Design And Mechanical Performance Of Insert Joints For Composite Lattice Truss Core Sandwich Structures

Lattice truss structures represent high specifc stiffness,high specific strength,high designability and multi-functional integration potentials,attracting tremendous attention in both mechanics and material science.However,the immaturity of joining technique severely restricts the development and application of lattice truss structures.On the one hand,concentrated loads of joints are difficult to be transferred by the unique topological configurations of lattice truss structures.On the other hand,the absence of comprehensive theoretical analysis leads to indistinctness of inherent relations between joinining behaviors and structural paprameters.Hence,this dissertation focuses on the design,fabrication and mechanical properties of insert joints for composite pyramidal lattice truss core sandwich structures.Concentrated load transfer paths for lattice truss structures are constructed and mechanisms of structural parameters on joining behaviors are revealed,providing theoretical foundations for engineering application of lattice truss structures.Mechanical behaviors of single-and multi-layered pyramidal lattice truss core sandwich structures by additive manufacturing are investigated.Theoretical analysis on the stiffness and strength under flat compression,shear and edgewise compression is carried out.Deformation mechanisms and failure modes are addressed by experimental validation and numerical modeling.Based on these investigations,a research foundation for insert joint design and characterization is supplied.A pre-embedded insert joint is proposed and fabricated for the composite sandwich plate with single-layered lattice truss cores.Failure modes and the effect of insert dimensions on the load capability are investigated by pull-out and in-plane shear experiments.Deformation characteristics and failure mechanisms are indicated utilizing finite element analysis.Reliability of the proposed insert is analyzed using machine learning.An improved metallic-composite hybrid insert joint is developed for the composite sandwich plate with single-layered lattice truss cores.Mechanical behaviors and failure modes are studied by pull-out and in-plane shear experimental tests for different joining positions.Finite element analysis is carried out to address failure mechanisms of the hybrid insert.The effect of joining positions on the pullout performance is discussed.According to the primary load forms,a boundary insert joint is proposed and fabricated for composite sandwich plate with multi-layered pyramidal lattice truss cores by additive manufacturing.Analytical models are derived of the boundary insert under in-plane pull-out,in-plane shear and out-of-plane shear loads to obtain the strength prediction formulas and failure mechanism maps.Finite element analysis and experimental validation are carried out to size the mechanical performance.A modular satellite structure is proposed and prepared employing composite pyramidal lattice truss core sandwich structures and the proposed insert joints.Responses of the satellite structure and the joining under typical dynamical environmental conditions through sinusoidal and random vibration tests.Equivalent models are developed for the satellite structure.Based on these,the feasibility of the satellite structure configuration and the joining behavior are investigated.