Title:
VIBRATION DAMPED SKI
United States Patent 3844576


Abstract:
A ski structure of the multi-layer type having a core and one or more intermediate load-bearing layers above and below the core wherein at least one of the intermediate layers is a laminate comprising a layer of material having a relatively high modulus of elasticity with elastomeric material bonded to opposite faces of the high modulus of elasticity material, with at least a portion of the elastomeric material possessing pronounced viscoelastic properties.



Inventors:
SCHULTES H
Application Number:
05/380309
Publication Date:
10/29/1974
Filing Date:
07/18/1973
Assignee:
OLIN CORP,US
Primary Class:
International Classes:
A63C5/14; A63C5/075; A63C5/12; C30B29/40; (IPC1-7): A63C5/00
Field of Search:
280/11.13L
View Patent Images:
US Patent References:
3635482SKI AND METHOD OF MANUFACTURE1972-01-18Holman
3537717DAMPED SKI AND METHOD OF MAKING1970-11-03Caldwell
3438828PROCESS FOR MAKING SKIS FROM PLASTICS REINFORCED WITH GLASS FIBERS1969-04-15Bjornestad
3208761Metal ski with cellular plastic structure1965-09-28Sullivan et al.
2526137Ski1950-10-17Hunt



Primary Examiner:
Tollberg, Stanley H.
Assistant Examiner:
Stack Jr., Norman L.
Attorney, Agent or Firm:
Motsko, Donald Kieser Samuel Jones William R. H. W.
Claims:
What is claimed is

1. A laminated ski structure of the type comprising a core, a top surface, a bottom surface, and one or more interbonded intermediate layers disposed between said top and bottom surfaces, the improvement comprising at least one of said intermediate layers being a vibration damping laminate comprising a layer of material having a relatively high modulus of elasticity and respective layers of elastomeric material bonded to opposite faces of said layer of high modulus material, at least one of said layers of elastomeric material having a loss tangent which is greater than about 0.8.

2. The ski structure of claim 1, wherein each of said layers of elastomeric material has a loss tangent which is greater than about 0.8.

3. The ski structure of claim 1, wherein said vibration damping laminate is offset downwardly from the neutral axis of the ski.

4. The ski structure of claim 1, wherein said vibration damping laminate extends for substantially the full length of the ski.

5. A laminated ski of the type comprising a top surface, a bottom surface, and a plurality of intermediate layers between said top and bottom surfaces at least one of said intermediate layers being a laminate including a member of a material of relatively high modulus of elasticity substandially completely surrounded by an elastomeric material, at least a portion of said elastomeric material having a loss tangent which is greater than about 0.8.

6. The ski of claim 5, wherein all of said elastomeric material has a loss tangent which is greater than about 0.8.

7. The ski of claim 5, wherein said laminate of high modulus material and elastomeric material extends for substantially the entire length of the ski.

8. The ski of claim 5, wherein said laminate of high modulus material and elastomeric material is downwardly offset from the neutral axis of the ski.

9. A laminated ski structure of the type comprising a core, a top surface, a bottom surface and one or more intermediate layers disposed between said top and bottom surfaces, the improvement comprising at least one of said intermediate layers being a vibration damping laminate comprising a material having a loss tangent which is greater than about 0.8 substantially completely surrounding a layer of material having a relatively high modulus of elasticity.

10. A laminated ski structure of the type comprising a top surface, a bottom surface, and a plurality of intermediate layers disposed between said top and bottom surfaces, at least one of said intermediate layers comprising a member of material having a high modulus of elasticity substantially completely encased in an elastomeric material, at least a portion of which has a loss tangent which is greater than about 0.8, a rearward end portion of said high modulus member being secured to at least one other intermediate layer of the ski.

11. The ski structure of claim 10, wherein all of said elastomeric material has a loss tangent which is greater than about 0.8.

12. The ski structure of claim 10, wherein said high modulus member and said encasing elastomeric material extend for substantially the entire length of the ski.

13. The ski structure of claim 10, wherein said high modulus member and said encasing elastomeric material are offset downwardly from the neutral axis of the ski.

