END-TO-END CONNECTION FOR LIGHTWEIGHT AIRFIELD MATTING SYSTEM

Abstract

In one embodiment, a kit for airfield matting comprises a plurality of matting panels each including a rectangular mat core having a first side, a second side, a first end, and a second end. The first side has a first side connector. The second side has a second side connector. The first side connector of one matting panel of the plurality of matting panels is configured to couple with at least a part of the second side connector of one or more side neighboring matting panels of the plurality of matting panels to be connected therewith. The first end has a first end connector. The second end has a second end connector. The first end connector of one matting panel of the plurality of matting panels is configured to couple with the second end connector of an end neighboring matting panel of the plurality of matting panels to be connected therewith. The matting panels each have a length of not greater than about 84 inches.

Claims

1. In an airfield matting system which comprises a plurality of matting panels each including a rectangular mat core having a first side, a second side, a first end, and a second end, the first end having a first end connector, and the second end having a second end connector; an end-to-end connection, between the first end connector of one matting panel of the plurality of matting panels and the second end connector of an end neighboring matting panel, comprising: the first end connector of one matting panel of the plurality of matting panels configured to couple with the second end connector of an end neighboring matting panel of the plurality of matting panels to be connected therewith; the first end connector including an overlap end connector having a top slot portion; the second end connector including an underlap end connector having a bottom slot portion; the top slot portion and the bottom slot portion forming a locking bar slot; and a locking bar configured to be disposed in the locking bar slot formed by the top slot portion of the overlap end connector and the bottom slot portion of the underlap end connector, and substantially filling the locking bar slot.

2. The end-to-end connection of claim 1, wherein the locking bar slot is rectangular.

3. The end-to-end connection of claim 1, wherein the overlap end connector includes a top hook with a top hook distal portion; wherein the underlap end connector includes a bottom hook with a bottom hook distal portion; and where in the top hook distal portion and the bottom hook distal portion are configured to engage one another.

4. The end-to-end connection of claim 1, wherein the overlap end connector includes a top hook having a top hook proximal portion and a top hook having a top hook distal portion; wherein the underlap end connector includes a bottom hook having a bottom hook proximal portion and a bottom hook having a bottom hook distal portion; and where in the top hook distal portion and the bottom hook distal portion are configured to engage one another.

5. The end-to-end connection of claim 4, wherein the top hook distal portion is disposed between the top slot portion and the top hook proximal portion, the top hook distal portion and the bottom hook distal portion are disposed between the top hook proximal portion and the locking bar slot, the top hook distal portion is disposed between the bottom hook distal portion and the bottom hook proximal portion, and the bottom hook distal portion is disposed between the top hook distal portion and the top hook proximal portion.

6. The end-to-end connection of claim 4, wherein the bottom slot portion is disposed in the bottom hook proximal portion; and wherein the locking bar is a rectangular locking bar disposed above the top hook distal portion and the bottom hook distal portion.

7. The end-to-end connection of claim 4, wherein the top hook comprises a J-shaped top hook having a generally vertical orientation as a generally upright top hook having a top hook distal portion oriented generally vertically upward; wherein the bottom hook comprises a J-shaped bottom hook having a generally vertical orientation as a generally inverted vertical bottom hook having a bottom hook distal portion oriented generally vertically downward; and wherein the top hook distal portion and the bottom hook distal portion are disposed adjacent to one another.

8. The end-to-end connection of claim 7, wherein the locking bar slot is an inclined slot which is inclined at an angle of about 10-30 relative to horizontal, downward on a side of the top hook distal portion and upward on a side of the bottom hook distal portion.

9. An end-to-end connection for end neighboring matting panels in an airfield matting system, the end-to-end connection comprising: a first end connector of one matting panel of a plurality of matting panels each including a rectangular mat core having a first side, a second side, a first end, and a second end, the first end connector to be attached to the first end, the first end connector including an overlap end connector having a top slot portion; a second end connector of another matting panel of the plurality of matting panels, the second end connector being configured to be attached to the second end and to couple with the first end connector, the second end connector including an underlap end connector having a bottom slot portion, the top slot portion and the bottom slot portion forming a locking bar slot; a locking bar configured to be disposed in the locking bar slot formed by the top slot portion of the overlap end connector and the bottom slot portion of the underlap end connector, and substantially filling the locking bar slot.

10. The end-to-end connection of claim 9, wherein the locking bar slot is rectangular.

11. The end-to-end connection of claim 9, wherein the overlap end connector includes a top hook with a top hook distal portion; wherein the underlap end connector includes a bottom hook with a bottom hook distal portion; and where in the top hook distal portion and the bottom hook distal portion are configured to engage one another.

12. The end-to-end connection of claim 9, wherein the overlap end connector includes a top hook having a top hook proximal portion and a top hook having a top hook distal portion; wherein the underlap end connector includes a bottom hook having a bottom hook proximal portion and a bottom hook having a bottom hook distal portion; and where in the top hook distal portion and the bottom hook distal portion are configured to engage one another.

13. The end-to-end connection of claim 12, wherein the top hook distal portion is disposed between the top slot portion and the top hook proximal portion, the top hook distal portion and the bottom hook distal portion are disposed between the top hook proximal portion and the locking bar slot, the top hook distal portion is disposed between the bottom hook distal portion and the bottom hook proximal portion, and the bottom hook distal portion is disposed between the top hook distal portion and the top hook proximal portion.

14. The end-to-end connection of claim 12, wherein the bottom slot portion is disposed in the bottom hook proximal portion; and wherein the locking bar is a rectangular locking bar disposed above the top hook distal portion and the bottom hook distal portion.

15. The end-to-end connection of claim 12, wherein the top hook comprises a J-shaped top hook having a generally vertical orientation as a generally upright top hook having a top hook distal portion oriented generally vertically upward; wherein the bottom hook comprises a J-shaped bottom hook having a generally vertical orientation as a generally inverted vertical bottom hook having a bottom hook distal portion oriented generally vertically downward; and wherein the top hook distal portion and the bottom hook distal portion are disposed adjacent to one another.

16. The end-to-end connection of claim 15, wherein the locking bar slot is an inclined slot which is inclined at an angle of about 10-30 relative to horizontal, downward on a side of the top hook distal portion and upward on a side of the bottom hook distal portion.

17. The end-to-end connection of claim 9, wherein the first end connector includes a first end connector insert configured to slide in between ribs of the first end of the rectangular mat core; wherein the second end connector includes a second end connector insert configured to slide in between ribs of the second end of the rectangular mat core.

