功能梯度三周期极小曲面静动态力学特性

QUASI-STATIC AND DYNAMIC MECHANICAL PROPERTIES OF FUNCTIONALLY GRADED TRIPLY PERIODIC MINIMAL SURFACE STRUCTURES

功能梯度设计能够有效提高结构的力学特性及吸能性能.为探讨功能梯度极小曲面结构在静动态载荷下的力学响应以及梯度壁厚分布方式对其力学特性的影响规律,构建了包含线性梯度和多种非线性梯度(对数梯度、Sigmoid梯度以及指数梯度)Gyroid结构,通过3D打印光敏树脂制备样件开展了准静态压缩试验,采用LS-DYNA构建仿真模型并与试验结果对比,验证了仿真方法的有效性.研究发现,功能梯度壁厚分布方式显著影响结构力学性能及变形模式.在准静态压缩下,功能梯度结构呈现逐层压溃的变形模式,在接触端产生局部的致密化带,这一模式导致梯度结构吸能特性有一定提升.基于准静态测试数据以及试验变形模式分析,构建了Gibson-Ashby模型,揭示了均质结构弹性模量和屈服强度随等效密度的变化规律;利用该Gibson-Ashby模型,预测了功能梯度结构屈服强度,并构建等应力模型预测了梯度结构的弹性模量,预测结果与实验值具有良好的一致性.对于其动态力学性能,构建了4种冲击速度仿真模型,深入探讨不同冲击速度对梯度结构力学性能的影响规律.功能梯度结构在高速冲击下,由于其壁厚逐层递增的特性,其局部压溃现象更为明显,导致其在高速冲击下的致密化应变显著增大,其吸能特性也有所提升.其中,对数梯度结构具有最高的屈服强度,而Sigmoid梯度结构具有最高的平均平台应力和吸能特性,其比吸能特性为13.01 J/g,相较于相对密度为45%的均质结构而言提升了45%.此外,基于刚性-完美塑性-锁定模型对梯度结构的动态平台应力进行拟合预测,拟合结果与仿真结果吻合度较高,为预测功能梯度结构的动态力学响应提供了计算方法.

The functional gradient design can effectively improve the mechanical properties and energy absorption performance of the structure.In order to investigate the mechanical response of triply periodic minimal surface structure with functional gradient thickness under static and dynamic loads and the influence of gradient wall thickness distribution on its mechanical properties,gyroid structures consisting of linear gradient and several nonlinear gradients(logarithmic gradient,sigmoid gradient and exponential gradient)are constructed.The structures are fabricated by 3D printing photosensitive resin and the quasi-static compression test is carried out.The numerical model is constructed by LSDYNA and compared with the test results to verify the effectiveness of the numerical method.It is found that the functional gradient wall thickness distribution significantly affects the mechanical properties and deformation modes of the structures.Under quasi-static compression,the functionally graded structure presents a deformation mode of layer-bylayer collapse,and a local densification zone is generated at the contact end,which leads to a certain improvement in the energy absorption characteristics of the gradient structure.Based on quasi-static test and experimental deformation model analysis,the Gibson-Ashby model is constructed to reveal the variation of elastic modulus and yield strength of uniform structure with equivalent density.Using this Gibson-Ashby model,the yield strength of the functionally graded structure is predicted,and the iso-stress model is also constructed to predict the elastic modulus of the gradient structure.The predicted results are in good agreement with the experimental results.For the dynamic mechanical properties of the gradient structure,four kinds of impact velocity simulation models are constructed,and the influence of different impact velocities on the mechanical properties of the gradient structure is investigated.Under high-speed impact,the local collapse phenomenon of the functionally graded structure is more obvious due to the gradually increase thickness.As a result,the densification strain and energy absorption characteristics of the functionally graded structures are significantly increased under high-speed impact.Among them,the logarithmic gradient structure has the highest yield strength,while the sigmoid gradient structure has the highest average plateau stress and energy absorption characteristics,with a specific energy absorption characteristic of 13.01 J/g,which is 45%higher than the uniform structure with a relative density of 45%.In addition,the rigid-perfect plastic-locking model is used to predict the dynamic plateau stress of the gradient structure,and the fitting results are in good agreement with the simulation results,which provides a calculation method for predicting the dynamic mechanical response of the functional gradient structure.