The Mechanical Behavior Of Fiber-Metal Laminates And The Reinforced Gradient Sandwich Panels Under Intensive Loading

Fiber metal laminates(FMLs)is a hybrid composites,which formed by alternately stacked metal and fiber-reinforced composite layers in the thickness direction.Compared with the mechanical properties of the traditional metallic material(i.e.higher density,weaker fatigue resistance and lower strength),FMLs have better features of both constituents in terms of high specific strength,good damage tolerance,excellent fatigue and impact resistance.In addition,basalt fiber also has other good physical performance,such as high temperature resistance,oxidation resistance,radiation resistance,heat insulation and sound insulation,environmental friendliness,which have attracted a lot of attention.The sandwich panels,with the FMLs as skins and gradient cellular metal as cores which have higher tensile and flexural capacity of FMLs,high energy absorption ability of porosity cellular metal.Thus,in order to develop gradient sandwich panels with FMLs as skins,we should analyze their deformation/ failure and the energy dissipation mechanism under intensive loading,establish its typical dynamic analysis model,choose the suitable geometric size and gradient distribution of cores.The research of this project will provide theoretical and technical supports for the applications of sandwich structures in the integrated functional-structural design of aerospace,high-speed railway and national defense engineering.In this research,experimental,computational and analytical investigations were conducted on the basalt fiber-metal laminates and their enhanced gradient honeycomb sandwich panels subjected intensive loading.The main study of this dissertation concerns the following aspects:(1)3-D progressive damage model for the woven fiber composites;(2)Dynamic behavior of basalt fiber-metal laminates under blast loading;(3)Dynamic behavior of gradient honeycomb sandwich panels with FML as skins under blast loading.And the deformation/failure modes,energy absorption,deformation mechanism and impact resistance of the structures under blast loading are also discussed in this dissertation.The main achievements are as follows:Based on the Hashin criterion for unidirectional composites,a relatively simple 3-D progressive damage model for the woven fiber composites has been proposed and implemented into the main program of ABAQUS through a user-defined subroutine.The model incorporates 3D constitutive behavior,damage initiation criteria with stress components,a damage evolution law with strain components,rate-dependency in fiber direction and in-plane shear nonlinear behavior of the woven composite material.By comparisons of the numerical predictions with existing experimental data,it has shown that the model can be used to simulate the dynamic response of the structure.Several typical dynamic deformation/failure modes of fiber-metal laminates under different loading impulse levels were obtained by used the ballistic impact pendulum system,i.e.large global inelastic deformation,in-plane buckling/folding,fiber rupture,interface failure.Compared with aluminum laminates,basalt FMLs have greater blast resistance,due to the fiber/epoxy composite layer has higher tensile strength than aluminum sheet.Considering the integrity,damage degree and residual deflection of the structure after impact loading,the basalt fiber-metal laminates shown superior anti-explosion performance than the carbon fiber-metal laminates in the same lay-ups.And the blast resistance property of basalt fiber-metal laminate depends on the number of composite layers.When the thickness of metal layer in the basalt fiber-metal laminate kept unchanged,increasing the number of composite layers can significantly improve the anti-explosion performance of laminates.By comparing the maximum transient deflection and residual deflection of structure,it found that the elastic resilience value of the structure was increased with the metal volume fraction decreased,due to the higher specific stiffness of fiber material.Thus,in the blast resistance performance assessment,the maximum transient deflection and the final deflection of the structure should be considered comprehensively according to the different service.The blast responses gradient aluminum honeycomb sandwich panels with FML as skins were experimentally investigated.The deformation/failure modes of sandwich panels were obtained in the experiments,in terms of FML face-sheets and gradient honeycomb cores,i.e.flower-shaped tearing,indentation and debonding of the top face-sheets,buckling,densification,fragmentation in the central region of cores,large elastic deformation and debonding of bottom face-sheets.The energy absorption of gradient honeycomb cores was quantitatively analyzed by digitizing the deformation/failure region of cores.The effects of face-sheet material,geometric configuration and loading condition on the structural deformation/failure modes and their blast resistance were analyzed.It shown that when the cell side length is fixed,the sandwich panel with the cores arrangement from small relative density(impact side)to large relative density(back side)obtained the best blast resistance in terms of permanent deflection and core energy absorption.When the wall thickness of honeycomb is fixed,the sandwich panel with the cores arrangement from large relative density(impact side)to small relative density(back side)has the best performance under small impulse,but when the impulse is increased,ungradient sandwich panels performs better than other core arrangements.