18. An end-to-end connection for two end neighboring matting panels in an airfield matting system which comprises a plurality of matting panels each including a rectangular mat core having two ends, the end-to-end connection comprising: an overlap end connector to be attached to an end of a first rectangular mat core of a first one of the two end neighboring matting panels, the overlap end connector having a top slot portion; an underlap end connector to be attached to an end of a second rectangular mat core of a second one of the two end neighboring matting panels, the underlap end connector having a bottom slot portion, the top slot portion and the bottom slot portion forming a locking bar slot; and a locking bar configured to be disposed in the locking bar slot formed by the top slot portion of the overlap end connector and the bottom slot portion of the underlap end connector, and substantially filling the locking bar slot.

19. The end-to-end connection of claim 18, wherein the overlap end connector includes a top hook having a top hook proximal portion and a top hook having a top hook distal portion; wherein the underlap end connector includes a bottom hook having a bottom hook proximal portion and a bottom hook having a bottom hook distal portion; where in the top hook distal portion and the bottom hook distal portion are configured to engage one another; and wherein the top hook distal portion is disposed between the top slot portion and the top hook proximal portion, the top hook distal portion and the bottom hook distal portion are disposed between the top hook proximal portion and the locking bar slot, the top hook distal portion is disposed between the bottom hook distal portion and the bottom hook proximal portion, and the bottom hook distal portion is disposed between the top hook distal portion and the top hook proximal portion.

20. The end-to-end connection of claim 19, wherein the top hook comprises a J-shaped top hook having a generally vertical orientation as a generally upright top hook having a top hook distal portion oriented generally vertically upward; wherein the bottom hook comprises a J-shaped bottom hook having a generally vertical orientation as a generally inverted vertical bottom hook having a bottom hook distal portion oriented generally vertically downward; wherein the top hook distal portion and the bottom hook distal portion are disposed adjacent to one another; and wherein the locking bar slot is an inclined slot which is inclined at an angle of about 10-30 relative to horizontal, downward on a side of the top hook distal portion and upward on a side of the bottom hook distal portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements.

[0023] FIG. 1 is a plan view of an example of an airfield matting system assembled from mats or matting panels.

[0024] FIG. 2 is a Table detailing the number of mats that would be able to fit on a 463L pallet for two configurations based on varying mat lengths and widths.

[0025] FIG. 3 is a Table representing the number of mats that would be able to fit in an ISO Container for each configuration based on different mat lengths and widths.

[0026] FIG. 4 shows three different base mat core designs as examples.

[0027] FIG. 5 shows a hinge joint as an example of a mat core connector for connecting side edges of adjacent mat panels.

[0028] FIG. 6 shows a loading example, for brevity, of the MV22 Osprey loading across the middle, left, and right side of a hinge joint mat core connection between side edges of adjacent mat panels on California bearing ratio (CBR) of 6% or CBR 6 soil.

[0029] FIG. 7 shows cross-sections illustrating formation of a 2-piece friction stir welded (FSW) mat core design (FSWA-Mat).

[0030] FIGS. 8A-8D show examples of early end connector designs including Design-1A, Design-2A. Design-3A, and AMX.

[0031] FIGS. 9A-9D show (A) AM-X, (B) AM-R, (C) AM-M, and (D) AM-2 geometries of additional examples of end connectors, with the overlapping connector on the left and the underapping connector on the right.

[0032] FIG. 10 shows a Table which summarizes test specimen dimensions for the geometries of FIGS. 9A-9D.

[0033] FIG. 11 is an exploded perspective view of a full-length panel of the matting system illustrating an overlap end connector and an underap end connector on opposite longitudinal ends of the panel.

[0034] FIG. 12 is a side view of the overlap end connector of FIG. 11 showing the mating surfaces thereof prior to fit-up, as viewed from a female hinge joint side. The mating surfaces at the top skin are top butting surfaces. The mating surfaces at the bottom skin are bottom butting surfaces. Parallel mating surfaces are denoted by dashed lines in the longitudinal direction (Y-axis). The Z-axis is along the lateral direction. The X-axis is running out of the page.

[0035] FIG. 13A shows the overlap end connector prior to fit-up with the mat core and FIG. 13B shows the overlap end connector fit-up with the mat core and ready for friction stir welding.

[0036] FIG. 14 is an exploded perspective view of the overlap end connector of FIGS. 13A-13B prior to fit-up with the mat core.

[0037] FIGS. 15A-15C show (A) a plan view of the panel, (B) a front elevational view of a female hinge joint and a male hinge joint on opposite lateral sides of the panel, and (C) a rear elevational view of the female hinge joint and the male hinge joint.

[0038] FIG. 16A is a front elevational view of one piece of the two-piece panel having the male hinge joint and vertical stiffeners, and FIG. 16B is a cross-sectional view of the panel along section A-A.

[0039] FIG. 17A is a rear elevational view of the other piece of the two-piece panel having the female hinge joint and vertical stiffeners, and FIG. 17B is a cross-sectional view of the panel along section B-B.

[0040] FIGS. 18A-18B show an example of an overlap end connector of FIG. 11 including (A) a top plan view standing on top of the mat core and looking down, and (B) an elevational view from the back face of the overlap end connector looking through the open end of the mat core on opposite side.

[0041] FIG. 19 is an elevational view of the overlap end connector detail on the male hinge side of the mat core of FIGS. 18A-18B.

[0042] FIG. 20 is an elevational view of the overlap end connector detail on the female hinge side of the mat core of FIGS. 18A-18B.

[0043] FIGS. 21A-21C show a male hinge side of the overlap end connector of FIGS. 18A-18B including (A) a top plan view, (B) an elevational view, and (C) a side view looking from the male hinge side.

[0044] FIG. 22 is a side view of the underlap end connector of FIG. 11 showing the mating surfaces thereof, as viewed from a male hinge joint side. The mating surfaces at the top skin are top butting surfaces. The mating surfaces at the bottom skin are bottom butting surfaces. Parallel mating surfaces are denoted by dashed lines in the longitudinal direction (Y-axis). The Z-axis is along the lateral direction. The X-axis is running out of the page.

[0045] FIG. 23A shows the underlap end connector prior to fit-up with the mat core and FIG. 23B shows the underlap end connector fit-up and ready for friction stir welding.

[0046] FIG. 24 is an exploded perspective view of the underlap end connector of FIGS. 23A-23B prior to fit-up with the mat core.

[0047] FIGS. 25A-25B show an example of an underlap end connector including (A) atop plan view standing on top of the mat core and looking down, and (B) an elevational view from the back face of the underlap end connector 1120 looking through the open end of the mat core 1300 on opposite side.

[0048] FIG. 26 is an elevational view of the underlap end connector detail on the female hinge side of the mat core of FIGS. 25A-25B.

[0049] FIG. 27 is an elevational view of the underlap end connector detail on the female hinge side of the mat core of FIGS. 25A-25B.

