U.S. patent application number 13/380579 was filed with the patent office on 2012-04-26 for omni-directional angular acceration reduction for protective headgear.
This patent application is currently assigned to WAYNE STATE UNIVERSITY. Invention is credited to Albert I. King, King Hay Yang, Liying Zhang.
Application Number | 20120096631 13/380579 |
Document ID | / |
Family ID | 43386882 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120096631 |
Kind Code |
A1 |
King; Albert I. ; et
al. |
April 26, 2012 |
OMNI-DIRECTIONAL ANGULAR ACCERATION REDUCTION FOR PROTECTIVE
HEADGEAR
Abstract
Protective headgear includes an outer shell rotatable relative
to an inner shell via a thin layer of elastically and/or
plastically yielding material disposed between and secured to the
inner and outer shells. The yielding material deforms continuously
but non-linearly at least in the tangential or shear direction to
mitigate angular acceleration of the head during an impact. The
yielding material prevents the inner and outer shells from
separating or stopping suddenly to avoid imparting a large angular
acceleration to the head. In one embodiment, a protective helmet
includes an outer shell secured to an inner shell by a yielding
material that elastically deforms continuously but non-linearly
when subjected to an angular acceleration below a first threshold
and plastically deforms when subjected to an angular acceleration
above the first threshold.
Inventors: |
King; Albert I.; (Bloomfield
Hills, MI) ; Yang; King Hay; (West Bloomfield,
MI) ; Zhang; Liying; (Troy, MI) |
Assignee: |
WAYNE STATE UNIVERSITY
Detroit
MI
|
Family ID: |
43386882 |
Appl. No.: |
13/380579 |
Filed: |
June 24, 2010 |
PCT Filed: |
June 24, 2010 |
PCT NO: |
PCT/US2010/039769 |
371 Date: |
December 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61220268 |
Jun 25, 2009 |
|
|
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Current U.S.
Class: |
2/411 ;
2/410 |
Current CPC
Class: |
A42B 3/064 20130101 |
Class at
Publication: |
2/411 ;
2/410 |
International
Class: |
A42B 3/12 20060101
A42B003/12; A42B 3/00 20060101 A42B003/00 |
Claims
1. A helmet comprising: an inner shell; an outer shell generally
surrounding the inner shell; a thin layer disposed between, and
secured to, the inner shell and the outer shell, the thin layer
having a non-linear rate-dependent shear characteristic such that
the thin layer deforms during impact so the outer shell is
displaced relative to the inner shell to reduce angular
acceleration imparted to a head of a user.
2. The helmet of claim 1 wherein the inner shell comprises an
energy absorbing material.
3. The helmet of claim 1 wherein the thin layer comprises an
elastically deformable material.
4. The helmet of claim 1 wherein the thin layer comprises an
elastically deformable material having a shear stiffness that
increases non-linearly as a function of increasing
strain/deformation.
5. The helmet of claim 1 wherein the thin layer deforms
continuously but non-linearly with increasing stiffness as
deformation increases.
6. The helmet of claim 1 wherein the thin layer is generally
isotropic in the shear direction such that the outer shell rotates
with respect to the inner shell regardless of the direction of
impact or location of impact.
7. The helmet of claim 1 wherein the thin layer comprises a
material having shear properties such that relative rotation
between the inner and outer layers begins at a desired torque
corresponding to a tightness of fit for a particular type of
helmet.
8. The helmet of claim 7 wherein resistance to rotation increases
as a function of extent of rotation.
9. The helmet of claim 1 wherein the thin layer comprises a
deformable yielding material that deforms elastically when angular
acceleration is below a first threshold, but plastically when
angular acceleration exceeds the first threshold.
10. The helmet of claim 9 wherein the first threshold is about 6000
radians per second squared.
11. The helmet of claim 1 wherein the thin layer comprises a
yielding material that prevents the inner and outer shells from
stopping suddenly to avoid imparting a large angular acceleration
to the head.
