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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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This content will become publicly available on July 12, 2026
Additive manufacturing of triply periodic minimal surface structures with geometrical porosity
The advent of additive manufacturing, i.e., 3D printing, has enabled the flexibility to realize complex shapes and structures, such as triply periodic minimal surface (TPMS) structures, which are desirable in many engineering applications due to their unique mechanics. Common applications include protective armor or structural reinforcement for military or civilian uses. In this report, three TPMS structures (gyroid, Schwarz diamond, and Schwarz primitive) were fabricated using a hyperelastic photocurable resin and vat photopolymerization (VPP) technique. Additional sets of the same structures were fabricated with geometrical porosity to ascertain the mechanical response of each porous structure as a function of different strain rates (quasi-static and low-velocity impact), i.e., the effect of higher surface area to volume ratio. The results showed that irrespective of geometry, including pores in the TPMS structures causes reduced stress and truncated strain levels achieved under quasi-static loading. Gyroid structures outperformed the other TPMS structures, resulting in higher deformation, irrespective of porosity level. Alternatively, the drop impact results indicated that adding porosity decreased the stress levels and extended the plateau region, achieving greater strains than neat resin structures. The effects of porosity and glass microballoon reinforcement were investigated under the same loading regimes for the gyroid structure. The response of the dual hybridized structures proved to increase the impact efficacy of the gyroid structures compared to all other variations investigated. The results of this paper indicate the potential of additively manufactured TPMS structures made of hyperelastic materials and decorated with stochastic pores for improved impact response.
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- Award ID(s):
- 2035663
- PAR ID:
- 10634783
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Progress in Additive Manufacturing
- ISSN:
- 2363-9512
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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