ENERGY ABSORBER

Abstract: An energy absorber is described which in its simplest embodiment is a pair of shear dampers mounted back to back on a common axis. Each shear damper has a central core of damping material, such as lead, confined by a laminated structure of rigid plates, preferably separated by resilient material. The cores and surrounding laminates are compressed between a pair of distal end plates and an end plate common to both dampers. The common end plate may be attached to one structural member and the distal end plates to another structural member to dampen relative motion between them. The absorber can dampen many kinds of motions caused by forces ranging from wind to earthquakes to vibrations in general such as vibrations in heavy machinery, rolling stock or penstocks.

Description: ENERGY ABSORBER TECHNICAL FIELD This invention relates to energy absorbers. More particularly this invention relates to shear damper able to be used in a wide range of applications. BACKGROUND ART For the purposes of this specification a shear damper means a cyclic shear energy absorb ofthe type described in WO94/13974; US 4, 1 17,637, US 4,499,694; US 4,593,502; an US 4,713,917, the specifications of which are hereby incorporated by reference. She dampers have been used primarily in seismic isolation of structures. Seismic isolatio involves increasing the natural period of a structure to outside the period ofthe excitin motion. This reduces the forces transmitted into a building through decoupling. Th addition of a damping mechanism to dissipate the associated energy, thereby controllin the displacements and further reducing the accelerations transmitted to the structur establishes a seismic protection system. This method of protection is suitable f structures with natural periods of less than 1.5 seconds. More of the principles of seismi isolation are described in Skinner et al, (see references at the end ofthe description). Energy absorbers of this type to date have been designed to be weight bearing and ar known in the art as lead rubber bearings. That is, the structure or parts of a structure t be damped from induced motion rest on top ofthe bearing and the bearings themselves re either on the ground or on another part of the structure. These devices are intended t absorb earthquakes or wind loads, but are resistant to lesser forces. It has been known for some time that energy absorbers can be used as dampers to contr the elastic and plastic deformation of tall structures with natural periods greater than 1. seconds (Scawthom et al, 1995). Dampers can be inteiposed laterally between structure or parts of structures to damp motion. The vibrations which may be damped may be ver small. It would be useful to be able to take advantage of shear dampers for uses other than a bearings in damping motion induced on structures. For example, shear dampers would b useful in applications such as damping vibrations in machinery, in penstocks of hydr electric power stations or the like, in rolling stock such as heavy trucks or railway freig cars, carriages or engines or any similar vibrations. It is an object of this invention to go some way towards achieving this desideratum or at least to offer the public a useful choice. DISCLOSURE OF INVENTION The invention may be said broadly to consist in an energy absorber comprising: a pair of shear dampers mounted back to back along a common axis, each said damper comprising a pair of rigid end plates, a laminated structure of rigid plates able to slide past one another and a core of plastically deformable material in a bore through said rigid plates from the inner face of one end of said end plate to the inner face of the other said end plate, means to urge said end plates toward one another to maintain each said core at a hydrostatic pressure at least approaching the shear yield stress of said plastically deformable material, the two end plates at the distal ends of said pair of dampers being commonly attachable to a first portion of a structure, the two dampers having a common end plate at their adjacent ends, said common end plate being attachable to a second portion of a structure, the average cross-sectional area ofthe core in each said damper being from about 5% to about 95% of the average total cross-sectional area of each said damper, the arrangement and construction being such that in use said energy absorber, when attached to a first and second structure or portions of a structure, dampens relative motion therebetween. Preferably each said core is lead. Alternatively each said core is of high purity aluminium, tin, zinc, indium or iron, or alloys of lead, aluminium, tin, zinc, indium or iron or any superplastic alloy or other material having a low rate of work hardening. In still a further alternative each said core is densely packed granular material such as is described in US 4,713,917. Preferably said granular material is steel, glass beads, alumina, silicon carbide or any other similar hard granular material. Alternatively said granular material is granular iron, lead, aluminium or other similar less hard material. Preferably said end plates and said rigid plates are of steel. Alternatively said end plates and said rigid plates are of aluminium or aluminium allo Alternatively said end plates and said rigid plates are of ceramic material or other suitabl material. Preferably said rigid plates are separated by resilient material. Preferably said resilient material is rubber. Preferably said means urging said end plates toward one another comprises a pair clamping members which clamp said distal end plates towards one another. Preferably said pair of end plates at said distal ends are attachable to said first structure b means of a connecting member connected to said clamping members. Preferably said common end plate to said bearings is attachable by an attachment memb to a second portion of a structure. Preferably said attachment member is a lateral