Patent GB-1351735-A (GB)
Title: Shock attenuators
IPC: F16F7/12
Filed: 1970-04-13
Abstract: 1351735 Energy-absorbing shock attenuators YARROW & CO Ltd 19 April 1971 [13 April 1970] 17439/70 Heading F2E A shock attenuator comprises a solid rod 1 partially inserted into a tube 2 and in operation when the rod 1 is moved in one direction relative to the tube 2, successive annular portions of the tube 2 along its length are deformed in turn by the rod 1 and the material of each such portion is stretched beyond its elastic limit but not to its ultimate limit, at which buckling or rupture occurs, so that a substantially constant retarding force between the members 1, 2 is attained during the relative movement, one of the members 1, 2 having a surface of low frictional resistance normal to the direction of said relative movement so that the forces transmitted by the attenuator are in the direction of relative movement even if the surface is subjected to an oblique blow. In the embodiment of Fig. 1, the tube 2 is secured to a base 3 and the load of the equipment to be supported acts through the rod 1 which has a hemi-spherical end portion. When the rod 1 is inserted into the tube 2 the force transmitted by the mounting gradually increases until it reaches a constant value and remains substantially constant until the rod 1 reaches the base 3. This constant value is attained when the rod 1 has been inserted into the tube 2 by a distance approximately equal to the internal diameter of the tube 2, and so in order that the mounting will transmit a substantially constant force the rod 1 is initially inserted into the tube 2 by this distance, whereupon the mounting is ready for use. In operation if either the rod 1 or the base 3 receives shock of sufficient magnitude the rod 1 is forced further into the tube 2 with resultant deformation thereof. In the embodiment of Fig. 4, a plurality of rods 4 and tubes 5, both of mild steel are positioned between a support 6 and a base-plate 8. The portion 9 of each rod 4 that deforms the respective tube 5 is frusto-conical and below the portion 9 there is an extension 10 which tapers from a diameter substantially equal to the diameter of the tube 5 to a diameter slightly less. A rod 12 screwed into the base-plate 8 passes through a nylon plug 13 into an axial bore 11 in the rod 12 and acts to maintain each rod 4 in position in the respective tube 5. In the embodiment of Fig. 5 is shown a double acting attentuator which will operate whether shaft 20 moves upward or downward relative to the tube 21. The shaft 20 has a portion 22 of approximately the internal diameter of the tube 21, a portion 23 of larger diameter and an optional portion 24 of tapered configuration. The tube 21 is formed of two parts welded together with a backing ring 25. In a further attenuator (not shown) three tubes and three rods are arranged in respective pairs as in Fig. 1 and the tubes are swaged to a base-plate and the rods are screwed to a top-plate. The upper end of the attenuator is covered with low friction material so that the rods move axially with respect to the tubes even if the shock deflection is oblique to the upper surface. Thin metal straps bent slightly outwardly at a position near their centres are secured between the upper and lower ends of the attenuator and act to maintain the rods and tubes in position until a shock is received whereupon the straps buckle. As a further alternative, frictional means, such as a rod secured to one of the members and being an interference fit with a bore in the other member, act to prevent relative movement between the members when the shock force is below a certain value.