[0050] FIGS. 28A-28C show a female hinge side of the underlap end connector of FIGS. 25A-25B including (A) a top plan view, (B) an elevational view, and (C) a side view looking from the male hinge side.

[0051] FIG. 29 shows is a sketch of the details of the load application and boundary conditions.

[0052] FIG. 30 is a graphical diagram of field and laboratory displacement prediction models illustrating an increasing amplitude displacement function used to test the specimens.

[0053] FIG. 31 is a test matrix Table summarizing the tests performed on the specimens.

[0054] FIG. 32 is a Table summarizing the average cycles to failure for each of the prototype geometries.

[0055] FIG. 33 is a Table detailing the results from each individual test for the AM-X design.

[0056] FIG. 34 is a Table detailing the results from each individual test for the AM-R design.

[0057] FIG. 35 is a Table detailing the results from each individual test for the AM-M design.

[0058] FIG. 36 is a graphical plot of average cycles to failure for the four connector embodiments, including AM2, for comparison.

DETAILED DESCRIPTION

[0059] Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. The present invention may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention.

[0060] As used herein, the singular forms a, an, and the, are intended to include the plural forms as well, unless the context clearly indicates otherwise. It further will be understood that the terms comprises, comprising, includes, and/or including, specify the presence of stated features, steps, or components, but do not preclude the presence or addition of one or more other features, steps, or components. It also should be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

1. Overview

[0061] One aspect of the invention is to develop, design, and optimize a lighter and thinner mat core and connectors in a rapid airfield panel that are able to withstand the loads of DOD/NATO Rotary Wing, Tiltrotor, and other modern aircrafts. The current status of expeditionary airfield matting is a system of large aluminum panels that connect together to support operational needs for a variety of aircraft. These capabilities are limited by at least three main drawbacks. First, the logistical footprint of the current panel is not designed to transport on International Organization for Standardization (ISO) 20-ft standard flat-rack container systems. This results in added energy required to transport the necessary number of panels to fabricate a desired rapid airfield operating system. Second, besides the transportation issues with large container of panels, the individual panels themselves exceed Occupational Safety and Health Administration standards for a two-man carry. The third issue is that current manufacturing practices do not use the latest joining techniques such as friction stir welding that has improved weld efficiency compared to fusion welding techniques. This results in lower performance and life expectancy of the current design. A new lightweight, light-duty expeditionary airfield operating surface solution is needed to overcome limitations and improve the energy footprint associated with manufacturing, transportation, and panel life cycle.

[0062] FIG. 1 is a plan view of an example of an airfield matting system assembled from mats or matting panels. The longitudinal matting panels have two side edges and two end. Side edges of adjacent panels are connected and ends of adjacent panels are connected to assemble the panels into a matting system. This example shows a brickwork pattern and a 2-1 lay pattern of mat assemblies on a California bearing ratio (CBR) of 6% or CBR 6 soil. The airfield matting system in this example is used for simulated dual wheel MV-22 Osprey loading and simulated F-35B loading.

2. Mat Transportation

[0063] Mat dimensions are evaluated for efficient transportation in the ISO Container and 463L pallets. The mats can be packaged in two configurations having various mat lengths and widths.

[0064] FIG. 2 is a Table detailing the number of mats (14, 16, 18, 19, 21, 23, or 25) that would be able to fit on a 463L pallet for two configurations based on varying mat lengths (84 or 102 inches) and widths (12, 14, 16.8, or 21 inches).

[0065] FIG. 3 is a Table representing the number of mats (14, 16, 18, 19, 21, or 25) that would be able to fit in an ISO Container for each configuration based on different mat lengths (84 or 102 inches) and widths (12, 14, 16.8, or 21 inches). The Table also depicts the amount of remaining space available in the ISO Container for each configuration (in length, width, and height).

[0066] Embodiments of the AM-L system are assembled from lightweight aluminum panels that are no more than 21 inches in. width, 84 inches in length, 1.0 inch in height/thickness, and 3.8 lb/ft2 in unit weight. The AM-L system may be made primarily of full panels that are about 21 inches wide (e.g., 2% or 1%) by 84 inches long (e.g., 2% or 1%) and 1 inch tall (e.g., 2% or 1%), and half panels that have the same dimensions but are only about 42 inches long (e.g., 2% or 1%). The panels can fit on a 463L aircraft pallet and/or into any ISO shipping container. As such, the AM-L system can be easily transported and rapidly deployed. In addition to the logistics savings, each mat panel weighs less than 50 lb. so that it can be carried safely by service men/women.

3. Mat Core Design

[0067] FIG. 4 shows three different base mat core designs as examples. Core Design A is a vertical stiffener design, Core Design B is an extrudable truss configuration, and Core Design C is a horizontal honey-comb cross-section. The mat core designs for each width and length underwent 3D modeling, weight analysis, and preliminary Finite Element Analysis (FEA) in the commercial software, SolidWorks. More computationally intensive FEA may be performed in the software, Abaqus Computer-Aided Engineering (CAE). The FEA shows the extrudable truss configuration under Core Design B outperforms the vertical stiffener design under Core Design A. On the other hand, the extrudable truss configuration has more fabrication difficulties and challenges.

[0068] FIG. 5 shows a hinge joint as an example of a mat core connector for connecting side edges of adjacent mat panels. The mat core connector 500 includes a male hinge joint member 510 and a female hinge joint member 520.

[0069] FIG. 6 shows a loading example of a matting system 600, for brevity, of the MV22 Osprey loading across the middle, left, and right side of a hinge joint mat core connection 610 between side edges of adjacent mat cores or panels 620, 622 on California bearing ratio (CBR) of 6% or CBR 6 soil. In terms of mat core connector boundary conditions, the mat core was placed on CBR 6 soil and rollers applied at the end of each mat core. An MV22 Osprey loading was then applied and evaluated for the left, right, and middle loading of the mat core connectors 610. The simulation results show that the largest stress was experienced in the mat core during the left Loading condition and not in the mat core connectors for the boundary conditions in this simulation.

[0070] FIG. 7 shows cross-sections illustrating formation of a 2-piece friction stir welded (FSW) mat core design (FSWA-Mat). The two-piece mat is designed in order to increase the possible number of extrusion companies capable of producing the mat. A first piece 710 has a male hinge joint side 712 and a first edge side 714. A second piece 720 has a female hinge joint side 722 and a second edge side 724. The first edge side 714 of the first piece 710 is to be joined together with the second edge side 724 of the second piece 720. The center stiffener at the second edge side 724 has a greater thickness than the other stiffeners (e.g., up to 100% greater in thickness or more). The thicker center stiffener can withstand reaction forces during FSW joining of the two pieces and increase the service life of the FSW. The two-piece mat will be joined together through friction stir welding (FSW) to form the FSW joint or connection 730. The FSWA-Mat was evaluated and compared to the vertical stiffener design under Core Design A in Abaqus CAE. The FSWA-Mat and Core Design A underwent the various aircraft loadings, and for brevity, under the MV22 osprey loading conditions on a hard surface and MV22 Osprey loading over a 4 divot on CBR 6 soil. The simulation results show that the FSWA-Mat experiences only a 10% difference in stress experienced by the mat core compared to Core Design A. Therefore, the FSWA-Mat design is a viable option, which enables more extruders capable of producing the mat cores.