Description:
This invention relates to a ski structure which is highly damped against vibration, and more particularly, to a ski structure utilizing viscoelastic material as the vibration damping agent, the viscoelastic material being disposed internally of the ski body.

The skier who favors a fast style and the racer who must control his skis at high speeds demand a ski that remains in steady contact with the slope even at high speeds and a ski that absorbs vibration caused by uneven places in the terrain. A highly vibratory ski is not responsive for precise turns on icy slopes, this fact having been verified by many years of testing. To execute a proper carving or sliding turn, the steel edge of the ski must be in precise contact with the slope surface in such a way that the skier can balance his moment forces against the resistance forces of the slope. Not every ski meets these requirements. The metal ski's use under these conditions is precluded by its tendency to vibrate. After an intensive investigation into the factors which influence the steadiness and vibration characteristics of the ski, it was recognized that there are two physical parameters that deserve attention: the vibrational frequency and the vibrational damping of the ski. Where vibration is not desired, a design with high shock absorbtion capabilities or vibration damping is necessary.

Having recognized the fact that a highly vibration damped ski has desirable characteristics, the prior art has made several attempts to provide this vibration damping feature to a ski. Most modern high performance skis are made up of a plurality of layers of various materials such as fiberglass, metal, wood, synthetic resins, and rubber which are bonded together to form the ski, the various mateials being carefully selected for certain desirable characteristics which they contribute to the ski. Thus the search for a means to damp vibration of the ski has been concentrated or focussed upon the multi-layer type of ski.

U.S. Pat. No. 2,995,379 issued Aug. 8, 1961 to H. Head and U.S. Pat. No. 3,194,572 issued July 13, 1965 to J. Fischer disclose the use of an internal layer of rubber which is utilized to damp vibration of the ski imparted thereto during use. While rubber does contribute a vibration damping function to a multilayer ski, the amount or degree of vibration damping imparted to the ski by rubber is minimal, and for example, it is not enough to damp a metal ski sufficiently so that it may be used at high speeds on hard, icy slopes.

Other efforts have been made to modify multi-layer ski construction to improve vibration damping and have provided adequate damping, but have included other drawbacks not related to vibration damping. For example, hardwood cores have been used to improve vibration damping of ski, but hardwood cores are heavy and expensive, thus adding to the cost of the ski and undesirably increasing the weight of the ski. Glass reinforced polyester resins have been used in place of epoxy resin, to increase internal friction, but polyester resin is not durable enough thus resulting in a low fatigue life for the ski. Plastic top edges rather than metal top edges have been used, but plastic top edges are softer than metal top edges thus giving inferior edge protection. Cracked steel running edges rather than continuous steel running edges have been used, however, cracked steel running edges are extremely expensive, thus undesirably adding to the cost of the ski.

Still another means for damping the vibration of a ski is disclosed in U.S. Pat. No. 3,537,717 issued Nov. 3, 1970 to D. B. Caldwell. A conventional ski is damped according to the Caldwell patent by applying to the top surface of the ski a laminate of a layer of viscoelastic material and a stretch resistant constraining layer, such as metal, with the viscoelastic layer being sandwiched between the top surface of the ski and the constraining layer and serving to bond the constraining layer to the top surface of the ski. This method of damping the ski displayed superior results, however, it also featured some pronounced disadvantages. Specifically, the disadvantages to this method are: that the viscoelastic material and constraining layer are exposed to mechanical forces such as shocks or impact by the other ski, and weathering; the constraining layer is attached to the ski only by the viscoelastic material thus resulting in poor durability; when applied to the top surface of an already engineered ski, the constraining layer influences other characteristics of the ski, such as overall stiffness, stiffness balance, frequency of the ski, and temperature balance; and the constraining layer must be relatively short when compared to the full length of the skis since the constraining layer, when placed on the top surface of the ski, must terminate at the binding area. Thus the damping system disclosed in U.S. Pat. No. 3,537,717 does improve the vibration damping characteristics of a ski, but has sufficient disadvantages to render it of little practical value for use on commercially produced skis.