extension of said common end plate. Preferably the average cross-sectional area of each said core is about 50-95% of th average total cross-sectional area ofthe bearing. Preferably said cross-sectional area of each said core is about 50% of the average tot cross-sectional area of said bearing. Preferably each said core has a regular geometric cross-section. Preferably each said core is cylindrical. Alternatively each said core has a square cross-section. Alternatively each said core is of variable geometric cross-section. Preferably each said core has an hour glass shape when viewed in side elevation. Preferably each said damper has a regular geometric cross-section. In one alternative said regular cross-section is circular. In another alternative said regular cross-section is square. In another alternative said regular cross-section is rectangular. In another alternative said regular cross-section is elliptical. Preferably there is a bond between the inner face of each of said distal end plates and the inner face of said common end plate with the ends of the core of each said shear damper. Preferably the bond is a mechanical bond. Preferably said mechanical bond is formed by grooving the inner faces of said end plates. Preferably said grooving is in a circular or spiral pattern. Alternatively said mechanical bond is formed by soldering. Alternatively said bond is formed by adhesive. Alternatively said bond is formed by vulcanised rubber. Alternatively said grooving is in the form of stiaight grooves at right angles to the direction of movement of forces to be damped by said absorber. Alternatively said grooving is in the form of straight grooves at any angle to the direction of movement of forces to be damped by said absorbers. Alternatively said grooving has been effected by peening or sand blasting. Alternatively said grooving is in the foπn depicted in any one of Figures 3a-d. Preferably when said core is cylindrical, said alternating layers of steel and resilient material form an annulus therearound. Preferably when said core is lead, said hydrostatic pressure is from about 5MPa to about 80MPa. More preferably when said core is lead said hydrostatic pressure is equal from abo lOMPa to about 30MPa. Most preferably when said core is lead said hydrostatic pressure is about 50MPa. Preferably said cores within said energy absorber contain elements embedded therein material stiffer than the core material to thereby reduce migration of core material durin damping. Preferably said elements are aligned to provide rigidity in the planes of deformation of sai cores. Preferably when said cores are of lead said elements are of metal, carbon fibre, fibreglas or other material which is stiffer than lead. Preferably said elements are in the form of rods, wire strips, mesh, disks or any simil form. In one alternative embodiment said elements comprise said rigid plates in said laminate structure, said rigid plates extending through said core of plastically deformable materi across substantially the whole cross-section of each said shear damper whereby said cor is discontinuous consisting of alternating layers of core material and rigid plates. In another embodiment the invention may be said broadly to consist in an energy absorb comprising: two pairs of shear dampers, each pair mounted back to back along a common axi each said damper pair comprising a pair of rigid end plates, a laminated structure of rigi plates able to slide past one another and a core of plastically deformable material in a bor through said rigid plates from the inner face of one end of said end plate to the inner fac of the other said end plate, means to urge said end plates of each said pair toward one another to maintain eac said core at a hydrostatic pressure at least approaching the shear yield stiess of sai plastically deformable material, the two end plates at the distal ends of each of said pairs of dampers being joine to one another, the two dampers of each said pair having a common end plate at their adjacent end said common end plate of one said pair being attachable to a first structure and sai common end plate of the second said pair being attachable to a second structure, the average cross-sectional area of the core in each said damper being from about 5% to about 95% ofthe average total cross-sectional area of each said damper, the arrangement and construction being such that in use said energy absorber, when attached to a first and second structure or portions of a structure, dampens relative motion therebetween. The invention may be said broadly to consist in an energy absorber as defined above in combination with two structures or two parts of a structure to dampen motion therebetween. The invention may also be said broadly to consist in an energy absorber substantially as herein described with reference to Figures 1 to 3d and 7 to 17 of the drawings. In another embodiment the invention may be said broadly to consist in a method of damping relative motion between two structures or between two parts of a structure which comprises selecting an energy absorber as defined herein with energy absorbing properties to damp forces anticipated to act on said two structures or two parts of a structure and attaching the respective connecting members of said energy absorber to said two structures or two parts of a structure. In another embodiment the invention may be said broadly to consist in a method of manufacturing an energy absorber ofthe type defined herein which comprises, forming a laminate of one said end plate and said rigid plates and (where present) said resilient material, inserting a plug of damping material into the core of said damper and securing the other said end plate onto said laminate, subjecting said end plates of said damper to a pressure and for a time sufficient to allow said damping material to flow into the interstices in the sides of the bore through said rigid plates and resilient material adjacent said