Composite Hat Stiffener Reduces Delamination in Pressure Webs

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Solution Overview

Problem

Existing composite I-beam stiffened panels in aircraft construction face high pull-off loads at the radius filler regions, leading to delamination issues, which are mitigated with additional radius filler elements, fasteners, and angle fittings, increasing complexity, production time, and costs.

Innovation Solution

A composite hat stiffener configuration with a pre-cured composite hat section and multiple plies, including a body ply, wrap ply, base ply, and outer ply, with radius filler noodles between them, bonded to an uncured pressure web, reducing pull-off loads and improving stability without the need for additional reinforcement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If I-beam stiffeners are used to reinforce composite pressure web panels, then structural strength and stiffness are improved, but high pull-off loads at the radius filler regions cause delamination issues

Engineering Contradiction:

Improvestructural strengthVSAvoiddelamination resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The stiffener cross-section is segmented into a hat-shaped configuration with multiple flanges and webs, distributing stress more effectively than a traditional I-beam. This segmentation reduces concentration of pull-off loads at any single radius filler location, thereby preventing delamination while maintaining structural strength.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The stiffener design transitions from a two-dimensional I-beam cross-section to a three-dimensional hat-shaped structure with vertical webs and horizontal flanges. This dimensional change creates a more distributed load path and reduces pull-off loads at the radius filler regions by spreading forces across multiple attachment points.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If additional radius filler elements, fasteners, and angle fittings are used to prevent delamination, then delamination risk is reduced, but production time, part count, and manufacturing complexity increase

Engineering Contradiction:

Improvedelamination resistanceVSAvoidstructural complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The radius filler function is merged into the hat stiffener structure itself, where the flanges and webs are bonded directly to the pressure web panels. This integration eliminates the need for separate radius filler elements, fasteners, and angle fittings, reducing structural complexity while maintaining delamination resistance through the distributed load path.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The hat stiffener structure serves multiple functions simultaneously: it provides structural reinforcement, distributes loads to prevent delamination, and eliminates the need for additional fastening hardware. This multi-functionality reduces the overall part count and simplifies manufacturing while maintaining reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Strength

If fasteners and angle fittings are used to reinforce attachment joints, then structural reinforcement is improved, but specialized tooling and manufacturing costs increase

Engineering Contradiction:

Improvejoint reinforcementVSAvoidmanufacturing simplicity

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The mechanical fastening system (fasteners, angle fittings, specialized tooling) is replaced with a bonded structural system. The hat stiffener flanges and webs are directly bonded to the pressure web panels using adhesive bonding, eliminating the need for mechanical fasteners and the specialized tooling required to install them, thereby simplifying manufacturing while maintaining joint strength.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

The composite hat-stiffened pressure web minimizes pull-off loads at the radius filler noodle regions, enhancing stability and buckling resistance, while reducing the need for additional reinforcement elements, thus lowering production costs and complexity.

Implementation Method 1

bonded to an uncured composite pressure web

Methodology Applied

Scientific EffectAdhesive bonding: Adhesive

Data Source

PatentUS9387629B2Composite hat stiffener, composite hat-stiffened pressure webs, and methods of making the same

Publication Date: 2016.07.12 THE BOEING CO

AI summary

There is provided a method of making a composite hat stiffener. The method has the steps of curing a composite hat stiffener in a hat tool to form a pre-cured composite hat stiffener. The pre-cured composite hat stiffener has a composite hat section, a plurality of composite stiffening plies with a body ply, a wrap ply, and a base ply, all coupled to the composite hat section, wherein the body ply is coupled to a first side of the composite hat section, the wrap ply is coupled to the body ply, and the base ply is coupled to the body ply and the wrap ply, a pair of radius filler noodles coupled to the composite hat section and disposed between the plurality of composite stiffening plies, and an outer ply coupled to the composite hat section. The method further includes bonding the pre-cured composite hat stiffener to a structure surface.