Composite Stiffener with Foam Core and Fibre Shell

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Solution Overview

Problem

Existing composite stiffeners, such as blade and hat stiffeners, face challenges including damage susceptibility, buckling, and increased weight, as well as complex and difficult-to-automate manufacturing processes.

Innovation Solution

A stiffener design featuring a core with first and second battens arranged side by side, a spacer between them, and a shell formed from fibre material, which surrounds the core. This design allows for a tailored width and varying mechanical properties along the length of the stiffener, enhancing structural integrity and manufacturing efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If blade stringers with high aspect ratio are used, then the stiffener depth is increased for better structural performance, but the free edge becomes prone to damage and the blade becomes prone to buckling

Engineering Contradiction:

Improvestructural performanceVSAvoiddamage and buckling susceptibility

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The stiffener is segmented into a shell structure with multiple walls (foot, crown, and side walls) rather than a single blade element. This segmentation distributes structural loads across multiple components, reducing stress concentration at any single location and eliminating the free edge vulnerability of blade stringers.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The stiffener combines foam core material with fibre-reinforced composite shell material to create a hybrid structure. The foam provides bulk volume and compressive strength while the fibre-reinforced shell provides tensile strength and structural integrity, creating a more reliable structure than single-material blade stringers.

Inventive Principle:

Principle #40Composite materials

2Reliability

If hat stiffeners with low aspect ratio are used, then damage susceptibility and buckling are reduced, but weight and pitch between stiffeners increase

Engineering Contradiction:

Improvedamage and buckling resistanceVSAvoidstiffener weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The stiffener employs local quality by using foam material specifically in the core regions where compressive strength is needed, and fibre-reinforced composite material in the shell where tensile strength and structural integrity are critical. This localized material assignment optimizes weight by using each material only where its properties are most beneficial.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The design transitions from traditional single-dimensional blade or hat profiles to a three-dimensional shell structure with foot, crown, and side walls. This dimensional expansion allows the stiffener to achieve equivalent structural performance to deeper blade stringers while maintaining the lower aspect ratio benefits of hat stiffeners, reducing weight without sacrificing reliability.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of manufacture

If composite material is laid up over foam on inside mold line tools, then stiffener manufacturing is achieved, but the process becomes complex and difficult to automate

Engineering Contradiction:

Improvestiffener manufacturing capabilityVSAvoidmanufacturing process complexity

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The foam core is pre-formed and placed into the mold before the fibre-reinforced composite shell is applied. This preliminary action simplifies the manufacturing process by establishing the core structure first, allowing the shell to be wrapped around it in a more straightforward automated process rather than attempting to form the entire stiffener simultaneously.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The foam core acts as an intermediary form that simplifies the manufacturing process. It provides a pre-shaped substrate that guides the application of the fibre-reinforced composite shell, making the automated wrapping process easier compared to forming the entire complex geometry in a single step.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Productivity

If stiffener width is increased to reduce pitch between stiffeners, then structural coverage is improved, but weight increases

Engineering Contradiction:

Improvestiffener spacing efficiencyVSAvoidstiffener weight

Core Design Contradiction:

ProductivityVSWeight of moving object

Solution Approach 1:

The fibre-reinforced composite shell provides high strength-to-weight ratio, allowing the stiffener to maintain adequate structural performance with reduced width compared to traditional single-material stiffeners. This enables closer spacing without increasing weight, improving productivity by allowing more efficient use of structural coverage.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS12269588B2Stiffener with core and shell

Publication Date: 2025.04.08 AIRBUS OPERATIONS LTD

AI summary

A stiffener is disclosed including a core and a shell which surrounds the core. The shell is formed from a fibre material, and the core includes first and second battens arranged side by side, and a foam spacer between the battens. The stiffener extends in a lengthwise direction, and the battens and the foam spacer have respective lengths which extend in the lengthwise direction of the stiffener. The core is assembled with the spacer between the battens, then surrounded with the shell. The stiffener may be a stringer for an aircraft wing.