Composite Stringer Edge Protection and Visual Damage Indication

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Solution Overview

Problem

Composite blade stringers are prone to delamination and buckling under compressive loads due to impact damage, making it difficult to detect and address damage, which can lead to structural failure.

Innovation Solution

An edge treatment is applied to the composite blade stringer, comprising multiple fiberglass fabric layers with a color contrasting layer, such as CFRP tape, to provide impact protection, inhibit buckling, and facilitate visual detection of damage through color contrast and epoxy resin crazing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If multiple layers of composite material are bonded together to form the stringer, then the stringer achieves sufficient structural strength, but the layers are prone to delamination under impact damage which reduces buckling strength

Engineering Contradiction:

Improvebuckling strengthVSAvoidresistance to delamination

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

A sacrificial protector layer is applied to the end surface of the stringer before use. This layer absorbs impact energy through controlled delamination, preventing the impact forces from reaching the structural composite layers and causing harmful delamination that would reduce buckling strength.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The stringer employs a composite structure consisting of multiple bonded composite layers (plies) arranged in specific orientations. This composite construction provides the necessary buckling strength while the layered structure allows for controlled delamination of the sacrificial protector layer without compromising the integrity of the load-bearing structural layers.

Inventive Principle:

Principle #40Composite materials

2Strength

If the stringer is made with multiple bonded layers to achieve structural integrity, then the stringer can support compressive loads, but impact damage causes delamination that is difficult to detect visually

Engineering Contradiction:

Improvecompressive load capacityVSAvoiddetectability of delamination

Core Design Contradiction:

StrengthVSDifficulty of detecting and measuring

Solution Approach 1:

The sacrificial protector layer is manufactured with a color different from the underlying structural layers. When delamination occurs between the protector layer and structural layers, the color contrast provides immediate visual indication of the damage location and extent, making previously undetectable delamination easily observable.

Inventive Principle:

Principle #32Color changes

Solution Approach 2:

The colored sacrificial protector layer serves as an intermediary indicator system. It mediates between the invisible internal delamination events and the external observer, translating the hidden damage state into visible color-based signals that indicate when and where delamination has occurred.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If a thick sacrificial protector layer is applied to prevent impact damage, then the stringer gains better impact resistance, but the overall weight of the stringer increases

Engineering Contradiction:

Improveimpact resistanceVSAvoidstringer weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

Instead of making the entire stringer structure thicker to prevent impact damage, only a thin sacrificial protector layer is applied to the impact-prone end surface. This partial application provides sufficient impact protection through controlled delamination of the thin layer, avoiding the weight penalty of thickening the entire structural stringer.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The stringer is segmented into two functional zones: a thin sacrificial protector layer at the impact-exposed end surface and the main structural body with optimized thickness. This segmentation allows the protector layer to absorb impact energy while the main structure maintains minimal weight for load-bearing functions.

Inventive Principle:

Principle #1Segmentation

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 edge treatment enhances the residual strength of the stringer, allows for early detection of damage, and prevents buckling, enabling timely repair and reducing the risk of failure while enabling lighter, more efficient stringer construction.

Implementation Method 1

epoxy resin crazing

Methodology Applied

Scientific EffectCrazing:

Data Source

PatentEP3028845B1Composite blade stringer edge protection and visual damage indication

Publication Date: 2019.03.06 THE BOEING CO

Figure 1A~1B
Figure 1C
Figure 2

AI summary

Systems and methods provide for edge protection and visual damage indication for a composite blade stringer. According to one aspect, an edge protection and visual indication system may be an edge treatment (202) provided over an outer edge of a web (102) of a composite blade stringer. The edge treatment (202) may include a number of material layers (308) encompassing the outer edge of the web and extending from a first surface of the web to a second surface of the web. The material layers may include a color contrasting layer (306) and fiberglass layers (308). The material layers may alternatively include two overlapping, precured angles (602).