Anti-blast Mechanism Analysis And Core-structural Design Of Honeycomb-type Sandwich Panels

Sandwich structure is generally composed of thin high-strength outer sheets and a thick soft core layer for cushioning and energy absorption.It has excellent properties such as light weight,high specific strength,large specific stiffness and good energy absorption.Sandwich structure can not only improve the impact resistance of the structure,and reduce the weight of the structure as well.It is widely used in the field of explosion and impact protection.In the study of anti-blast sandwich panels,the structures of core layers such as foam,honeycomb,lattice and corrugated materials have significant impact on the explosion resistance performance,but there are still some arguments about the selection of core layer materials.Thin-walled circular tubes and foam materials can collapse in axial crushing and have stable plateau stage.Both are excellent energy absorbing components.Due to the interaction between the foam and the tube wall,the energy absorption in foam-filled tube is shown to be higher than the sum of the energy absorptions of empty tube(alone)and foam(alone),and has stronger designability due to the density variation.In this dissertation,the influence of honeycomb structure of different core layers on the anti-blast performance of sandwich panels was studied,and the anti-blast mechanism of sandwich panels is further revealed.The theoretical analysis model of sandwich panels subjected to blast loading is developed.The influence of anisotropy of mechanical properties of the core layer on the explosion resistant performance is studied,and the design guidance of sandwich panels is proposed.The design method of sacrificial cladding with graded foam-filled tubes is studied based on the shock wave model.Before designing and manufacturing anti-explosion honeycomb-type sandwich panels,it is necessary to study the mechanical properties of honeycomb-type structures under static/dynamic constant velociy compression,and then guide the research and design of sandwich panels.Three kinds of structures,including hexagonal,circular hole and hexagonal arrayed circular tube honeycomb,are studied by finite element simulation.Under quasi-static compression,the circular hole honeycomb is the strongest out-of-plane,that is,the initial collapse and plateau stress are the highest,and the hexagonal arrayed circular tubes is the weakest.At the same relative density,the geometric parameters of hexagonal arrayed circular tubes have little effect on its quasi-static stress-strain curves.Based on the three-dimensional gradient Voronoi technology and the variable cell size method,the meso finite element model of the continuous density graded foam-filled circular tube was established.Under constant velocity compression,the low-density end of the gradient foam-filled tube will collapse at the initial stage,which indicates that the filling gradient is an important factor in determining the deformation mode.The fitting formula of force-displacement curve of uniform foam-filled tube can well establish the relation between the parameters of empirical formula and structural parameters.An equivalent method of explosion simulation using air blast loading to approximate the blast loading of shallow-buried explosive in soil is proposed.The response of steel plate under blast loading of shallow-buried explosive in soil is experimentally studied.The deviation between the deflection of numerical simulation results and that of experimental result is small.The configuration of honeycomb has a significant effect on the anti-blast performance of sandwich panels.To further reveal the anti-blast mechanism of sandwich panels,the mechanical response of three sandwich panels with hexagonal,circular holes and hexagonal arrayed circular tube honeycomb under air blast is compared by finite element simulation.Under the same blast loading,the sandwich panel with hexagonal array circular tubes has the smallest deflection of back plate with the same structural parameters.The influence of geometric parameters on the sandwich panel is studied.Combined with the load transfer and core compression deformation,the anti-explosion mechanism of the sandwich panel is clarified,and the approximate optimal solution within a specific range of parameters is obtained.When comparing the energy absorption of sandwich panel and the deflection of back plate,it is found that the larger the energy absorption is,the greater the deformation of back plate is.Therefore,when the deformation of back plate is taken as the main anti-blast performance index,the total energy absorption cannot be directly used as the criterion to judge the anti-deformation ability of sandwich panel.Inspired by the multi-layer anti-blast sandwich panel,the double-layer circular tube sandwich panel is proposed,which has improved the anti-blast performance compared with the single-layer sandwich panel.When the surface density is constant,the analysis results of the influence of geometric parameters show that increasing the wall thickness of the tube on the front side and reducing the wall thickness of the tube on the back side can significantly improve the blast resistance of the sandwich panel.The arrangement of circular tubes determines the mechanical properties of the core layer in all directions.In order to study the effect of the arrangement of circular tubes on the anti-blast performance of sandwich panels,experiments were carried out on the horizontal and vertical square arrayed circular tube sandwich panels under the blast loading of shallow buried explosives in soil.Under the same blast loading,the anti-blast performance of the vertical tube sandwich panel is better than that of the horizontal tube sandwich panel.The simulation results of the sandwich panel against the blast loading of shallow buried explosives in soil are in good agreement with the experiment.The fluid-structure coupling simulation method is basically the same as the deflection of the back plate under approximate equivalent loading.The theoretical analysis model of the anti-blast sandwich panel is developed based on the energy method,which taking into account the anisotropy of mechanical properties in and out-of-the plane of the core layer.The theoretical model can well predictes the center deflection of the back plate of the sandwich panels with different wall thickness and mass of charge.The influence of the anisotropy of core layer on the anti-balst performance of the sandwich panel is discussed.The results show that the back plate deflection of the sandwich panel with in-plane isotropic core layer is the smallest.The influence of the in-plane and out-of-plane anisotropy of the transversely isotropic core layer is discussed.The results show that the influence of the in-plane and out-of-plane plateau stress ratio on the back plate deflection is highly related to the sum of the platform stresses.Therefore,the sum of the strength values in each direction of the core layer and the strength of the blast loading jointly determine the deflection of the sandwich panel back plate,that is,the back plate deflection is the result of the coupling effect of the two quantities.For the case of ignoring deformation of back plate,the sacrificial cladding structure with density-graded foam-filled tubes as a core layer is proposed,and their anti-blast response is investigated numerically and theoretically.One-dimensional analytical shock models based on an empirical force-displacement relationship are developed and employed to analyze the axial collapse wave propagation in graded foam-filled circular tubes.It is found that the theoretical predictions are in good agreement with the finite element results.The positive and uniform foam-filled tubes present a single-wave deformation pattern and the negative ones present a double-wave deformation pattern,while the negative ones with gradient parameters close to zero may also show a single-wave deformation pattern.This demonstrates that the deformation mode of the filled-tube is determined by the gradient of foam and the wall thickness of the tube.A contour map of the critical lengths required to absorb the impulse of blast loading for different gradient parameters and diameter-thickness ratios of the tube is established.In addition,the negatively graded foam-filled tube with a smaller density gradient has a shorter critical length and a slightly higher transmitted force at the support end than the uniform foam-filled tube.