U.S. patent application number 11/044430 was filed with the patent office on 2005-09-15 for ball bat with a strain energy optimized barrel.
Invention is credited to Chauvin, Dewey, Chuang, Hsing-Yen, Giannetti, William B..
Application Number | 20050202909 11/044430 |
Document ID | / |
Family ID | 32716879 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050202909 |
Kind Code |
A1 |
Giannetti, William B. ; et
al. |
September 15, 2005 |
Ball bat with a strain energy optimized barrel
Abstract
A ball bat exhibits minimal strain energy losses associated with
bat-ball collisions by employing one or more integral interface
shear control zones (ISCZs) in the bat barrel, and/or by the
selection and placement of specific composite materials with
respect to the neutral axes in the barrel walls.
Inventors: |
Giannetti, William B.;
(Woodland Hills, CA) ; Chauvin, Dewey; (Simi,
CA) ; Chuang, Hsing-Yen; (Studio City, CA) |
Correspondence
Address: |
PERKINS COIE LLP
POST OFFICE BOX 1208
SEATTLE
WA
98111-1208
US
|
Family ID: |
32716879 |
Appl. No.: |
11/044430 |
Filed: |
January 26, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11044430 |
Jan 26, 2005 |
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10712251 |
Nov 13, 2003 |
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6866598 |
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10712251 |
Nov 13, 2003 |
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10336130 |
Jan 3, 2003 |
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6764419 |
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Current U.S.
Class: |
473/567 |
Current CPC
Class: |
A63B 59/50 20151001;
A63B 2102/18 20151001; A63B 2209/02 20130101; A63B 2209/00
20130101 |
Class at
Publication: |
473/567 |
International
Class: |
A63B 059/06 |
Claims
What is claimed is:
1. A ball bat including a barrel, a handle, and a tapered section
joining the barrel to the handle, with the barrel comprising: a
substantially cylindrical outer wall; a substantially cylindrical
inner wall located within the outer wall; and an ISCZ comprising a
flexible material, and separating the outer wall from the inner
wall, wherein the outer wall and the inner wall blend together at
at least one end of the barrel.
2. The ball bat of claim 1 wherein the flexible ISCZ material
comprises a fluoropolymer.
3. The ball bat of claim 2 wherein the flexible ISCZ material
comprises polytetraflouroethylene.
4. The ball bat of claim 1 wherein the flexible ISCZ material
comprises polyamide.
5. The ball bat of claim 1 wherein the flexible ISCZ material
comprises cellophane.
6. The ball bat of claim 1 wherein the ISCZ comprises a layer of a
bond-inhibiting material.
7. The ball bat of claim 1 wherein the outer wall and the inner
wall each comprise at least one fiber-reinforced resin composite
material.
8. The ball bat of claim 7 wherein the composite material includes
at least one material selected from the group consisting of glass,
graphite, boron, carbon, aramid, and ceramic.
9. The ball bat of claim 1 wherein the outer wall is divided into a
first outer section and a first inner section by a first neutral
axis, and the inner wall is divided into a second outer section and
a second inner section by a second neutral axis.
10. The ball bat of claim 9 wherein the first and second outer
sections each comprise a structural glass-reinforced epoxy resin,
and the first and second inner wall sections each comprise a
graphite-reinforced epoxy resin.
11. The ball bat of claim 1 further comprising a substantially
cylindrical additional wall located within the inner wall.
12. The ball bat of claim 11 wherein the additional wall is
separated from the inner wall by an additional interface shear
control zone.
13. The ball bat of claim 1 wherein the ISCZ is located
approximately at the radial midpoint of the barrel, such that the
outer wall and the inner wall have approximately the same radial
thickness.
14. The ball bat of claim 1 wherein the outer wall and the inner
wall blend together at both ends of the barrel.
15. The ball bat of claim 1 wherein the outer wall and the inner
wall blend together at the tapered section of the ball bat.
16. A ball bat including a barrel, a handle, and a tapered section
joining the barrel to the handle, with the barrel comprising: a
substantially cylindrical outer wall; a substantially cylindrical
inner wall located within the outer wall; and an ISCZ separating
the outer wall from the inner wall, with the ISCZ comprising at
least one material selected from the group consisting of
fluorinated ethylene propylene, polyvinyl fluoride,
ethylenetetrafluoroethylene, polychlorotrifluoroethylene,
polytetraflouroethylene, polymethylpentene, polyamide, and
cellophane.
