Nitinol ski structures

A torsionally-damped ski having a durable, low friction ski base and non-rusting durable ski edges that have exceptional edge-retaining qualities, including an elongated snow-contacting base surface made of a Nitinol sheet having two opposed longitudinal edges on opposite sides of an elongated medial portion. A Nitinol ski edge structure extends longitudinally along both of the edges of the sheet, having a greater thickness than the medial portion of the sheet. The edge structures form an integral part of the Nitinol base sheet by welding the sheet along opposite edges thereof to the edge structures. Preferably, the ski edge structure is Type 60 Nitinol. The base sheet can be superelastic Nitinol or Martensitic Nitinol having shape memory characteristics. A torsional vibration structure is built into the ski, including Nitinol structures extending along one or more axes lying oblique to the longitudinal axis of the ski.

BACKGROUND OF THE INVENTION
 Since the advent of modern skis in the 1940's and 1950's, ski manufacturers
 have worked, with considerable success, to design and build skis that are
 torsionally stiff and have longitudinal stiffness that can be selected for
 each type and size of ski, enabling the customer to select a ski optimized
 for the type of snow conditions, skiing style and size of that customer.
 With improvements in skis, skiing has become easier to learn and has
 become a very popular recreational activity, to the great profit of ski
 equipment manufacturers and ski resorts.
 Even with the improvements made to skis in the last ten or so years, there
 remain some problems that have resisted the efforts of large ski
 manufacturers to solve. One such problem is ski chatter when skiing in icy
 conditions. Ski chatter is a natural result of a stiff ski weighted in the
 center by the skier's weight and extending stiffly forward and rearward
 therefrom to the tip and tail, like a big leaf spring. When the tip and/or
 tail is perturbed by the rough ice surface, the ski vibrates, or
 "chatters" on the ice. The chatter has a deleterious effect of the ability
 of the ski edges to hold in the groove they are cutting in the ice, and it
 can cause the ski to break loose and skid down hill. It also causes a
 sense of roughness and poor control to the skier.
 Ski manufacturers have tried mightily to solve the problem of chatter.
 Among such attempts to reduce chatter are dampers of various kinds
 attached to the ski intended to absorb vibration energy and thereby reduce
 the amplitude and/or reduce the frequency of the vibration. One difficulty
 with dampers is in achieving optimal damping to reduce chatter
 sufficiently without reducing the springiness of the ski so much that it
 would make a "dead" ski. These schemes have been only partially successful
 and ski chatter remains a problem, particularly with aggressive skiers and
 ski racers.
 Another problem that ski manufacturers have been unable to solve is
 developing a durable ski base material that can withstand abuse and
 provide low friction with the snow surface. The ski base now commonly used
 is sintered polyethylene. It is relatively soft and easily gouged by rocks
 in the snow, a common occurrence. Gouges can be repaired, at least
 temporarily, using melted plastic material in a "P-tex candle" but more
 serious and unrepairable damage can be done if a rock gouges the ski base
 and hooks the edge structure. The force of the moving ski and skier
 concentrated at the inside of the edge can pull the edge piece right out
 of the ski. Although this type of damage is rare, ski manufacturers and
 skiers would welcome a ski improvement that eliminates this kind of base
 damage and edge piece pull-out.
 Ski edges are made of hard, high strength steel to provide the hardness and
 strength needed for the severe demands on that structure. The edge
 occasionally passes over rocks, and must be hard enough to resist gouges
 and burrs that would affect the ski performance. The edge pieces also
 contribute some degree of longitudinal stiffness to the ski and that
 stiffness is difficult to control without changing the size of the edge
 pieces. Most annoying to skiers is the speed at which the ski edges become
 dull and rusty. After returning from a hard day of skiing, the skier is
 obliged to resist the temptation to hop right into the hot tub because he
 knows that his ski edges will be rusted the next morning if he fails to
 dry them off before beginning the evening's activities. The rust makes the
 skis run slower, but more seriously, it attacks first the sharp edge of
 the edge piece, dulling it quickly. A ski with hard and durable edges that
 are immune to rust or corrosion would be a welcome improvement to skiers.
 SUMMARY OF THE INVENTION
 Accordingly, this invention provides a lively ski with a damping structure
 that can be designed and/or tuned to provide damping for skis to eliminate
 the most serious effects of chatter without deadening the ski. The
 invention also provides a ski base that is extremely slippery and robust,
 and can be repaired to as-new condition easily, quickly and inexpensively
 by the owner of the skis without expensive equipment or special skill.
