by a universal joint as before. The levers are pivoted to one another at 115, and the lever 19 actuates the dial indicator through an adjustable socket 26 and a rod 27. The brackets 113 of the cross-member 112 are adjustable to accommodate varying lengths of test piece. Figs. 19 and 20 show the arrangement for making torsion tests. Levers 120, 121 secured to opposite ends of the test piece 1 by centre points 122, are connected to the extensometer levers 13, 19 by a link 118 and a rod 119 respectively. In any of the modifications the lever 56 may be dispensed with, the gauge or microscope being arranged to work in a slide and to contact directly with the inclined plane. By disconnecting the gear driving the carriage of the inclined plane, the apparatus may be used as an ordinary extensometer, in which case the strain is indicated by the dial gauge, or by a reading in the microscope, or by the adjustment which must be given to the milled head 103, Fig. 10, to keep the cross-wire in the centre of the field of the microscope.