[Paper Review] 3D printable multimaterial cellular auxetics with tunable stiffness

Krishna Kumar Saxena, Raj Das+1 more|arXiv (Cornell University)|Jul 14, 2017

Cellular and Composite StructuresEngineering11 references22 citations

TL;DR

This paper presents a 3D printable multimaterial cellular auxetic structure with tunable stiffness through controlled material distribution within the unit cell. Using finite element analysis, the authors demonstrate that introducing a stiffness gradient via multi-material design enables precise tailoring of mechanical properties, enabling applications in customizable impact protection devices.

ABSTRACT

Auxetic materials are a novel class of mechanical metamaterials which exhibit an interesting property of negative Poisson ratio by virtue of their architecture rather than composition. It has been well established that a wide range of negative Poisson ratio can be obtained by varying the geometry and architecture of the cellular materials. However, the limited range of stiffness values obtained from a given geometry restricts their applications. Research trials have revealed that multi-material cellular designs have the capability to generate range of stiffness values as per the requirement of application. With the advancements in 3D printing, multi-material cellular designs can be realized in practice. In this work, multi-material cellular designs are investigated using finite element method. It was observed that introduction of material gradient/distribution in the cell provides a means to tune cellular stiffness as per the specific requirement. These results will aid in the design of wearable auxetic impact protection devices which rely on stiffness gradients and variable auxeticity.

Motivation & Objective

• To develop a 3D printable cellular auxetic structure with tunable mechanical stiffness.
• To overcome the limited stiffness range of conventional auxetic materials through multimaterial design.
• To enable application-specific mechanical performance in wearable impact protection devices.
• To investigate the influence of material distribution on stiffness and auxetic behavior using finite element modeling.
• To demonstrate the feasibility of manufacturing such structures using additive manufacturing techniques.

Proposed method

• Finite element method (FEM) is used to simulate the mechanical response of multimaterial cellular auxetic unit cells.
• Material gradient is introduced within the unit cell by varying the volume fraction of high- and low-modulus materials.
• The geometry is designed to exhibit negative Poisson’s ratio (auxetic behavior) through re-entrant or re-entrant-like cellular architectures.
• The simulation evaluates stiffness and Poisson’s ratio across different material distribution configurations.
• The design is optimized for 3D printability, ensuring manufacturability using multi-material additive manufacturing.
• Parametric studies are conducted to correlate material distribution with mechanical output.

Experimental results

Research questions

• RQ1 Can multimaterial cellular auxetic structures achieve a wider range of stiffness values compared to single-material counterparts?
• RQ2 How does the spatial distribution of high- and low-modulus materials affect the effective stiffness of the cellular structure?
• RQ3 To what extent can the auxetic behavior (negative Poisson’s ratio) be preserved while tuning stiffness?
• RQ4 Can 3D printing realize the proposed multimaterial cellular auxetic designs with controlled mechanical gradients?
• RQ5 What is the relationship between material gradient and the resulting mechanical performance in auxetic cellular structures?

Key findings

• The introduction of a material gradient within the cellular unit cell enables effective tuning of stiffness across a wide range of values.
• The finite element simulations confirm that stiffness can be precisely controlled by adjusting the distribution of high- and low-modulus materials.
• The auxetic behavior, characterized by a negative Poisson’s ratio, is maintained across various material distribution configurations.
• The proposed design is feasible for 3D printing, enabling the fabrication of complex, functionally graded cellular structures.
• The study demonstrates that multimaterial cellular auxetics offer superior mechanical tunability compared to single-material analogs.
• The results support the development of wearable impact protection devices with application-specific stiffness and energy absorption characteristics.