U.S. patent application number 11/682200 was filed with the patent office on 2007-11-08 for new al-cu-li-mg-ag-mn-zr alloy for use as structural members requiring high strength and high fracture toughness.
This patent application is currently assigned to ALCAN ROLLED PRODUCTS-RAVENSWOOD, LLC. Invention is credited to Alex Cho.
Application Number | 20070258847 11/682200 |
Document ID | / |
Family ID | 33490603 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070258847 |
Kind Code |
A1 |
Cho; Alex |
November 8, 2007 |
NEW Al-Cu-Li-Mg-Ag-Mn-Zr ALLOY FOR USE AS STRUCTURAL MEMBERS
REQUIRING HIGH STRENGTH AND HIGH FRACTURE TOUGHNESS
Abstract
An improved aluminum lithium alloy comprising 0.1 to 2.5 wt. %
Li, 2.5 to 5.5 wt. % Cu, 0.2 to 1.0 wt. % Mg, 0.2 to 0.8 wt. % Ag,
0.2 to 0.8 wt. % Mn, up to 0.4 wt. % Zr or other grain refiner such
as chromium, titanium, hafnium, scandium or vanadium, the balance
aluminum. The present alloy exhibits an improved combination of
strength and fracture toughness, over any thickness range. The
present invention is further directed to methods for preparing and
using Al--Li alloys as well as to products comprising the same.
Inventors: |
Cho; Alex; (Charleston,
WV) |
Correspondence
Address: |
Womble Carlyle Sandridge & Rice, PLLC;Attn: Patent Docketing 32nd Floor
P.O. Box 7037
Atlanta
GA
30357-0037
US
|
Assignee: |
ALCAN ROLLED PRODUCTS-RAVENSWOOD,
LLC
Ravenswood
WV
|
Family ID: |
33490603 |
Appl. No.: |
11/682200 |
Filed: |
March 5, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10853721 |
May 26, 2004 |
7229509 |
|
|
11682200 |
Mar 5, 2007 |
|
|
|
60473443 |
May 28, 2003 |
|
|
|
Current U.S.
Class: |
420/533 ;
148/417 |
Current CPC
Class: |
C22C 21/16 20130101 |
Class at
Publication: |
420/533 ;
148/417 |
International
Class: |
C22C 21/16 20060101
C22C021/16 |
Claims
1. An aluminum alloy having improved strength and fracture
toughness comprising: Cu: 2.5-5.5 wt. % Li: 0.8-2.5 wt. % Mg: 0.2-1
wt. % Ag: 0.2-0.8 wt. % Mn: 0.2-0.8 wt. % Zr: up to 0.3 wt. %
balance A1 and normal and/or inevitable elements and
impurities.
2. An alloy according to claim 1, comprising 3 to 4 wt. %
copper.
3. An alloy according to claim 1, comprising 0.8 to 1.8 wt. %
lithium.
4. An alloy according to claim 1, comprising 0.8 to 1.5 wt. %
lithium.
5. An alloy according to claim 3, comprising 0.8 to 1.2 wt. %
lithium.
6. An alloy according to claim 1, comprising 0.3 to 0.5 wt. %
magnesium.
7. An alloy according to claim 1, comprising 0.3 to 0.5 wt. %
silver.
8. An alloy according to claim 1, comprising 0.3 to 0.5 wt. %
manganese.
9. An alloy according to claim 1, comprising 0.05 to 0.15%
zirconium.
10. An aluminum alloy having improved strength and fracture
toughness comprising: from about 2.5 to 5.5 wt. % copper, from
about 0.8 to 2.5 wt. % lithium, from about 0.2 to 1 wt. %
magnesium, from about 0.2 to 0.8 wt. % silver, from about 0.2 to
0.8 wt. % manganese, optionally one or more elements selected from
the group consisting of: (i) up to 0.3 wt. % Zr, (ii) up to 0.8 wt.
% Cr, (iii) up to 0.12 wt. % Ti, (iv) up to 0.8 wt. % Sc, and (v)
up to 0.2 wt. % V.