4. Material Selection

[0071] The new AMX mat system uses a material that will help to achieve AM2 performance with a thinner mat system, including strength performance and fatigue performance. AA6061 aluminum alloy is selected as the material for the matting system (e.g., utilizing AMX matting panels). Other suitable materials may be used. For instance, new aluminum alloys recently developed for commercial use, primarily aerospace, are significantly stronger, have a lower density, and are extrudable. AA2099 is a relatively new lithium-based aluminum alloy with a lower density but higher fatigue performance than AA6061. The yield strengths for heat treated AA2099-T83 and AA6061-T6 are 70 ksi and 40 ksi, respectively. Therefore, AA2099 is nearly 75% stronger than AA6061. In one possible embodiment, a majority (e.g., 80%) of the matting panels of the airfield matting system may be AA2099 aluminum lithium alloy matting panels (e.g., AMX), and the remaining (e.g., 20%) may be AA6061-T6 AM2 matting to be used for runway surfaces).

5. End Connector Designs, Testing, and Comparison

[0072] FIGS. 8A-8D show examples of early end connector designs including Design-1A, Design-2A. Design-3A, and AMX. The AMX end connector design is a specific embodiment of the AM-L system. As with the mat core designs, multiple end-connector geometries were explored, and polymer 3D printed to examine designs that meet metal fabrication, form, and functionality requirements. The four different end connector designs as shown in FIGS. 8A-8D were evaluated in Abaqus CAE.

[0073] The end connector designs each include two separate extrusions that are assembled to the main body panel extrusion by friction stir welding to form a complete panel. The two end connectors consist of a top and bottom hook joint that when connected create an angled opening that allows for the insertion of an aluminum locking bar. In Design-1A, Design-2A, and Design-3A, the locking bar (814, 824, 834) is disposed between the top hook (810, 820, 830) and the bottom hook (812, 822, 832). The top hook (810, 820, 830) has a generally horizontal orientation as a generally horizontal top hook having a top hook tip or top hook distal portion oriented generally horizontally. The bottom hook (812, 822, 832) also has a generally horizontal orientation as a generally horizontal bottom hook having a bottom hook tip or bottom hook distal portion oriented generally horizontally. Design-1A has an angled or inclined slot to receive an inclined rectangular locking bar. Design-2A has an elliptical slot to receive an elliptical locking bar. Design-3A has a horizontal slot to receive a horizontal rectangular locking bar. In Design-1A, Design-2A, and Design-3A, the top hook forms a top slot portion or top half-slot adjacent the top hook distal portion and the bottom hook forms a bottom slot portion or bottom half-slot adjacent the bottom hook distal portion. The top half-slot and the bottom half-slot form a slot in which the locking bar is disposed.

[0074] In contrast, the locking bar 844 in the AMX design is disposed not between the top hook 840 and the bottom hook 842 which are engaged with one another, but above the top and bottom hooks as an inclined locking bar 844 having a rectangular shape. The J-shaped top hook 840 has a generally vertical orientation as a generally vertical top hook having a top hook tip 846 or top hook distal portion 846 oriented generally vertically upward (e.g., 5 or 2). The J-shaped bottom hook 842 has a generally vertical orientation as a generally vertical bottom hook having a bottom hook tip 848 or bottom hook distal portion 848 oriented generally vertically downward (e.g., 5 or 2). The top hook distal portion 846 and the bottom hook distal portion 848 are disposed adjacent to one another or in close proximity with one another without a locking bar therebetween. The inclined slot in which the locking bar 844 is disposed is inclined at an angle of about 10-30 or about 20 (e.g., 2 or 10) relative to horizontal, downward on the side of the top hook tip 846 and upward on the side of the bottom hook tip 848. The locking bar 844 has a length extending along the end of the panel (e.g., 620, 622), a width extending along the length of the slot formed by the top slot portion or top half-slot of the top hook 840 and the bottom slot portion or bottom half-slot of the bottom hook 842, and a height extending along the width of the slot. The slot is generally perpendicular to the top hook distal portion 846 and the bottom hook distal portion 848 (e.g., 20 or 10). The top hook 840 is an inverted J-shaped hook having a top hook proximal portion 847 disposed below the top hook distal portion 846 and a top half-slot above the top hook distal portion 846 opposite from the top hook proximal portion 847. As such, the top hook distal portion 846 is disposed between the top hook proximal portion 847 and the slot. The bottom hook 842 is an upright J-shaped hook having a bottom hook proximal portion 849 disposed above the bottom hook distal portion 848 and a top half-slot at or above the bottom hook proximal portion 849 and above the bottom hook distal portion 848.

[0075] The inclined locking bar slot for the locking bar 844 is formed by the top slot portion or top half-slot in the top hook 840 and the bottom slot portion or bottom half-slot in the bottom hook 842. The top half-slot is disposed on the opposite side of the top hook proximal portion 847. As such, the top hook distal portion 846 is disposed between the top half-slot and the top hook proximal portion. The bottom half-slot is disposed in the bottom hook proximal portion 849. As a result, the top hook distal portion 846 and the bottom hook distal portion 848 are disposed between the top hook proximal portion 847 and the locking bar 844, with the bottom hook distal portion 848 being more centered in position and the top hook distal portion 846 being more off-centered in position between the top hook proximal portion 847 and the locking bar 844. Between the top hook 840 and the bottom hook 842, the top hook distal portion 846 is disposed between the bottom hook distal portion 848 and the bottom hook proximal portion 849, and the bottom hook distal portion 848 is disposed between the top hook distal portion 846 and the top hook proximal portion 847. The locking bar is configured to be disposed in the locking bar slot formed by the top and bottom half-slots and substantially fill the locking bar slot (e.g., 80% fill or 90% fill or 95% fill).

[0076] FIGS. 9A-9D show (A) AM-X, (B) AM-R, (C) AM-M, and (D) AM-2 geometries of additional examples of end connectors, with the overlapping connector on the left and the underlapping connector on the right. FIG. 10 shows a Table which summarizes test specimen dimensions for the geometries of FIGS. 9A-9D.

