Composite Leaf Spring Eye Structure to Prevent Delamination
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Solution Overview
Problem
Leaf springs made entirely of composite material face issues with delamination and failure at the eyes due to high tensile forces, inferior mechanical properties compared to steel, increased thickness for strength, and higher material costs, along with difficulties in manufacturing and assembly.
Innovation Solution
A leaf spring design featuring a central body and eyes made of composite material with fibre fabrics embedded in a polymeric matrix, where the fibre orientation and geometry enhance resistance and adhesion, allowing for a 50-60% weight reduction compared to metallic solutions, and a manufacturing process that includes RTM and compression moulding to integrate the eyes with the central body without adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If leaf spring eyes are made of composite material, then weight is reduced, but delamination occurs due to high tensile forces
Solution Approach 1:
The patent applies different fibre orientations in different zones of the eye: 0° fibres for tensile strength in the horizontal direction, 90° fibres for tensile strength in the vertical direction, and 45°/135° fibres for shear resistance. This local differentiation of material properties resolves the contradiction by providing targeted reinforcement where needed while maintaining overall weight reduction.
Solution Approach 2:
The patent uses a composite material system with multiple fibre orientations embedded in a polymeric matrix, specifically designed to resist delamination. The combination of different fibre orientations creates a synergistic effect that provides both weight reduction and enhanced resistance to the complex stress states in the eye zone.
2Weight of moving object
If composite material is used for the entire leaf spring, then weight is reduced, but mechanical properties are inferior to steel
Solution Approach 1:
The patent optimizes fibre orientation locally in different zones: the central body uses primarily 0° fibres for longitudinal strength, while the eyes use a combination of 0°, 90°, 45°, and 135° fibres to handle multi-directional stresses. This local optimization ensures that the composite material achieves steel-level mechanical properties in critical areas while maintaining weight advantages.
Solution Approach 2:
The patent changes the material parameters by varying fibre orientation angles and stacking sequences in different zones. This allows the composite material to adapt its mechanical properties to match the stress distribution, achieving superior strength-to-weight ratio compared to steel while maintaining overall structural integrity.
3Strength
If leaf spring thickness is increased to compensate for inferior composite material properties, then strength is improved, but assembly difficulty increases
Solution Approach 1:
Instead of uniformly increasing thickness, the patent uses local reinforcement through optimized fibre orientation in the eye zones. This allows the spring to maintain steel-level strength in critical areas while keeping the overall thickness reduced, thereby improving assembly ease without sacrificing strength.
4Manufacturing precision
If fibre fabrics are stacked in Z-direction perpendicular to longitudinal direction, then manufacturing precision is improved, but resistance to braking forces is reduced
Solution Approach 1:
The patent combines Z-direction stacking for manufacturing precision with local 45° and 135° fibre orientations in the eye zones to provide resistance to braking forces. This local addition of angled fibres compensates for the reduced braking resistance of Z-direction stacking while maintaining the manufacturing advantages of perpendicular stacking.
Solution Approach 2:
The patent uses a multi-orientation composite material system that combines the benefits of Z-direction stacking (manufacturing precision) with angled fibres (braking resistance). The composite structure integrates multiple fibre orientations to simultaneously achieve manufacturing ease and mechanical performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a leaf spring with dynamic behavior comparable to steel, reduced weight, and improved resistance to forces, addressing delamination and manufacturing challenges while lowering material costs.
Implementation Method 1
a manufacturing process that includes RTM and compression moulding to integrate the eyes with the central body without adhesives
Implementation Method 2
a composite material with a polymeric matrix, preferably thermostable, for example, epoxy, and eyes made also of a composite material with a polymeric matrix
Data Source
AI summary
Leaf spring comprising at least one leaf of composite material that comprises:a central body (1), andtwo eyes (2),wherein the central body (1) comprises its longitudinal end zones (1.1) embedded in a cavity (2.1) of the eyes (2), wherein the sections transversal to the longitudinal direction of the central body (1) of the longitudinal end zones (1.1) of the central body (1) and the cavities (2.1) of the eyes (2) present increasing dimensions towards the longitudinal end of the leaf spring and that comprises fibre fabrics (7, 8, 9) of the central body (1) stacked in a Z-direction perpendicular to the longitudinal direction of the central body (1) and to the longitudinal direction of the hole (3) of the eyes (2) and comprises fibre fabrics (10, 11) of the eyes (2) stacked in a parallel direction to the longitudinal direction of the longitudinal axis of the hole (3).