core and into the scoring in the inner faces of the end plates of said damper. Preferably said plug of damping material is lead and said end plates are subjected to a pressure of at least 50MPa. Preferably when said pressure is about 50MPa it is applied for at least 5 minutes. Preferably said end plates are subject to a pressure of at least lOOMPa. This invention may also be said broadly to consist in the parts, elements and featur referred to or indicated in the specification of the application, individually or collectivel and any or all combinations of any two or more of said parts, elements or features, an where specific integers are mentioned herein which have known equivalents in the art t which this invention relates, such known equivalents are deemed to be incorporated herei as if individually set forth. The invention consists in the foregoing and also envisages constructions of which th following gives examples. BRIEF DESCRIPTION OF THE DRAWINGS One prefeπed form of the present invention will now be described with reference to th accompanying drawings in which; Figure 1 is a top plan view of an absorber according to the invention. Figure 2 is the sectional view II-II of Figure 1. Figure 3 is a detailed sectional view showing the scoring on the inner face of an en plate forming a mechanical bond with a lead core. Figures 3a-d are sectional views on a larger scale than Figures 3 of alternativ shapes for forming a mechanical bond between the end plate faces and the lead core. Figure 4 is an hysteretic force-displacement curve for an absorber according to th invention tested at ± lOμm. Figure 5 is an hysteretic force-displacement curve for an absorber according to th invention tested at ±1.1mm. Figure 6 is an hysteretic force-displacement curve for an absorber according to th invention tested at ±6.9mm. Figure 7 is a top plan view of a second embodiment of an energy absorbe according to the invention. Figure 8 is the view VIII - VIII in figure 7. Figure 9 is the view IX - IX shown in figure 10 of the embodiment of the inventio shown in figure 9 position to be attached to a channel girder. Figure 10 is the same view of the second embodiment as is shown in figure 8 wit the attachment member between two girders to which the energy absorber is to b attached. Figure 11 is the sectional view XI - XI shown in figure 12 of two energy absorber ofthe type shown in figures 7-10 joined in parallel to one another. Figure 12 is a top plan view of the embodiment of figure 11. Figures 13a-f show alternative shapes for the cores of the energy absorbers o figures 1-3 and 7-12. Figure 14a is a schematic sectional representation of a core of an energy absorber according to the invention in which reinforcing disks have been embedded to reduce migration of core material. Figure 14b is a cross-sectional view of an energy absorber as shown in Figure 2 modified to have alternating layers of core material and rigid plates. Figure 15 is a perspective representation of another core in which a pair of stiffening wire rings have been incoφorated into a core of an energy absorber according to the invention. Figure 16 is a sectional representation of a pair of rods in a rectangular core to provide stiffening to reduce migration of core material. Figures 17a-g are cross-sectional views of stiffening elements to be embedded in a core. MODES OF CARRYING OUT THE INVENTION As modern structures have evolved so too have the requirements placed on the materials from which they are constructed. In response, new technology has been developed to counter new problems presented by increasingly larger structures. The energy absorber of this invention may be used to damp small and persistent vibrations encountered in the wind response of very tall structures while also reducing the large deflections associated with earthquake motion. This is achieved through the concept of "added damping" or "supplementary damping" which involves a uniform increase of damping of a structure by distributing many small damping devices throughout the structure. In addition absorbers according to this invention may be used to increase the stiffness of a building in which they are installed. Lead Shear Damper The prefeπed embodiment of the energy absorber of this invention is called a lead shear damper. The lead shear damper is a compact device which is sensitive to very small displacements. Significant hysteretic damping can be achieved at displacements as low as ±2μm. It can be used as "added" or "supplementary" damping in flexible structures through the distribution of many small capacity devices throughout the structure. This approach is suitable for structures whose periods fall outside the practical range of seismic isolation. The uniform distribution of damping thus achieved is able to create a highly damped structure. The preferred range of the lead shear damper is from ±2μm to ±10 mm. Larger displacements are available with larger devices but sensitivity decreases as size increases. A 100 mm displacement damper will begin to give appreciable hysteretic damping 20μm. Such a device has a dynamic range of 4 orders of magnitude. The force achievable with a prototype of the energy absorber of this invention range from lkN t 200kN. The lead shear damper of this invention is capable of sustaining thousands o cycles at any amplitude within its design range without deterioration or needin maintenance. The damping of this device is achieved by plastic deformation of the lead core. Thi allows dissipation of plastic energy while maintaining mechanical properties. This i achieved by dynamic and meta-dynamic recrystallization of lead. [See Monti et a (1995)]. The lead shear damper is preferably designed to be included in a flexibl structure at any point of flexure where displacement can be converted to damping, suc as cross bracing in a beam-column, moment resisting frame or in tie down spars on heav pipe-work or in an industrial plant. A shear damper according