GB1321345A - Machines for the creation of mechanical shocks on a sample or specimen undergoing tests - Google Patents

Abstract

1321345 Shock testing COMMISSARIAT A L'ENERGIE ATOMIQUE 25 Nov 1971 [9 Dec 1970] 54712/71 Heading G1S A pneumatic machine for generating mechanical shocks comprises a movable cylinder 8 having a top closure member 9 constituting a test sample carrying platform and a bottom closure member 10 through which the piston rod 21 of a piston 19 passes, a fixed member 2 having bearings 15, 16 guiding the cylinder 8 for axial movement and having an impact member 25 for the bottom 24 of piston 21 and a sleeve 29 in the fixed member which is engaged by a shoulder 32 on the cylinder. The chambers 34 and 35 respectively below and above shoulder 32 external of the cylinder 8 communicate through channels 36, 38 and valves 37, 39 with a source of fluid pressure. Chamber 34 communicates through a narrow channel 40 with the internal chamber 27 above piston 19 and this communicates through orifices 28 in the piston with the chamber 26 below the piston. In use, a first pressure is applied to chamber 35 and a second higher pressure applied to chamber 36 and thence via channel 40 to chambers 26 and 27, thus causing cylinder 8 to move to its uppermost position in the fixed member 1, and the piston to move to its lowermost position in the cylinder. Valve 41 is then operated to quickly release the pressure in chamber 34, the pressure in chamber 27 being unaffected because of the fineness of channel 40. The cylinder 8 then moves downwardly under the action of the pressure in chamber 35 and the piston rod strikes the impact member 25. Thereafter the piston rises in the cylinder, and the air flows from chamber 27 to chamber 26 through orifices 28 so that the rise in pressure in chamber 26 is controlled by orifices 28. The net decelerating force on the cylinder 8 at any instant after the impact of piston rod 21 is the resultant of the fluid pressure forces on the top and bottom closure members and is thus controlled by the orifices and the initial pressures. The deceleration profile of the shock may be saw-tooth, rectangular, trapezoidal or semi-sinusoidal, the latter being obtained by interposing a spring between the piston rod and the fixed body. The orifices may be adjustable or may be partially or totally closed off.