Honeycomb Core Composite Stitching for Delamination Prevention
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Solution Overview
Problem
Sandwich components with honeycomb cores, despite their high mechanical strength and low weight, suffer from low resistance to damage due to the risk of progressive delamination of cover layers, which limits their use in primary aircraft structures.
Innovation Solution
A method involving the introduction of a core filler material, mechanical bonding of cover layers to the folded honeycomb core using stitching or adhesion, infusion with a curable plastic material, and hardening under pressure and temperature, effectively preventing progressive delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If sandwich components with honeycomb cores are used to achieve high mechanical strength and low weight, then the strength-weight ratio is improved, but the resistance to damage deteriorates due to progressive delamination of cover layers
Solution Approach 1:
The core filler material is introduced in segmented form into the honeycomb core cells, creating discrete bonding points that prevent continuous delamination propagation. The stitching process also creates segmented bonding zones along the cover layer-core interface, interrupting potential delamination paths.
Solution Approach 2:
The core filler material is introduced into the honeycomb core before the cover layers are applied. This preliminary action ensures that bonding sites are pre-prepared and positioned optimally to prevent delamination during subsequent operational loading, rather than attempting to repair delamination after it occurs.
2Reliability
If mechanical bonding of cover layers to folded honeycomb core is implemented to prevent progressive delamination, then reliability is improved, but device complexity increases due to additional manufacturing steps
Solution Approach 1:
The patent combines multiple functions into integrated process steps: the core filler material serves both as a bonding medium and as a structural support element during manufacturing. The mechanical bonding process is merged with the existing sandwich composite manufacturing workflow, incorporating stitching or adhesion into the standard layering and curing sequence rather than adding entirely separate operations.
Solution Approach 2:
The core filler material acts as an intermediary substance between the honeycomb core and the cover layers, facilitating mechanical bonding without requiring direct complex bonding mechanisms. This intermediary material simplifies the bonding process by providing a compliant, adhesive interface that accommodates manufacturing variations and thermal expansion differences.
3Ease of manufacture
If core filler material is introduced into the folded honeycomb core to enable mechanical bonding, then ease of manufacture is improved, but loss of substance increases due to removal of the filler material
Solution Approach 1:
The core filler material is designed as a temporary, disposable component that serves its bonding function during manufacturing and then is completely removed. Materials such as water-soluble polymers, low-melting-point waxes, or biodegradable substances are used, which can be easily eliminated through rinsing, heating, or decomposition, minimizing waste and simplifying removal processes.
Solution Approach 2:
The core filler material's physical or chemical parameters are changed during the manufacturing process to enable easy removal. For example, water-soluble fillers are removed by changing from a solid suspended state to a dissolved state through water rinsing; or thermoplastic fillers are removed by changing from a solid state to a molten state through heating, allowing complete elimination without residue.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enhances the damage tolerance of core composites, making them suitable for use in the primary structure of aircraft by ensuring secure bonding between cover layers and the honeycomb core, preventing delamination under various operating conditions.
Implementation Method 1
The core filler material is a curable material which can be removed again without residue after fabrication of the core composite by suitable solvents or the use of temperature. As core filler material can be used by way of example the material 'AquaCore®' which is soluble in water and can thus be rinsed out from inside the core composite without residue.
Implementation Method 2
Alternatively low-melting wax or metal alloys can also be used as the core filler material.
Implementation Method 3
hardening the entire core composite by applying pressure and/or temperature
Data Source
AI summary
The invention relates to a method for manufacturing a core composite (1, 20, 26) having a folded honeycomb core (2, 21, 29) provided on both sides with cover layers (3, 4, 22, 23, 27, 28) wherein the folded honeycomb core (2, 21, 29) has a number of drainage-enabling channels (5). First a core filler material (16, 17) is introduced into the folded honeycomb core (2, 21, 29) at least in some areas in order to provide the filler material with sufficient stability for the subsequent sewing process. The cover layers (3, 4, 22, 23, 27, 28) which are not yet impregnated with a curable plastics material are then placed on the folded honeycomb core (2, 21, 29) and stitched to this along the base lines (6 to 8) and/or apex lines (9, 10) at least in some sections by means of a sewing thread (19). The infiltration of the overall structure with a curable plastics material is then carried out followed by hardening by applying pressure and/or temperature. The core filler material (16, 17) can to complete the process be removed again completely from the folded honeycomb core (2, 21, 29) by being dissolved and washed out or by melting and flowing out. Delamination of the cover layers (3, 4, 22, 23, 27, 28) from the folded honeycomb core (2, 21, 29) is prevented by the stitching so that core composites (1, 20, 26) manufactured by the method according to the invention can be used in the primary structure of aircraft.The invention further relates to a core composite (1, 20, 26) manufactured according to the provisions of the method.