to the invention has a core of plastically deformable materi surrounded by stiffening plates with a resilient or low friction material inteφosed betwee the stiffening plates. There are a pair of end plates over each end of the core. The cor is preferably of pure lead. However, alloys of lead, aluminium, tin, zinc, iron, indium supeφlastic alloys or other materials having a low rate of work hardening may be use High purity aluminium, tin, zinc, indium or iron may also be employed. It also is possibl to use densely packed granular materials such as sand, steel shot, glass beads, alumin silicon carbide or any other hard granular material as a core. Densely packed granula materials which are not hard including iron, lead, aluminium and other similar substance may also be used. The laminated stπicture sunounding the core preferably consists o steel plates with rubber inteφosed between them. However, the laminated structure ca comprise any construction of plates which can move laterally relative to one anothe during induced motion to apply shear forces to the core. The core may also consist of stack of plates coded with a material of low co-efficient of friction to allow them to slid past one another. DETAILED DESCRIPTION OF THE DRAWINGS Referring to Figure 2 the energy absorber according to a first embodiment of the inventio consists of a pair of lead shear dampers mounted end to end along a common axis. Th upper lead shear damper consists of a distal end plate 10, a lead core 28, a common en plate 18 and a laminate in the form of an annulus sunounding the lead core 28. Th laminate consists of a steel plate 22 in the form of an annulus of a first thickness and a se of steel plates 26 each in the form of an annulus of a lesser thickness separated by layer of rubber 24. The lower lead shear damper is of identical construction. End plates 12 and 10 are held in position by means of fixing screws 32 which pass through bores 29. At opposite ends ofthe construction a pair of circular clamps 14 and 16 are urged together by six clamping bolts 30 which pass through bores 31 in the upper clamping plate 14 and into corresponding threaded bores in clamping plate 16. Preferably bolts 30 are friction bolts but any other means of locking the bolts 30 in place can be used. In order to achieve a mechanical bond between the end plates 10, 12 and 18 and the lead core 28 the inner surfaces of plates 10 and 12 and both surfaces of plate 18 are grooved so that when the clamping plates 14 and 16 are urged together the lead flows into the grooving 11. The grooving 1 1 in Figure 3 is of a spiral pattern on each of the relevant faces of the end plates. The sectional views in Figures 3a to d show other possible grooving patterns which allow suitable mechanical bonding of lead to steel. When the grooving is done in a straight line the main grooving lines are preferably at right angles to the direction of forces to be imported to the damper. The inner faces of plates 10 and 12 and both faces of plate 18 may be peened, sand blasted or plated with a rough surface as form of grooving. In a still further embodiment a layer of rubber may be inteφosed between the relevant steel faces of plates 10, 12 and 18 and the ends lead cores 28 and the rubber vulcanised or glued in place. The lead may also be soldered or otherwise bonded to the steel. Bolts 30 are tightened until there is a hydrostatic pressure in the order of the shear stress yield pressure ofthe core material. In the prefeπed embodiment the core material is lead and the hydrostatic pressure is greater than about 5MPa, more preferably between about lOMPa and 80 MPa. A prefeπed range of pressure is from about lOMPa to about 30Mpa. A most prefeπed pressure is about 50MPa. In tiie manufacture of absorbers according to this invention the two dampers are assembled without the distal end plates 10 and 12 and the lead cores or plugs 28 inserted. The end plates 10 and 12 are secured in place by fixing screws 32. The end plates are then subjected to an external pressure, for example in an hydraulic press, of at least 50MPa for at least 5 minutes so that the lead in cores 28 flows into the interstices between the core edges of plates 24 and resilient material 28 and into the grooving 11 of the inner faces of end plates 10, 12 and 18. At higher pressures a residence time of less than 5 minutes may be sufficient. The compressive pressure applied to the core is preferably of the same order th compressive yield pressure ofthe core. In the case of lead in a lead shear damper this i 50MPa. In the embodiment shown in Figures 1 to 3 the average percentage of the cross-section area ofthe shear damper made up of the lead core is about 50%. This provides an elasti stiffness of about the middle range for this embodiment. The stiffness can be increase by having a greater percentage of the cross-section as lead and the elasticity increased b having a lesser percentage ofthe cross-section as lead. In operation, the ends 15 and 17 of clamping rings 14 and 16 receive a connecting membe (not shown) which is attached by bolts 33. The connecting member connects a structur or one part of a structure to the energy absorber. Common end plate 18 has a flange 2 which may also be joint to a connecting member to another structure or part of a structur by means of bolts 33. The second embodiment of the invention illustrated in figures 7-10 is substantially th same as that of the first embodiment described with reference to figures 1-3. Where th construction is identical reference may be made to the description of figures 1-3. The energy absorber also comprises a pair of shear dampers having distal end plates 1 and a common end plate 18. The cores 28 are compressed together by clamping plates 1 On the left side of each of figures 7-10 attachment to a structural unit is done through bolt as in the embodiment illustrated in figures 1 and 2. Where the construction ofthe secon embodiment differs from that of the first