[0077] The experiment described in this disclosure evaluated three unique prototype airfield mat end connector designs. The three designs are described herein as AM-X, AM-R, and AM-M. FIGS. 9A-9C display the three designs and FIG. 9D displays the standard AM2 end connector for comparison. Each test specimen was comprised of an underlapping and an overlapping side. The left side of each connector in FIGS. 9A-9D is considered the overlapping side (910A, 910B, 910C, 910D), and the right side is the underlapping side (920A, 920B, 920C, 920D). A locked joint is achieved by inserting a rectangular locking key or locking bar (930A, 930B, 930C, 930D) through the rectangular slot formed by joining the two sides of each connector.

[0078] Aside from the differences in the connection geometries, each prototype test specimen was manufactured to the same global dimensions. Both halves of the specimens measured 1 in. tall by 2 in. wide by 15 in. long. In comparison, AM2 measured 1.5 in. tall by 2 in. wide and 18 in. long. All end connector prototypes were machined from AA6061-T6 solid rolled bar stock. Additionally, all locking bars were machined to the appropriate sizes from the same AA6061-T6 material. Researchers analytically determined that one way to meet the performance of the existing AM2 system while reducing both the thickness and the weight was through a material change to AA2099-T83.

[0079] The AM-X geometry is shown in FIG. 9A. The AM-X locking bar dimensions were 0.625 in. by 0.19 in. by 2.0 in with a corner radius of 0.13 in. The dimensions of the locking bar for the AM-X prototype were purposely chosen to be interchangeable with AM2. The purpose of this decision was to avoid confusion if both the prototype mat and the AM2 were used at an installation location. If the locking bars looked similar but were not interchangeable, they might get mixed up and keep a matting array from being installed until the proper locking bars could be delivered. Furthermore, interchangeable locking bars would allow for a single source of supply and might assist with acquisition or even cost reduction.

[0080] The AM-X design was optimized using an ABAQUS 3-D finite element computer program. One key discovery during the joint optimization was that by angling the locking bar slot, the maximum allowable stress through the joint increased significantly (the cross-sectional area across the fatigue critical part is increased), and the fatigue performance was expected to improve by several orders of magnitude. Researchers expected that the AMX geometry would be the best performing design based on the analytical studies. This same end connector profile was used on a lightweight mat for MV-22 operations. During a full-scale experiment, the joint performed well, although the method of joining the connector to the mat using friction stir welding techniques required additional refinement.

[0081] The AM-R geometry is shown in FIG. 9B. The AM-R locking bar dimensions were 0.385 in. by 0.125 in. by 2.0 in. The AM-R design was applied to lightweight mats for MV-22 operations. The design showed great promise in ABAQUS simulations but had issues with dislodgement during full-scale trafficking experiments.

[0082] The AM-M geometry is shown in FIG. 9C. The AM-M locking bar dimensions were 0.416 in. by 0.125 in. by 2.0 in. The AM-M design is a scaled down version of the original AM2 design with increased radii in critical stress locations. A commercial matting system called ALMATS by Alfab Inc. used a similar scaled AM2 design. The ALMATS system was evaluated under simulated MQ-9 Reaper aircraft and P-19 crash/rescue vehicles. The matting system performed very well but proved difficult to install because the tolerances in the joint were also scaled. This caused the mat to be rather difficult to install on a semi-prepared soil surface. The AM-M design increased the tolerances to improve installation fit. ABAQUS finite element analysis showed good performance, and researchers expected the design to perform well in this study.

5.1. End Connectors and Mat Panel Assembly

[0083] FIG. 11 is an exploded perspective view of a full-length panel 1100 of the matting system illustrating an overlap end connector 1110 and an underlap end connector 1120 on opposite longitudinal ends of the panel 1100. The panel 1100 includes a male hinge joint 1130 on one longitudinal side and a female hinge joint 1140 on the opposite longitudinal side. In this embodiment, the panel 1100 is a 2-piece friction stir welded (FSW) mat core formed by a friction stir welding (FSW) joint 1150.

[0084] FIG. 12 is a side view of the overlap end connector 1110 of FIG. 11 showing the mating surfaces thereof prior to fit-up, as viewed from a female hinge joint side. The overlap end connector 1110 includes a top hook 1112 with a top hook distal portion 1111 and top slot portion or top half-slot 1113 facing away from the end of the panel 1100 and an overlap end connector insert 1114 facing toward the end of the panel 1100 to be connected to the end of the panel 1100. The overlap end connector insert 1114 is a slotted insert in this example. The overlap end connector insert 1114 has a longitudinal array of insert members configured to slide in between the ribs of the mat core or panel 1100. The mating surfaces at the top skin are top butting surfaces 1210. The mating surfaces at the bottom skin are bottom butting surfaces 1220. Parallel mating surfaces are denoted by dashed lines in the longitudinal direction (Y-axis). The Z-axis is along the lateral direction. The X-axis is running out of the page.

[0085] FIG. 13A shows the overlap end connector 1110 prior to fit-up with the mat core 1300 and FIG. 13B shows the overlap end connector 1110 fit-up with the mat core 1300 and ready for friction stir welding to form the FSW joint or connection 1310.

[0086] FIG. 14 is an exploded perspective view of the overlap end connector 1110 of FIGS. 13A-13B prior to fit-up with the mat core 1300.

[0087] FIGS. 15A-15C show (A) a plan view of the panel 1100, (B) a front elevational view of a female hinge joint and a male hinge joint on opposite lateral sides of the panel, and (C) a rear elevational view of the female hinge joint and the male hinge joint. The panel 1100 includes FSW SEAM 1 of the two-piece mat core 1300, FSW SEAM 2 for the overlap end connector 1110, and FSW SEAM 3 for the underlap end connector 1120. Each full panel, including the end connectors at opposite ends and edge connectors on opposite edges, is 21-in.-wide by 84-in.-long and 1-in.-tall.

[0088] FIG. 16A is a front elevational view of one piece of the two-piece panel 1100 having the male hinge joint 1130 and vertical stiffeners 1610, and FIG. 16B is a cross-sectional view of the panel 1100 along section A-A.

[0089] FIG. 17A is a rear elevational view of the other piece of the two-piece panel 1100 having the female hinge joint 1140 and vertical stiffeners 1610, and FIG. 17B is a cross-sectional view of the panel 1100 along section B-B.

[0090] FIGS. 18A-18B show an example of an overlap end connector 1110 of FIG. 11 including (A) a top plan view standing on top of the mat core 1300 and looking down, and (B) an elevational view from the back face of the overlap end connector 1110 looking through the open end of the mat core 1300 on opposite side.

[0091] FIG. 19 is an elevational view of the overlap end connector 1110 detail on the male hinge 1130 side of the mat core 1300 of FIGS. 18A-18B.

