GB596888A - Improvements in and relating to testing machines - Google Patents

Abstract

596,888. Testing physical qualities of material. HAMMOND, A. B. Aug. 3, 1945, No. 20001.' [Class 106 (ii)] In a tensile testing machine having a load indicator and a drive for the straining-device, an electrical condenser 10 associated with the straining-device 7, 9 is so arranged that on any variation in the capacity thereof due to alteration in the rate of straining or loading the load is automatically increased or decreased as required to restore the capacity of the condenser to its former value whereby the rate of loading of the test-piece is maintained constant. A motor 5 drives gearing 6 to rotate screws 1, 2 with which a bar 7 has screwthreaded engagement, and the test-piece 8 is secured at its ends to the bar 7 and a spring 9. An indicator connected to the spring 9 registers the load applied. One plate of the condenser 10 is connected to the spring 9, and the other plate is connected so as to be moved by a motor 11, the arrangement being such that uniform movement of the spring 9 due to uniform stretching of the test-piece 8 will not vary the distance between the condenser plates. The condenser may be connected to the motor 5 through a valve relay circuit employing gasfilled valves, a bridge network, photo-electric cells and a mirror galvanometer. If, due to a sudden extension of the test-piece, such as when the elastic limit has been reached, or a stiffening of the material, the load on the testpiece decreases or increases the distance between the condenser plates will vary, and the change in capacity will be communicated to the valve relay which will correct the speed of the motor 5 and restore the plates of the condenser to normal.