Composite Stringer Edge Profiling for Stronger Skin Joints

Solution Overview

Problem

Existing methods for manufacturing composite material structural components with stringers in aircraft components result in suboptimal load transfer and increased moisture infiltration due to sharp surface discontinuities at the edges of the stringers, leading to potential delamination and corrosion issues.

Innovation Solution

The process involves cutting the side edges of the stringers at an angle relative to the lying surface during formation, forming a semi-trapezoidal profile, and applying a composite material coating or patch elements to seal the edges, ensuring a smoother connection with the skin and improved stress distribution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If stringers are manufactured with straight side edges perpendicular to the lying surface, then manufacturing is simpler and faster, but load transfer is suboptimal and moisture infiltration increases

Engineering Contradiction:

Improveload transfer efficiencyVSAvoidstringer edge processing complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies asymmetry by cutting the side edges of stringers at an angle (e.g., 45 degrees) relative to the lying surface, creating a semi-trapezoidal profile instead of a rectangular one. This asymmetric geometry improves load transfer efficiency and reduces moisture infiltration while maintaining manufacturing feasibility through standard cutting processes.

Inventive Principle:

Principle #4Asymmetry

2Strength

If stringers are joined rigidly to the skin, then structural strength is improved, but stress concentration and delamination risk increase at sharp edges

Engineering Contradiction:

Improvestructural strengthVSAvoidstress concentration and delamination

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent applies curvature by rounding the side edges of stringers with a specified radius (e.g., R5 or R10). This curved geometry eliminates sharp edges, reduces stress concentration, and minimizes delamination risk while maintaining rigid structural strength through the composite material bonding.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Object-affected harmful factors

If standard rectangular stringer profiles are used, then manufacturing is more straightforward, but surface discontinuities cause increased moisture infiltration

Engineering Contradiction:

Improvemoisture infiltrationVSAvoidstringer profile geometry

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies asymmetry by cutting the side edges of stringers at an angle (e.g., 45 degrees) relative to the lying surface, creating a semi-trapezoidal profile instead of a rectangular one. This asymmetric geometry improves load transfer efficiency and reduces moisture infiltration while maintaining manufacturing feasibility through standard cutting processes.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent applies curvature by rounding the side edges of stringers with a specified radius (e.g., R5 or R10). This curved geometry eliminates sharp edges, reduces stress concentration, and minimizes delamination risk while maintaining rigid structural strength through the composite material bonding.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS12544990B2Process for manufacturing a structural component in composite material stiffened with at least one stringer

Publication Date: 2026.02.10 LEONARDO SPA

AI summary

A process for manufacturing a structural component made of composite material comprising a skin and at least one stiffening stringer applied rigidly and integrally to one face of the skin. The process comprises a) arranging, on a tool, a plurality of first layers of uncured or pre-cured composite material, forming the stringer and having a raised portion protruding from at least one flange; b) arranging, on the tool, a plurality of second layers of uncured or pre-cured composite material forming the skin; c) making a face of the skin and the flange of the stringer adhere to each other; d) applying a predetermined temperature and pressure on the assembly to compact the layers together, possibly curing the uncured material and rigidly joining the skin to the stringer; and e) performing a cutting operation on the free end side edge/s of the flange in a slanted direction.