[0092] FIG. 20 is an elevational view of the overlap end connector 1110 detail on the female hinge 1140 side of the mat core 1300 of FIGS. 18A-18B.

[0093] FIGS. 21A-21C show a male hinge 1130 side of the overlap end connector 1110 of FIGS. 18A-18B including (A) a top plan view, (B) an elevational view, and (C) a side view looking from the male hinge side. The overlap end connector 1110 includes a top hook 1112 with a top hook distal portion 1111 and top slot portion or top half-slot 1113 facing away from the end of the panel 1100 and an overlap end connector insert 1114 facing toward the end of the panel 1100 to be connected to the end of the panel 1100.

[0094] FIG. 22 is a side view of the underlap end connector 1120 of FIG. 11 showing the mating surfaces thereof, as viewed from a male hinge joint side. The underlap end connector 1120 includes a bottom hook 1122 with a bottom hook distal portion 1121 and bottom slot portion or bottom half-slot 1123 facing away from the end of the panel 1100 and an underlap end connector insert 1124 facing toward the end of the panel 1100 to be connected to the end of the panel 1100. The underlap end connector insert 1124 is a slotted insert in this example. The underlap end connector insert 1124 has a longitudinal array of insert members configured to slide in between the ribs of the mat core or panel 1100. The mating surfaces at the top skin are top butting surfaces 2210. The mating surfaces at the bottom skin are bottom butting surfaces 2220. Parallel mating surfaces are denoted by dashed lines in the longitudinal direction (Y-axis). The Z-axis is along the lateral direction. The X-axis is running out of the page.

[0095] FIG. 23A shows the underlap end connector 1120 prior to fit-up with the mat core 1300 and FIG. 23B shows the underlap end connector 1120 fit-up with the mat core 1300 and ready for friction stir welding to form the FSW joint or connection 2310.

[0096] FIG. 24 is an exploded perspective view of the underlap end connector 1120 of FIGS. 23A-23B prior to fit-up with the mat core 1300.

[0097] FIGS. 25A-25B show an example of an underlap end connector 1120 including (A) a top plan view standing on top of the mat core 1300 and looking down, and (B) an elevational view from the back face of the underlap end connector 1120 looking through the open end of the mat core 1300 on opposite side.

[0098] FIG. 26 is an elevational view of the underlap end connector 1120 detail on the female hinge 1140 side of the mat core of FIGS. 25A-25B.

[0099] FIG. 27 is an elevational view of the underlap end connector detail on the male hinge 1130 side of the mat core 1300 of FIGS. 25A-25B.

[0100] FIGS. 28A-28C shows a female hinge 1140 side of the underlap end connector 1120 of FIGS. 25A-25B including (A) a top plan view, (B) an elevational view, and (C) a side view looking from the male hinge 1130 side. The underlap end connector 1120 includes a bottom hook 1122 with a bottom hook distal portion 1121 and bottom slot portion or bottom half-slot 1123 facing away from the end of the panel 1100 and an underlap end connector insert 1124 facing toward the end of the panel 1100 to be connected to the end of the panel 1100.

5.2. Testing of End Connectors

[0101] This section describes the experimental methods used to test the three prototype mat joint samples (AM-X, AM-R, AM-M) in the laboratory. All experiments were conducted using an MTS servo-hydraulic load frame and a custom-built fixture. The fixture and test method were used to simulate the boundary conditions experienced by the mat connectors during full-scale experiments subjected to simulated F-15E and C-17 aircraft loads.

[0102] FIG. 29 shows is a sketch of the details of the load application and boundary conditions. Areas labeled 1 and 2 identify critical stress locations in the AM2 style end connector, AM-M. The loads were applied vertically using a 55,000-lb maximum capacity MTS hydraulic load frame.

[0103] The test fixture was calibrated by repositioning the inner constraint until 3,000 lb of vertical force was required to displace the specimens 0.625 in. This calibration procedure was used to mimic the global stiffness of a full array of installed AM2 matting. While the global stiffness of the new mat design may vary somewhat from AM2, the same calibration procedure allowed for relative comparisons of performance of the prototype designs. Using this procedure, the calibration distance of the inner constraints from the center of the connected joint was determined to be 10.5 in. for the AM-X geometry, 9.0 in. for the AM-R geometry, and 10.0 in. for the AM-M geometry. The difference in the calibrated support locations was related to the amount of free rotation provided by each of the joints prior to engaging the locking key. Joints with larger free rotation required shorter distances from the joint location to the first inner constraint for calibration, thus resulting in a stiffer section on the supported side of the joint. Conversely, joints with smaller angles of free rotation required longer distances between the joint location and the first constraint, resulting in a reduced stiffness.

[0104] FIG. 30 is a graphical diagram of field and laboratory displacement prediction models illustrating an increasing amplitude displacement function used to test the specimens. The program was designed to simulate the predicted subgrade deformation for any subgrade bearing capacity in terms of California Bearing Ratio (CBR) and was developed using empirical data gathered from full-scale AM2 experiments. During each load cycle, the joint was displaced downward according to the program and returned to its pretest unloaded position. The vertical displacement was increased with each successive loading to simulate a rut, or plastic deformation, forming in the subgrade underneath the joint similar to displacements observed during full-scale traffic experiments on AM2.

[0105] FIG. 31 is a test matrix Table summarizing the tests performed on the specimens. Each of the three connection geometries was tested with simulated 6-, 10-, 15-, and 25-CBR subgrades. These simulations were chosen to allow for comparison to full-scale experiments and previous AM2 experiments and to encompass a range of low-strength soils expected for an expedient airfield installation. Experimentation programs have shown that the failure mode form matting systems typically moves to the mat core at about a 25 CBR because the deformation of the subgrade decreases significantly. Five specimens (5 replicates) from each geometry were tested at 6, 10, and 15 CBR. Only one specimen from each geometry was tested at 25 CBR due to time and material constraints.

[0106] Each test specimen was tested according to the increasing amplitude displacement curve shown in FIG. 30 until failure. A test specimen was considered failed when the underlapping and overlapping sides of the joint were unable to transfer load through the joint. Typically, portions of each test specimen failed catastrophically in areas of high stress concentration by fatigue, thus disassembling the connection. In most cases, a portion of the locking mechanism of the mat broke free from the body of the connector.

5.3. Testing Results

[0107] FIG. 32 is a Table summarizing the average cycles to failure for each of the prototype geometries. FIG. 33 is a Table detailing the results from each individual test for the AM-X design. FIG. 34 is a Table detailing the results from each individual test for the AM-R design. FIG. 35 is a Table detailing the results from each individual test for the AM-M design.

5.3.1.6 CBR

[0108] Five specimens from each prototype connection geometry were evaluated with the 6 CBR program.