11. A rolled product comprising an aluminum alloy according to
claim 10, with a thickness of at least about 3 inches, exhibiting
in a solution heat-treated, quenched, stress-relieved and
artificially aged condition, at least one set of properties
selected from the group consisting of: (a) UTS (L)>70 ksi (482.6
MPa) and KE (L)>34 ksNinch (37.4 MPaJm), (b) TYS (L)>65 ksi
(448.2 MPa) and K.sub.ic (L)>34 ksi''Jinch (37.4 MParlm), (c)
UTS (LT)>70 ksi (482.6 MPa) and K.sub.ic (L-T)>27 ksiAlinch
(29.7 MPa-Jm), (d) TYS (LT)>62 ksi (427.5 MPa) and K.sub.1c
(L-T)>26 ksi .sup.qinch (28.6 MPaVm), (e) UTS (ST)>70 ksi
(482.6 MPa) and K.sub.ic (S-T)>24 ksi-.sup.qinch (26.4 MPaVm)
and (f) TYS (ST)>60 ksi (413.7 MPa) and K.sub.ic (S-T)>23
ksiAlinch (25.3 MPajm).
12. A rolled product comprising an aluminum alloy according to
claim 9, with a thickness of less than about 3 inches (76.2 mm),
exhibiting in a solution heat-treated, quenched, stress-relieved
and artificially aged condition at least one set of properties
selected from the group consisting of: (a) UTS (L)>76 ksi (524.0
MPa) and K.sub.IC (L)>35 ksi inch (38.5 MPa m), (b) TYS
(L)>71 ksi (489.5 MPa) and K.sub.IC (L)>35 ksi inch (38.5 MPa
m), (c) UTS (LT)>75 ksi 517.1 MPa) and K.sub.IC (L-T)>29 ksi
inch (31.9 MPa m), (d) TYS (LT)>68 ksi (468.8 MPa) and K.sub.IC
(L-T)>29 ksi inch (31.9 MPa m), (e) UTS (ST)>76 ksi (524.0
MPa) and K.sub.IC (S-T)>26 ksi inch (28.6 MPa m) and (f) TYS
(ST)>65 ksi (448.2 MPa) and K.sub.IC (S-T)>26 ksi inch (28.6
MPa m).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. Ser. No.
10/853,721 filed May 26, 2004 which claims priority from U.S.
Provisional Ser. No. 60/473,443, filed May 28, 2003, the content of
each are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the invention
[0003] The present invention relates to aluminum-lithium based
alloy products, particularly those suitable for use as structural
members in aircraft construction, such as in bulkhead, spars, wing
skin, frames, extruded structural members, and fuselage
applications, as well as other applications where a combination of
high strength and high fracture toughness are typically desirable
and/or required.
[0004] 2. Description of Related Art
[0005] In many industries and particularly in the aircraft
industry, reducing the weight of structures has always been a
concern. One effective way of doing this is to reduce the density
of aluminum alloys used in such structures. It is well known in the
art that aluminum alloy densities may be reduced by the addition of
lithium. However, it is also known that some problems arise when
lithium is added to aluminum based alloys. One of the problems
encountered is the possible decrease in ductility and fracture
toughness.
[0006] Most structural applications in the aircraft industry, and
particularly applications such as products intended for use in
lower wing skin structures, require a high level of strength, as
well as a high level of fracture toughness. It is also desirable
for aircraft and other similar applications, that ductility and
corrosion behavior remain at an acceptable level.
[0007] Among aluminum-lithium based alloys, Al--Cu--Li--Mg--Ag
alloys are well-known in the prior art for their interesting
properties. Specifically, U.S. Pat. No. 5,032,359 discloses an
alloy with a broad composition of 2.0 to 9.8 wt. % of an alloying
element, which may be copper, magnesium, or mixtures thereof, the
magnesium being at least 0.05 wt. %, from about 0.01 to about 2.0
wt. % silver, from about 0.2 to about 4.1 wt. % lithium, and from
about 0.05 to about 1.0 wt. % of a grain refining additive selected
from zirconium, chromium, manganese, titanium, boron, hafnium,
vanadium, titanium diboride, and mixtures thereof.
[0008] U.S. Pat. No. 5,389,165 discloses a preferred composition of
1.10 wt. % Li, 3.61 wt. % Cu, 0.33 wt. % Mg, 0.40 wt. % Ag and 0.14
wt. % Zr. An alloy composition corresponding to such a range was
registered at The Aluminum Association in June 2000 as AA 2098.