 This invention also provides ski edges that are immune to rust and
 corrosion, are long lasting and resistant to damage by rocks, and can be
 made so that they are absolutely immune from being pulled out by rocks or
 other impacts.
 These benefits are provided by a ski having Nitinol structures embedded
 into the torsion box of the ski so that the Nitinol structures are
 strained when the ski flexes, and the vibration energy of the flexing ski
 is absorbed by the Nitinol structures and converted to heat. The ski base
 is made of a sheet of Nitinol that is very slippery and has a shape memory
 effect, enabling any dents or gouges to be removed merely by heating with
 a blow dryer or an iron. The sheet Nitinol base can also be treated to
 have an extremely hard and slippery surface that can be colored with a
 permanent integral color for beauty and marketing pizzazz. The invention
 also provides Nitinol ski edges that are immune from rust and corrosion
 and are hard and tough to resist damage from rocks. The ski edges can be
 made integral with the ski base to provide an integral base structure that
 can be designed to offer any desired stiffness and whose edges cannot be
 pulled out under any circumstances.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Turning now to the drawings, wherein like reference characters designate
 identical or corresponding parts, and more particularly to FIG. 1 thereof,
 a ski 30 is shown schematically having Nitinol strips 32 and 34 embedded
 in the ski forward and rearward, respectively, of the binding attachment
 area 36, such that flexing of the ski during vibration or chattering
 causes the Nitinol strips to flex and strain. The strain is maximized when
 the Nitinol strips 32 and 34 are embedded near the top or bottom surfaces
 of the ski.
 Reference is made to "skis" herein, but it will be understood that the
 invention applies equally well if not better to snowboards. Therefore, the
 term "ski" as used in this description and in the claims should also be
 interpreted to include the term "snowboard".
 In FIG. 3, the Nitinol strips 32 and 34 of FIGS. 1 and 2 have been replaced
 with Nitinol wires 40 disposed in narrow tubes 42 between a top sheet 44
 of the ski 45 and the core 48, and also between the bottom sheet 50 and
 the core 48. The tubes 42 lie in aligned grooves in the top sheet and the
 core, and in aligned grooves in the bottom sheet and the core to prevent
 shifting during skiing. The grooves may be omitted if the wires 40 remain
 in place without shifting during skiing. The tubes 42 prevent the adhesive
 that binds the top and bottom sheets 44 and 50 to the core 48 from
 preventing the wires 40 from straining freely along their length for
 maximum damping. However, Nitinol is very difficult to bond to anything,
 and the tubes 42 may be unnecessary and may be omitted if the damping
 provided by the wires unprotected by the tubes 42 is sufficient.
 The Nitinol of the wires 40 is preferably 55 Nitinol, which is an atomic
 50/50 intermetallic compound of nickel and titanium having about 55%
 nickel and 54% titanium by weight. The Nitinol has a Martensitic state and
 an Austenitic state on opposite sides of a transition temperature of about
 80.degree. C. The Nitinol in its Martensitic state has very high damping
 capacity, on the order of about 60% of input strain energy.
 If the damping provided by the 55 Nitinol wires 40 is excessive and makes
 the ski insufficiently lively, some of the wires 40 may be removed or may
 be replaced with superelastic Nitinol wires. Superelastic Nitinol is a
 known composition, very nearly the same as 55 Nitinol, but is cold worked
 to give it remarkable elastic properties. Although providing somewhat less
 damping capacity than the 55 Nitinol, superelastic Nitinol also has good
 damping capacity. The compination of extreme elasticity (technically known
 as "pseudoelasticity") and damping capacity may make superelastic Nitinol
 a better material for all the wires 40 in the ski structure shown in FIG.
 3.
 The attachment of the wires 40 adjacent the binding attachment area 36 of
 the ski 45 is shown in FIG. 4. This structure is of particular use in
 developing the ski of this invention to achieve the desired tension in the
 wires 40. It may also be of value to expert skiers who would want to tune
 the stiffness and damping of their skis for the particular conditions of
 the day.
 The structure shown in FIG. 4 includes a titanium mounting plate 60 having
 a flange 62 at each end front and rear (only one flange being shown in
 FIG. 4). The titanium mounting plate provides a secure mounting structure
 that can be drilled and tapped for bomb-proof mounting of the ski
 bindings. The flanges 62 are drilled at spaced positions laterally across
 the ski at positions corresponding to the positions of the wires 40 shown
 in FIG. 3.
