Flexible Hexagonal Core Element for Sandwich Panel Delamination
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Solution Overview
Problem
The aerospace and rocketry industries face challenges with delamination in sandwich construction panels due to limited bonding areas and moisture retention in honeycomb cores, leading to costly failures and detection difficulties, and there is a need for a core material that is lightweight, formable, and ventable to prevent cryo-pumping in rocket fuel tanks.
Innovation Solution
A flexible core element made from a continuous sheet of material die-cut into a repeating geometrical design with hexagonal nodes and rectangular wall members, folded concertina-style to create a double-surfaced core with a large bonding area, allowing for venting and exhibiting good bending and shear strength, while being stackable and formable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If honeycomb cores are used in sandwich construction, then the panel achieves stiffness and light weight, but the bonding area between skin and core is minimal leading to delamination
Solution Approach 1:
The core is divided into multiple discrete foam cells arranged in a grid pattern, where each cell provides an independent bonding interface. This segmentation increases the total bonding area between the skin and core compared to continuous honeycomb structures, while maintaining the lightweight and stiff characteristics through the cellular geometry.
Solution Approach 2:
The core structure transitions from a two-dimensional honeycomb pattern to a three-dimensional foam cell arrangement with vertical walls. This dimensional change creates multiple bonding surfaces (top, bottom, and side walls of each cell), significantly increasing the bonding area without compromising the panel's stiffness or increasing weight.
2Stability of the object's composition
If honeycomb cores are used, then the panel structure is established, but moisture is trapped in closed cells causing delamination at high altitudes
Solution Approach 1:
The core uses an open-cell foam structure rather than closed honeycomb cells. This porous configuration allows moisture and air to pass through the core material, preventing moisture accumulation that would otherwise cause delamination at high altitudes. The foam cells remain interconnected, maintaining structural integrity while providing venting capability.
3Adaptability or versatility
If a core material is made lightweight and formable, then it is suitable for various applications, but bending strength may be compromised
Solution Approach 1:
The core combines foam material with a woven fabric reinforcement layer. The foam provides lightweight properties and formability, while the woven fabric reinforcement enhances bending strength and structural stability. This composite approach allows the core to be shaped into various configurations without sacrificing mechanical strength.
Data Source
AI summary
A flexible core element having a large bonding surface area suitable for sandwich type construction comprising a plurality of first hexagonal nodes defining a first surface, a plurality of second hexagonal nodes defining a second surface spaced apart from and parallel to the first surface, and a plurality of rectangular wall members which interconnect said first hexagonal nodes to said second hexagonal nodes and define the depth of the core element. Each hexagonal node corresponds to an open hexagonal cell on its obverse surface and serves as a bonding surface. The core element is fabricated from a continuous sheet of material that has been die-cut with a repeating geometrical design, creased and folded, concertina style, in upon itself to make a double-sided core material that is flexible, able to vent, exhibits good bend and shear strength, and has a large surface bonding area rendering it suitable in the construction of lightweight sandwich panels and offering a wide array of other applications.