Rotational Expansion Auxetic Structures for Tailored Poisson's Ratio
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Solution Overview
Problem
Conventional materials exhibit limited design flexibility in achieving negative Poisson's ratio and tailored structural properties, restricting their application in industries like aerospace and biomedical engineering.
Innovation Solution
The design of Rotational Expansion Novel Auxetic (RENA) structures, which include unique planar, three-dimensional, and spherical arrangements of strands with varying waveforms and connectors, allowing for the creation of auxetic materials with customizable stiffness and Poisson's ratios, enabling negative Poisson's ratio, high shear modulus, and high impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional materials are used, then material availability is high, but design flexibility for achieving negative Poisson's ratio and tailored structural properties is limited
Solution Approach 1:
The structure is divided into repeating unit cells, each containing strands arranged in specific geometric patterns (e.g., reentrant honeycomb, gyroid). By segmenting the material into these modular units, the patent achieves negative Poisson's ratio behavior while maintaining manufacturability through repetition of standardized components.
Solution Approach 2:
The patent varies geometric parameters such as strand thickness, unit cell dimensions, and relative density to tailor the mechanical properties including Poisson's ratio, stiffness, and strength. This allows continuous adjustment of structural properties without changing the fundamental auxetic mechanism.
2Strength
If auxetic structures with high negative Poisson's ratio are designed, then impact resistance and elastic energy absorption improve, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs porous auxetic structures with controlled void spaces arranged in specific geometric patterns. The porosity is designed to enable large elastic deformations that absorb impact energy, while the regular geometric patterns facilitate manufacturing through techniques like foam molding or additive manufacturing.
Solution Approach 2:
The patent combines auxetic structural geometry with various materials including polymers, metals, and composites to achieve both high impact resistance and manufacturability. The composite approach allows optimization of both mechanical performance and fabrication processes.
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
These auxetic materials exhibit desirable properties such as negative Poisson's ratio, high shear modulus, and high impact resistance, making them suitable for diverse applications, including aerospace and biomedical engineering, where they can be tailored for specific applications across various scales and dimensions.
Implementation Method 1
Poisson's ratio is defined as the ratio of lateral contraction to the longitudinal extension of a material subjected to tensile loading, and the ratio of lateral expansion to the longitudinal contraction in case of compressive loading.
Implementation Method 2
The physical explanation of the auxetic nature of the open-cell foam invented by Lakes, U.S. Pat. No. 4,668,557, is due to the unfolding lateral expansion of the strands of the reentrant polyhedron structure when subjected to tensile loads, involving three deformation mechanisms, namely, stretching, flexure, and hinging effects at the strand joints.
Implementation Method 3
high impact resistance due to greater elastic energy absorption
Data Source
AI summary
Auxetic structures exhibiting negative Poisson's ratios are disclosed including planar auxetic structures formed from x-axis and y-axis strands of selected waveforms. Portions of the auxetic structure referred to as unit cells comprise four joints formed by two adjacent x-axis strands overlapping two adjacent y-axis strands display symmetry about x and y axes. Each unit cell comprises four sub-unit cells formed from segments of ½ wavelength of the wave form. The planar auxetic structures may be formed into three-dimensional auxetic structures or cylindrical or spherical auxetic structures.