Turbomachine Blade Root Groove for Stress Reduction

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Solution Overview

Problem

Turbomachine blades experience high stress concentrations at the connection zones between the airfoil and the root, particularly due to direct force transmission through the flange, which compromises fatigue strength.

Innovation Solution

Incorporating a groove between the platform and the flange that extends axially and penetrates beyond the connection point of the airfoil, with a thinned neck connecting the flange to the heel, to redirect force transmission and reduce stress concentrations by creating a more sinuous stress path.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the blade is designed as a single piece with direct connection between airfoil and flange, then manufacturing simplicity is improved, but stress concentrations increase compromising fatigue strength

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidfatigue strength

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The root is segmented into distinct functional zones: a first zone connecting the airfoil to the platform, a second zone (the groove) separating the first zone from the flange, and a third zone connecting the flange to the platform. This segmentation creates a more sinuous stress path that distributes forces away from direct transmission points, reducing stress concentrations while maintaining manufacturing feasibility through controlled geometric features.

Inventive Principle:

Principle #1Segmentation

2Strength

If the flange is thick and rigid for strong connection, then connection strength is improved, but stress concentrations increase at the flange end

Engineering Contradiction:

Improveconnection strengthVSAvoidstress concentration

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

The groove creates a local geometric modification that changes the stress distribution characteristics. By introducing this localized feature in the root zone between the airfoil connection and the flange, the stress path is redirected away from the flange end, allowing the flange to maintain its thick, rigid structure for strong connection while the groove area manages stress concentrations through its geometric configuration.

Inventive Principle:

Principle #3Local quality

3Reliability

If the groove extends deeply axially beyond the flange, then stress concentration reduction is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvestress concentration reductionVSAvoidgroove geometry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The groove extends axially beyond the flange by a controlled amount that is sufficient to achieve the primary objective of reducing stress concentrations at the critical zones. The extension depth is optimized to provide adequate stress relief without creating excessive geometric complexity or manufacturing difficulty, balancing reliability improvement with manufacturing feasibility.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS10858957B2Turbomachine blade, comprising a root with reduced stress concentrations

Publication Date: 2020.12.08 SAFRAN AIRCRAFT ENGINES SAS

AI summary

A flange of a blade root platform is separated from an adjacent edge of the blade by a groove that prevents direct transmission of forces created by the bolted attachment of the platform flange to the adjacent part of the blade and reduces stress concentrations.