17. The ball bat of claim 16 wherein the outer wall and the inner
wall blend together at at least one end of the barrel.
18. A ball bat including a barrel, a handle, and a tapered section
joining the barrel to the handle, with the barrel comprising: a
substantially cylindrical outer wall; a substantially cylindrical
inner wall located within the outer wall; and a flexible
bond-inhibiting layer separating the outer wall from the inner
wall.
19. The ball bat of claim 18 wherein the outer wall and the inner
wall blend together at at least one end of the barrel.
20. The ball bat of claim 18 wherein the bond-inhibiting layer
comprises at least one material selected from the group consisting
of fluorinated ethylene propylene, polyvinyl fluoride,
ethylenetetrafluoroethylene, polychlorotrifluoroethylene,
polytetraflouroethylene, polymethylpentene, polyamide, and
cellophane.
Description
[0001] This application is a Continuation of U.S. patent
application Ser. No. 10/712,251, filed Nov. 13, 2003, and now
pending, which is a Continuation-In-Part of U.S. patent application
Ser. No. 10/336,130, filed Jan. 3, 2003, which issued as U.S. Pat.
No. 6,764,419 on Jul. 20, 2004, each of which are incorporated
herein by reference.
BACKGROUND
[0002] Baseball and softball bat manufacturers are continually
attempting to develop ball bats that exhibit increased durability
and improved performance characteristics. Ball bats typically
include a handle, a barrel, and a tapered section joining the
handle to the barrel. The outer shell of these bats is generally
formed from aluminum or another suitable metal, and/or one or more
composite materials.
[0003] Barrel construction is particularly important in modern bat
design. Barrels having a single-wall construction, and more
recently, a multi-wall construction, have been developed. Modern
ball bats typically include a hollow interior, such that the bats
are relatively lightweight and allow a ball player to generate
substantial "bat speed" or "swing speed."
[0004] Single-wall bats generally include a single tubular spring
in the barrel section. Multi-wall barrels typically include two or
more tubular springs, or similar structures, that may be of the
same or different material composition, in the barrel section. The
tubular springs in these multi-wall bats are typically either in
contact with one another, such that they form friction joints, are
bonded to one another with weld or bonding adhesive, or are
separated from one another forming frictionless joints. If the
tubular springs are bonded using a structural adhesive, or other
structural bonding material, the barrel is essentially a
single-wall construction. U.S. Pat. No. 5,364,095, the disclosure
of which is herein incorporated by reference, describes a variety
of bats having multi-walled barrel constructions.
[0005] It is generally desirable to have a bat barrel that is
durable, while also exhibiting optimal performance characteristics.
Hollow bats typically exhibit a phenomenon known as the "trampoline
effect," which essentially refers to the rebound velocity of a ball
leaving the bat barrel as a result of flexing of the barrel
wall(s). Thus, it is desirable to construct a ball bat having a
high "trampoline effect," so that the bat may provide a high
rebound velocity to a pitched ball upon contact.
[0006] The "trampoline effect" is a direct result of the
compression and resulting strain recovery of the barrel. During
this process of barrel compression and decompression, energy is
transferred to the ball resulting in an effective coefficient of
restitution (COR) of the barrel, which is the ratio of the post
impact ball velocity to the incident ball velocity (COR=Vpost
impact/Vincident). In other words, the "trampoline effect" of the
bat improves as the COR of the bat barrel increases.
[0007] Multi-walled bats were developed in an effort to increase
the amount of acceptable barrel deflection beyond that which is
possible in typical single-wall designs. These multi-walled
constructions generally provide added barrel deflection, without
increasing stresses beyond the material limits of the barrel
materials. Accordingly, multi-wall barrels are typically more
efficient at transferring energy back to the ball, and the more
flexible property of the multi-wall barrel reduces undesirable
deflection and deformation in the ball, which is typically made of
highly inefficient material.
[0008] Additionally, a multi-wall bat differs from a single-wall
bat because there is no shear energy transfer through the interface
shear control zone(s) ("ISCZ"), i.e., the region(s) between the
barrel walls. As a result of strain energy equilibrium, this shear
energy, which creates shear deformation in a single-wall barrel, is
converted to bending energy in a multi-wall barrel. And since
bending deformation is more efficient in transferring energy than
is shear deformation, the walls of a multi-wall bat typically
exhibit a lower strain energy loss than a single wall design. Thus,
multi-wall barrels are generally preferred over single-wall designs
for producing efficient bat-ball collision dynamics, or a better
"trampoline effect."
