Composite Honeycomb Layup Tie-Down for Core Stability in Curing
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Solution Overview
Problem
Existing methods for fabricating composite honeycomb core sandwich structures using unidirectional tape fail to prevent core movement and crush during autoclave curing, as they lack effective tie-down mechanisms applicable to woven fabric materials.
Innovation Solution
A method involving automated fiber placement of unidirectional tows to form under-core and over-core composite plies, which are oriented quasi-isotropically and extend beyond the structure's trimline to engage a rough textured surface, securing the honeycomb core in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the tie down method using woven fabric plies is applied, then core movement and crush are prevented, but the method is not applicable to unidirectional tape materials
Solution Approach 1:
The invention changes the material parameter from woven fabric to unidirectional tape, requiring a modification of the tie-down mechanism. The solution involves laying unidirectional tows in specific orientations (0 degrees and 90 degrees) to replicate the bidirectional restraint function of woven fabrics, thereby maintaining core stability while adapting to the constraints of unidirectional material geometry
Solution Approach 2:
The invention transitions from the planar constraint mechanism of woven fabric (which relies on in-plane fiber orientation) to a three-dimensional restraint system using stacked unidirectional plies at different orientations. This dimensional approach allows the unidirectional tows to collectively provide multi-directional restraint against core movement and crush
2Ease of manufacture
If unidirectional tows are used without proper tie-down mechanism, then automated fiber placement process is simplified, but core movement and crush occur during autoclave curing
Solution Approach 1:
The invention applies preliminary action by pre-positioning the unidirectional tows in specific orientations before core placement and autoclave curing. The tows are laid up in predetermined patterns (with plies at 0 degrees and 90 degrees extending beyond the core edges) to create a restraint system that will actively prevent core movement when autoclave pressure is applied
Solution Approach 2:
The unidirectional tows act as an intermediary element between the autoclave pressure and the honeycomb core. Rather than allowing direct pressure contact that could cause crushing, the tows distribute and redirect the lateral forces, mediating the interaction between the curing process and the core structure
3Ease of operation
If woven fabric plies are tied down to grit strip, then friction prevents ply movement, but unidirectional tows lack bidirectional fiber structure for effective friction-based restraint
Solution Approach 1:
The invention segments the restraint function into separate unidirectional plies oriented at different angles, rather than relying on a single bidirectional woven fabric structure. Each unidirectional ply provides restraint in its specific fiber direction, and the combination of plies at 0 degrees and 90 degrees collectively provides comprehensive restraint against core movement in multiple directions
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
Prevents core movement and crush during autoclave curing, enabling the production of complex composite honeycomb core sandwich structures without rework or scrap.
Implementation Method 1
The unidirectional tows are laid up using an automated fiber placement process to form a stack of under-core composite plies that are tied down to a rough textured surface bonded to the tool
Data Source
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AI summary
A method for fabrication of a layup for a composite honeycomb core sandwich structure includes laying up a first plurality of unidirectional tows over a tool for layup of the composite honeycomb core sandwich structure using an automated fiber placement process to form a stack of under-core composite plies that are tied down to a rough textured surface bonded to the tool; placing a honeycomb core on the stack of under-core composite plies within the rough textured surface; and laying up a second plurality of unidirectional tows over the honeycomb core using the automated fiber placement process to form a stack of over-core composite plies that tie down the honeycomb core to the rough textured surface. The method may also include placing an under-core film adhesive on the stack of under-core composite plies and placing an over-core film adhesive on the honeycomb core.