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This study provides an in-depth analysis of the mechanical behavior of rotating-square auxetic structures under various strain rates. The structures are fabricated using stereolithography additive manufacturing with a flexible resin. Mechanical tests performed on structures include quasi-static, intermediate, and high strain rate compression tests, supplemented by high-speed optical imaging and two-dimensional digital image correlation analyses. In quasi-static conditions (5 × 10–3 s-1), multiscale measurements reveal the correlation between local and global strains. It is shown that cell hinges play a significant role in structural deformation and load-bearing capacity. In drop tower impact conditions (intermediate strain rate of ca. 200 s-1), the auxetic structures display significant strain rate hardening compared to loading at quasi-static rates. The thin-hinge structures maintain a Poisson's ratio of approximately -0.8, showing higher auxeticity than slow-rate compression tests. High strain rate conditions (ca. 2000s-1) activate additional deformation mechanisms, including a delayed state of equilibrium exemplified by a heterogeneous distribution of lateral strains, possibly due to stress wave interactions and inertial stresses. The study further reveals nonlinear correlations between Poisson's ratio, strain, and strain rate, indicating reduced auxeticity at higher strain rates. These observations are discussed in terms of complex wave interactions and the strain rate hardening characteristics of the base polymer.
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Multiscale Strain Field Characterization in Flexible Planar Auxetic Metamaterials with Rotating Squares
Auxetic mechanical metamaterials show significant potential to impact many engineering fields and have been a topic of considerable research interest in recent years. Existing literature on the topic often aims to achieve larger negative Poisson's ratios or tailorable responses by carefully designed and distributed unit cells. Herein, it is aimed to investigate the relationships between global and local strain fields in rectangular center‐symmetric perforated planar structures, thus highlighting the role of local morphology on the macroscopic material response. Additively manufactured samples with hyperelastic constitutive behavior are characterized under tension. The structures are designed and developed with several perforation aspect ratios, leading to various degrees of auxeticity. Global and local strain fields are characterized using a multiscale digital image correlation measurement approach. The local rotation and in‐plane strain fields generated within the solid portions of the unit cells are correlated with the global strain fields and macroscopic Poisson's ratios for a range of cell geometries. The interplay between cell rotation and strain at the meso (unit cell) scale is shown to be the dominant factor in the strain‐dependent evolution of the Poisson's ratio in the structures.
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- PAR ID:
- 10377634
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Engineering Materials
- Volume:
- 25
- Issue:
- 2
- ISSN:
- 1438-1656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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