Composite Stringer Bladder with Collapsible Foam Core
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Solution Overview
Problem
The fabrication of composite stringers and assemblies is challenging due to the complexity of tools required, especially when hat-style stringers are co-formed or co-cured with a stringer base, and conventional bladders are difficult to remove from the cavity formed by the stringer assembly.
Innovation Solution
A bladder system comprising a foam bladder core and an elastic bladder skin, where the bladder skin is stretched to conform to the bladder core, allowing for support during forming and easy removal by collapsing the bladder core, facilitating the formation and assembly of composite stringer assemblies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional supporting structure (mandrel) is used to shape composite stringer, then the stringer can be properly formed, but the supporting structure becomes difficult to remove from the cavity formed by the stringer assembly
Solution Approach 1:
The bladder is divided into two functional parts: an expandable bladder body for shaping and a collapsible core for removal. The bladder body remains in the cavity to provide structural support, while the collapsible core can be easily extracted through the stringer assembly cavity after deflation.
Solution Approach 2:
The bladder core transitions from a rigid or semi-rigid state during inflation to a collapsible state during removal. The core is designed to change its mechanical properties, allowing it to be compressed and folded for easy extraction after the bladder body has completed its shaping function.
2Manufacturing precision
If complex sophisticated equipment is used for fabrication of composite structures, then manufacturing precision can be achieved, but device complexity increases
Solution Approach 1:
The bladder system serves multiple functions: it acts as a supporting structure during curing, a shaping tool during formation, and a removable core after deflation. This multi-functionality eliminates the need for separate mandrels and supporting structures, simplifying the overall fabrication equipment while maintaining manufacturing precision.
Solution Approach 2:
The bladder material properties are changed through parameter selection to achieve both rigidity during inflation for precise shaping and collapsibility during removal. The core uses materials or structures that can transition from a stable inflated state to a compressed removable state, reducing equipment complexity while maintaining form accuracy.
3Strength
If the bladder core is made rigid for structural support, then support strength during curing is improved, but removability from the cavity is worsened
Solution Approach 1:
The bladder is segmented into the bladder body and collapsible core, where each part has optimized properties for its specific function. The bladder body provides structural support strength, while the collapsible core is designed specifically for easy removal through compression and folding mechanisms.
Solution Approach 2:
The collapsible core utilizes flexible materials or thin-walled structures that can maintain rigidity when inflated but become flexible and collapsible when deflated. This allows the core to provide necessary support strength during curing while enabling easy removal through compression after the curing process is complete.
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
Enables efficient shaping and curing of composite stringer assemblies with improved removability of the bladder system, simplifying the fabrication process and reducing the complexity of equipment needed for aircraft manufacturing.
Implementation Method 1
The bladder core is formed from foam
Implementation Method 2
The bladder skin is formed from an elastic material and encloses the bladder core
Implementation Method 3
the bladder core is collapsible for the removal of the bladder from the cavity of the stringer assembly
Data Source
AI summary
Described herein are methods and systems for forming composite stringer assemblies or, more specifically, for shaping composite charges while forming these stringer assemblies. A system comprises a bladder, having a bladder core, and a bladder skin. The bladder core is formed from foam. The bladder skin is formed from an elastic material and encloses the bladder core. When a composite stringer assembly is formed, the bladder is positioned over a charge base. The charge base later becomes a stringer base, such as a fuselage section or a wing skin. A charge hat is then positioned over the bladder and is conformed to the bladder. A combination of the bladder skin and the bladder core provides support during this forming operation and later while the stringer assembly is cured. In some examples, the bladder core is collapsible for the removal of the bladder from the cavity of the stringer assembly.