Abstract
In this study, the cyclic compression and crush behavior of chiral auxetic lattice structures produced from titanium alloy (Ti6Al4V) metallic powder using electron beam melting (EBM) additive manufacturing technology is investigated numerically and experimentally. For material characterization and understanding the material behavior of EBM printed parts, tensile and three-point flexural tests were conducted. Log signals produced during the EBM process were investigated to confirm the stability of process and the health of the produced parts. Furthermore, a compressive cyclic load profile was applied to the EBM printed chiral units having two different thicknesses to track their Poisson’s ratios and displacement limits under large displacements in the absence of degradation, permanent deformations and failures. Chiral units were also crushed to investigate the effect of failure and deformation mechanisms on the energy absorption characteristics. Moreover, a surface roughness study was conducted due to high surface roughness of EBM printed parts, and an equation is offered to define load-carrying effective areas to prevent misleading cross-section measurements. In compliance with the equation and tensile test results, a constitutive equation was formed and used after a selection and calibration process to verify the numerical model for optimum topology design and mechanical performance forecasting using a non-linear computational model with failure analysis. As a result, the cyclic compression and crush numerical analyses of EBM printed Ti6Al4V chiral cells were validated with the experimental results. It was shown that the constitutive equation of EBM printed as-built parts was extracted accurately considering the build orientation and surface roughness profile. Besides, the cyclic compressive and crush behavior of chiral units were investigated. The regions of the chiral units prone to prematurely fail under crush loads were determined, and deformation modes were investigated to increase the energy absorption abilities.
Highlights
Lightweight structures such as sandwich structures play a crucial role in aviation, automotive and military applications, due to the importance of crush and compression strength at impact and blast conditions
The decreasing change in Poisson’s ratio was caused by the nonlinear deformation of the chiral units and a residual displacement at unloading, which can be attributed to plastic deformations that occurred in the regions in which the maximum stress levels emerged
The material characterization results show that Ti6Al4V components printed with electron beam melting (EBM) exhibit isotropic behavior under elastic deformation; anisotropic behavior is displayed under large deformations, causing plastic deformation
Summary
Lightweight structures such as sandwich structures play a crucial role in aviation, automotive and military applications, due to the importance of crush and compression strength at impact and blast conditions. Auxetic lattice solid structures reach a negative Poisson’s ratio by showing a significantly different behavior from conventional materials: shrinkage under a compressive load and expansion under a tensile load. Zhu et al [25] used wavy ligaments in their study to increase the auxeticity limit of chiral cells for large elasto-plastic deformation, and as a result, the new structure experienced better performance. Another auxeticity study was conducted by Alderson et al [3] to elaborate on the elastic properties and auxetic behavior of different chiral cells having 3, 4 or 6 ligaments connected to one node.
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