[0009] In a single wall bat, a single neutral axis, which is
defined as the centroid axis about which all deformation occurs, is
present for both radial and axial deformations. The shear stress in
the barrel wall is at a maximum, and the bending stress is zero,
along this neutral axis. In a multi-wall bat, an additional
independent neutral axis results from each ISCZ present, i.e., each
wall of a multi-wall barrel includes an independent neutral axis.
As the bat barrel is impacted, each barrel wall deforms such that
the highest compressive stresses occur radially above (i.e., on the
impact side of) the neutral axis, while the highest tensile
stresses occur radially below (i.e., on the non-impact side of) the
neutral axis.
[0010] In general, as the wall thickness or barrel stiffness is
increased in a bat barrel, the COR decreases. It is important to
maintain a sufficient wall thickness, however, because the
durability of the ball bat typically decreases if the wall(s) are
too thin. If the barrel wall(s) are too thin, the barrel may be
subject to denting, in the case of metal bats, or to progressive
material failure, in the case of composite bats. As a result, the
performance and lifetime of the bat may be reduced if the barrel
wall(s) are not thick enough.
[0011] The use of composite materials has become increasingly
popular in modern barrel design. The impact and fracture behavior
of composite materials is very complex. Structural composite
materials do not undergo plastic deformation, like metals, but
undergo a series of local fractures resulting in a highly
complicated redistribution of stress. When these resultant stresses
exceed a predefined limit, ultimate breakdown of the structure
occurs. It is very difficult, if not impossible, to accurately
predict the initiation and progression of failure in these complex
structures based on the behavior of unidirectional laminates in the
structure. There is a way, however, to predict the amount of
elastic energy that can be stored per unit mass for a particular
mode of stressing. This is defined as the specific energy storage,
which is the amount of energy that can be stored in a material
before the material fails.
[0012] The specific energy storage capability of a material for
tensile or compression loading is defined as follows:
.xi.=.sigma..sub.It.sup.2/E.sub.It.rho.
[0013] where
[0014] .xi.=specific energy storage
[0015] .sigma..sub.It=ultimate longitudinal tensile (or
compressive) strength
[0016] E.sub.It=Young's longitudinal tensile (or compressive)
modulus
[0017] .rho.=density
[0018] Thus, a material with high tensile/compressive strength and
low modulus and density will have good energy storage
properties.
[0019] Elastic materials undergo deformation (i.e., spring like
behavior) when influenced by the application of a force. Under
conditions such as impact loading, when large forces are applied
over short periods of time, kinetic energy is transformed at the
elastic material interface into potential energy in the form of
deformation. As a result of entropy, some irreversible losses, in
the form of noise and heat, occur during this energy transfer
process.
[0020] When the available kinetic energy of impact is transformed
into deformation in the elastic material, the elastic material
releases this stored energy in the form of kinetic energy back to
the impacting body (i.e., the ball), if it is in contact, and/or
the stored energy is dissipated within the elastic material, if the
impacting body is not in contact with the elastic material. As a
result of irreversible energy losses, the elastic material
eventually returns to its original stress-free condition.
[0021] The total conservation of energy equation for a bat-ball
collision is as follows:
U.sub.K1b+U.sub.K2b=U.sub.K1a+U.sub.K2a+U.sub.II+U.sub.BM+U.sub.MS
[0022] where,
[0023] U.sub.K1b=ball kinetic energy before impact
[0024] U.sub.Kb2=bat kinetic energy before impact
[0025] U.sub.K1a=ball kinetic energy after impact
[0026] U.sub.K2a=bat kinetic energy after impact
[0027] U.sub.II=local bat and ball strain energy loss
[0028] U.sub.BM=energy loss associated with bat beam modes
[0029] U.sub.MS=energy losses associated with heat and noise
[0030] (Mustone, Timothy J., Sherwood, James, "Using LS-DYNA to
Develop a Baseball Bat Performance and Design Tool", 6th
International LS-DYNA Users Conference, Detroit, Mich., Apr. 9-10,
2000).