 An inner wedge structure 65, laterally elongated to extend laterally across
 the full width of the ski, is disposed under the mounting plate 60 between
 the two flanges. A series of holes 67 is drilled longitudinally in the
 inner wedge structure 65 and each hole 67 receives an end of an individual
 wire 40 where it is secured by laser welding or the like. The inner wedge
 structure 65 has a downwardly facing wedge surface 69 which engages a
 corresponding upwardly facing wedge surface 70 on an outer wedge structure
 75. Two tapped holes 77 (only one of which is shown in FIG. 4) in opposite
 ends of the outer wedge structure receive threaded shanks of two screws 80
 that are seated in counterbored holes in the mounting plate 60 and are
 accessible to the skier through suitable access openings in the top of the
 ski. Slots 83 are provided in the inner wedge structure 65 to allow the
 screws 80 to reach the outer wedge structure 75.
 In operation, the skier torques the screw 80, which lifts the outer wedge
 structure 75 and cams the inner wedge structure 65 to the left in FIG. 4,
 putting additional tension on the wires 40. Turning the screw 80 in the
 opposite direction lowers the outer wedge structure 75 and allows the
 wires 40 to pull the inner wedge structure to the right in FIG. 4 to the
 extent permitted by the wedge surface 70 on the outer wedge structure 75.
 For lower priced skis that do not require an adjustment capability, the
 wires can be attached to attachment bars and fixed in known positions in
 the ski to provide a predetermined damping capability and stiffness.
 Turning now to FIG. 5, a ski 90 is shown having a Nitinol base 95. The base
 may be Type 55 Martensitic Nitinol or may be superelastic Nitinol. The
 superior damping capacity of 55 Martensitic Nitinol would make it a highly
 damped. Moreover, 55 Nitinol has a shape memory effect, so that dents and
 grooves created by skiing over rocks and the like could be removed merely
 by heating the base 95 with a blow drier or a pressing iron to a
 temperature above the transition temperature of the Nitinol, whereupon the
 dents and grooves would spontaneously disappear and the surface would be
 restored to its original smoothness. Superelastic Nitinol does not have
 the shape memory effect, but it is much stronger than 55 Nitinol and has a
 "pseudo-elastic" range of about 7% so it would not be as likely to suffer
 plastic deformation so it would not be as likely to suffer permanent dents
 and gouges. Moreover, superelastic Nitinol is much stiffer than 55 Nitinol
 and does have good damping capacity, so the ski with a superelastic base
 95 would be stiff and damped. The stiffness of superelastic Nitinol can be
 adjusted by the heat treatment.
 Referring back to FIG. 3, the edge pieces 100 (only one of which is shown
 in FIG. 3) along each longitudinal edge of the ski 45 are bonded in place
 by an adhesive, the same adhesive that holds the top and bottom sheets 44
 and 50 to the core 48. In accordance with this invention, these edge
 pieces may be made of Nitinol to provide superior edge holding ability and
 to be immune to rust and corrosion. The material of the edge is preferably
 superelastic Nitinol because of its hardness and property of increasing in
 strength when subjected to cold work. Thus, the edge piece would not be so
 strong and stiff that it would interfere with the desired stiffness of the
 ski, but its strength would increase when it encounters a rock and thereby
 avoid damage that a normal end piece would sustain. The edge piece 100
 could also be made of Type 60 Nitinol, which is an intermetallic compound
 of 60% by weight nickel and 40% by weight titanium. Type 60 Nitinol is
 very hard material, on the order of 55-62 RC, depending on the heat
 treatment, so it would be very good at holding an edge and resisting
 damage from contact with rocks. Type 60 Nitinol, like the two other types,
 is corrosion-proof.
 Turning now to FIG. 6, an integral edge and ski base 110 is shown on a ski
 115. As in the ski shown in FIG. 3, a top plate 117 may be bonded to a
 core 120, such as laminated wood, as is known in the industry. The
 integrated edge and base structure 110 may be made by plasma spraying
 superelastic Nitinol onto a cleaned aluminum plate 125 which forms a
 diffusion bond between the Nitinol and the aluminum plate 125. The
 thickened edge portion 130 is formed at the same time by filling the space
 between the edge of the aluminum plate and a stainless steel form that is
 polished to prevent the Nitinol from sticking. The top surface of the
 aluminum plate 125 bonds readily to the core 120 and the fiberglass
 beveled ski side 135. This structure gives no edge for a rock to hook into
 and tear the ski edge out, as is possible with the ski shown in FIG. 3.
