Deformation behavior and energy absorption capability of polymer and ceramic-polymer composite microlattices under cycli
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Jeffrey M. Wheeler
Department of Materials, ETHZ – Swiss Federal Institute of Technology, Zurich 8093, Switzerland
Ruth Schwaigera) Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe 76021, Germany (Received 29 September 2017; accepted 13 December 2017)
Specifically designed microlattices are able to combine outstanding mechanical and physical properties and, thus, expand the actual limits of the material property space. However, post-yield softening induced by plastic buckling or crushing of individual ligaments limits performance under cyclic loading, which affects their energy absorption capabilities. Understanding deformation under repeated loading is key to further optimizing these high-strength materials. While until now mainly hollow metallic microlattices and multistable or tailored buckling structures have been analyzed, this study investigates deformation and failure of polymer and ceramic-polymer microlattices under cyclic loading to understand the (i) influence of the microarchitecture and (ii) influence of processing conditions on the energy absorption capability. Despite fracture of individual struts, the stretching-dominated microarchitectures possess a superior behavior especially for larger cycle numbers. In combination with a specific annealing treatment of the polymer material, high recoverability and energy dissipation can be achieved.
I. INTRODUCTION
Lattice materials with designed three-dimensional (3D) microarchitecture, which combine high strength with low density, have been studied extensively over the past few years.1–9 New limits of the material property space were demonstrated and realized through a miniaturization of the individual building blocks within the lattice and a specific or hierarchical microarchitecture. Foam-like structures, in contrast, achieve rather low strength values because of their random structure.10,11 However, they are, in general, superior when it comes to absorbing energy during deformation, which is reflected in the typical, long and flat plateau in the stress–strain curve after yield.11 Most microarchitected lattices, though, show post-yield softening, after reaching the high initial maximum stress, caused by plastic buckling or crushing of the ligaments.11–13 Hollow metallic microlattices have shown a lot of promise for energy absorbing applications.4,12–15 However, until now, high-strength solid-beam microlattices have not been analyzed in detail regarding their energy absorption capability during several loading cycles. To repeatedly absorb energy during compression, specifically designed structures with tailored buckling elements16 Contributing Editor: Katia Bertoldi a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.485
or structures with multistable configurations17,18 were presented. The optimization of the energy absorption capability of high-strength microlattices is strongly desirable, but it requires a better understanding of cyclic deformation and failure of the stre
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