is in the attachment member 34 which is a extension of an integral with common end plate 18. In the embodiment illustrated attache with member 34 has six bores 36 therethrough which may be used to attach it to structural member in use. Attachment member 38 has a pair of slots 34 which allo clamping bolts 30 to pass therethrough when the energy absorber has been assembled. One mode of attaching the attachment member 34 to a structural member is illustrated i figures 9 and 10. A girder 40 is a U-shaped in cross-section. Girder 40 consists of a mai member 42 and side members 41 and 43 extending at right angles to the main member 42 As is illustrated in figure 10 an energy absorber according to the invention may be attache to a pair of girders 40. On the face of each main member 42 between the side member 43 there is provided an attachment plate 45 having six bores 47 positioned to be in registr with the bores 36 through attachment member 34. In one prefeπed embodiment a frictio bolt 44 passes through bores 36 and 47 and is secured by a nut 46. By this means the pai of girders 40 are attached to the attachment member 34 of the energy absorber illustrated in figures 7-10. Other means of attachment such as rivetting or welding may be used. The number of cycles to be damped by the energy absorber will determine which form of attachment is needed. For structures subject to frequent wind loading friction bolts have been shown to provide the optimum connection. Another embodiment ofthe invention in which two pairs of shear dampers are connected in parallel is illustrated in figures 11 and 12. The construction of each pair of shear dampers is identical to that in figures 7-10. In the assembly of figures 11 and 12 each pair of shear dampers shares common clamping members 48, 50 at their distal ends. The other details of construction and means of attachment to structural members such as girders is as illustrated with relation to figures 9 and 10. The difference in construction between the double pair embodiment of figures 11 and 12 and the embodiments of figures 1 and 2 and 7 to 10 is that the clamping plates 48 and 50 are not able to be connected to structures or parts of structures. Instead the attachment members 34 extending from common end plates 18 of each pair of shear dampers are used for this puφose. In operation each pair of shear dampers operates in series with the other pair. This enables the stroke ofthe energy absorber shown figures 11 and 12 to be double that of the absorber shown in figures 7 to 10. Similarly, if one pair of dampers were connected to another pair in parallel the damping force could be doubled. A number of different shapes can be employed for the cores and surrounding laminate. Six alternatives to the cylindrical cores in the embodiments illustrated are shown in figures 13a-13f. In figure 13a, the core 28 is elliptical in cross-section with straight sides. The cores 28 of figures 13b and c are cylindrical in cross-section with stiaight sides. Figure 13d illustrates a core 28 which is two intersecting ellipses in cross-section and straight sides. Figure 13e shows a core 28 which is rectangular in section with a variable cross-sectional area. The minimum cross-sectional area is at the centre and the maximum at the ends giving side 25 a bowed configuration. In figure 13f an elliptical core 28 is illustrated with a variable cross-section. This also produces a bowed side 27. The shape of shear damper cores is not limited to the embodiments illustrated in figure 13a- 13f and other embodiments will be useful for other applications of the invention. In applications where shear dampers are subjected to many thousands of cycles over the lifetimes there is a tendency for core material to migrate into the surrounding layers plates and resilient material. This migration will occur in the same direction as the motio which is being damped. One way of reducing this migration is to embed stiffenin elements into the core material. The reduction of migration is most effective if th stiffening elements are aligned so as to impart the maximum stiffness in the direction o displacement ofthe energy absorber. Possible ways of doing this are illustrated in figure 14, 15 and 16. In figure 14a, the core material 28 has embedded therein disks or plates 52. Discs 52 ma be of a diameter less than the diameter of core 28 or they may be the same. The faces o discs 52 are preferably grooved in the same way as is illustrated in figures 3a-d to assi in retarding migration of core material. Such an embodiment is, in effect, a laminate structure which may be constructed without embedding stiffening elements in the cor Rather, a laminate is formed of alternating layers of core 28 and discs 52. In figure 14b there is illustrated a pair of back to back shear dampers in which each ste plate 21, instead of being in the form of an annulus as in figure 2, extends acros substantially the cross-section of each shear damper of the energy absorber. Alternatin with each plate 21 is a layer of lead 19 (the prefeπed core material). An annulus of rubbe 24 (a prefeπed elastomer material) encircles each layer of lead 29 at its circumferenc The remainder of the assembly is the same as that illustrated in figure 2. Common en plate 18 separates the pair of dampers. Distal end plates 10 and 12 are clamped betwee clamping plates 14 and 16 in the manner described in relation to figure 2. In operation as motion from side to side, relative to figure 14b, is damped, plates 21 ac to reduce migration of lead in the directions of motion damped by the absorber. Migratio of lead into rubber annuli 24 at either side is reduced in this application. As in the other embodiments the upper and bottom faces of plates 21 are preferabl grooved where they contact lead layers 19 in order to increase mechanical bondin between them. In a further embodiment annuli 24 may be omitted entirely and layers of lead 19 exten to the same circumference as the plates 