This alloy exhibits high fracture toughness and strength at
elevated temperatures, after having been subjected to a specific
process. An alloy as disclosed in the '165 patent may be suitable
for some thin or medium gauge plate products used in aircraft
structures, but may be less suitable for use as thick gauge plates,
because of rather low mechanical properties in the ST
direction.
[0009] Another aluminum-lithium based alloy has also been proposed
for thick gauges. This alloy, registered at The Aluminum
Association as AA 2297 in August 1997, contains lithium, copper,
manganese, and optionally magnesium, but no silver. U.S. Pat. No.
5,234,662 discloses a preferred composition of 1.6 wt. % Li, 3.0
wt. % Cu, 0.3 wt. % Mn, 0.12 wt. % Zr. The alloy, produced in thick
gauges, exhibits a good combination of low density, strength,
toughness, fatigue resistance and corrosion resistance.
SUMMARY OF THE INVENTION
[0010] An object of the present invention was to provide a low
density, high strength, high fracture toughness aluminum alloy,
which advantageously contains lithium, copper, magnesium, silver,
manganese, and a grain refiner, preferably zirconium. Alloys of the
present invention are particularly suitable for many if not all
structural applications in aircraft, over a wide range of product
thicknesses. Because the inventive alloy exhibits improved
properties in virtually any thickness range, the inventive product
can be used in virtually all forms and for all applications, such
as sheets, plates, forgings and extrusions. It can also be machined
to form structural members such as spars; it is also suitable for
use in welded assemblies.
[0011] The present invention comprises an
Al--Cu--Li--Mg--Ag--Mn--Zr alloy and demonstrates an unexpected and
surprising effect, inter alia, relating to the addition of a small
amount of manganese to Al--Cu--Li--Mg--Ag--Zr alloys. The addition
of a small amount of Mn to an Al--Cu--Li--Mg--Ag--Zr alloy improves
the fracture toughness of the alloy at a similar strength
level.
[0012] Thus, there is provided by the present invention an improved
aluminum lithium alloy comprising 0.1 to 2.5 wt. % Li, 2.5 to 5.5
wt. % Cu, 0.2 to 1.0 wt. % Mg, 0.2 to 0.8 wt. % Ag, 0.2 to 0.8 wt.
% Mn, up to 0.4 wt. % Zr and/or other grain refiner such as
chromium, titanium, hafnium, scandium or vanadium, with the balance
aluminum and inevitable elements and impurities such as silicon,
iron and zinc. The present alloy exhibits an improved combination
of strength and fracture toughness, over virtually any thickness
range.
[0013] The present invention is further directed to methods for
preparing and using Al--Li alloys as well as to products comprising
the same.
[0014] Additional objects, features and advantages of the invention
will be set forth in the description which follows, and in part,
will be obvious from the description, or may be learned by practice
of the invention. The objects, features and advantages of the
invention may be realized and obtained by means of the
instrumentalities and combination particularly pointed out in the
appended claims.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0015] In the present invention, it was discovered that minor
additions of manganese to Al--Cu--Mg--Ag alloys suitable for thin
gauges, such as AA 2098, unexpectedly provided improved results,
inter alia in terms of fracture toughness. It was also discovered
that a minor addition of magnesium or silver to Al--Cu--Li--Mn--Zr
alloys such as AA 2297, which is more suitable for thick gauges,
also unexpectedly provided improved strength while possessing
similar or even higher fracture toughness. Potentially even more
importantly, the present alloy has improved strength and fracture
toughness in the ST direction, which is very often a critical
direction for certain applications such as very thick plates
applications. Therefore, the present inventive alloy, which in some
embodiments comprises certain preferred amounts of magnesium,
silver and manganese, surprisingly shows better properties in
thin,-medium and thick gauge applications, than the closest alloys
from the prior art.
[0016] A copper content between about 3 to about 4 wt. %, and a
lithium content between 0.8 and 1.5 wt. % are preferred. In one
preferred embodiment, the lithium content is between about 0.9 and
about 1.3 wt. %. In the new inventive alloy, magnesium in the range
of about 0.2 to about 1 wt. %, preferably from 0.3 to 0.5 wt. %,
silver in the range of about 0.2 to about 0.8 wt. % and preferably
from 0.3 to 0.5 wt. %, and manganese in the range of about 0.2 wt.