[0031] Control and optimization of these losses is important to the
design of high performance durable ball bats, particularly the
losses associated with local bat and ball strain energy. The other
losses, such as those associated with heat and noise, although a
significant component in the overall equilibrium equation, are
minor in comparison to the strain energy losses. Thus, to design a
high performance durable bat, it is desirable to minimize strain
energy losses in the barrel of the ball bat.
SUMMARY OF THE INVENTION
[0032] The invention is directed to a ball bat that exhibits
minimal strain energy losses associated with bat-ball collisions by
employing one or more integral interface shear control zones in the
bat barrel, and/or by the selection and placement of specific
composite materials with respect to the neutral axes in the barrel
walls.
[0033] Further embodiments, including modifications, variations,
and enhancements of the invention, will become apparent. The
invention resides as well in subcombinations of the features shown
and described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] In the drawings, wherein the same reference number indicates
the same element throughout the several views:
[0035] FIG. 1 is a perspective view of a ball bat.
[0036] FIG. 2 is a perspective partially cutaway view of the ball
bat illustrated in FIG. 1.
[0037] FIG. 3 is a close up sectional view of Section A of FIG.
1.
[0038] FIG. 4 is a diagrammatic view of the barrel cross section
illustrated in FIG. 3.
[0039] FIG. 5 is a table showing various properties of common
composite structural materials.
DETAILED DESCRIPTION OF THE DRAWINGS
[0040] Turning now in detail to the drawings, as shown in FIGS. 1
and 2, a baseball or softball bat 10, hereinafter collectively
referred to as a "ball bat" or "bat," includes a handle 12, a
barrel 14, and a tapered section 16 joining the handle 12 to the
barrel 14. The free end of the handle 12 includes a knob 18 or
similar structure. The barrel 14 is preferably closed off by a
suitable cap 20 or plug. The interior 19 of the bat 10 is
preferably hollow, which allows the bat 10 to be relatively
lightweight so that ball players may generate substantial bat speed
when swinging the bat 10.
[0041] The ball bat 10 preferably has an overall length of 20 to 40
inches, more preferably 26 to 34 inches. The overall barrel
diameter is preferably 2.0 to 3.0 inches, more preferably 2.25 to
2.75 inches. Typical bats have diameters of 2.25, 2.69, or 2.75
inches. Bats having various combinations of these overall lengths
and barrel diameters are contemplated herein. The specific
preferred combination of bat dimensions is generally dictated by
the user of the bat 10, and may vary greatly between users.
[0042] The present invention is primarily directed to the ball
striking area of the bat 10, which typically extends throughout the
length of the barrel 14, and which may extend partially into the
tapered section 16 of the bat 10. For ease of description, this
striking area will generally be referred to as the "barrel"
throughout the remainder of the description.
[0043] As illustrated in FIG. 2, the barrel 14 is made up of one or
more substantially cylindrical layers. The actual shape of each
barrel layer may vary according to the desired shape of the overall
barrel structure. Accordingly, "substantially cylindrical" will be
used herein to describe cylindrical barrel layers, as well as other
similar barrel shapes. The barrel 14 preferably includes an outer
barrel wall 22 and an inner barrel wall 24 located within the outer
barrel wall 22, each preferably made up of one or more plies 38 of
a composite material. Alternatively, the barrel 14 may include only
a single wall, or may include three or more walls. The barrel
wall(s) may additionally or alternatively be made of one or more
metallic materials, such as aluminum or titanium.
[0044] A bond inhibiting layer 30, or a disbonding layer,
preferably separates the outer barrel wall 22 from the inner barrel
wall 24. The bond inhibiting layer 30 acts as an interlaminar shear
control zone ("ISCZ") between the outer wall 22 and the inner wall
24. Accordingly, the bond inhibiting layer 30 prevents shear
stresses from passing between the outer wall 22 and the inner wall
24, and also prevents the outer wall 22 from bonding to the inner
wall 24 during curing of the bat 10, and throughout the life of the
bat 10. Because the bond inhibiting layer 30 acts as an ISCZ, the
outer barrel wall 22 has a first neutral axis 32, and the inner
barrel 24 wall has a second neutral axis 34, as described
above.
[0045] The bond-inhibiting layer 30 preferably has a radial
thickness of approximately 0.001 to 0.004 inches, more preferably
0.002 to 0.003 inches. The bond-inhibiting layer is preferably made
of a fluoropolymer, such as FEP (fluorinated ethylene propylene),
PVF (Polyvinyl Fluoride), ETFE (EthyleneTetrafluoroethylene), PCTFE
(PolyChloroTriFluoroEthylene), or PTFE/Teflon.RTM.
