GB448130A - Improvements in or relating to mechanical testing machines for making impact tests on materials - Google Patents

Abstract

448,130. Testing physical qualities of materials. QUINNEY, H., Pontesbright, Hills Road, and LEAN, R. J., Haldon, Sedley Taylor Road, both in Cambridge. Dec. 1, 1934, No. 34578. [Class 106 (ii)] Impact tests are made by tensioning a spring so that its initial energy is greater than that required to fracture the test piece, connecting the latter between the tensioned spring and a fixed part and releasing the spring suddenly, and then measuring the residual energy in the spring by measuring the amplitude of vibration after fracture of the specimen. The flat spring 24 rests at its ends between roller bearings carried in bases secured to the frame. The spring carries at its centre a holder to which one end of the specimen is secured. Also journalled in the frame, and running at right angles to the spring, is a shaft 80 the central part of which is formed as an eccentric 81. This can be rotated to any of five positions determined by passing a bolt through any of five holes in a plate on the end of the shaft into a hole in the frame. A tensioning member comprising two arms 87, 88 is mounted by means of ball bearings on the shaft and connected together at the lower ends by bolts 90. Each carries a roller 91 at the upper end. The lower end of the member 87, 88 is connected by a link 100 to the shaft of rollers 104, running on a guide way 105. To tension the spring 24, the bolt 85 is placed in a selected hole and a stop rod 98 also eccentrically mounted so that its height in the frame may be adjustable is adjusted to a corresponding amount. The wheel 115, Fig. 1, is then turned to move the screw 113, and attached carriage 109 to the right so that the tail 116 of pointed catch 107 engages a cross piece 205, and turns the catch to the position shown in Fig. 3, with the back part engaging the shaft 103 and the tail part clicked over a detent 117. The wheel 115 is then turned to move the screwed shaft to the left turning the tensioning member 87, 88 clockwise and tensioning a spring 92. During this movement, a block 89 on the member 87, 88 engages a spring phmger 125 on a trip member 121 journalled on the eccentric 81 between the arms 87, and turns the member 121 clockwise so that an abutment 122 engages under an abutment 123 on the member 50 the lost motion between the trip and member 87, 88 allowing the spring 24 to be first flexed by the engagement of rollers 91. A stop 126 engages the stop 98 when the trip is correctly engaged. The member 87, 88 is now moved back clear of the spring, leaving the latter flexed and supported on the trip. Grips. The specimen 69 is now inserted in the grips which are alike. A cup 60 receives a ball 63 with a screwed bore into which the end of the specimen is introduced so that it engages a centre on a plug to locate it, whereupon it is secured by surrounding split screwed grips 73. To apply the load a Bowden wire 119 is pulled to release the detent 117 whereupon the spring 92 rotates the tensioning member and the block 89 strikes the stop 127, knocking out the trip from under the spring, whereupon the load on the spring is suddenly transferred to the specimen which fractures. The amplitude of the vibration of the spring after fracture of the specimen is a measure of the energy remaining in the spring. Recording. A stylus 130 on the part 45 co-operates with paper surrounding a drum 131. The drum shaft finds a bearing at one end in a bracket 136 and engages a slot in the end of the shaft of a motor 163. The other end finds a bearing in a lever 137 which is normally locked by a catch, and may be released to free the drum. The spring 24 may be replaced by a spring having a different cross-section and a different constant, the bases 25 being made adjustable if necessary. The specimen may be tested under bending strain by the use of shackles one of which is forked to receive the specimen and has knife edges engaging the ends while the specimen is passed through a large hole in the other shackle which has knife edges engaging the specimen in the centre. In another form, the upper grip is attached to a rod suspended from the upper cross frame and the stress applied measured by the extension of this rod using a suitable extensometer. The Provisional Specification describes also the use of a cantilever flat spring or a spiral spring instead of a flat spring 24. It also describes a stress-strain recorder in which a casing is rotated by a relative movement between the holders and a flat spring supported by the casing along its axis carries a mirror rocked by a part connected with the restrained holder, so as to reflect a beam of light to a photographic plate. Specification 354,623 is referred to.