12. The helmet of claim 1 wherein the thin layer comprises a
material having an isotropic rate-dependent shear stiffness that
increases non-linearly as deformation approaches a separation limit
of the inner and outer shells by relative rotation.
13. A method for mitigating angular acceleration imparted through
protective headgear to a user, the method comprising: securing an
inner shell of the headgear to an intermediate layer; securing an
outer shell of the headgear to an opposite side of the intermediate
layer; wherein the intermediate layer is a yielding material having
a shear stiffness that increases nonlinearly with increasing
relative displacement of the inner and outer shells due to
increasing deformation of the yielding material.
14. The method of claim 13 wherein the intermediate layer comprises
a material having a rate-dependent shear stiffness.
15. The method of claim 13 wherein the intermediate layer comprises
a yielding material that elastically deforms continuously but
nonlinearly.
16. The method of claim 13 wherein the intermediate layer is a
yielding material that elastically deforms continuously but
nonlinearly when subjected to an angular acceleration above below a
first threshold and plastically deforms when subjected to an
angular acceleration above the first threshold.
17. The method of claim 16 wherein the first threshold is about
6000 radians per second squared.
18. The method of claim 13 wherein the intermediate layer is
isotropic with respect to the shear stiffness.
19. A helmet comprising: an inner shell; an outer shell surrounding
the inner shell; an intermediate layer disposed between and
connected to the inner shell and the outer shell, the intermediate
layer comprised of a substantially isotropic yielding material that
deforms continuously, nonlinearly, and with a rate dependent shear
characteristic such that the intermediate layer deforms during
impact to allow rotation of the inner shell relative to the outer
shell to reduce angular acceleration imparted to a head of a
user.
20. The helmet of claim 19 wherein the intermediate layer
elastically deforms in response to an acceleration up to about 6000
radians per second squared and plastically deforms in response to
an acceleration exceeding about 6000 radians per second squared.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure is related to apparatus and methods
for reducing brain injuries associated with head impacts by
mitigating angular acceleration of the head during impacts.
[0003] 2. Background Art
[0004] Various types of protective headgear have been developed to
reduce injuries to the brain, skull, and neck resulting from head
impacts. Existing helmet designs often employ a hard outer shell in
combination with internal padding made of an energy-absorbing
material. The internal padding may be secured to the outer shell by
chemical fasteners, such as adhesives, or by mechanical fasteners,
such as hook and loop closures, or similar structures, for
example.
[0005] While conventional helmet designs generally reduce injuries
associated with linear acceleration due to impacts, they may not
adequately protect users from brain injuries such as subdural
hematoma and diffuse axonal injuries, for example, that may be
associated with angular or rotational acceleration. These types of
injuries have been recognized in the prior art with one proposed
solution providing a protective helmet having an outer shell
separated from an inner shell by a sliding layer to allow relative
displacement between the inner and outer shells. Relative movement
is constrained by a deformable connecting member secured to both
the inner and outer shells. Another prior art strategy allows an
outer layer to yield relative to an inner layer when subjected to a
tangential force that exceeds a selected threshold by using
rupturing means for attaching the outer layer to the remainder of
the headgear. A similar approach relies on a frictional coupling
between the outer and inner shells to allow relative movement
during an impact. However, movement between frictionally coupled
surfaces is generally difficult to control and requires a larger
starting force to overcome the static friction and lower sustaining
force to overcome the dynamic friction during an impact event.
SUMMARY
[0006] The apparatus and methods of the present disclosure solve
one or more problems of the prior art by providing protective
headgear having an outer shell designed to rotate with respect to a
user's head by insertion of a thin layer of elastically and/or
plastically yielding material between the outer shell and an inner
shell. The yielding material deforms continuously but non-linearly
at least in the tangential or shear direction to control angular
acceleration of the head. The yielding material prevents the inner
and outer shells from separating or stopping suddenly to avoid
imparting a large angular acceleration to the head. In one
embodiment, a protective helmet includes an outer shell secured to
an inner shell by a yielding material that elastically deforms
continuously but non-linearly when subjected to an angular
acceleration below a first threshold and plastically deforms when
subjected to an angular acceleration above the first threshold. In
one embodiment, the first threshold is about 6000 rad/s/s
(rad/s.sup.2). In another embodiment, the yielding material of the
inner layer has a rate-dependent shear stiffness that increases
non-linearly as the deformation approaches the limit of separating
the two layers by relative rotation.