(Polytetraflouroethylene), and/or another material, such as PMP
(Polymethylpentene), Nylon (polyamide), or Cellophane. Other ISCZs,
such as a friction joint, a sliding joint, or an elastomeric joint,
may be used as an alternative to the bond inhibiting layer 30. The
bond inhibiting layer 30, or other ISCZ, may be located at the
radial midpoint of the barrel 14, such that each barrel wall 22, 24
has approximately the same radial thickness, or it may be located
elsewhere in the barrel 14. Thus, the bond-inhibiting layer 30 is
shown at the approximate radial midpoint of the barrel 14 by way of
example only.
[0046] If the barrel 14 includes three or more walls, a
bond-inhibiting layer 30 or other ISCZ is preferably located
between each of the barrel walls, to increase barrel deflection.
Thus, a three-wall barrel preferably includes two bond-inhibiting
layers 30 or other ISCZs, a four-wall barrel preferably includes
three bond-inhibiting layers 30 or other ISCZs, etc. Alternatively,
bond-inhibiting layers 30 or ISCZs may be located between selected
barrel walls only. For ease of description, a two-wall barrel 14
will be discussed herein, but any other number of barrel walls may
be employed in the ball bat 10.
[0047] In the embodiment illustrated in FIGS. 2 and 3, the outer
barrel wall 22 and the inner barrel wall 24 each include a
plurality of composite plies 38. The composite materials used are
preferably fiber-reinforced, and may include glass, graphite,
boron, carbon, aramid, ceramic, kevlar, and/or any other suitable
reinforcement material, preferably in epoxy form. Each composite
ply preferably has a thickness of approximately 0.003 to 0.008
inches, more preferably 0.005 to 0.006 inches. The overall radial
thickness of each barrel wall 22, 24 (including barrel portions on
both sides of the central axis of the bat) is preferably
approximately 0.060 inches to 0.100 inches, more preferably 0.075
to 0.090 inches. Optimal selection and placement of the specific
composite materials employed in the ball bat 10 is described in
detail below.
[0048] The radial location of the neutral axis in each wall varies
according to the distribution of the composite layers, and the
stiffness of the specific layers. Only the radial components of
stress are considered herein, due to their high relative magnitude
in comparison to the axial stresses present. If a barrel wall is
made up of homogeneous isotropoic layers, the neutral axis will be
located at the midpoint of the wall. If more than one composite
material is used in a wall, and/or if the material is not uniformly
distributed, the neutral axis may reside at a different radial
location. Thus, the first and second neutral axes 32, 34 are shown
at the approximate radial midpoints of their respective walls 22,
24 by way of example only.
[0049] As illustrated in the diagram of FIG. 4, a double-wall
barrel structure may be broken down into four zones, numbered 1, 2,
3, and 4. Zones 1 and 3 are the outer and inner barrel wall
compressive stress regions, as they are located above, or radially
outwardly from (i.e., on the impact side of), their respective
neutral axes. Zones 2 and 4 are the outer and inner barrel wall
tensile stress regions, as they are located below, or radially
inwardly from (i.e., on the non-impact side of), their respective
neutral axes.
[0050] Materials in compressive zones 1 and 3 are used primarily to
increase the durability of the barrel 14. Materials in tensile
zones 2 and 4 are used primarily to increase the stiffness of the
barrel 14, and to substantially match the fundamental frequencies
of the outer and inner barrel walls 22, 24 to minimize energy
losses in the barrel 14. The fundamental frequency of each barrel
wall 22, 24 preferably falls within a constructive coupling range
between the walls 22, 24, such that minimal losses are encountered
during the energy transfer from the outer barrel wall 22 to the
inner barrel wall 24. In a preferred embodiment, the fundamental
hoop frequency (i.e., the vibration measured around the diameter of
the barrel wall) of the outer barrel wall 22 is within 20%, more
preferably 10%, of the fundamental hoop frequency of the inner
barrel wall 24. The fundametal hoop frequency of each of the outer
and inner walls 22, 24 is preferably in the range of 900 to 2000
Hz, more preferably 1000 to 1200 Hz.