It will be noted that the disadvantages of the structure shown in U.S. Pat. No. 3,537,717 arise chiefly from the fact that the vibration damping laminate is secured to the top surface of the ski. It will be readily apparent that these disadvantages could be eliminated by disposing the vibration damping laminate inside of the ski rather than on its top surface, however, it has been demonstrated that a simple transfer of the vibration damping laminate shown in U.S. Pat. No. 3,537,717 from a location on the top surface of the ski to a location internally of the ski may in fact produce a ski whose vibration damping characteristics are actually worse, test results demonstrating this worsening of the vibration damping characteristics being presented hereinafter in Table I.

The problem solved by my invention concerns the incorporation of a constrained viscoelastic vibration damping laminate into a ski as an internal component thereof. I have discovered that in order to properly function as a vibration damping component, the constraining member must be substantially completely isolated from the remainder of the structural members of the ski by elastomeric material, preferably disposed in layers above and below the constraining member, with at least one of the layers of the elastomeric material possessing pronounced viscoelastic properties. The constraining member can, if desired, be secured directly to the remainder of the ski at one point, preferably spaced as far as possible away from the shovel area of the ski, with the securement being in the form of an adhesive, screws, or the like, however, the remaining surfaces of the constraining member must be isolated from the remainder to the ski structure by the elastomeric material. In order to maximize the vibration damping performance of the internal constrained viscoelastic laminate, it should be positioned as far as possible away from the neutral axes of the ski, preferably below the neutral axis of the ski so as to be free from contact with binding screws conventionally embedded in the ski at the binding area.

By utilizing a constrained viscoelastic laminate as an internal component of a multi-layer ski, the vibration damping laminate can be properly designed in conjunction with the remaining ski components to accurately control proper ski flexibility, frequency, and the like. The vibration damping laminate is protected against delamination, impact, weathering, and other adverse influences. The viscoelastic material is protected and reinforced by other stronger components of the ski. Internally positioning the vibration damping laminate permits the designer to use a constrained laminate substantially equal in length to the length of the ski which doubles the maximum shear strain in the laminate as compared to the prior art viscoelastic vibration damping laminate. When the constraining member is attached directly to the tail end of the ski, it can be shown that the maximum shear strain is about four times that of the prior art viscoelastic vibration damping laminate.

It is, therefore, an object of this invention to provide a damped ski having a constrained viscoelastic vibration damping laminate incorporated into the interior portion of the ski.

It is yet another object of this invention to provide a ski of the character described wherein the constraining member of the vibration damping laminate is substantially completely isolated from the remaining components of the ski by an elastomeric material, at least a portion of which possesses pronounced viscoelastic properties.

It is a further object of this invention to provide a ski of the character described wherein the constrained viscoelastic laminate is protected from adverse effects by the remaining components of the ski.

These and other objects and advantages of the ski of this invention will become more readily apparent from the following detailed description of an embodiment of a ski formed in accordance with the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectioned perspective view of an embodiment of a ski made in accordance with the invention;

FIG. 2 is a sectioned perspective view of a prior art ski;

FIG. 3 is a sectioned perspective view of a modified prior art ski; and

FIG. 4 is a vertical sectional view of an additional embodiment of the ski of this invention.

Referring now to the drawings, a multi-layer laminated fiberglass ski 2 is shown. The top layer 4 is an ABS plastic protective layer. Beneath the top layer 4 are disposed top protective edges 6 of metal such as aluminum or steel. Two load-bearing layers of fiberglass 8 and 10 are positioned below the top layer 4 and top edges 6 respectively and above a wood core 12. A binding plate 14 may be embedded in the wood core 12 for strengthening the binding area of the ski. Sidewall layers 16 of phenolic resin extend from the fiberglass layer 10 to a further load bearing fiberglass layer 18 beneath the core 12. Steel running edges 20 are bonded to the fiberglass layer 18 by means of intermediate rubber layers 22. The bottom running surface of the ski is a polyethylene layer 24 sold under the trademark P-Tex. Sandwiched between the running surface layer 24 and the lower fiberglass layer 18 is the vibration damping laminate which comprises a layer 26 of highly viscoelastic material preferably surrounding the top, bottom and side surfaces of a constraining member 28 of a material having a high modulus of elasticity, such as aluminum, steel, fiberglass, or the like. The viscoelastic material layer 26 is elastomeric and inherently adhesive so as to bond itself to the constraining member 28 and the fiberglass layer 18, running edges 20 and running surface layer 24, however, this bond may be strengthened by proper application of epoxy resin which is used to bond the remaining layers together to form the ski. Preferably the damping laminate extends for substantially the entire length of the ski. The constraining member 28 may be completely surrounded by viscoelastic material so that the front, rear, top, bottom and side surfaces of the constraining member are covered by viscoelastic material, or the constraining member may be permitted to project beyond the viscoelastic material at its rear terminal at the rear end of the ski so that the projecting portion of the constraining member can be directly secured to the remaining layers of the ski with a screw S, as shown in FIG. 4, adhesive, or the like. In any event, the major portion of the constraining member should be isolated from the rest of the ski layers by the viscoelastic material for best performance.