[0007] Embodiments of the present disclosure have various
advantages. For example, protective headgear according to the
present disclosure reduces angular acceleration of the head to
reduce the risk of brain injury to the wearer. Use of a yielding
material with rate-dependent shear characteristics provides
continuous displacement between inner and outer shells with a low
or near-zero threshold for initial movement upon impact. Use of an
elastically deformable yielding material with nonlinear shear
characteristics facilitates applications where repeated impacts may
occur, such as in football helmets, for example. In addition, in
one embodiment, the yielding material is generally isotropic to
allow relative rotation between the inner and outer shell
regardless of the direction of impact or the location of the
impact. Protective headgear embodiments according to the present
disclosure can also control for the tightness of fit between the
head and the headgear using appropriate selection of the yielding
material for a particular application.
[0008] The above advantages and other advantages and features will
be readily apparent from the following detailed description of the
preferred embodiments when taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Exemplary embodiments of the present disclosure will become
more fully understood from the detailed description and the
accompanying drawings, wherein:
[0010] FIG. 1 is a partial cross-section cut-away of a protective
helmet according to one embodiment of the present disclosure;
and
[0011] FIG. 2 is a curve illustrating representative shear
characteristics of a yielding material for use in an apparatus or
method for reducing angular acceleration of the head during impacts
according to one embodiment of the present disclosure.
DETAILED DESCRIPTION
[0012] As those of ordinary skill in the art will understand,
various features of the embodiments illustrated and described with
reference to any one of the Figures may be combined with features
illustrated in one or more other Figures to produce embodiments
that are not explicitly illustrated or described. The combinations
of features illustrated provide representative embodiments for
typical applications. However, various combinations and
modifications of the features consistent with the teachings of the
present disclosure may be desired for particular applications or
implementations. The representative embodiments used in the
illustrations relate generally to protective headgear for various
types of competitive and recreational applications where single or
multiple impacts may occur such as football, as well as motorcycle,
scooter, bicycle, and horseback riding, for example. However, the
teachings of the present disclosure may also be used in other
applications. Those of ordinary skill in the art may recognize
similar applications or implementations with other engine/vehicle
technologies.
[0013] Reference will now be made to embodiments of the present
disclosure, which include the best mode of practicing the invention
presently contemplated by the inventors. The Figures are not
necessarily to scale. However, it is to be understood that the
disclosed embodiments are merely exemplary and that various other
embodiments are within the scope of the disclosure. Therefore,
specific details disclosed herein are not to be interpreted as
limiting, but merely as a representative basis for any aspect of
the disclosure and/or as a representative basis for teaching one
skilled in the art to variously employ the teachings herein.
Furthermore, the terminology used herein is used only for the
purpose of describing particular embodiments of the present
invention and is not intended to be limiting in any way.
[0014] With reference to FIG. 1, a cross-section of a
representative helmet 10 includes an inner shell 12 and an outer
shell 14 generally surrounding inner shell 12. Outer shell 14 and
inner shell 12 are separated by a thin layer 16 of a yielding
material to allow relative displacement or movement between inner
shell 12 and outer shell 14 during an impact. As shown in FIG. 1,
layer 16 is disposed between, and secured to, both inner shell 12
and outer shell 14. Inner shell 12 is generally made of an
elastically or plastically deformable energy absorbing material
that may vary depending on the type of protective headgear or
helmet 10. For example, headgear intended for a single impact, such
as a bicycle or motorcycle helmet, may include a plastically
deformable inner shell 12, while headgear intended for repeated
impacts of generally lesser force, such as a football helmet, may
include an elastically deformable inner shell 12.