21. In the embodiment illustrated in figure 15 the core material 28 has embedded therein continuous wire ring 54 of cross-sections as illustrated in figure 17. The cores 28 of each of figures 14a and 15 are cylindrical. The core 28 in figure 16 is of rectangular cross-section. Embedded within that core 28 are illustrated a pair of stiffening rods 56. The number of stiffening rods and their alignments can vary according to the overall shape of the core. Possible cross-sections of wires 54 or rods 56 are illustiated in figure 17a-g. Rod or wire 58 in figure 17a is circular. Wire or rod 59 in figure 17b and c are elliptical. Wire or rod 60 in figures 17d and f are rectangular in cross-section. Wire or rod 61 illustrated in figure 17e has a square cross-section. The cross-section of wire or rod 62 in figure 17g roughly approximates the letter "S". The stiffening elements for use in reducing migration of the core material may be composed of a number of different materials. It is necessary that the elements have a greater stiffness than the core material itself. It is also advantageous that the rigidity is in the plane of deformation of the core. EXAMPLE 1: Test of First Embodiment Six devices ofthe embodiment illustrated were tested on the double shear test rig (750kN) and Instron test machine (250kN) of Penguin Engineering Limited in Gracefield New Zealand. The operation of the text rigs is described in Robinson 1995. The design displacements ofthe devices tested were in the order of ±2μm to ±lOmm. Successful tests were achieved across the range from ±2μm to ±17mm. The second experimental device tested sustained 1226 cycles at various amplitudes across its working range, including a 1000 cycle test at ± 0.7mm, with negligible change in the hysteretic properties of the device. The device of which the results are shown here, sustained 217 cycles at a range of displacements including three cycles at ± 1.7 times the design displacement, with little change in the hysteretic properties ofthe device. That the devices tested show hysteretic behaviour over a range of displacements is shown by the curves in Figures 4 to 6. These show hysteretic behaviour at very small (±lOμm), medium ( ± 1.1mm) and large (±6.9mm) displacements respectively. The testing programme has shown the lead shear damper to behave as an almost perfect plastic device. It provides significant hysteretic damping at displacements as low as 2μ and a reliable range of operating displacements of four orders of magnitude. It h exhibited constant and reliable properties through extensive testing after 1000 cycle After a large displacement at the top end of its working range the device remained just sensitive when tested at the bottom end. At displacements of the order of twice t working range the damper provided reliable damping for many cycles. However, t elastomer was stretched beyond its elastic limit and fractured. EXAMPLE 2: Test of Second Embodiment A prototype energy absorber as described in figures 7 and 8 was subjected to a testin programme using the same testing machines as in Example 1. The energy absorb according to the second embodiment ofthe invention was subjected to 141,440 cycles various amplitudes until the testing machine itself failed. The absorber in the last suc cycle had a damping force within 15% of the first cycle and this was regarded as a pa within the design parameters. Installation The distribution of energy absorbers according to the invention throughout new an existing structures provides control ofthe performance of structures. The advantage of th approach is that it enables specific damping to be prescribed by the designer/enginee The prototype lead shear damper according to the invention has a hysteretic behavio which is "plastic" or "Coulombic" in nature exhibiting very little rate dependence in th damping force. Prototype dampers tested have had damping forces of lOkN to 200kN, an operate at displacements of 2μm to 10mm. The energy absorber according to the invention is suitable for reducing the motion induce in flexible structures by wind and earthquakes on the one end of the scale down to sma vibration and small displacements at the other end of the scale. The energy absorbers according to the invention are easy to install and allow th architect designer greater freedom and design choice. The ranges of damping force and displacement expected for commercial devices are fro the very small ofthe order of at IN, with ± 0.0001 μm to ± 1mm displacement, to the ver large at 10GN, with ± 50μm to 1.0m. The energy absorbers of this invention may be used for a wide range of application involving the damping of vibrations. These range from damping vibrations in penstock of hydro-electrical installations to damping of vibrations in heavy machineiy or rolling stock, such as heavy trucks, railway freight cars, carnages or engines. Other embodiments of the invention will be apparent to those skilled in the art. REFERENCES Kustov, S., Golyandin, S., Sapozhnikov, K. and Robinson, W.H., "Influence of Prestrain on Internal Friction of Aluminium, Indium and Lead Poly cry tals. " IX International Conference on Imperfections and Anelastic Phenomena in Solids, Tula, Russia, September 1997. Monti, M.D. ( 1994) "HIGH STRAIN CYCLIC SHEAR OF LEAD" Masters Thesis, University of Auckland Monti, M.D; Ferguson, W.G and Robinson, W.H (1995) "LEAD AS A SEISMIC ENERGY DISSIPATOR" IPENZ Annual Conference vo! 2 p444-p450 Monti, M.D; Ferguson, W.G and Robinson, W.H (1995) "LEAD AS A CYCLIC MOTION DAMPER" Pacific Conference on Earthquake Engineering vol 3 p323-p330 Monti, M.D and Robinson, W.H (1996) "A LEAD-SHEAR DAMPER SUITABLE FOR REDUCING THE MOTION INDUCED BY WIND AND EARTHQUAKE" Proceedings of 11 WCEE Mexico City Robinson, W.H (1982) "LEAD-RUBBER HYSTERETIC BEARINGS SUITABLE FOR PROTECTING STRUCTURES DURING EARTHQUAKES" Earthquake Eng. and Sir. Dyn vol 10 p593-p604 Robinson, W.H and Greenbank L.R (1976) "AN EXTRUSION ENERGY ABSORBER SUITABLE FOR THE PROTECTION OF STRUCTURES DURING AN EARTHQUAKE" Earthquake Eng. and Sir. Dyn vol 4 p251-p259 Robinson, W.H (1995) "SEISMIC ISOLATION, THE NEW ZEALAND EXPERIENCE" ASME/JSME PVP Conference Hawaii 1995 Robinson, W.H (1996) "RECENT DEVELOPMENTS IN SEISMIC ISOLATION" Proceedings of 1 I WCEE Mexico Cit Scawthorn, C; Kato, B and Lu, L.W (1995) "CRITERIA AND LOADING" Fifth World Congress on Habitat and the High-Rise p839- pl l50 Skinner, R.I and McVerry, G.H (1975) "BASE ISOLATION FOR INCREASED EARTHQUAKE RESISTANCE" Bulletin ofthe New Zealand Society for Earthquake Engineering vol 8 No. 2 Skinner, R.I; Robinson, W.H and McVeπy, G.H (1993) "AN INTRODUCTION TO SEISMIC ISOLATION" John Wiley and Sons Ltd, West Sussex, England