% to about 0.8 wt. %, and preferably from 0.3 to 0.5 wt. %,
produces an alloy having surprisingly high strength and high
fracture toughness. This will become apparent in the examples
provided below, where the new alloy will be compared to
Al--Cu--Li--Mg--Ag--Zr alloy products such as AA 2098 alloy
products, which are used for thin gauge products, and will also be
compared to Al--Cu--Li--Mn--Zr alloy products such as AA 2297 alloy
products, which are currently used for thick gauge products.
[0017] The composition of the present inventive alloy may also
optionally include minor amounts of grain refinement elements such
as zirconium, chromium, titanium, hafnium, scandium and/or
vanadium, that is, particularly up to about 0.3wt. % of Zr, up to
about 0.8 wt. % of Cr, up to about 0.12 wt % of Ti, up to about 1.0
wt. % of Hf, up to about 0.8 wt. % of Sc, up to about 0.2 wt. % of
V are envisioned. A zirconium content between about 0.05 and 0.15
wt. % is preferred. In one preferred embodiment, the total amount
of grain refining elements advantageouly does not exceed about 0.25
wt. %. A preferred embodiment of the present invention is an alloy
comprising between about 0.8 and about 1.2 wt. % of lithium.
[0018] The present alloy is preferably provided as an ingot or
billet by any suitable casting technique known in the art. Ingots
or billets may be preliminary worked or shaped if desired for any
reason to provide suitable stock for subsequent operations. The
alloy stock can then be processed in a classical way, such as by
performing one or more homogenization operations, hot rolling
steps, solution heat treatment, a water quench, stretching, and one
or more aging steps to reach peak strength.
[0019] According to the present invention, it is possible to obtain
a thick (typically at least about 3 inches (76.2 mm) thick)
aluminum based alloy product that exhibits in a solution
heat--treated, quenched, stress-relieved and artificially aged
condition, at least one set of properties selected from the group
consisting of: [0020] (a) UTS (L)>70 ksi (482.6 MPa) and
K.sub.IC (L)>34 ksi inch (37.4 MPa m) [0021] (b) TYS (L)>65
ksi (448.2 MPa) and K.sub.IC (L)>34 ksi inch (37.4 MPa m) [0022]
(c) UTS (LT)>70 ksi (482.6 MPa) and K.sub.IC (L-T)>27 ksi
inch (29.7 MPa m) [0023] (d) TYS (LT)>62 ksi (427.5 MPa) and
K.sub.IC (L-T)>26 ksi inch (28.6 MPa m) [0024] (e) UTS
(ST)>70 ksi (482.6 MPa) and K.sub.IC (S-T)>24 ksi inch (06.4
MPa m) [0025] (f) TYS (ST)>60 ksi (413.7 MPa) and K.sub.IC
(S-T)>23 ksi inch (25.3 MPa m).
[0026] According to another embodiment of the present invention, it
is possible to obtain an aluminum based alloy rolled product with a
thickness of less than about 3 inches, that exhibits in a solution
heat-treated, quenched, stress-relieved and artificially aged
condition, at least one set of properties selected from the group
consisting of [0027] (a) UTS (L)>76 ksi (524.0 MPa) and K.sub.IC
(L)>35 ksi inch (38.5 MPa m) [0028] (b) TYS (L)>71 ksi (489.5
MPa) and K.sub.IC (L)>35 ksi inch (38.5 MPa m) [0029] (c) UTS
(LT)>75 ksi (517.1 MPa) and K.sub.IC (L-T)>29 ksi inch (31.9
MPa m) [0030] (d) TYS (LT)>68 ksi (468.8 MPa) and K.sub.IC
(L-T)>29 ksi inch (31.9 MPa m) [0031] (e) UTS (ST)>76 ksi
(524.0 MPa) and K.sub.IC (S-T)>26 ksi inch (28.6 MPa m) [0032]
(f) TYS (ST)>65 ksi (448.2 MPa) and K.sub.IC (S-T)>26 ksi
inch (28.6 MPa m).
[0033] The following examples are provided to illustrate the
invention but the invention is not to be considered as being
limited thereto. In these examples and throughout this
specification, parts are by weight unless otherwise indicated.
