Foam Stiffened Structure for Composite Skin Tooling
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Solution Overview
Problem
Aerospace structural assemblies, such as rotorcraft airfoils, require extensive effort and expense for assembly and are prone to corrosion and stress concentrations due to the use of fasteners, with tolerance variations affecting surface quality.
Innovation Solution
A foam stiffened structure method where a molded foam member provides structural integrity and acts as a tooling surface for a composite skin, allowing for reduced assembly complexity and increased structural stiffness, with the foam member's density tailored to match predicted loading conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional structural members (ribs and spars) with fasteners are used, then structural integrity is provided, but assembly complexity and expense increase significantly
Solution Approach 1:
The foam core integrates multiple structural functions (ribs, spars, and spacing elements) into a single monolithic component that is molded in one piece. This eliminates the need for separate structural members and their associated fasteners, directly reducing assembly complexity while maintaining structural integrity through the foam's inherent stiffness and load-distributing properties
Solution Approach 2:
The foam core serves multiple functions simultaneously: it provides structural stiffness, maintains spacing between skin layers, distributes loads across the structure, and acts as a substrate for skin bonding. This multi-functionality replaces what previously required multiple separate components, resolving the contradiction between structural integrity and assembly complexity
2Strength
If fasteners are used to assemble structural members, then structural integrity is achieved, but corrosion and stress concentrations are promoted
Solution Approach 1:
The invention extracts and eliminates fasteners from the structural assembly process. By using a molded foam core that integrates structural functions, the patent removes the harmful element (fasteners) that cause corrosion and stress concentrations, while maintaining structural integrity through the foam's continuous, homogeneous structure
Solution Approach 2:
The foam core, typically made from composite materials like polyurethane or phenolic foam, provides structural integrity through its material properties (compressive strength, stiffness) without requiring metal fasteners. This composite material approach eliminates the galvanic corrosion and stress concentration issues associated with metal-fastener assemblies
3Strength
If multiple individual parts are assembled, then structural integrity is provided, but tolerance variations lead to surface quality irregularities
Solution Approach 1:
By merging multiple structural components (ribs, spars, spacing elements) into a single molded foam core, the invention eliminates tolerance accumulation that occurs when assembling multiple parts. The monolithic foam structure ensures consistent geometry and smooth surfaces, directly improving manufacturing precision and surface quality while maintaining structural integrity
4Strength
If traditional structural assemblies are used, then structural support is provided, but weight increases
Solution Approach 1:
The foam core uses lightweight composite materials (such as polyurethane, phenolic, or polyester foam) that provide adequate structural support with significantly lower density than traditional metal or solid composite structures. The foam's cellular structure offers high strength-to-weight ratio, reducing overall structure weight while maintaining necessary structural support
Solution Approach 2:
By combining multiple structural functions into a single foam core component, the invention eliminates the weight of multiple separate structural members and their fasteners. The integrated foam structure achieves the same structural support with reduced material quantity and weight
Data Source
AI summary
A structure includes a skin and a foam member. The foam member has a molded contour, the mold contour being configured to provide tooled surface for the skin. When the skin is a composite skin, the foam member provides support for the skin so that the skin can be cured under heat and pressure. A method of making the foam member for a foam stiffened structure includes creating a mold having an interior cavity which resembles a desired shape the foam member. A subsequent step involves introducing a foam mixture into the mold. Next, the foam mixture is allowed to polymerize so as to expand and distribute within the cavity of the mold. The method further includes selectively controlling a density of the foam member in the mold. The foam member is at least partially cured. The foam member is assembled with a skin to produce the foam stiffened structure.