Unbonded Braided Composite Spring for Stiffness Control
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Solution Overview
Problem
Conventional braided, lattice structure fiber-reinforced composites face challenges in forming complex shapes and extracting the mandrel, leading to limitations in stiffness, flexibility, and practical size for springs, as they rely heavily on material properties and geometry, resulting in low stiffness and high unrestrained travel.
Innovation Solution
A braided, open architecture composite structure formed from high filament number yarns pre-impregnated with resin, braided without bonded crossover points, allowing for controlled spring constants in bending, torsion, tension, or compression, and enabling complex geometries by preventing bonding at yarn intersections during initial formation on a conventional braiding machine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional braided lattice structure fiber-reinforced composites are used to form springs, then the structure provides lightweight construction, but the stiffness is low and travel is high due to reliance on material properties and geometry
Solution Approach 1:
The invention segments the braid structure into discrete yarns that remain unbonded at crossover points, creating a lattice structure where individual yarns can deform independently. This segmentation allows the structure to achieve desired stiffness through geometric configuration rather than relying solely on material properties, enabling lightweight construction with controlled mechanical properties
Solution Approach 2:
The invention changes the structural parameters by controlling yarn spacing, braid angle, and yarn diameter to optimize stiffness characteristics. By adjusting these geometric parameters rather than relying on material selection alone, the design achieves high stiffness-to-weight ratio through optimized lattice geometry
2Stability of the object's composition
If bonded crossover points are used in braided composite structures, then structural integrity is improved, but the ability to form complex shapes and remove mandrels is reduced
Solution Approach 1:
The invention applies preliminary action by pre-impregnating yarns with resin before braiding, but delays the bonding action until after mandrel removal. This allows the green state composite to be formed around complex mandrels without permanent bonding, enabling easy mandrel extraction while maintaining structural integrity through subsequent curing
Solution Approach 2:
The invention introduces dynamics by transitioning the composite structure from an unbonded flexible state during manufacturing to a bonded rigid state after curing. This dynamic property change enables easy mandrel removal during fabrication while achieving structural integrity in the final product
3Strength
If conventional spring designs are used with cylindrical elements, then torsional stiffness is provided, but bending stiffness is very low requiring additional constraint mechanisms
Solution Approach 1:
The invention transitions from conventional cylindrical spring elements to a three-dimensional lattice structure where yarns are oriented in multiple directions including axial, radial, and circumferential components. This dimensional change provides stiffness in multiple load directions simultaneously, eliminating the need for additional constraint mechanisms while maintaining torsional performance
4Strength
If high filament number yarns are used in braided structures, then strength-to-weight ratio is enhanced, but the complexity of preventing bonding at crossover points increases
Solution Approach 1:
The invention uses resin pre-impregnation as an intermediary that protects yarns during braiding without causing bonding. The resin coating acts as a release agent that prevents inter-yarn adhesion in the green state, allowing complex high-filament yarns to be braided without bonding at crossovers, while still providing structural integrity after curing
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 lightweight composite with enhanced strength-to-weight ratio, flexibility, and stiffness comparable to metal coil springs, enabling the creation of longer, more flexible structures with reduced weight and improved deformation resistance, and allows for complex shapes and easy mandrel removal.
Implementation Method 1
large (i.e. high filament number) yarns known as 'tows' can be pre-impregnated with an adhering resin or substrate and cured without bonding at the yarn intersections
Data Source
AI summary
A braided, open structure composite made with large prepreg tow can be cured without bonding at the yarn crossovers and after removal from the mandrel, it can be used directly as a spring in which the spring constant in bending, torsion, tension or compression can be controlled by the geometry of the braided structure as well as the size of the structural elements. Alternatively the spring may be curved in multiple directions to form complex shapes and then crossovers can be re-bonded to make more rigid open structure composites that would be difficult or impractical to manufacture by conventional techniques.