Claims: CLAIMS 1. An energy absorber comprising: a pair of shear dampers mounted back to back along a common axis, each said damper comprising a pair of rigid end plates, a laminated stπicture of rigid plates able to slide past one another and a core of plastically deformable material in a bore through said rigid plates from the inner face of one end of said end plate to the inner face of the other said end plate, means to urge said end plates toward one another to maintain each said core at a hydrostatic pressure at least approaching the shear yield stress of said plastically deformable material, the two end plates at the distal ends of said pair of dampers being commonly attachable to a first portion of a structure, the two dampers having a common end plate at their adjacent ends, said common end plate being attachable to a second portion of a structure, the average cross-sectional area of the core in each said damper being from about 5% to about 95% ofthe average total cross-sectional area of each said damper, the arrangement and construction being such that in use said energy absorber, when attached to a first and second structure or portions of a structure, dampens relative motion therebetween. 2. An energy absorber as claimed in claim 1 wherein said core is lead. 3. An energy absorber as claimed in claim 1 wherein each said core is of high purity aluminium, tin, zinc, iron or indium or alloys of lead, aluminium, tin, zinc, iron or indium or any supeφlastic alloy or other material having a low rate of work hardening. 4. An energy absorber as claimed in claim 1 wherein each said core is densely packed granular material. 5. An energy absorber as claimed in claim 4 wherein said granular material is steel, glass beads, alumina, silicon carbide or any other similar hard granular material. 6. An energy absorber as claimed in claim 4 wherein said granular material is granular iron, lead, aluminium or other similar less hard material. 7. An energy absorber as claimed in any one ofthe preceding claims wherein said end plates and said rigid plates are of steel. 8. An energy absorber as claimed in any one of claims 1 to 6 wherein said end plate and said rigid plates are of aluminium or aluminium alloy. 9. An energy absorber as claimed in any one of claims 1 to 6 wherein said end plate and said rigid plates are of ceramic material or other suitable material. 10. An energy absorber as claimed in any one of the preceding claims wherein sai rigid plates are separated by resilient material. 11. An energy absorber as claimed in claim 10 wherein said resilient material is rubbe 12. An energy absorber as claimed in any one of the preceding claims wherein sai means urging said end plates toward one another comprises a pair of clamping member which clamp said distal end plates towards one another. 13. An energy absorber as claimed in any one ofthe preceding claims wherein said pai of end plates at said distal ends are attachable to said first structure by means of connecting member connected to said clamping members. 14. An energy absorber as claimed in any one of the preceding claims wherein sai common end plate to said dampers is attachable by an attachment member to a secon portion of a struction. 15. An energy absorber as claimed in claim 14 wherein said attachment member is lateral extension of said common end plate. 16. An energy absorber as claimed in claim 15 wherein the average cross-sectional are of each said core is about 50-95% ofthe average total cross-sectional area of said damper 17. An energy absorber as claimed in claim 16 wherein said cross-sectional area of eac said core is about 50% of the average total cross-sectional area of said damper. 18. An energy absorber according to any one of the preceding claims wherein each sai core has a regular geometric cross-section. 19. An energy absorber as claimed in claim 18 wherein each said core is cylindrical. 20. An energy absorber as claimed in claim 18 wherein each said core has a squar cross-section. 21. An energy absorber as claimed in claim 18 wherein each said core has a rectangual cross-section. 22. An energy absorber as claimed in claim 18 wherein each said core has an elliptical cross-section. 23. An energy absorber as claimed in any one of claims 1 to 17 wherein each said core is of a variable geometric cross-section. 24. An energy absorber as claimed in claim 23 wherein each said core has an hour glass shape when viewed in side elevation. 25. An energy absorber as claimed in any one of the preceding claims wherein each said damper has a regular geometric cross-section. 26. An energy absorber as claimed in claim 25 wherein said regular cross-section is circular. 27. An energy absorber as claimed in claim 25 wherein said regular cross-section is square. 28. An energy absorber as claimed in claim 25 wherein said regular cross-section is rectangular. 29. An energy absorber as claimed in claim 25 wherein said regular cross-section is elliptical. 30. An energy absorber as claimed in any one ofthe preceding claims wherein there is a bond between the inner face of each of said distal end plates and the inner face of said common end plate with the ends of the core of each said shear damper. 31. An energy absorber as claimed in claim 30 wherein said bond is a mechanical bond. 32. An energy absorber as claimed in claim 31 wherein said mechanical bond is formed by grooving the inner faces of said end plates. 33. An energy absorber as claimed in claim 32 wherein said grooving is in a circular or spiral pattern. 34. An energy absorber as claimed in claim 30 wherein said bond is formed b soldering. 35. An energy absorber as claimed in claim 30 wherein said bond is formed b adhesive. 36. An energy absorber as claimed in claim 30 wherein said bond is formed b vulcanised rubber. 37. An energy absorber as claimed in claim 32 wherein said grooving is in the form o straight grooves at right angles to the direction of movement of forces to be damped b said absorber. 38. An energy absorber as claimed in claim 32 wherein said grooving is in the form o straight grooves at any angle to the direction of movement of forces to the damped by sai absorbers. 39. An energy absorber as claimed in claim 32 wherein said grooving has been effecte by peening or sand blasting. 40. An energy absorber as claimed in claim 32 wherein said grooving is in the for depicted in any one of figures 3a-d. 41. An energy absorber as claimed in any one of claims 1-19, 25, 26 and 30-40 wherei said core is cylindrical and said alternating layers of rigid plates and resilient material for an annulus therearound. 42. An energy absorber as claimed in any one of claims 1, 2 and 7-41 wherein each sai core is lead and said hydrostatic pressure is from about 5MPa to about 80MPa. 43. An energy absorber as claimed in claim 42 wherein said hydrostatic pressure i equal from about lOMPa to about 30MPa. 44. An energy absorber as claimed in claim 42 wherein said hydrostatic pressure i about 50MPa. 45. An energy absorber as claimed in any one of the preceding claims wherein sai cores contain elements imbedded therein of material stiffer than the core material t thereby reduce migration of core material during damping. 46. An energy absorber as claimed in claim 46 wherein said elements are aligned to provide rigidity in the planes of deformation of said cores. 47. A energy absorber as claimed in claim 45 or 46 wherein said cores are lead and said elements are of metal, carbon fibre, fibreglass or other material which is stiffer than lead. 48. An energy absorber as claimed in any one of claims 45 to 47 wherein said elements are in the form of rods, wire, strips, mesh, discs or similar forms. 49. An energy absorber as claimed in any one of claims 45 to 48 wherein said elements comprise said rigid plates in said laminated structure, said rigid plates extending through said core of plastically deformable material across substantially the whole cross-section of each said shear damper whereby said core is discontinuous consisting of alternating layers of core material and rigid plates. 50. An energy absorber comprising: two pairs of shear dampers, each pair mounted back to back along a common axis, each said damper pair comprising a pair of rigid end plates, a laminated structure of rigid plates able to slide past one another and a core of plastically deformable material in a bore through said rigid plates from the inner face of one end of said end plate to the inner face ofthe other said end plate, means to urge said end plates of each said pair toward one another to maintain each said core at a hydrostatic pressure at least approaching the shear yield stress of said plastically deformable material, the two end plates at the distal ends of each of said pairs of dampers being joined to one another, the two dampers of each said pair having a common end plate at their adjacent ends, said common end plate of one said pair being attachable to a first structure and said common end plate ofthe second said pair being attachable to a second structure, the average cross-sectional area of the core in each said damper being from about 5% to about 95% ofthe average total cross-sectional area of each said damper, the arrangement and construction being such that in use said energy absorber, when attached to a first and second structure or portions of a structure, dampens relative motion therebetween. 51. An energy absorber as claimed in any one of the preceding claims in combination with two structures or two parts of a stπicture to dampen motion therebetween. 52. A method of damping relative motion between two structures or between two part of a structure which comprises selecting an energy absorber as claimed in any one o claims 1-50 with energy absorbing propeities to damp forces anticipated to act on said tw structures or two parts of a structure and attaching the respective connecting members o said energy absorber to said two structures or two parts of a structure. 53. A method of manufacturing an energy absorber as claimed in any one of claims 1 2 and 7-50 which comprises, forming laminate of one said end plate and said rigid plates and (where present said resilient material, inserting a plug of damping material into the core of said damper and securing th other said end plate onto said laminate, subjecting said end plates of said damper to a pressure and for a time sufficient t allow said damping material to flow into the interstices in the sides of the bore throug said rigid plates and resilient material adjacent said core and into the scoring in the inne faces ofthe end plates of said damper. 54. A method as claimed in claim 53 wherein said damping material is lead and sai end plates are subjected to a pressure of at least 50MPa. 55. A method as claimed in claim 54 wherein said pressure is applied for at least minutes. 56. A method as claimed in claim 53 wherein said damping material is lead and sai end plates are subject to a pressure of at least lOOMPa.

Inventors: ROBINSON WILLIAM HENRY, ROBINSON, WILLIAM, HENRY
Applicants: PENGUIN ENGINEERING LIMITED, ROBINSON WILLIAM HENRY, ROBINSON, WILLIAM, HENRY
Application year: 1997
Main classification: F16F
IPC codes: F16F1, F16F7, F16F15