Gas Turbine Blade Repair Using Asymmetric D-Shaped Cutback
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Solution Overview
Problem
Conventional repair methods for damaged compressor blades in gas turbine engines often fail due to coincidence of peak steady stress and peak vibratory stress at the cutback radius, leading to reduced durability.
Innovation Solution
A method involving a 'D' shaped cutback with paired fillets r1 and r2 on opposite ends, a depth d, and a length l along the edge, which decouples the stress locations by concentrating vibratory stress at r1 and steady stress at r2, thereby improving blade durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional C-shaped cutback is used to repair blade damage, then the damaged area can be removed and the blade can be made flight worthy, but peak steady stress and peak vibratory stress coincide at the cutback radius reducing durability
Solution Approach 1:
The patent applies asymmetry by transitioning from a conventional symmetric C-shaped cutback to an asymmetric D-shaped cutback with a flat bottom and rounded ends. This asymmetric geometry redistributes stress concentrations away from the cutback radius, separating peak steady stress and peak vibratory stress locations to improve blade durability
Solution Approach 2:
The patent uses curvature principles by incorporating rounded fillet ends (with radius R) on the D-shaped cutback instead of sharp corners. This curvature at the transition zones reduces stress concentration effects while maintaining the asymmetric geometry that separates stress peaks
2Ease of repair
If a cutback is made to remove damaged areas, then the blade can be repaired, but the cutback creates stress concentration that reduces blade durability
Solution Approach 1:
The patent applies curvature by rounding the ends of the cutback with fillets of radius R, eliminating sharp corners that would create severe stress concentrations. This curved geometry maintains material continuity and reduces stress concentration while still allowing complete removal of damaged areas
Solution Approach 2:
The patent applies local quality by creating a specific D-shaped geometry with rounded ends only at the critical transition zones of the cutback, while the rest of the blade structure remains unchanged. This localized geometric modification targets stress concentration relief precisely where needed without affecting overall blade design
Data Source
AI summary
A method for repairing a blade in a gas turbine engine comprises the steps of: isolating the damage on the airfoil of the blade; forming a cut back in the shape of elongated “D” shaped recess with a pair of fillets, a depth and a longitudinal axis of the “D” shaped recess having a length along the leading or trailing edge of the airfoil; and the fillets having a respective radius.