In order to implement the idea of increasing specific strength and stiffness, in addition to introducing new materials, various methods were invented to create architected structures. Eventually, these efforts led to structures called lattice metal structures, followed by fibrous lattice composite structures. Fibrous lattice composite structures have been very popular in recent years by industry and researchers due to the favorable mechanical behavior including the high ratio of strength and stiffness to weight. One of the manufacturing methods of these structures is using textile preforms and especially braided preforms. As these structures have been introduced in recent years and due to time-consuming and inaccurate fabrication methods, complete and comprehensive research has not been conducted on the manufacturing, analysis, and function of these structures. In this research, a new type of braided lattice composite structures without foam and hybrid with foam was presented. The manufacturing method of these structures is simple and has the ability to be industrialized. Initially, the required preforms to manufacture these structures were produced from carbon yarn using a circular braiding machine. Then resin was added to these preforms and after curing the resin, the desired lattice tubes were obtained. To study the effect of cross-sectional shape, structures with square, rectangular, hexagonal, octagonal and circular cross-sections with the same perimeter were constructed. The effect of changing the perimeter was also investigated for samples with the same cross-sectional shape. In some cases, polyurethane foam was injected into these lattice structures and hybrid of lattice structures and foam were made. For experimental eva‎luation, the samples were subjected to quasi-static axial compression loading. For better investigation of the effective mechanisms in the compressive behavior of each structure, the finite element method was used. In order to measure the elastic properties and strength of the carbon composite struts, which constitute the lattice structures, the impregnated resin yarn was subjected to quasi-static compressive and tensile loading in the longitudinal direction. Using Python programming, the geometric and material complexities of each structure were simulated in Abaqus software. Due to the relatively low thickness of the structures, the shell element was used for simulations. The mechanical behavior of each resin impregnated yarn was considered as linear elastic and transversely isotropic before the onset of damage. Hashin damage criterion was also used to predict the onset and propagation of damage of the struts. In addition to the obtained properties from experimental investigation, other elastic and strength properties of structural struts members were extracted from Chamis relationships. Finally, in this study, the compressive properties of braided lattice composite tubes without foam and hybrid with foam were investigated experimentally and numerically. There was a good correlation between the numerical and experimental results. In both methods, promising results were obtained from the structures, which show that these structures can be used as an energy absorber. Also, the role of struts failure mechanisms and buckling of structures in energy absorption was fully investigated. In summary, this research introduces a lattice composite structure with a new and fast production process, as well as having more potential to absorb energy with acceptable crushing force efficiency in comparison with similar lattice structures. The highest specific absorbed energy (3030.96 J/kg) was obtained by the single-layer foamless lattice composite structure with the circular cross-section. Also, the highest specific absorbed energy (7917.79 J/kg) and crushing force efficiency (83%) were obtained by the multi-layer lattice composite structure hybrid with foam with the circular cross-section.

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محمد شيخ زاده

غلامحسين لياقت، عبدالرضا كبيري عطاآبادي، مهدي حجازي، محمدرضا فروزان، مهدي كاروان