Study On The Low Velocity Impact And Compression After Impact Properties Of Composite Honeycomb Sandwich Structures

Composite Honeycomb Sandwich Structure(CHSS)has been widely used in the fields of aerospace,transportation and wind power because of its high specific strength and stiffness,excellent sound insulation and heat insulation,outstanding designability characteristic.However,during the manufacturing and service period,the CHSS is susceptible to foreign object impacts,among which the most common one is low velocity impact.The low velocity impacts often cause comprehensive damages in the CHSS.These low velocity impact damages lead to significant decline in the bearing capacity of CHSS,especially the compression properties.Fruitful research achievements have been obtained by foreign and domestic researchers in studying the low velocity impact and compression after impact for CHSS.However,further research is needed in the following areas:(1)Predicting the fracture details of the honeycomb core under the flatwise compression,shear loading,the low velocity impact and compression after impact;(2)The effect of honeycomb core parameters and low velocity impact damage parameters on the strength of CHSS;(3)The effect of biaxial loading on the mechanical properties of CHSS;(4)Research on analytical model of CHSS with low velocity impact damage.The main work finished by this paper as follows:(1)The flatwise compression and shear FE models with the honeycomb core details of the haploid and diploid cell walls were generated by parametric modeling program written in Python.The results predicted by FE models were in good agreement with the experimental results.Meanwhile,the failure mechanism of the honeycomb core was revealed: under the flatwise compression,the haploid cell wall bulked preceding the diploid cell wall;under the shear loading,the diploid cell wall of W direction did not sustain shear load,could only sustain flexural load.Due to the geometrical defects of honeycomb core cell wall introduced in manufacturing process,the flatwise compression test cannot capture the buckling of honeycomb core haploid cell wall.However,the geometrical defects introduced in manufacturing process showed little effect on the flatwise compression strength.(2)The low velocity impact performance of CHSS was studied by experiments,including influence of the impact energy,the impactor diameter and the honeycomb core height.The low velocity impact performance of CHSS was also studied by using a progressive damage model with honeycomb core details and considering the nonlinear shear response of facesheets.The effect of impact point location on the low velocity impact performance of CHSS was studied by using validated FE model.The results showed that for the CHSS with thin facesheets,the maximum contact force decreased with the increase of the impact energy when the low velocity impact energy exceeded the threshold;the location of the impact point showed apparent effect on the diameter and depth of the indentation.(3)The effect of honeycomb core parameters and low velocity impact damage parameters on the strength of CHSS were studied experimentally,analytically and numerically.In the FE model,the indentation was simplified by material parameters varied with the depth of the indentation.The results showed that the uniaxial compression strength of CHSS increased with the increase of honeycomb core height,however,when the height of honeycomb core exceeded the threshold,the uniaxial compression strength did not change significantly;the uniaxial compression strength in L direction was significantly higher than that in W direction;under uniaxial compression loading,the failure mechanism of the CHSS with/without low velocity impact damage was different,the failure mechanism of the structure without damage was facesheet fracture induced by the macroeconomic buckling,the failure mechanism of the structure with damage was facesheet fracture induced by failure of indentation;the residual strength of CHSS with low velocity impact damage could be determined by the coupling of the indentation diameter and depth,since the diameter of the crushed honeycomb core has a certain relevance with the diameter of the indentation.(4)The biaxial loading test of CHSS was firstly conducted by using the self-designed biaxial loading device combined with the electronic universal testing machine.The performance of CHSS under biaxial loading was studied by an improved analytical model.The results showed that the longitudinal residual compression strength of CHSS was increased by the transverse tensile load.On the contrary,the transverse compression load can lead to the reduce of the longitudinal residual compression strength of the structure.