Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
1999-02-01
2001-03-06
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
C428S116000
Reexamination Certificate
active
06197402
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to heavy density non-metallic honeycomb structures. More particularly, the present invention involves increasing the formability of such honeycomb structures so they can be made into a wide variety of non-planar shapes.
2. Description of Related Art
Honeycomb structures which include bisector sheets are generally referred to as “high density honeycomb”. These types of reinforced honeycombs are usually composed of a stack of alternating corrugated and bisector sheets which are glued or otherwise bonded together. A portion of a typical high density honeycomb is shown at
10
in FIG.
5
. The honeycomb
10
includes bisector sheets
12
and corrugated sheets
14
which are bonded together at node junctures
16
. As can be seen from
FIG. 5
, the bisector sheets
12
split the hexagonal honeycomb cells down the center. This configuration adds density, strength and bonding surface to the core. The high density honeycombs are well-suited for use in situations where high structural strength is required. However, the inherent stiffness of high density honeycomb and the presence of the bisector sheets makes it difficult to form such structures into non-planar shapes without damaging the honeycomb.
As shown in
FIG. 5
, honeycombs are three dimensional structures which are characterized as having a thickness (T direction) which is measured parallel to the honeycomb cell and provides a measure of the honeycomb depth. The width (W direction) of the honeycomb is measured perpendicular to the T direction and provides a measure of the height of the stacked honeycomb cells. The length (L direction) of the honeycomb is measured perpendicular to both the T and W directions and provides a measure of the length of the corrugated and bisector sheets present in the honeycomb (see FIG.
5
).
When forming non-planar high density honeycomb structures, planar honeycombs of the type shown in
FIG. 5
are formed in the L and/or W directions by applying heat and/or pressure to the honeycomb. When forming in the L direction, the outside radius of the core must expand in the L direction and inside radius of the core must contract in the L direction. The bisector sheet passing through the cell will not allow the cell to expand on the top of the radius. As a result, the inside of the cell must condense more. This causes the inside cell to deform or crush to such a degree that the resulting core may have reduced strength and/or the corrugated and bisector sheets may separate at the node junctures.
When forming non-planar high density honeycombs in the W direction, the outside radius of the cell must expand in the W direction and the inside radius of the core must contract in the W direction. The bisector sheets limit the movement of the cell walls so that the usual result is that the relatively stiff node junctures are torn apart.
Various approaches have been taken to try and increase the formability of high density honeycombs. For example, attempts have been made to increase node strength by using higher strength adhesives. Various thermosetting resins have been used in the resin matrix of composite honeycomb walls to enhance heat formability and various thermosetting dip resins have been used to coat honeycomb walls. The use of hybrid weaves for composite honeycomb walls has also been proposed. Although all of these approaches have achieved some improvement in formability of high density honeycomb, there still is a continuing need to increase and enhance the formability of such honeycomb structures.
SUMMARY OF THE INVENTION
In accordance with the present invention, it was discovered that the formability of high density honeycomb can be enhanced and increased by orienting the primary corrugated sheets and bisector sheets in a specific fashion which increases honeycomb flexibility without unduly affecting the overall strength of the high density honeycomb. This increase in flexibility is achieved by offsetting the honeycomb nodes so that the stiff node structures are separated and redistributed throughout the honeycomb to provide for increased formability. The offsetting of the honeycomb nodes allows for more deformation of the inside cells without failure when forming in the L direction. In the W direction, the offset node configuration allows the outside of the cell to expand and the inside to condense more without undue crushing or failure of the structure.
The honeycomb structures of the present invention include a plurality of primary corrugated sheets with each primary corrugated sheet having a plurality of alternating upper nodes and lower nodes. Each upper node includes a top surface and a bottom surface, and each lower node also includes a top surface and a bottom surface. A plurality of bisector sheets which each includes a top surface and a bottom surface are combined with the corrugated sheets to form the high density honeycomb structure which includes alternating layers of primary corrugated sheets and bisector sheets. The top surfaces of the upper nodes are bonded to the bottom surface of the bisector sheets at upper node bond locations on the bisector sheets. The bottom surfaces of the lower nodes are bonded to the top surfaces of the bisector sheets at lower node bond locations on the bisector sheets. As a feature of the present invention, the upper node bond locations and lower node bond locations on each bisector sheet are displaced from each other. This provides an offset node configuration which, as mentioned above, separates the node junctures and redistributes the density of the cells more evenly to allow for increased formability of the overall honeycomb structure.
The offset node design provided by the present invention is well suited for use in a wide variety of metallic and non-metallic, high density honeycomb structures where it is desired to form non-planar structures from the initially prepared planar honeycomb. The invention does not depend upon the use of specialized high strength adhesives or specialized thermal set resins or specialized weave patterns. Instead, the invention involves a basic reorientation of the honeycomb layers to provide increased and enhanced flexibility regardless of the specific materials being used for the primary corrugated sheets and bisector sheets.
The above described and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5346367 (1994-09-01), Doolin et al.
Ayle Earl F.
Miller P. Shane
Morrison Robert B.
Bielawski W. Mark
Hexcel Corporation
Lorin Francis J.
Oldenkamp David J.
LandOfFree
Formable heavy density honeycomb does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Formable heavy density honeycomb, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Formable heavy density honeycomb will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2445430