Also, compositions include normal and/or inevitable impurities,
such as silicon, iron and zinc. Example 1
[0034] An alloy according to the invention, referenced Al, was
produced in gauge 2.5 inches, and compared to an
Al--Cu--Li--Mg--Ag--Zr (AA 2098) alloy plate, referenced B1. Actual
compositions of cast alloy A1 and B1 products are provided in Table
1 below. Alloy B1 was produced in thinner gauge of 1.7 inches (43.2
mm), because the properties of this alloy in 2.5 inch (63.5 mm)
gauge, especially its fracture toughness in ST direction are too
poor to enable the product to be a viable commercial product.
[0035] Alloy Al product was processed according to a prior art
practice to obtain a plate in a peak aged temper. Namely, alloy Al
product was homogenized for 24 hours at 980.degree. F.
(526.7.degree. C.), hot rolled at a temperature range of 780 to
900.degree. F. (415.6-482.2.degree. C.) to obtain a n2.5 inch (63.5
mm) gauge, then solution heat treated at 980.degree. F.
(526.7.degree. C.) for 2 hours, then water quenched, stretched at a
level of 3%, and artificially aged for 48 hours at 290.degree. F.
(155.3.degree. C.) in order to reach the peak strength (T8
temper).
[0036] Alloy B1 plate was also homogenized for 24 hours at
980.degree. F. (526.7.degree. C.), hot rolled at a temperature
range of 780 to 900.degree. F. (415.6-482.2.degree. C.) to obtain a
1.7 inches (43.2 mm) thick plate, then solution heat treated at
980.degree. F. (526.7.degree. C.) for 2 hours, water quenched,
stretched at a level of 3%, and artificially aged for 17 hours at
320.degree. F. (160.0.degree. C.), in order to reach the peak
strength (T8 temper).
[0037] Respective Ultimate Tensile strength (UTS), Tensile Yield
Strength (TYS), and Elongation (E) of alloy A1 and B1 samples were
determined in L, LT, and ST directions according to ASTM B557. The
fracture toughness of alloy A1 and B1 were determined, using the
method of evaluation of the plain-strain Fracture Toughness
(K.sub.IC), according to ASTM E399. This method is appropriate when
in plain-strain deformation, which is applicable for the samples
analyzed in this example, since these samples are relatively thick
(over 1 inch (25.4 mm) thick). All results for alloy A1 and B1
samples are provided in Table 2 below. Most of these values are
average values for two duplicate tests on the same plate sample.
TABLE-US-00001 TABLE 1 Compositions of cast alloys A1 and B1 in wt.
% Cu Li Mg Ag Zr Mn Alloy A1 sample 3.59 0.9 0.34 0.30 0.09 0.43
(invention) Alloy B1 sample 3.58 0.99 0.34 0.34 0.14 <0.01
[0038] TABLE-US-00002 TABLE 2 Mechanical Properties of inventive
alloy A1 (thickness 2.5 inches (63.5 mm)) compared to alloy B1
(thickness 1.7 inches (43.2 mm)) K.sub.IC Direction of UTS (ksi)
TYS (ksi) (ksi {square root over (inch))} Measurement [MPa] [MPa] E
(%) [MPa {square root over (m])} Sample A1 - L 80.6 77.0 10 39.5
2.5 inches [555.7] [530.9] [43.4] (63.5 mm) LT 78 71.0 9.5 30.9
thick [537.8] [489.5] [34.0] (invention) ST 77.9 67.0 5.6 27.5
[537.1] [462.0] [30.2] Sample B1 - L 80.6 76.3 14.5 31.1 1.7 inches
[555.7] [526.1] [34.2] (43.2 mm) LT 80.5 74 11 28.4 Thick [555.0]
[510.2] [31.2] ST 83.3 70.3 6.4 24.9 [574.3] [484.7] [27.4]
[0039] The alloy plate according to the invention exhibits better
fracture toughness in all three directions, as compared with those
from sample B1 from the prior art, with similar strengths in L, LT
and ST directions. Fracture Toughness of the present alloy is
unexpectedly improved by up to 27% in the L direction (or even
greater), by up to or more than 10% in the ST direction, and by up
to or more than 8% in the LT direction. Example 2
[0040] An Al--Cu--Li--Mn--Zr alloy plate from the prior art (AA
2297 alloy), referenced B2, was produced in a thicker gauge than in
example 1; namely thickness of plate B2 was 5 inches (127 mm).