It will be noted that the particular ski structure illustrated in FIG. 1 is only one of many possible ski structures of the multi-layer type with which the invention may be used to improve vibration damping characteristics. While the load-bearing members of the ski structure of FIG. 1 are referred to as being fiberglass, they could also be made of metal or other conventional load-bearing material without departing from the spirit of the invention. Similarly, the core structure need not be wood, but could instead be made from a rigid plastic foam, a metal honeycomb, or any other conventional and known material utilized for cores of skis.

It is noted that many materials exhibit some degree of viscoelasticity, an elastic material being defined as a material whose stress is proportional to strain, and a viscous material being defined as a material whose stress is proportional to strain rate. A viscoelastic material is a material whose behaviour is a mixture of these two simple cases. In order to be useful in providing vibration damping in accordance with this invention, the elastomeric material used must possess pronounced viscoelastic properties. By pronounced viscoelastic properties, it is meant that the loss tangent of the viscoelastic material must be greater than about 0.8. When a viscoelastic material is subjected to a sinusoidal strain, the resultant stress is approximated by a sine wave which leads the strain by the phase angle β. The relationship between the components of the tension or compression modulus of any specimen is defined by the equation:

E* = E' + i E"

where:

E* is the complex modulus of elasticity;

E' is the storage modulus of elasticity;

E" is the loss modulus; and

i is square root of -1.

The loss tangent is the tangent of the phase angle β which equals E"/E'. As previously noted, the loss tangent of the viscoelastic material must be greater than about 0.8 to be useful in vibration damping in accordance with this invention.

The constraining member which forms a part of the vibration damping laminate must be of a material having a relatively high modulus of elasticity, such as steel, aluminum, fiberglass, or the like.

Several measurements which may be made to determine the amount of vibration damping present in a ski include: the Log Decrement which is defined as the natural logarithm of the ratio of any two successive vibration amplitudes wherein:

Log Decrement = 1n A1 /A2

it being noted that the greater the value of the Log Decrement, the better vibration damping characteristic of the ski; and

The Half Life Time which is defined as the time period required for the vibration amplitude to decay to one-half of its initial value, it being noted that the shorter the Half Life Time, the better vibration damping characteristic of the ski.

Generally, in determining the vibration damping characteristic of a ski, the Frequency is also determined, the Frequency being defined as the number of complete vibration cycles, or cycles of motion in a unit of time, wherein by international convention, 1 cycle per second equals 1 Hertz.

Tests showing the vibration damping ability of the structure shown in FIG. 1 were conducted with comparisons being made between this structure and the structures shown in FIG. 2 and FIG. 3 which are respectively a commercially available ski sold under the trademarks OLIN MARK III, and a ski structure similar thereto but incorporating as an internal component, the vibration damping composite shown in U.S. Pat. No. 3,537,717, noted above, the ski of FIG. 3 being referred to hereinafter as the "Modified MARK III." The MARK III ski used in comparison tests was of the construction shown in FIG. 2, it being noted that the rubber layer 22 extends laterally across the full width of the ski. The space between the rubber layer 22 and running base 24 is filled with viscoelastic clear polyethylene material 27. The "Modified MARK III" ski used in the comparison test was of the same construction shown in FIG. 3. It will be noted that the constraining member 28 is not surrounded with viscoelastic material. The viscoelastic material 26 was sandwiched only between the constraining member 28 and the fiberglass layer 18, the side surfaces of the constraining member 28 are adjacent the running edges 20 and the bottom surface of the constraining member is adjacent the running surface layer 24. Other numerals in FIGS. 2 and 3 denote structural members similar to those described in connection with FIG. 1.