[0015] In one embodiment, layer 16 is a yielding material having a
non-linear rate-dependent shear characteristic such that layer 16
deforms during an impact so outer shell 14 is displaced relative to
inner shell 12 to reduce angular acceleration imparted to a head of
a user (not shown). As generally illustrated in FIG. 2 and
described herein, layer 16 may be made of a yielding material that
is elastically deformable and/or plastically deformable depending
upon the particular application.
[0016] FIG. 2 is a graph 30 illustrating shear characteristics of a
representative yielding material for use in forming intermediate
layer 16 in protective headgear 10 according to one embodiment of
the present disclosure. As illustrated by graph 30, the
representative yielding material has a non-linear increasing shear
stiffness/stress as the strain/deformation increases. The yielding
material may have an elastically deformable characteristic 32 up to
a first threshold, generally represented by peak 34, where plastic
deformation occurs and the shear stiffness may decrease with
increasing deformation beyond peak 34. However, according to the
teachings of the present disclosure, the yielding material
characteristics should generally be selected so that shear
stiffness continually and non-linearly increases from a near-zero
starting point with peak 34 representing failure of the material to
avoid separation of the inner shell 12 from the outer shell 14, and
a large angular acceleration being imparted to the head due to a
sudden stop in relative movement between inner shell 12 and outer
shell 14. As also illustrated by portion 32 of graph 30, thin layer
16 deforms continuously but non-linearly with increasing shear
stiffness as deformation/strain increases.
[0017] According to one embodiment of the present disclosure, layer
16 includes a material that is generally isotropic in the shear
direction such that outer shell 14 rotates with respect to inner
shell 12 regardless of the direction of impact, or the location of
impact. As also shown in FIG. 2, the representative yielding
material may be selected with shear properties such that relative
rotation between the inner and outer layers begins at a desired
torque corresponding to a tightness of fit for a particular type of
helmet. In the illustrated example, the shear stiffness is near
zero for an application such as a bicycle helmet, but may be
increased for tighter fitting helmets, such as a football helmet,
for example. In general, the yielding material should have a shear
stiffness wherein resistance to relative rotation between inner
shell 12 and outer shell 14 increases as a function of extent of
rotation or displacement to avoid a sudden stop and associated
large angular acceleration to the head as previously described.
[0018] As those of ordinary skill in the art will appreciate, the
protective headgear as generally illustrated in the cross-section
of FIG. 1 using an intermediate layer 16 between inner shell 12 and
outer shell 14 having the characteristics generally illustrated and
described with respect to FIG. 2 illustrates one embodiment of a
method according to the present disclosure. The method for
mitigating angular acceleration imparted through protective
headgear to a user includes securing inner shell 12 of the headgear
10 to an intermediate layer 16 and securing outer shell 14 of
headgear 10 to an opposite side of intermediate layer 16, wherein
intermediate layer 16 is a yielding material having a shear
stiffness that increases nonlinearly with increasing relative
displacement of inner shell 12 and outer shell 14 due to increasing
deformation of the yielding material.
[0019] As such, embodiments of the present disclosure include
protective headgear having various advantages. For example,
protective headgear 10 according to the present disclosure reduces
angular acceleration of the head to reduce the risk of brain injury
to the wearer. Use of a yielding material for intermediate layer 16
with rate-dependent shear characteristics provides continuous
displacement between inner 12 and outer shells 14 with a low or
near-zero threshold for initial movement upon impact. Use of an
elastically deformable yielding material with nonlinear shear
characteristics facilitates applications where repeated impacts may
occur, such as in football helmets, for example. In addition, use
of a yielding material that is generally isotropic allows relative
rotation between the inner 12 and outer shell 14 regardless of the
direction of impact or the location of the impact. Protective
headgear embodiments according to the present disclosure can also
control for the tightness of fit between the head and the headgear
using appropriate selection of the yielding material for a
particular application.
[0020] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *