Co-cured Composite Stringer Flange Shaping via Segmented Bladder
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Solution Overview
Problem
The existing methods for co-curing composite stringers face challenges in maintaining smoothness and pressure at the flanges, particularly due to venting issues with flexible bladders near the flanges, which complicates the formation of smooth and precisely shaped flanges during the curing process.
Innovation Solution
A part forming apparatus comprising a forming tool with a rigid plate and a hollow bladder, where the rigid plate is configured to rest within a recessed pocket and extend over a bladder extension trough, allowing the bladder to be positioned between the plate and the extension trough, enabling precise shaping and pressure distribution, and a method involving the use of a vacuum bag and autoclave for co-curing composite material with a skin laminate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a flexible hollow bladder is used to apply pressure during co-curing, then the composite material can be consolidated, but the bladder cannot maintain smoothness and pressure at the flange regions where venting is required
Solution Approach 1:
The bladder is segmented into different regions: a reinforced rigid portion at the end opposite the vent that extends into the flange region to maintain smoothness and pressure, and a flexible portion that can expand to consolidate the composite material. This segmentation allows each region to perform its specific function without interfering with the other.
Solution Approach 2:
Different portions of the bladder have different physical properties: the rigid portion provides structural support and maintains smooth flange surfaces, while the flexible portion provides consolidation pressure. This local differentiation of material properties resolves the contradiction between maintaining smoothness and applying pressure.
2Stress or pressure
If the bladder is vented at the ends of the stringer to apply internal pressure, then pressure can be applied to the composite material, but the flanges near the vent locations cannot maintain smoothness and precise shape
Solution Approach 1:
The rigid portion of the bladder acts as an intermediary element between the vent and the flange region. It transmits the pressure from the vented bladder interior to the composite material while simultaneously maintaining the smooth external surface of the flange, preventing direct interference between the venting process and flange shaping.
3Manufacturing precision
If the bladder is made rigid to maintain flange smoothness, then pressure distribution can be improved, but the bladder loses its ability to conform to the composite material during consolidation
Solution Approach 1:
The bladder is divided into rigid and flexible segments, allowing the rigid portion to maintain pressure distribution and smoothness while the flexible portion conforms to the composite material contours during consolidation.
Solution Approach 2:
Different regions of the bladder have different rigidity properties: the rigid portion provides stable pressure distribution and surface smoothness, while the flexible portion adapts to the composite material shape, achieving both precision and conformity.
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
This solution ensures consistent pressure and smoothness across the flanges, facilitating the formation of high-quality, co-cured composite stringers with precise flange shapes, overcoming the limitations of previous methods by maintaining pressure and smoothness effectively during the curing process.
Implementation Method 1
A vacuum bag is then placed over the skin laminate and sealed to the lay-up tool. Vacuum and heat via an autoclave can then be used to co-cure the composite material and the skin laminate into a monolithic structure.
Implementation Method 2
Vacuum and heat via an autoclave can then be used to co-cure the composite material and the skin laminate into a monolithic structure.
Data Source
AI summary
A method and part forming apparatus configured for forming an aircraft stringer. The part forming apparatus may comprise a forming tool, a rigid plate, and a hollow bladder. The forming tool may comprise a material trough, a bladder extension trough laterally aligned with and open to the material trough, and a recessed pocket extending from either side of the bladder extension trough and adjacent to the material trough. The method comprises placing composite material into the material trough, placing the bladder onto the composite material and through the bladder extension trough, placing the rigid plate into the recessed pocket and over the bladder, and then placing skin laminate over the bladder and the composite material. Once each of these components is in place, the forming tool may be vacuum bagged and the composite material and skin laminate may be co-cured to form the stringer.