 A ski 150 shown in FIGS. 7 and 8 includes a Nitinol ski edge structure 152
 extending longitudinally along both of the ski edges (only one of which is
 shown in FIG. 7) and having a bottom surface 154 flush with the bottom
 surface 156 of a ski base sheet 160. A shallow recess 162 extends
 longitudinally along the full length of the inside bottom edge of the edge
 structure 152 to receive one edge of the ski base sheet 160 where it is
 welded by laser welding or tungsten inert gas arc. The ski base sheet 160
 is preferably superelastic Nitinol or martensitic 55 Nitinol having shape
 memory characteristics as noted above.
 The ski edge structure 152 is preferably cast from Type 60 Nitinol using an
 investment casting process. The edge structure 152 has a top flange 165
 having a series of key-hole notches along its inner edge by which the edge
 structure is locked in the ski when the epoxy bonding the elements of the
 ski together cures. The cast edge structure is treated in a hot isostatic
 press at 1760.degree. F. for several hours at 1500 PSI to consolidate the
 as-cast structure, and then is ground and polished on the outside and
 bottom edges. It is then heat treated to about 900.degree. C. and water
 quenched to make to tough and give it a lasting oxide finish.
 The edge structures are welded to the outside longitudinal edges of the
 base sheet 160 and the ski elements, including the ski core 170, the top
 sheet 175, the bottom sheet 176 of epoxy-impregnated fiberglass or the
 like, and the edge/base sheet assembly, are all assembled in a ski mold
 and are pressed in the mold while heating. The epoxy cures quickly under
 heat and pressure and forms a strong flexible ski 150 with durable edges
 and extremely low friction base.
 Torsional stiffening may be provided by at least one vibration absorbing
 member made of Nitinol embedded in the ski and attached thereto in such a
 way that flexing and vibration of the ski causes straining of the Nitinol
 member, whereby a portion of vibration energy in the ski during skiing is
 absorbed by the Nitinol member to damp the vibration. One torsional
 vibration absorber, shown in FIGS. 9 and 10, includes a Nitinol pad 180
 having structure extending along two crossed axes lying oblique to the
 longitudinal axis of the ski. The vibration absorbing member 180 can be
 provided with arms 182 extending along the two oblique axes and
 terminating short of the longitudinal edges of the ski. The pad 180 is on
 the order of about 0.020"-0.070" thick and can be placed over the top
 sheet of the ski where it is visible for marketing interest. The under
 surface of the pad should be roughened or grooved to ensure good bonding
 to the ski since it must be strained during torsional flexing of the ski
 to provide damping of the torsional vibration.
 A second form of torsional damping that does not depending on adhesion of
 the Nitinol structure is shown in FIG. 11. The vibration absorbing member
 shown in FIG. 11 includes an elongated ribbon 190 of Nitinol wrapped in a
 double helix around the core 170 of the ski. The ribbon is preferably
 Martensitic Type 55 Nitinol having a thickness on the order of
 0.010"-0.70", preferably about 0.050", and having a width of about
 3/4"-2", preferably about 1" wide. As shown, there are about four complete
 wraps of Nitinol ribbon around the ski core, and the ends of the ribbon
 are welded together or crimped together to prevent the ribbon from
 creeping during torsional flexing of the ski, so the ribbon 190 will be
 strained and will absorb torsional vibration energy.
 The invention disclosed herein utilizes various Nitinol elements attached
 to or embedded in the ski to improved its function. For purposes of
 definition in the following claims, I intend the term "integral with" to
 encompass both "attached to" and "embedded in".
 Obviously, numerous modifications and variations of the preferred
 embodiment described above are possible and will become apparent to those
 skilled in the art in light of this specification. For example, many
 functions and advantages are described for the preferred embodiment, but
 in some uses of the invention, not all of these functions and advantages
 would be needed. Therefore, I contemplate the use of the invention using
 fewer than the complete set of noted functions and advantages. Moreover,
 several species and embodiments of the invention are disclosed herein, but
 not all are specifically claimed, although all are covered by generic
 claims. Nevertheless, it is my intention that each and every one of these
 species and embodiments, and the equivalents thereof, be encompassed and
 protected within the scope of the following claims, and no dedication to
 the public is intended by virtue of the lack of claims specific to any
 individual species. Accordingly, it is expressly intended that all these
 embodiments, species, modifications and variations, and the equivalents
 thereof, are to be considered within the spirit and scope of the invention
 as set forth in the following claims,