【作者】 刘勇；

【导师】 树学峰；

【作者基本信息】 太原理工大学 ， 力学， 2022， 硕士

【摘要】 内凹蜂窝材料以其可设计性强、高吸能性及负泊松比效应被相关学者广泛研究,并在航天航空、生物医疗及军事设备等领域被广泛应用。内凹蜂窝材料在实际服役环境中普遍承受复杂加载工况,如多轴加载、斜冲击等。因此,对内凹蜂窝材料在复杂加载下的研究十分必要。然而,在生产过程中易导致蜂窝材料的胞壁不均匀或产生缺陷,且在试验测试中无法进行复杂加载导致数据点缺少,因此对内凹蜂窝材料在复杂加载下的研究较少。本文利用有限元软件,以内凹负泊松比蜂窝材料为基础,构建了不同旋转角度和不同不规则度的内凹蜂窝材料。对内凹蜂窝材料在单轴及多轴准静态的力学性能进行研究,同时分析了内凹负泊松比蜂窝材料在斜冲击下的变形模式和能量吸收。具体内容如下:(1)建立不同边界条件的内凹蜂窝模型进行对比分析,并得到了其单轴准静态加载的弹性常数和屈服强度。结果表明:旋转角度和不规则度对内凹蜂窝材料的力学性能影响较大。当不规则度相同时,泊松比、弹性模量和屈服强度以旋转角度λ=45°为对称轴;当旋转角度大于30°时弹性模量和屈服强度迅速减小,泊松比逐渐减弱并转为正泊松比。当不规则度K=0时,在旋转角度λ=41.9°左右泊松比接近于0。当旋转角度相同时,随着不规则度的增大,泊松比、弹性模量和屈服强度均逐渐减小。(2)采用塑性耗散能与弹性应变能、塑性耗散能之和的比值作为多轴加载屈服判据,得到了蜂窝材料在主应力空间下的屈服点分布。与普通泡沫材料不同,负泊松比蜂窝材料的屈服强度在二、四象限最大,且呈现出一定的各向异性、拉压不对称性和剪切不对称性;Voronoi多孔材料的最大屈服强度处于一、三象限。此外,随着旋转角度和不规则度的增大,内凹蜂窝材料的屈服强度呈下降趋势,屈服面面积逐渐减小。同时,采用奇函数形式得到了适用于内凹蜂窝材料和Voronoi多孔材料的唯象屈服准则。(3)基于内凹负泊松比蜂窝模型,对内凹负泊松比蜂窝材料在不同冲击倾角(0°～10°)与不同冲击速度(6～100m/s)下的面内动态力学响应进行了系统研究。采用了一种新的截面计算公式,能够反映斜冲击中蜂窝材料与冲击板接触面积的变化和斜冲击过程中应力从局部到整体的变化,有效地捕捉蜂窝结构的初始峰值应力。研究结果表明:内凹负泊松比蜂窝材料在斜冲击与正冲击时的变形模式不同,在低速斜冲击下为局部变形,在中高速斜冲击下为整体变形,而在正冲击下均为整体变形。与正六边形蜂窝材料相比,内凹负泊松比蜂窝材料受到负泊松比效应的影响,在相同工况下内凹负泊松比蜂窝材料的变形模式晚于正六边形蜂窝材料,变形模式产生延迟。此外,结合能量吸收时程曲线,对比分析了两种截面计算方法下的平台应力,为蜂窝材料在斜冲击下的承载和稳定性研究提供了依据。更多还原

【Abstract】 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.更多还原