Composite Hybrid Fuselage Frame Slowing Crack Propagation

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Solution Overview

Problem

Current methods for enhancing damage tolerance in secure aircraft fuselage structures, such as those with metallic strong frames, often result in increased mass or reduced inspection intervals due to the rapid propagation of cracks, which are costly and inefficient.

Innovation Solution

A composite hybrid structure is introduced, featuring U-shaped metal parts with a carbon fiber composite material splice that redistributes mechanical forces locally, slowing down crack propagation by transferring forces directly along the crack line, rather than globally redistributing them across the structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional metallic structures are used to ensure damage tolerance, then structural strength is maintained, but mass increases and inspection intervals remain limited due to rapid crack propagation

Engineering Contradiction:

Improvedamage toleranceVSAvoidframe mass

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent applies composite materials by bonding a composite structural element to the metal frame parts. This composite element slows down crack propagation through its material properties, improving damage tolerance while the lightweight nature of composites helps control the overall mass increase of the structure.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent implements local quality by applying the composite structural element only to specific regions where crack propagation needs to be controlled, rather than making the entire frame composite. This localized application optimizes the balance between damage tolerance improvement and mass control.

Inventive Principle:

Principle #3Local quality

2Reliability

If conventional metallic structures are used to ensure damage tolerance, then structural strength is maintained, but inspection intervals remain limited due to rapid crack propagation

Engineering Contradiction:

Improvedamage toleranceVSAvoidinspection interval

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The composite structural element bonded to the metal frame slows down crack propagation rates, extending the time available for detection between inspections. This directly increases the inspection interval while maintaining damage tolerance.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The composite structural element is pre-applied to the frame to prevent rapid crack propagation before cracks reach critical sizes. This preliminary protective action extends the functional life of the structure between inspections.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If composite material elements are added to slow crack propagation, then damage tolerance improves, but mass increases

Engineering Contradiction:

Improvedamage toleranceVSAvoidframe mass

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The composite structural element is applied locally to specific regions of the frame where crack propagation control is most needed, rather than throughout the entire structure. This localized application minimizes the mass increase while achieving the damage tolerance improvement.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The use of composite materials provides a favorable strength-to-weight ratio, allowing crack propagation control with minimal mass addition compared to traditional metallic reinforcement methods.

Inventive Principle:

Principle #40Composite materials

4Reliability

If the structure uses multiple metal parts assembled together, then load paths are diversified for safety, but crack propagation spreads rapidly when one part fails

Engineering Contradiction:

Improvefail-safe capabilityVSAvoidcrack propagation speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The composite structural element bonded to the metal frame parts slows down crack propagation through the structure. When one metal part develops a crack, the composite element acts as a barrier that reduces the propagation speed, preventing rapid failure even though load paths are diversified.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The composite structural element serves as an intermediary between the metal frame parts, mediating the stress distribution and slowing crack propagation. It acts as a buffer that prevents direct, rapid stress transfer that would cause fast crack propagation across the fail-safe structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP2508419B1Method of slowing the propagation of cracks in a fail safe structure and fail safe frame, especially for fuselage

Publication Date: 2015.06.03 AIRBUS OPERATIONS (SAS)

Figure 1~2
Figure 3~4e

AI summary

The invention aims to improve the resistance to damage resulting from crack propagation in fail-safe structures. To achieve this, the invention proposes forming a hybrid composite structure within the fail-safe structure. A highly secure frame (2), particularly for an aircraft fuselage (3), equipped with a structural element made of composite material (9) according to the invention, has longitudinal profiled structural members (2a, 2b) assembled back-to-back by fasteners (5). The first two sides (20; 20a, 20b) are aligned longitudinally and bonded to the fuselage skin (3), while the other two sides (24; 24a, 24b) are aligned longitudinally at a distance from the first two sides (20; 20a, 20b). Fasteners (5) couple the composite structural element (9) to the external face (24e) of the sides (24; 24a, 24b) of the metal parts (2a, 2b) aligned longitudinally at a distance from the first sides (20; 20a, 20b).