Study On Numerical Modeling Of Composite Structures And The Applications Based On Smoothed Particle Hydrodynamics Method

Composites have been widely used as lightweight components in aircrafts,vehicles and equipments,due to the excellent mechanical properties.However,when the traditional fiber reinforced composite structures are subjected to mechanical or thermo load at a high level,the delamination failure or micro-crack are always accompanied,seriously reducing the service performance.To overcome this problem,some novel composites like functionally graded(FG)composites,carbon nanotube(CNT)reinforced composites and laminated composites come into being.Due to its unique structural advantages,these novel composites are of very broad application prospect in fields of aerospace,transportation and new energy.Studies on the nonlinear mechanical behaviors and dynamic characteristics of these composites under various loadings,can establish the theoretical basis for composition and structure designs.The work can not only lightweight the composite components,but also improve the performances,of important scientific and engineering significance.The mechanical behaviors of the novel composite structures are usually analyzed by analytical and numerical methods.Due to the heterogeneous and anisotropy characteristics,a large number of complex partial differential equations are hard to or even cannot be solved.In addition,when dealing with complex boundary conditions or large deformation problems,the gird-based numerical methods often suffer from the mesh distortion and the subsequent remeshing,resulting in low computational accuracy,efficiency and even large prediction errors.Based on the particles rather than grids,meshless Smoothed Particle Hydrodynamics(SPH)method can get rid of the boresome mesh.SPH is suitable for the problems like large deformation,transient loading,free surface and fluid-structure interaction,therefore it is chosen in this thesis for the modeling of the novel composites under different loadings.In the present study,the problems in the tradional SPH method are analyzed and the improving technologies are proposed,then 2D solid model,beam model and plate model are established and applied to analyze the mechanical behaviors of the FG,CNT and laminated composites subjected static bending,low-velocity impact and fluid-structure interactions.The main research contents and results are as follows,(1)The causes for the inherent deficiencies in the tradional SPH method are studied and solved by the proposed total Lagrangien(TL)Corrective Smoothed Particle Method(CSPM).The 2D composite solid model is constructed based on TL CSPM with good computation precision,efficiency and stability,especially suitable for the FG composites with variable section or two-directionally varying properties.By comparing the SPH results with the finite element(FE)solutions or analytical data,the computation stability and precision of the present model are illustrated.The effects of the different sections,gradient indexes and boundary conditions on the deformation behaviors are analyzed by the SPH model.(2)Based on Reddy-Bickford third-order shear deformation beam theory,the governing equations of bi-directional functionally graded composite materials were derived,including the concept of physical neutral layer and the FG material properties.A symmetric SPH(SSPH)method,which can accurately solve the function derivatives of any order,is adopted to discretize the problem domain and establish the bending analysis model for the bi-directional FG composite beams.Through the comparison between the tip deflections of the cantilever beam obtained from the SSPH beam model and experiment,the accuracy of the present beam model is verified.When comparing the prediction results between the SSPH models based on neutral line and middle line,the necessity of the physical neutral line in the present SSPH beam model is demonstrated.(3)Based on the first-order shear deformation theory,the motion and equilibrium equations of the composite plate are derived.By combining the CNT distribution and the gradient material properties,the nonlinear SSPH plate model is established for the FG CNT composites.By comparing the numerical solution of SSPH model with the experimental,FE and analytical solutions,it is found that the established model is of good convergence ability and prediction accuracy.The effects of boundary conditions,CNT volume fraction,arrangement,temperature and layering angle on the bending behaviors of FG CNT composites are studied.(4)The distribution of the contact load between the impactor and the composite plate is deduced.The contact loads in the impacting and unloading process are described by the modified nonlinear Hertz contact law.The motions of the impactor and the plate are updated by the explicit time integration based on the central difference method,and finally the low-velocity impact model is built using the SSPH plate model.The transient response containing the contact load,duration and plate deformation are obtained and compared with those from experiments,FE and analytical methods,revealing the computation ability of the present model.The influence of the CNT distribution and content,plate thickness,impactors' number,mass and impact velocity on the dynamic behaviors of the CNT reinforced composites are studied.(5)An experimental system was established for observing the impact process of the ramie fiber reinforced silica composite plate by free-surface fluid.By comparing the liquid flow and plate deformation behaviors between the simulated and experimental results,the fluid-structure SPH model is verified.The action of the fiber in the fluid-structure interaction is also analyzed.