Composite Turbomachine Blade Root Attachment for Bending Stiffness
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Solution Overview
Problem
Existing blade attachment methods for turbomachinery, particularly for aircraft, either require geometric modifications that shift stress types or result in reduced structural rigidity and resistance to bending modes, limiting the effectiveness of composite materials.
Innovation Solution
A three-dimensionally woven composite material blade preform with a cavity and flared attachment elements that maintain in-plane stress distribution and increase the second moment of area, enhancing structural stiffness and rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a clamping attachment with 90° blade root geometry is used, then the second moment of area and flexural/torsional stiffness are increased, but the stress distribution shifts from in-plane to out-of-plane stresses which limits composite technology effectiveness
Solution Approach 1:
The invention transitions from a traditional 90° blade root geometry to a tangential attachment configuration where the blade root extends parallel to the disk surface. This dimensional reorientation allows the blade root to remain within the weave plane of the composite material, maintaining in-plane stress distribution while achieving adequate stiffness through the tangential arrangement of multiple blade roots around the hub circumference
Solution Approach 2:
The invention optimizes the utilization of composite material properties by maintaining stress within the weave plane. The blade root is designed with a geometry that aligns with the fiber orientation of the composite material, ensuring that loads are carried efficiently along the fiber directions rather than perpendicular to them, thereby maximizing the strength-to-weight ratio of the composite structure
2Stress or pressure
If a tangential fastening is used, then out-of-plane stresses are avoided and in-plane stress distribution is maintained, but the second moment of area is reduced making the structure much less rigid and resistant to bending modes
Solution Approach 1:
The invention compensates for the lower second moment of area of individual blade roots by increasing the number of blade roots segmented around the hub circumference. The collective effect of multiple tangentially arranged blade roots provides adequate overall rigidity and resistance to bending modes while maintaining the advantage of in-plane stress distribution in each individual root
Solution Approach 2:
The invention achieves adequate stiffness not by increasing the cross-sectional dimensions of individual blade roots (which would increase out-of-plane stresses), but by utilizing the spatial arrangement of multiple roots in the tangential direction. This dimensional approach distributes the bending loads across multiple roots while keeping each root within its optimal stress plane
3Strength
If geometric modification of the blade root is made to increase the second moment of area, then flexural stiffness is improved, but the stress transformation from in-plane to out-of-plane stresses occurs which is limiting for composite technologies
Solution Approach 1:
The invention avoids geometric modification of the blade root cross-section that would create out-of-plane stresses. Instead, it achieves the necessary flexural stiffness through the tangential arrangement of multiple blade roots, utilizing the spatial configuration rather than cross-sectional geometry modification, thereby maintaining compatibility with composite material manufacturing and stress characteristics
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The invention relates to a system for attaching a turbomachine blade, comprising: - a blade comprising, at the blade root, two portions (54, 56) that are separated from one another in a transverse direction X so as to provide a cavity (C) therebetween extending downwards in the direction Y from the top of the blade, from a cavity bottom (Cl) to a cavity opening (C2) on the outside, located at the lower end of the blade root, - an element (60) for attaching the blade partially engaged inside the cavity with the engaged portion having a shape, in a plane defined by the directions X and Y, which extends towards the bottom (Cl) flaring in the direction X, the two separated portions (54, 56) of the blade root that are in contact with the flared shape of the attachment element (60) having corresponding flared shapes.