[0051] Various properties of several common structural composite
materials are listed in Table 1 of FIG. 5. High specific energy
storage compression materials are best suited to zones 1 and 3,
while high stiffness (i.e., high tensile modulus) materials are
best suited to zones 2 and 4. The composite materials used in zones
1 and 3 define the resultant durability of the structure, while the
composite materials used in zones 2 and 4 adjust the stiffness of
the barrel for maximum coupling of energy transfer between the
outer and inner walls 22, 24. Accordingly, by placing specific
materials in specific zones, the performance and durability of the
structure can be modified independently of one another.
[0052] In a preferred embodiment, structural (S) glass-reinforced
epoxy resin, or S-glass epoxy, is used predominantly in zones 1 and
3, due to its extremely high specific energy storage in compression
(approximately 2230 psi). Boron-reinforced epoxy resin, or boron
epoxy, which has a specific energy storage in compression of
approximately 2220 psi, may additionally or alternatively be used
in zones 1 and 3. Other materials having a high specific energy
storage in compression may additionally or alternatively be used in
zones 1 and 3. Preferably, the materials used in zones 1 and 3 have
a specific energy storage in compression of at least 2000 psi, and
more preferably, 2200 to 2400 psi. The material(s) used in zone 1
may be the same, or may differ, from those used in zone 3.
[0053] S-glass epoxy may also be utilized in zones 2 and 4, due to
its high tensile specific energy storage (approximately 4790 psi).
Indeed, from a durability standpoint, the entire barrel would
benefit from a 100% S-glass multi-wall structure. S-glass epoxy,
however, has a relatively low stiffness, or tensile modulus
(approximately 6.91 million psi). Thus, if S-glass epoxy were used
predominantly in zones 2 and 4, barrel performance would suffer due
to a lack of barrel stiffness and poor energy coupling between the
barrel walls 22, 24. Accordingly, graphite-reinforced epoxy resin,
or graphite epoxy, which has a stiffness or tensile modulus of
approximately 20 million psi, is preferably predominantly used in
zones 2 and 4, for adjusting the stiffness of the barrel. A limited
amount of S-glass epoxy may also be used in zones 2 and 4,
however.
[0054] Boron epoxy, which has a stiffness or tensile modulus of
approximately 29.6 million psi, may additionally or alternatively
be used in zones 2 and 4. Graphite epoxy is preferred over boron
epoxy, however, because the tensile specific energy storage of
graphite epoxy (approximately 1380 psi) is much greater than the
tensile specific energy storage of boron epoxy (approximately 565
psi).
[0055] Other materials having a high stiffness or tensile modulus,
preferably in conjunction with a relatively high tensile specific
energy storage, may additionally or alternatively be used in zones
2 and 4. Preferably, the materials used in zones 2 and 4 have a
stiffness or tensile modulus of at least 18 million psi, and more
preferably 20 to 30 million psi. The materials used in zones 2 and
4 also preferably have a tensile specific energy storage of at
least 1000 psi, although the stiffness of the material, which
dictates bat performance, is the more significant variable. The
material(s) used in zone 2 may be the same, or may differ, from
those used in zone 4.
[0056] The layers of selected composite materials may be oriented
at various angles relative to their respective neutral axes 32, 34
to further modify or enhance barrel performance and durability, and
to better match the fundamental frequencies of the outer and inner
barrel walls 22, 24. In a preferred embodiment, each of the
composite plies 38 in zones 1 and 3 is oriented at approximately 50
to 700 relative to their respective neutral axes 32, 34. Each of
the composite plies 38 in zones 2 and 4 is preferably oriented at
approximately 20 to 50.degree. relative to their respective neutral
axes 32, 34. Each ply within a zone may be oriented at the same or
different angles than other plies in that zone. Thus, the location
and orientation of specific structural layers with respect to the
neutral axes allows the barrel durability to be enhanced, while
minimizing strain energy losses in the barrel.
[0057] The idea of locating graphite epoxy in the tensile zones
(zones 2 and 4) was not initially intuitive. Previous barrel
designs, having graphite epoxy predominantly located in zones 1 and
3, were subjected to durability tests. When the tests were
concluded, no graphite epoxy fiber failure was witnessed in the
compressive zones (zones 1 and 3) of the barrel. Accordingly, there
was no motivation to move the graphite fibers into the tensile
zones, since compressive failure did not appear to occur in the
graphite epoxy fibers.