[0109] The average number of cycles to failure for the AM-X geometry using the 6-CBR program was 434 cycles. All five of the specimens failed by fracture along the top lug of the overlapping connector.

[0110] The average number of cycles to failure for the AM-R geometry using the 6-CBR program was 127 cycles. All five of the specimens failed by permanent deformation of the lug of the underlapping connector, which caused the joint to separate.

[0111] The average number of cycles to failure for the AM-M geometry using the 6-CBR program was 628 cycles. All five of the specimens failed when the top lug of the underlapping connector fractured.

5.3.2. 10 CBR

[0112] Five specimens from each prototype connection geometry were evaluated with the 10 CBR program.

[0113] The average number of cycles to failure for the AM-X geometry using the 10-CBR program was 1,092 cycles. All five of the specimens failed because the top lug of the overlapping connector fractured.

[0114] The average number of cycles to failure for the AM-R geometry using the 10-CBR program was 390 cycles. Four of the specimens failed by permanent deformation on the lug of the underlapping connector, while one of the specimens fractured the lug of the overlapping connector.

[0115] The average number of cycles to failure for the AM-M geometry using the 10-CBR program was 1,214 cycles. Three of the specimens broke on the upper lug of the underlapping connector, while two of the specimens fractured the lower lug of the overlapping connector.

5.3.3. 15 CBR

[0116] Five specimens from each prototype connection geometry were evaluated with the 15 CBR program.

[0117] The average number of cycles to failure for the AM-X geometry using the 15-CBR program was 2,710 cycles. All five of the specimens failed when the top lug of the overlapping connector fractured.

[0118] The average number of cycles to failure for the AM-R geometry using the 15-CBR program was 849 cycles. Four of the specimens failed by permanently deforming the lug of the underlapping connector, while one specimen failed when the lug of the overlapping connector fractured.

[0119] The average number of cycles to failure for the AM-M geometry using the 15-CBR program was 2,950 cycles. Two of the specimens fractured the upper lug of the underlapping connector, while three of the specimens fractured the lower lug of the overlapping connector.

5.3.4.25 CBR

[0120] One specimen from each prototype connection geometry was evaluated with the 25 CBR program.

[0121] The AM-X geometry survived 7,153 cycles using the 25-CBR program. The specimen failed in the same location as all other samples: the top lug of the overlapping connector.

[0122] The AM-R geometry survived 1,853 cycles using the 25-CBR program. The specimen failed by permanently deforming the lug of the underlapping connector.

[0123] The AM-M geometry survived 4,909 cycles using the 25-CBR program. The specimen broke the bottom lug of the overlapping connector.

5.4. Discussion of Test Results

[0124] The experiments were performed to compare the low-cycle fatigue performances of three prototype end connector designs to determine which was the most suitable for use in a new lightweight mat design for future AM2 replacement.

[0125] FIG. 36 is a graphical plot of average cycles to failure for the four connector embodiments, including AM2, for comparison. Overall, the performances of the three prototype geometries were less than traditional AM2 for the 6- and 10-CBR displacement profiles; however, the AM-M outperformed AM2 on the 15-CBR subgrade, and both AM-X and AM-M outperformed AM2 on the 25-CBR subgrade. Also, the AM-X was within 10% of AM2's performance at the simulated 15-CBR subgrade. At 10 CBR, however, the performances of both the AM-X and AM-M joints achieved 35% fewer cycles to failure compared to AM2. At a 6 CBR, the difference increased to 45 and 60%, respectively.

[0126] The geometries of the connectors were designed using ABAQUS 3-D finite element software. High-fidelity finite element modeling for monotonic loading was completed to create a comparison between in-lab results and finite element analysis (FEA) results. The boundary conditions created in the finite element models were developed to replicate the testing conditions of the in-lab experiments. Aluminum alloy 6061-T6 was the material used in the subsequent FEA analyses, with a coefficient of friction of 0.4. The results show that areas of high stress within the FEA model matched the points of ultimate failure within the in-lab experiments.

[0127] The primary reason the prototype geometries did not achieve the same number of cycles to failure compared to AM2 for the 6- and 10-CBR displacement programs was the reduced thickness of the prototype test specimens. AM2 is 1.5 in. thick while the tested prototype specimens were 1.0 in thick. Through previous test efforts and evaluations of commercial matting systems, researchers realized that simply scaling the AM2 joint directly (including installation tolerances) resulted in mat systems that were extremely difficult to install (there was not enough space between the parts of the connection system for easy installation). The new designs used in this study were designed to reduce the thickness while maintaining the same gaps or tolerances between the locking components to ensure installation was realistically achievable when installed over a semi-prepared soil surface. However, the reduction in the thickness by 0.5 in. still had a significant effect on the overall strength of each design. In most cases, the reduction in the overall thickness required a reduction in thickness of each component within the connector. When the same load was applied to a thinner joint, the stresses in each component increased, causing earlier fatigue failure than for the larger components within the AM2 joint. This type of performance was expected since the strains experienced in areas of high stress concentration caused significant weakening and eventual fracture of these critical components. Additionally, the results proved that as the strength of the soil foundation increases (especially greater than 15 CBR), the deformation of the subgrade (and, therefore, vertical displacement of the joint) decreases significantly, reducing the stress in the joint and allowing more direct load transfer to the core of the mat panels. This was proved based on the results of both the AM-X and AM-M geometries' ability to outperform AM2.

[0128] In addition, partly because of issues with material availability and mostly to ensure a direct comparison could be made to the performance of AM2, the prototype test specimens were produced from AA6061-T6 material; however, they were designed and optimized in an ABAQUS 3-D FEA software using AA2099.

[0129] Locking bar size could have had a contribution to joint performance. An inverse relationship was noted between the amount of tolerance in the locking bar channel and the amount of stiffness in the joint. For example, the AM-R design had the most tolerance in the locking bar channel, allowing for more free rotation of the joint. In contrast, the fit of the AM-X locking bar was rather tight, causing the joint to lock up much more quickly than the others. These observations were also reflected in the calibration distance for each joint. The joint with the smallest tolerances (AM-X) had a calibration distance of 10.5 in., while the joint with the most amount of free play (AM-R) had a calibration distance of 9.0 in. Therefore, the amount of tolerance in the joint caused by the locking bar was compensated for by changing the calibration distance.

[0130] One final factor to consider that could affect performance is the production method of the prototypes. All prototypes were machined, while the AM2 coupons previously tested were extruded. It is understood that typically a test coupon made from forged AA6061 would have a longer fatigue life than a coupon extruded from the same material. That could contribute to the good performance of AM-X and AM-M geometries versus AM2 at the 15-CBR and 25-CBR displacement profiles.

