Triangular Composite Filler for Aircraft Bond Line Integrity
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Solution Overview
Problem
In the aircraft industry, composite structural members often have gaps or voids along bond lines that need to be filled to increase strength, but existing methods like using pultruded material with laminate can result in cracking and undesirable weight, complexity, or cost due to differences in thermal expansion coefficients and material properties.
Innovation Solution
A method and apparatus for forming a composite filler with a substantially triangular cross-section, comprising a layer of composite material with a bent shape and a laminate stack, where each layer is bent to follow the radius of a stiffener, directing loads along the radius and minimizing thermal stresses by using the same material for both the bent layer and laminate stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pultruded material is used in combination with laminate material to form composite filler, then the filler can be produced efficiently, but cracks may occur between the pultruded material tip and laminate stack due to differences in thermal expansion coefficients
Solution Approach 1:
The patent applies homogeneity by using the same composite material for both the bent layer and laminate stack portions of the filler. This eliminates the interface between different materials (pultruded and laminate) that causes cracking due to thermal expansion differences. The entire filler is formed from uniformly bent layers of composite material, ensuring consistent thermal and mechanical properties throughout.
2Strength
If the gauge of the stiffener is increased to achieve adequate pull-off strength, then the bond strength is improved, but the weight of the aircraft increases
Solution Approach 1:
The patent segments the filler into two functional portions: a bent layer portion that follows the radius of the stiffener to distribute loads, and a laminate stack portion that provides additional strength. This segmentation allows the filler to achieve adequate pull-off strength through optimized geometry and material distribution rather than simply increasing the overall gauge of the stiffener, thereby avoiding unnecessary weight addition.
Solution Approach 2:
The patent applies curvature by forming the first layer into a bent shape that follows the radius of the stiffener. This curved geometry allows the filler to conform to the bond line interface, improving load distribution and stress transfer between the stiffener and base structure, thereby enhancing pull-off strength without requiring increased material thickness.
3Strength
If radius blocks are added to stiffeners to increase pull-off strength, then the bond strength is improved, but the complexity, weight, or cost of the aircraft increases
Solution Approach 1:
The patent merges the filler function with the bond line interface by forming the filler directly from bent layers of composite material that conform to the radius of the stiffener. This eliminates the need for separate radius blocks and integrates the load-transfer function into the filler itself, simplifying the overall structure while maintaining adequate pull-off strength.
Data Source
AI summary
A method and apparatus is presented. A layer of composite material is laid up on a forming tool. A bend is formed in the layer on the forming tool to form a bent layer. A laminate stack and the bent layer are assembled to form the composite filler.