Aircraft Engine Rotor Blade Rib for Crack Containment
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Solution Overview
Problem
Integrally bladed rotors in turbine engines are prone to crack propagation, which can lead to the release of uncontained fragments, posing safety risks due to the unitary structure of the rotor hub and blades.
Innovation Solution
Incorporating a crack-mitigating rib on the outer surface of the airfoil of the rotor blades to influence crack propagation, guiding it away from the hub and reducing stress intensity, thereby promoting a contained blade failure rather than an uncontained disc rupture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rotor blades are designed as integrally bladed rotors with unitary structure, then manufacturing efficiency and structural integrity are improved, but stress concentration and crack propagation risk increase at the blade root fillet region
Solution Approach 1:
The blade is segmented by introducing a crack-mitigating rib that divides the blade structure into distinct regions. This rib creates a predetermined crack arrest plane that segments the potential crack propagation path, preventing cracks from traveling unimpeded through the entire blade structure. The rib acts as a structural divider that maintains overall integrity while creating controlled segmentation for crack management.
Solution Approach 2:
The crack-mitigating rib serves as an intermediary structural element between the blade root and the blade tip. It mediates stress distribution in the critical fillet region and provides a predetermined barrier that intercepts and arrests cracks before they can propagate through the entire blade. The rib is positioned at a specific radial distance from the blade root to optimize its crack-arresting function while maintaining structural continuity.
2Reliability
If crack-mitigating ribs are positioned closer to the blade root, then crack arrest effectiveness is improved, but stress concentration at the rib location increases
Solution Approach 1:
The rib is designed with specific local geometric properties including a predetermined depth, width, and radial positioning that optimizes its crack-arresting function while minimizing stress concentration. The rib's cross-sectional dimensions and its position at a specific radial distance from the blade root create a localized structural feature that provides crack arrest without creating excessive stress concentrations that would compromise overall blade strength.
3Reliability
If the rib extends deeper radially outward, then crack propagation arrest is improved, but blade weight and manufacturing complexity increase
Solution Approach 1:
The rib is designed with a depth that provides sufficient crack arrest capability without being excessively deep. The predetermined radial distance and depth are optimized to provide just enough structural barrier to arrest cracks effectively while avoiding unnecessary material addition. This partial action approach ensures adequate crack mitigation while minimizing impact on blade weight and manufacturing complexity.
Data Source
Figure 1
Figure 2
Figure 3~3A
AI summary
A rotor (20) of an aircraft engine has a plurality of blades (40) extending radially from a disc (30). At least one of the blades (40) has an airfoil (46), a root (42) and a tip (44). The airfoil (46) has a crack-mitigating rib (48) extending chordwise along the airfoil (46). The crack-mitigating rib (48) is disposed radially closer to the root (42) than to the tip (44).