[0131] In conclusion, three prototype aluminum mechanical end connector geometries were evaluated for their low-cycle fatigue performances over four simulated subgrade strengths. The AM-X and AM-M designs provided the best fatigue-life performance for higher and lower CBR displacement profiles, respectively. More specifically, the AM-X geometry had the highest number of cycles to failure at 25 CBR, while the AM-M geometry had the most cycles at 6, 10, and 15 CBR. The AM-R design provided the fewest cycles to failure in all tests conducted. Based on the testing results, the AM-X and the AM-M designs are the best two designs. Even so, none of the prototype designs outperformed AM2 with the 6- or 10-CBR subgrades. A material change to AA2099 is expected to improve the fatigue performances of both the AM-X and AM-M designs significantly. In addition to fatigue performance, the ease of installation of the AM-X mats over the AM-M mat makes the AM-X design more suitable and desirable.

6. Lightweight Matting System

[0132] According to an aspect of the invention, a novel lightweight and rapidly deployable expeditionary airfield can withstand the loads of DOD/NATO Rotary Wing, Tiltrotor, and other modern aircrafts. The novel airfield matting system, AM-L, includes a lighter and thinner aluminum panel, with a redesign of the mat core and end connectors to accommodate in-field service and meet objective constraints on weight and area of the matting. The development of the mat core involved the usage of a physics-based high-fidelity modeling that underwent several iterations. The FSW two-piece mat core incorporates vertical stiffeners, similarly used with AM2, and with a thicker center stiffener to withstand reaction forces during FSW joining of the two pieces and to increase the service life of the FSW. A single extruded mat core was also considered, but upon further modeling and lab-scale testing the one-piece mat core was shown not to withstand higher forces that the two-piece mat could. End connector redesign involved the use of the high-fidelity modeling that resulted in two separate designs, which upon lab-scale testing showed the AMX end connector to be the superior design that is incorporated into the matting system.

[0133] The lightweight matting system underwent in-field service testing using a F15 tire load. The lightweight matting system was originally designed to withstand the MV22 Osprey tire loading in CBR 6 soil. Instead, the matting was tested with a F15 tire load, which was a more significantly strenuous loading condition, with CBR 15 soil. The matting withstood 98 passes before the permeant deformation of the soil, at 1.25 inches, resulted in a failure of the matting. Further cyclic loading of the matting by the F15 tire resulted in a total of 562 passes before unsafe tire hazards from mat breakage with cracking and rips along the skin prevented further passes. The lightweight matting system demonstrated significant design changes to the mat core and end connectors that withstood F15 loading with CBR 15 soil. If the matting had been tested with the original MV22 Osprey loading conditions, the matting would have surpassed initial design requirements.

[0134] In specific embodiments, the AM-L system is a lightweight rectangular aluminum panel with unique connectors on all four edges that allow multiple panels to be assembled in a modularly manner to form a modular system of airfield matting to be used as an aircraft operating surface. It is made from four unique extrusions and one rectangular locking bar extrusion. The extruded material is aluminum alloy 6061. After extrusion, each part is tempered to T6 condition. The extrusions are generally about 40 ft in length and cut to the desired length for assembly. The two 21 in. edge extrusions require significant machine work prior to assembly. The two main panel extrusions are friction stir welded on the top and bottom simultaneously along their length to join them into a single panel (e.g., FIG. 7). Two half-width mat core members (10.5 inches in width) are friction stir welded to form a full-width mat core (21 inches in width). The two 21 in. long edge connectors are machined, fitted into the main panel, and then friction stir welded along the top and bottom edges simultaneously to join them to the panel. Next, the vertical corners are manually welded to seal the panel for water tightness and any excess weld is ground off manually. Next, the panels are prepared for painting by shot blasting. A non-skid paint coating is then applied and cured. After curing, the panel is complete and ready for use.

[0135] The AM-L system has been tested by rolling simulated aircraft back and forth across its surface to measure its performance and durability. It survived more than 3000 passes of an MV-22 aircraft load and another 500 of an F-35B when placed directly on a soft soil with a California bearing ratio (CBR) of 6%. Only limited structural damage was observed. It also survived 24,000 passes of an F-15E when placed directly over Portland cement concrete pavement and 3,200 passes of an F-35B when placed directly on a soil with a CBR of 25%. These tests showed that the panel may bend, but none of the components broke and it did not create unsafe conditions for the moving aircraft. These full-scale tests validated the AM-L system's ability to work as a safe lightweight aircraft operating surface.

[0136] The AM-L assemblies may need occasional maintenance over time and individual panels may need to have paint and non-skid re-applied after long-term UV exposure. However, the AM-L panel should have an indefinite life if it is handled properly.

[0137] The inventive concepts taught by way of the examples discussed above are amenable to modification, rearrangement, and embodiment in several ways. Accordingly, although the present disclosure has been described with reference to specific embodiments and examples, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.

[0138] An interpretation under 35 U.S.C. 112(f) is desired only where this description and/or the claims use specific terminology historically recognized to invoke the benefit of interpretation, such as means, and the structure corresponding to a recited function, to include the equivalents thereof, as permitted to the fullest extent of the law and this written description, may include the disclosure, the accompanying claims, and the drawings, as they would be understood by one of skill in the art.

[0139] To the extent the subject matter has been described in language specific to structural features and/or methodological steps, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as example forms of implementing the claimed subject matter. To the extent headings are used, they are provided for the convenience of the reader and are not to be taken as limiting or restricting the systems, techniques, approaches, methods, devices to those appearing in any section. Rather, the teachings and disclosures herein can be combined, rearranged, with other portions of this disclosure and the knowledge of one of ordinary skill in the art. It is the intention of this disclosure to encompass and include such variation.

[0140] The indication of any elements or steps as optional does not indicate that all other or any other elements or steps are mandatory. The claims define the invention and form part of the specification. Limitations from the written description are not to be read into the claims.

[0141] Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word about or approximately preceded the value or range.

[0142] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, percent, ratio, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term about, whether or not the term about is present. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0143] It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain embodiments of this invention may be made by those skilled in the art without departing from embodiments of the invention encompassed by the following claims.

[0144] In this specification including any claims, the term each may be used to refer to one or more specified characteristics of a plurality of previously recited elements or steps. When used with the open-ended term comprising, the recitation of the term each does not exclude additional, unrecited elements or steps. Thus, it will be understood that an apparatus may have additional, unrecited elements and a method may have additional, unrecited steps, where the additional, unrecited elements or steps do not have the one or more specified characteristics.

[0145] It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the invention.

[0146] Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

[0147] All documents mentioned herein are hereby incorporated by reference in their entirety or alternatively to provide the disclosure for which they were specifically relied upon.

[0148] Reference herein to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase in one embodiment in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term implementation.

[0149] The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.