Stackable Negative Stiffness Elements for Compact Shock Protection
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Solution Overview
Problem
Existing negative stiffness elements are large, complex, and provide relatively low values of negative stiffness per unit volume or mass, making them inconvenient for applications like shock protection in small volumes and difficult to combine for larger stiffness values.
Innovation Solution
A compact, stackable negative stiffness element is designed using deformable components with a polygonal central portion and radially extending arms made of high elasticity materials, which buckle under a radially inward preload force, exhibiting negative stiffness over an axial range, and can be composed of materials like high strength metal alloys and secured with clamps and fasteners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If existing negative stiffness element designs are used, then negative stiffness functionality is achieved, but the elements are large and occupy excessive volume
Solution Approach 1:
The deformable component is segmented into multiple arms extending from a central portion, with each arm being a separate structural element. This segmentation allows the component to achieve negative stiffness through the collective behavior of multiple simple arm structures rather than a single complex structure, reducing overall manufacturing complexity while maintaining compact volume
Solution Approach 2:
The arms are configured to buckle in a lateral dimension perpendicular to the primary axial load direction. By utilizing lateral buckling deformation rather than axial compression, the element achieves negative stiffness in the axial direction while maintaining a compact axial footprint, effectively using a different dimensional deformation mode to solve the volume problem
2Force
If existing negative stiffness element designs are used, then negative stiffness functionality is achieved, but the specific negative stiffness per unit volume is relatively low
Solution Approach 1:
The arms are designed with specific local geometric properties including optimized length-to-thickness ratios (greater than 10 and less than 30) and controlled cross-sectional dimensions. These localized geometric optimizations maximize the buckling load and negative stiffness contribution of each arm, thereby increasing the specific negative stiffness per unit volume of the overall element
Solution Approach 2:
The deformable component is constructed from high elasticity materials such as hardened high strength metal alloys, titanium, aluminum, fiber-reinforced composites, polymers, or ceramics. These materials provide high elastic modulus and strength-to-density ratios, enabling the arms to generate large negative stiffness forces while minimizing the volume required for each element
3Force
If existing negative stiffness element designs are used, then negative stiffness functionality is achieved, but the elements cannot readily be combined to form compound structures with larger stiffness values
Solution Approach 1:
The deformable component features a standardized polygonal central portion with a central through hole and uniform arm configurations that serve multiple functions: structural load bearing, rotational freedom provision, and stacking interface. This universal geometry allows identical components to be stacked in series to achieve cumulative negative stiffness values, simplifying the combination process while scaling the total stiffness capability
Solution Approach 2:
The arms are pre-configured with rotating portions and flexing portions that are designed to buckle at predetermined loads. This preliminary configuration of the buckling mechanism ensures that when multiple elements are stacked, each element activates its negative stiffness response at the same load threshold, enabling predictable cumulative behavior without complex coordination mechanisms
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 compact and efficient means to achieve large negative stiffness values, enabling effective shock protection in small volumes and allowing for the creation of composite structures with higher negative stiffness values by stacking the elements.
Implementation Method 1
a deformable component which is initially flat and which can be caused to buckle by the application of a radially inward preload force
Implementation Method 2
The deformable component in the buckled configuration then exhibits negative stiffness over a portion of its axial range of travel
Implementation Method 3
the polygonal central portion and the plurality of arms being composed of an identical high elasticity material
Data Source
AI summary
A deformable component which is initially flat and which can be caused to buckle by the application of a radially inward preload force, applied using an outer clamp. The deformable component in the buckled configuration then exhibits negative stiffness over a portion of its range of travel, when an axial force is applied. The deformable component may be fabricated from metal sheet, and may take the form of a polygonal central portion and at least two arms extending radially outwards.