Composite Blade Root Shear Strength via Metal Patch Projections
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Solution Overview
Problem
The existing composite blades with metallic patches adhesively bonded to dovetails face challenges in securing sufficient shear strength when shear stress acts on the bonding interface, leading to potential separation under stress.
Innovation Solution
A composite blade design featuring a metal patch with protrusions that are jammed into the blade root, providing a stronger joint and distributing shear stress uniformly across the metal patch, with varying projection heights and orientations to enhance bonding and prevent separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If adhesive bonding is used to join the metal patch and dovetail, then the bonding process is simple, but the shear strength at the bonding interface is insufficient
Solution Approach 1:
The metal patch is divided into multiple protrusions distributed across its surface. Each protrusion acts as an independent bonding element that penetrates or engages with the blade root, transforming a single weak adhesive bond into multiple strong mechanical interlocks. This segmentation allows the bonding interface to distribute shear stress across multiple engagement points rather than relying on a single adhesive layer.
Solution Approach 2:
The invention replaces the chemical bonding mechanism of adhesive bonding with a mechanical interlocking system. The protrusions physically engage with the blade root through jamming or interference fit, creating a mechanical joint that resists shear stress through friction, geometry, and material strength rather than relying on adhesive chemistry. This substitution provides superior shear strength while maintaining manufacturing simplicity.
2Strength
If the metal patch is joined to the blade root, then the structural integrity is improved, but stress concentration occurs at the interface
Solution Approach 1:
The protrusions are strategically positioned and dimensioned to create localized stress distribution zones. By varying the height, spacing, and orientation of protrusions, the design concentrates stress in specific regions while distributing it across the entire metal patch-blade root interface. This local quality approach prevents stress concentration at any single point while maintaining overall structural integrity.
Solution Approach 2:
The protrusions extend in the thickness dimension of the blade root, creating a three-dimensional interlocking configuration. This dimensional engagement distributes stress across multiple spatial layers rather than concentrating it at a single interface plane. The protrusions engage with reinforcement fiber layers at different depths, creating a distributed stress transfer path that reduces stress concentration.
3Strength
If protrusions are added to the metal patch, then the shear strength and bonding are improved, but the manufacturing complexity increases
Solution Approach 1:
The protrusions are designed with optimized geometric parameters including height, spacing, diameter, and orientation that balance structural performance with manufacturing feasibility. By controlling these parameters, the design achieves strong mechanical interlocking while maintaining compatibility with conventional metal forming and assembly processes. The protrusions can be formed through standard stamping, bending, or additive manufacturing techniques without requiring complex specialized equipment.
Data Source
AI summary
A composite blade made of prepreg obtained by impregnating reinforcement fibers with resin and curing the resin-impregnated reinforcement fibers, the composite blade including: a blade root provided on a base end and fitted into a blade groove; an airfoil provided extending from the blade root toward a tip end; and a metal patch provided between the blade groove and the blade root and placed on the blade root. The metal patch includes a plurality of projections protruding toward the blade root.