Strut-based lattice structures of various types exhibited a common critical issue, namely, high tensile stress concentration occurred at node-to-strut sites, which often led to lowered energy absorbability as compared to triply periodic minimal surfaces structures. Therefore, this work aimed for improving the Octet-truss structure by a combined technique using hollow core and varying cross-section ratio. Firstly, test specimens were fabricated using a stereo-lithography based additive manufacturing of photopolymer hard resin. Elastic-plastic properties and damage criterion of the used polymer were experimentally determined and applied for finite element models. Validation by compressive tests of lattice samples showed deviations of stress–strain responses less than 12%, in which local deformation and subsequent damages were fairly predicted. Afterwards, finite element simulations of designed lattice structures subjected to compressive, combined shear, shear and tensile loads were performed and obtained stress–strain characteristics including total absorbed energies and deformation behaviors were studied. Under uniaxial compression and combined shear loads, modified Octet-truss structures exhibited considerable increases of energy absorptions up to 173% and 116%, respectively, and stress–strain responses were more stable. On the other hand, by tension mode peak stresses and elongations could be enhanced about 41% and 11%, accordingly. The improved performances of proposed strut-based structures were comparable to those of triply periodic minimal surfaces diamond structure. This was due to that local stress distributions in the structure became more uniform and previously dominated tensile stresses were switched to compressive stresses. Therefore, occurrences of shear bands and plastic hinges could be effectively inhibited.
In this study, a series of Sm2O3 micro-plates/B4C/HDPE composites composed of synthesized Sm2O3 fillers (Sm2O3 micro-plates) are prepared for shielding neutron and gamma radiation. The influence of micromorphology of Sm2O3 fillers on neutron and gamma radiation shielding properties of composites is investigated in detail. The XRD pattern reveals that the phase of synthetic Sm2O3 is cubic crystal systems, body-centered cubic lattices, and its space group is Ia3¯(206). SEM images and BET analyses reveal that the micromorphology of synthesized Sm2O3 is micro-plates. The BET-specific surface area of the Sm2O3 fillers is increased with addition of urea content. The differential scanning calorimetry (DSC) curves reveal that Sm2O3 fillers increase the melting temperature of the composites, which is up to 138.6 °C. The thermogravimetric analysis (TGA) results reveal that the initial thermal degradation temperatures of the composites are all above 440 °C. The neutron and gamma radiation shielding tests show that Sm2O3 fillers with high BET-specific surface area (8.20 m2/g) and uniform size improve the neutron and gamma shielding rate of composites. A superior composite containing 10 wt% Sm2O3 (R = 1:25, R value represents the molar ratio of rare earth elements to urea)/20 wt% B4C/70 wt% HDPE has a neutron radiation shielding rate of 98.7% with a thickness of 15 cm under the 252Cf neutron source and a gamma radiation shielding rate of 72.1% with a thickness of 15 cm under 137Cs gamma source. And these lead-free and environment-friendly composites can be widely used in the neutron and gamma complex radiation fields.