Alloy B2 plate was compared to alloy A1 according to the invention,
which was also produced in thicker gauge, namely 5 inches (127 mm).
Samples of A1 alloy in 5 inches (127 mm) gauge are referenced as A2
in this example. The actual composition of cast alloy A2 and B2
products is provided in Table 3 below.
[0041] Alloy A2 plate was processed according to a prior art
practice to obtain a plate in T8 temper. Namely, alloy A2 ingot was
homogenized for 24 hours at 980.degree. F. (526.7.degree. C.), hot
rolled at a temperature range of 800 to 900.degree. F.
(426.7-482.2.degree. C.), then solution heat treated at 980.degree.
F. (526.7.degree. C.) for 3.5 hours, then water quenched, stretched
at a level of 3%, and artificially aged for 40 hours at 290.degree.
F. (143.3.degree. C.) in order to reach the peak strength (T8
temper).
[0042] Alloy B2 plate was also processed according to a prior art
practice to obtain a plate in T8 temper. Namely, alloy B2 plate was
homogenized for 24 hours at 980.degree. F. (526.7.degree. C.), hot
rolled at a temperature range of 800 to 900.degree. F.
(426.7-482.2.degree. C.), then solution heat treated at 980.degree.
F. (526.7.degree. C.) for 3.5 hours, water quenched, stretched at a
level of 6%, and artificially aged for 22 hours at 320.degree. F.
(160.degree. C.), in order to reach the peak strength (T8
temper).
[0043] Respective Ultimate Tensile strength (UTS), Tensile Yield
Strength (TYS), and Elongation (E) of alloy A2 and alloy B2 samples
were determined in L, .LT, and ST directions according to ASTM
B557. The fracture toughness of alloy A2 and B2 were determined,
using the well-known method of evaluation of the plain-strain
Fracture Toughness (K.sub.IC), according to ASTM E399. All results
for alloy A2 and 132 samples are provided in Table 4 below.
TABLE-US-00003 TABLE 3 Compositions of cast alloys A2 and B2 Cu Li
Mg Ag Zr Mn Alloy A2 sample 3.59 0.9 0.34 0.30 0.09 0.43
(invention) Alloy B2 sample 2.89 1.17 -- -- 0.10 0.31
[0044] TABLE-US-00004 TABLE 4 Mechanical properties of inventive
alloy A2 in 5 inches (127 mm) gauge compared to prior art alloy B2
in 5 inches (127 mm) gauge K.sub.IC Direction of UTS (ksi) TYS
(ksi) (ksi {square root over (inch))} Measurement [MPa] [MPa] E (%)
[MPa {square root over (m])} Sample A1 - L 73.5 68.8 10.8 36.0
thick gauge [506.8] [474.4] [39.6] (invention) LT 73.8 65 8.8 28.3
[508.8] [448.2] [31.1] ST 74.3 64 6.5 26.9 [512.3] [441.3] [29.6]
Sample B2 - L 62.4 57.6 11.8 36.6 thick gauge [430.2] [397.1]]
[40.2] LT 63.7 57.3 8.8 29.1 [439.3] [395.1] [32.0] ST 63.1 56.6
4.5 22.4 [435.1] [390.2] [24.6]
[0045] A2 sample exhibits much higher strength and fracture
toughness in the ST direction, which is an important critical
direction for very thick gauge plate applications. In L and LT
directions, A2 sample exhibits much higher strength at similar
fracture toughness than sample B2 from the prior art. Specifically,
in the L and LT directions, the strength was improved by about 18%
and 14% respectively, at similar fracture toughness levels. In the
ST direction, UTS and TYS were increased by about 18% and 13%
respectively, while fracture toughness was increased by about
20%.
[0046] Additional advantages, features and modifications will
readily occur to those skilled in the art. Therefore, the invention
in its broader aspects is not limited to the specific details, and
representative devices, shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
[0047] All documents referred to herein are specifically
incorporated herein by reference in their entireties.
[0048] As used herein and in the following claims, articles such as
"the", "a" and "an" can connote the singular or plural.
* * * * *