Multiaxial Yield Behavior And Oblique Impact Response Of Re-entrant Negative Poisson’s Ratio Honeycomb Under Complex Loading

The re-entrant honeycomb material has been widely studied by relevant scholars for its strong designability,high energy absorption and negative Poisson’s ratio effect,and has been widely used in aerospace,biomedical and military equipment and other fields.The re-entrant honeycomb material generally bears complex loading conditions in the actual service environment,such as multi-axial loading,oblique impact,etc.Therefore,it is necessary to study the re-entrant honeycomb material under complex loading.However,the cell wall of the honeycomb material is easy to be uneven or defective during the production process,and the inability to perform complex loading in the experimental test results in a lack of data points.Therefore,there are few studies on re-entrant honeycomb materials under complex loading.In this paper,finite element software is used to construct re-entrant honeycomb materials with different rotation angles and irregularities on the basis of re-entrant negative Poisson’s ratio honeycomb materials.The uniaxial and multi-axial quasi-static mechanical properties of reentrant honeycomb materials are studied,and the deformation mode and energy absorption of re-entrant negative Poisson’s ratio honeycomb materials under oblique impact are analyzed.The details are as follows:(1)Re-entrant honeycomb models with different boundary conditions are established for comparative analysis,and the elastic constants and yield strengths of uniaxial quasi-static loading are obtained.The results show that the rotation angle and irregularity have a great influence on the mechanical properties of the re-entrant honeycomb material.When the irregularity is the same,the Poisson’s ratio,elastic modulus and yield strength take the rotation angle λ=45° as the symmetry axis;when the rotation angle is greater than 30°,the elastic modulus and yield strength decrease rapidly,and the Poisson’s ratio gradually weakens and converted to a positive Poisson’s ratio.When the irregularity K=0,the Poisson’s ratio is close to 0 at the rotation angle λ=41.9°.When the rotation angle is the same,as the irregularity increases,the Poisson’s ratio,elastic modulus and yield strength all decrease gradually.(2)Using the ratio of plastic dissipation energy to the sum of elastic strain energy and plastic dissipation energy as the yield criterion under multiaxial loading,the yield point distribution of honeycomb material in the principal stress space is obtained.Different from ordinary foam materials,the yield strength of negative Poisson’s ratio honeycomb materials is the largest in the second and fourth quadrants,and exhibits certain anisotropy,tensioncompression asymmetry and shear asymmetry.However,the maximum yield strength of Voronoi porous materials is in the first and third quadrants.In addition,with the increase of rotation angle and irregularity,the yield strength of the re-entrant honeycomb material showed a downward trend,and the yield surface area gradually decreased.Meanwhile,the phenomenological yield criterion for re-entrant honeycomb materials and Voronoi porous materials is obtained by using the odd function form.(3)The in-plane dynamic mechanical response of the auxetic hexagonal honeycomb under different impact angles,ranging from 0°–10°,and different impact speeds,ranging from 6–100m/s,is systematically studied based on the corresponding numerical model.A novel formula is adopted for the cross-section to reflect the change of contact area between honeycomb structure and impact plate during oblique impact.The formular can reflect the change of stress from local region to whole model in the impact process well and capture the initial peak stress of honeycomb structure effectively.The results show that the auxetic structure has different deformation modes under oblique impact and axial impact,exhibiting local deformation under low-speed oblique impact,overall deformation under medium-high speed oblique impact,and overall deformation under axial impact.Compared with the regular hexagonal honeycomb structure,the auxetic structure is affected by the negative Poisson?s ratio effect.Under the same loading condition,the deformation mode of the auxetic honeycomb deforms later than the regular hexagonal honeycomb structure does,exhibiting a delayed mode.In addition,focusing on the energy absorption historical curve,the plateau stress under the two calculation methods of cross-section area is compared and analyzed,which provides a basis for investigating the load-bearing and stability of honeycomb structures under oblique impact.