Invar Alloy Bracket Design for T-Shaped Stringer Curing
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Solution Overview
Problem
The 'Mexican hat effect' in T-shaped aircraft stringers, where the thickness of the stringer web is smaller than nominal at the end and greater at the flange, causes assembly difficulties due to uneven thickness, requiring solid supplements for other parts to be assembled, increasing time and work.
Innovation Solution
The method involves using invar alloy brackets with a cut radius to eliminate the flange portion over the stringer flange, optionally with an elastomeric support and pre-cured glass fiber to facilitate demolding and assembly, and using a filler between adjacent stringers to prevent edge effects during curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional invar alloy brackets are used during curing, then the stringer maintains its shape during curing, but the Mexican hat effect causes uneven thickness distribution at the stringer ends
Solution Approach 1:
The invar alloy bracket is designed with a cut radius that creates different geometries at different locations: the flat portion contacts the stringer web while the curved portion contacts the stringer flange. This local differentiation in bracket geometry compensates for the natural thickness variation in the stringer, achieving uniform thickness distribution without requiring solid supplements during assembly
Solution Approach 2:
The bracket design incorporates a specific cut radius parameter that transforms the uniform bracket geometry into a non-uniform geometry. This parameter change allows the bracket to locally compensate for the Mexican hat effect by providing different support characteristics at the web and flange regions during curing
2Reliability
If the invar alloy bracket covers the entire stringer flange, then the stringer is fully supported during curing, but the bracket weight increases and demolding becomes difficult
Solution Approach 1:
The unnecessary portion of the invar alloy bracket is removed by cutting a radius that eliminates the flange-covering portion. This extraction reduces the bracket weight and facilitates demolding while maintaining sufficient support during curing through the remaining flat and curved portions that contact the stringer web and flange respectively
Solution Approach 2:
The invar alloy bracket is designed with a cut radius configuration before the curing process begins. This preliminary geometric modification ensures that the bracket provides adequate support during curing while inherently facilitating easier demolding and reducing weight, eliminating the need for additional heavy components
3Adaptability or versatility
If solid supplements are added to level the stringer flange surface, then assembly of other parts becomes possible, but the assembly process becomes more complex and time-consuming
Solution Approach 1:
The invar alloy bracket with cut radius is configured before curing to pre-compensate for the Mexican hat effect. This preliminary action achieves uniform thickness distribution at the stringer ends, eliminating the need for solid supplements and subsequent leveling operations during assembly, thereby reducing assembly complexity and time
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 minimizes the 'Mexican hat effect' to tenths of a millimeter, eliminates the need for solid supplements, reduces assembly difficulties, and decreases the weight of the invar alloy brackets while maintaining high dimensional stability.
Implementation Method 1
The name 'invar' comes from the word 'invariable' referring to its lack of expansion or contraction with temperature changes
Implementation Method 2
curing the T-shaped stringer obtained inside a vacuum bag
Data Source
Figure 1A~1B
Figure 2~3
Figure 4
AI summary
The invention relates to a method for manufacturing T-shaped aircraft stringers, in which the T-shape stringers have a web and a flange and wherein the method includes: a first step of hot forming a carbon fiber laminate in order to achieve semi-stringers with a geometry with a L-shaped cross-section, a second step of joining the two L-shaped hot formed semi-stringers in order to form a T-shaped stringer, a third step in which the resulting T-shaped stringer is co-cured on a cured lining with an adhesive line separating said stringer and said lining, and a fourth step of curing the T-shaped stringer produced inside a vacuum bag using invar alloy brackets as curing tools. The method is characterized in that the invar alloy brackets are radial cut, eliminating a portion thereof that covers the stringer flange in order to define an invar alloy part having no flange.