Snap-Through Negative Stiffness Shells for High-Force Impact Absorption
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Solution Overview
Problem
Existing metamaterial structures that exhibit negative stiffness are limited by small force thresholds and energy dissipation capabilities, making them unsuitable for applications requiring higher forces or energy dissipation, such as impact protection and blast protection.
Innovation Solution
A shell structure designed to exhibit negative stiffness behavior with higher force thresholds and energy dissipation capabilities, featuring a dome-shaped member supported by a continuous annular sidewall, which allows the shell to transition from a convex to a concave shape under load, thereby increasing energy dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional honeycomb and curved beam structures are used to achieve negative stiffness, then the structure can exhibit negative stiffness behavior, but the force threshold and energy dissipation capability remain relatively small
Solution Approach 1:
The shell structure is divided into multiple segments or layers, each contributing to the overall negative stiffness behavior. This segmentation allows the structure to achieve higher force thresholds through cumulative effect while maintaining manageable complexity in each individual segment.
Solution Approach 2:
The invention employs composite shell structures combining different materials or structural configurations to achieve enhanced force thresholds. The composite nature allows optimization of both strength and negative stiffness characteristics simultaneously.
2Loss of energy
If existing negative stiffness beams and honeycomb are used, then the structure can provide sound and vibration damping, but the energy dissipation capability is insufficient for impact and blast protection applications
Solution Approach 1:
The invention utilizes curved shell geometries with optimized radius of curvature to enhance energy dissipation during impact. The curved configuration enables larger deformation capacity and higher energy absorption while maintaining structural integrity for protection applications.
Solution Approach 2:
The shell structure parameters such as thickness, curvature radius, and material properties are optimized to achieve the desired energy dissipation level. By adjusting these parameters, the structure can be tailored for specific protection requirements while ensuring reliable performance.
3Loss of energy
If the shell portion transitions from convex to concave shape under load, then the energy dissipation increases, but the base portion must resist higher hoop stresses
Solution Approach 1:
The base portion is pre-designed and pre-reinforced to anticipate and resist the hoop stresses that will develop during shell transition. This preliminary structuring ensures the base can handle the stress without failure while allowing the shell to achieve full energy dissipation potential.
Solution Approach 2:
The shell portion is designed as a flexible thin-walled structure that can undergo large deformations from convex to concave shape. This flexibility enables significant energy dissipation while the thin-walled design reduces the overall mass and inertia of the structure.
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 designed shell structure achieves significantly higher force thresholds and energy dissipation compared to traditional honeycombs and beams, enabling its use in applications such as impact protection, blast protection, and energy dissipater structures.
Implementation Method 1
One of the most promising properties of metamaterial structures is negative stiffness. When a structure is subjected to a force, the structure deforms. Should the load and deformation of the structure be in phase; then, the structure has a positive stiffness. Otherwise, the structure had a negative stiffness, i.e., the structure has increasing deformations with decreasing the applied force.
Implementation Method 2
Elastic instabilities of metamaterial structures can be triggered, based on the design and its application, by certain force or displacement threshold.
Implementation Method 3
curved beams subjected to axial compression can snap through from one stable mode of buckling to another experiencing negative stiffness region in which high levels of energy is dissipated
Implementation Method 4
The base portion is constructed to resist movement of the shell portion from the first position to the second position by resolving the load applied to the shell portion and transferred to the base portion at the connection of the perimeter edge base portion into a hoop stress resisted by the base portion.
Data Source
AI summary
A negative stiffness shell has a convex first position, but can transition or snap to a concave second position under a force applied to the exterior surface of the shell in the convex first position. During the transition, the shell exhibits negative stiffness that permits a large amount of energy to be absorbed. The negative stiffness shell can withstand a high initial force threshold prior to transitioning. In the second, concave position the shell can still resist force. Moreover, it is possible for the shell to revert back to the first, convex position with minimal plastic deformation for subsequent use. The negative stiffness shells can be used collectively and/or in layers to increase the efficiency of the overall negative stiffness shell unit.