Geometric Radius Filler for Composite Delamination

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Solution Overview

Problem

Laminated composite radius fillers in composite structures, such as those used in aircraft, experience delamination due to differences in thermal expansion coefficients between adjacent plies, leading to potential structural weaknesses and uncertainties about delamination growth under various environmental and loading conditions.

Innovation Solution

A laminated composite radius filler design featuring a stacked ply assembly with geometrically shaped filler elements that deform to change the direction of adjacent plies, aligning them with the wrap plies to minimize thermal expansion differences and interlaminar tension stresses, thereby reducing or eliminating delamination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If laminated composite radius fillers are used to fill radius filler regions, then structural reinforcement is provided, but delamination occurs due to differences in thermal expansion coefficients between plies

Engineering Contradiction:

Improvestructural reinforcementVSAvoiddelamination

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent changes the geometric parameters of the radius filler by introducing a curved or angled configuration instead of a straight linear form. This geometric parameter change allows the filler to accommodate thermal expansion differences between plies by distributing stress more effectively, thereby reducing delamination while maintaining structural reinforcement

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies curvature to the radius filler geometry, creating a curved or angled filler element that better matches the natural stress distribution in the composite structure. This curved configuration reduces concentrated stress points that would otherwise cause delamination during thermal cycling, while still providing the necessary structural reinforcement

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Area of stationary object

If larger laminated composite radius fillers are used, then more extensive radius filler regions are covered, but delamination occurs more frequently in the upper one-third area near the tip

Engineering Contradiction:

Improveradius filler region coverageVSAvoiddelamination frequency

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent segments the radius filler into multiple sections or zones along its length, with each segment having optimized geometric characteristics. This segmentation allows different portions of the filler to handle local stress conditions independently, preventing delamination from propagating through the entire structure while maintaining comprehensive coverage of the radius filler region

Inventive Principle:

Principle #1Segmentation

3Stability of the object's composition

If wrap plies are placed adjacent to the radius filler region, then structural continuity is maintained, but differences in coefficient of thermal expansion cause interlaminar tension stresses

Engineering Contradiction:

Improvestructural continuityVSAvoidinterlaminar tension stresses

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The curved or angled radius filler acts as an intermediary element between the wrap plies and the radius filler region. This intermediary geometry gradually transitions the stress distribution, reducing abrupt interlaminar tension stresses while maintaining structural continuity across the bond line

Inventive Principle:

Principle #24Intermediary (Mediator)

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 design effectively minimizes delamination and interlaminar tension stresses, enhancing the structural integrity and reliability of composite structures by aligning the laminate plies with the wrap plies, thus improving the composite structure's ability to handle loads and maintain stability under thermal cycling and environmental changes.

Implementation Method 1

delamination occurs in an upper one-third area near the tip of the laminated composite radius filler and may occur more frequently in larger laminated composite radius fillers. Such delamination is typically caused by a difference in the coefficient of thermal expansion (CTE) between the plies adjacent to the laminated composite radius filler

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentEP2871050B1Laminated composite radius filler with geometric shaped filler element and method of forming the same

Publication Date: 2017.01.11 THE BOEING CO

AI summary

A laminated composite radius filler for a composite structure has a stacked ply assembly (108) having a plurality of stacks (110) of laminate radius filler plies cut to a desired width and having a desired ply orientation. The laminated composite radius filler further has a geometric shaped filler element (100) positioned at a desired location on a first portion of the stacked ply assembly (108). The geometric shaped filler element (100) deforms a second portion of the stacked ply assembly (108) stacked over the geometric shaped filler element (100), such that the laminate radius filler plies of the second portion of the stacked ply assembly (108) change direction and have a component of direction including a horizontal direction and a vertical direction. The laminated composite radius filler having a shape substantially corresponding to a radius filler region of the composite structure.