| The new generation of military unmanned equipment is developing towards extreme environment service and multi-domain dexterous maneuvering,which requires ultralightweight,high maneuverability and high reliability.The service performance of unmanned equipment depends on the performance of key components to a large extent.For example,the weight of components restricts the maneuverability and endurance distance of equipment,while the bearing and impact resistance of components affect the load carrying capacity and anti-interference ability of equipment.In order to meet the multiple design requirements of lightweight,load-bearing and impact resistance of highperformance components,based on the concept of structure-function integration,a new design method of composite lattice structures for the integration of the load-bearing and impact resistance is proposed.Relevant basic theories and methods are studied,and the main research contents are as follows:1.The action mechanism of static and impact load of cubic lattice cells is explored from the single lattice cell.Six kinds of cubic lattice cells are selected,and the calculation formula of cell relative density is deduced.Based on the simple beam theory and equivalent material method,the cellular mechanical model and equivalent spring damping model are established,and the formulas of equivalent parameters are deduced.The deformation mechanism,stress characteristics and spatial anisotropy of cells are investigated by finite element analysis and quasi-static compression experiment.It is found that lattice cells mainly play the role of the load-bearing and impact resistance through the coupling deformation of straight rods and inclined rods.The topological configuration of cells is obviously dominant to the mechanical properties.The cell selection strategy for static load and impact conditions is established,and three cells,ECC(side cube),GBCC(body center cube)and BCCxy(body center with XY bars),are selected,which is helpful for cell selection for optimal design of lattice structure.2.The variable density lattice structure is constructed based on the stress distribution law,and the optimization trend of load-bearing and impact resistance is explored.According to the stress distribution of one-dimensional impact,the weight loss ratio matching and parameter mapping model of gradient(one-dimensional variable density)lattice structure are established to form the design method of gradient lattice structure.A discretization method for predicting the equivalent elastic properties of gradient lattice structures is proposed based on the idea of discretization.The accuracy of the formula is verified by simulation and experiment,and the error is 4.5%-9.7%.The two-dimensional and three-dimensional variable density lattice structure models are established based on the stress distribution.The optimization trend of mechanical properties is investigated by finite element analysis.The results show that compared with uniform lattice structure,the dynamic buffer coefficient of the gradient lattice structure is lowered,and the cushioning performance of materials is improved.The deformation and stress peak of twodimensional and three-dimensional variable density lattice structure is reduced,and the load-bearing and impact resistance capacity of materials are enhanced.3.The interlaminar toughening mechanism is introduced into the lattice structure,and the arrangement mode of the layered multi-configuration lattice is established.The layered arrangement mode of multiple lattice cells is established according to the interlayer toughening mechanism.The impact deformation law,stress propagation law,cushioning and energy absorption properties of the layered multi-configuration lattice are investigated by finite element analysis.The lattice samples of Inconel718 and PA6 materials were prepared by additive manufacturing technology,and the dynamic impact tests of the samples were carried out by Hopkinson SHPB test system and drop weight impact test system.The results show that the toughening layer reduces the stress propagation velocity and enhances the energy dissipation effect.The layered multiconfiguration lattice shows obvious buffering and energy absorption advantages,and helps to improve the local deformation and depression of the impact contact end.4.A design method of the composite lattice structure for structure-function integration is proposed by combining variable density design with variable configuration design.A composite lattice structure parameter mapping model is established.The automatic modeling program of composite lattice structure based on CREO-UDF was developed,which improved the modeling efficiency.Three composite patterns and corresponding lattice models are given.The deformation process,buffering effect and failure modes of composite lattice structures are studied by finite element analysis,quasistatic compression and dynamic impact experiments,and the enhancement effects of different composite modes were compared.The results show that compared with the variable density lattice structure,the composite mode 1 is helpful to thicken the thin bars and improve the manufacturability of lattice structure.The composite mode 2 is helpful to increases the bending stiffness by 8% and enhances the bending resistance(loadbearing)and impact resistance capacity.The composite mode 3 is helpful to increase the failure load by 77% and reduce the equivalent impact load by 47%,which effectively improves the toughness and cushioning performance of materials.The research proves that the composite lattice structure not only realizes weight reduction,but also shows obvious advantages of load bearing and impact resistance integration.5.Taking the track wheel mounting frame of an unmanned vehicle as an example,the power structure integration design and verification of specific parts are carried out.The lattice frame models are established by using the integrated design method proposed above.The load-deformation relationship,equivalent impact load and failure mode of the frame are investigated by finite element analysis and experimental verification.The results show that compared with the original mounting frame,the weight of the composite lattice structure mounting frame is reduced by 30%,the equivalent stiffness coefficient is about 83%～94% of the original mounting frame,the failure load is more than 10 times the predetermined static load,and the equivalent impact load(reaction force)is reduced by 28%.The research indicates that through the design of composite lattice structure,the comprehensive effects of effective weight reduction,equivalent load-bearing and better cushioning performance are obtained,the good structure function integration is realized,and the effectiveness of the design method is verified. |