The vibration damping characteristics of both the shovel area and the entire forebody area of the skis were measured with the results thereof being set forth in Table 1 below. In measuring the vibration damping characteristics of the shovel area, the skis were clamped approximately midway between the shovel and binding areas, and the shovel end of the ski was deflected and released to vibrate. In measuring the vibration damping characteristics of the forebody, the skis were clamped at the binding area, and the shovel end of the ski was deflected and released to vibrate. The viscoelastic material used in the skis was made generally in accordance with the disclosure of Kalleberg and Turner U.S. Pat. No. 3,062,683 except that the glass fibers were omitted from the viscoelastic material and the viscoelastic material was carried on a plastic cloth skrim.

TABLE 1 __________________________________________________________________________ SHOVEL FOREBODY LOG HALF FREQUENCY LOG HALF FREQUENCY SKI DECREMENT LIFE(sec) (Hertz) DECREMENT LIFE(sec) (Hertz) __________________________________________________________________________ 1. Olin Mark III .052 .45 28.4 .064 .75 14.0 2. Modified Mark III .050 .48 30.5 .056 .84 14.6 3. FIG. 1 Ski a. Tail Anchored .131 .18 28.5 .105 .49 14.3 b. Completely Isolated .120 .21 28.5 .102 .43 14.0 __________________________________________________________________________

As will be noted from the above results shown in Table I, the vibration damping characteristics of the ski construction shown in FIG. 1 was vastly superior to the vibration damping characteristics of either the prior art Olin Mark III ski construction or the Modified Mark III construction wherein the vibration damping laminate of U.S. Pat. No. 3,537,717 was incorporated into the ski as an internal component thereof.

In fact, it will be noted, contrary to what one might expect, the vibration damping characteristics of the Modified Mark III ski tested were shown to be inferior to vibration damping characteristics of the prior art Olin Mark III ski as evidenced by the decrease in log Decrement and the increase in vibration half life time. The Modified Mark III ski displayed the poorest vibration damping characteristics of the three skis tested. The poor vibration damping characteristics of the Modified Mark III ski is the result of the failure to isolate the constraining member 28 from the remainder of the ski with elastomeric material.

The Log Decrement of the ski made in accordance with this invention increased by more than 100 percent in the shovel area test and by more than 80 percent in the forebody area test. Furthermore, the vibration half life for both the shovel and forebody portions of the ski was dramatically decreased. In each of the test specimens having an internal constraining member, e.g., Specimens 2 and 3(a) and 3(b), the internal constraining member extended for substantially the entire length of the ski. Specimen 3(a) had the constraining member anchored to the remainder of the ski at its tail end, and Specimen 3(b) had the constraining member completely isolated by viscoelastic material.

It will be readily apparent to those skilled in the art that the vibration damping technique disclosed herein will result in much quieter and more skiable skis. This invention allows the ski designer to put as little or as much damping in a ski as required. Also, the other characteristics of the ski can be designed at optimum values. By varying five factors set forth below which control the amount of damping obtained from the constrained viscoelastic laminate, the ski designer can tune the ski to obtain optimum damping. The five factors are:

1. The loss tangent of the viscoelastic material (should be greater than about 0.8).

2. The thickness of the viscoelastic material.

3. The volume of the viscoelastic material

4. The magnitude of the shear strain in the viscoelastic material

5. The modulus of elasticity and cross-sectional area of the constraining member.

It should be noted that while the constraining member shown in the embodiment of the invention specifically disclosed above is in the form of a sheet-like member, the constraining member could also be in the form of a rod, tube, wire, or other such form without departing from the spirit of the invention.

Since many changes and variations of the disclosed embodiment of the invention may be made without departing from the inventive concept, it is not intended to limit the invention otherwise than as required by the appended claims.