[0058] The graphite epoxy was moved to the tensile zones in the
design of a sample bat according to one embodiment of the present
invention, and S-glass epoxy was used predominantly in the
compressive zones. Durability tests were then performed on the bat,
and it was surprisingly discovered that durability increased by a
factor of three (e.g., from approximately 150 ball hits until
failure, to approximately 450 ball hits until failure) over the
previous designs.
[0059] Thus, while initial analysis did not indicate compressive
failure of the graphite epoxy fibers in the previous bat designs,
it is likely that unseen graphite fiber failure was actually
occurring in the compressive zones. In other words, the discovery
of a dramatic increase in bat durability, resulting from moving
graphite epoxy fibers to the tensile zones of the bat barrel, and
using S-glass epoxy in the compressive zones of the bat barrel, was
unexpected, since analysis did not indicate that compressive fiber
failure was occurring in samples constructed following previous
designs.
[0060] The bat 10 is generally constructed by rolling the various
layers of the bat 10 onto a mandrel or similar structure having the
desired bat shape. The ends of the layers are preferably "clocked"
or offset from one another so that they do not all end in the same
location before curing. Accordingly, when heat and pressure are
applied to cure the bat 10, the various barrel layers blend
together into a distinctive "one-piece" multi-wall construction.
Put another way, all of the layers of the bat are "co-cured" in a
single step, and blend or terminate together at at least one end,
resulting in a single-piece multi-wall structure with no gaps (at
the at least one end), such that the barrel 14 is not made up of a
series of tubes, each with a wall thickness that terminates at the
ends of the tubes. As a result, all of the layers act in unison
under loading conditions, such as during striking of a ball.
[0061] The blending of the layers into a single-piece multi-wall
construction, like tying the ends of a leaf spring together, offers
an extremely durable assembly, particularly when impact occurs at
the extreme ends of the layer separation zones. By blending the
multiple layers together, the barrel 14 acts as a unitized
structure where no single layer works independently of the other
layers. One or both ends of the barrel 14 may terminate together in
this manner to form the one-piece barrel.
[0062] In a preferred embodiment, the bat 10 is constructed as
follows. First, the various layers of the bat 10 are pre-cut and
pre-shaped with conventional machinery. Composite plies 38 used to
form the inner wall tensile zone, such as graphite epoxy, and/or
other suitable materials, are rolled onto the bat-shaped mandrel.
Composite plies 38 used to form the inner wall compressive zone,
such as S-glass epoxy, and/or other suitable materials, are then
rolled onto the plies 38 of the inner wall tensile zone.
[0063] A bond-inhibiting layer 30, or other ISCZ layer or material,
may then be rolled onto the plies 38 of the inner wall compressive
zone, if such a layer is desired. Next, composite plies 38 used to
form the outer wall tensile zone, such as graphite epoxy, and/or
other suitable materials, are rolled onto the bond-inhibiting layer
30, or onto the plies 38 of the inner wall compressive section if a
bond-inhibiting layer 30 is not employed. Composite plies 38 used
to form the outer wall compressive zone, such as S-glass epoxy,
and/or other suitable materials, are then rolled onto the plies 38
of the outer wall tensile zone.
[0064] As described above, the composite plies 38 are preferably
rolled onto the mandrel such that their ends are offset from
another, so that they do not all end in the same location before
curing. Once all of the layers are arranged, heat and pressure are
applied to the layers to cure the bat 10 into a one-piece
multi-wall barreled structure, in which the ends of the layers all
terminate together such that there are no gaps between the barrel
walls and the ISCZ. The layers may be arranged to terminate in this
manner at one or both ends of the barrel 14.
[0065] The described bat construction, and method of making the
same, provides a bat having excellent "trampoline effect" and
durability. These results are primarily due to the selection and
placement of specific materials relative to the neutral axes in the
outer and inner barrel walls 22, 24. Specifically, locating
materials having a high specific energy storage in compression
above the neutral axes, and materials with a high stiffness or
tensile modulus below the neutral axes, yields a durable high
performance ball bat. Additionally, the blending of barrel layers
in a single curing step provides for increased durability,
especially during impact at the extreme ends of the barrel
layers.
[0066] Thus, while several embodiments have been shown and
described, various changes and substitutions may of course be made,
without departing from the spirit and scope of the invention. The
invention, therefore, should not be limited, except by the
following claims and their equivalents.
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