通过变厚度设计具有高刚度的弹性各向同性开孔极小曲面壳格构
Elastically-isotropic open-cell minimal surface shell lattices with superior stiffness via variable thickness design
摘要：
三重周期极小曲面（TPMS）壳晶格由于其独特的几何和力学性能以及开孔拓扑结构而受到越来越多的关注。然而，均匀厚度的TPMS壳体晶格通常在刚度上是各向异性的，即沿着不同的晶格方向具有不同的杨氏模量。为了减少弹性各向异性，我们提出了一个家庭的变厚度TPMS壳晶格的各向同性刚度设计的应变能为基础的优化算法。优化结果表明，通过改变壳体厚度，可以使所选的6种TPMS网格均达到各向同性刚度，其中N14可以保持90%以上的Hashin-Shtrikman体积模量上界。所有的优化壳格具有优越的刚度性能，并显着优于弹性各向同性桁架格等相对密度。采用激光粉末床熔凝技术制备了均匀的和优化的N14钢[100]、[110]和[111]三种不同方向的壳体结构，并对其进行了准静态压缩试验。实验结果表明，优化后的N14晶格的弹性各向异性较均匀晶格有所降低。大变形压缩试验结果表明，沿不同方向的破坏变形行为不同。[100]方向为逐层塑性屈曲破坏模式，[110]和[111]方向的破坏与剪切变形有关。优化的N14晶格具有降低的平台应力的各向异性，甚至可以获得接近各向同性的能量吸收能力。
英文摘要：
Triply periodic minimal surface (TPMS) shell lattices are attracting increasingly attention due to their unique combination of geometric and mechanical properties, and their open-cell topology. However, uniform thickness TPMS shell lattices are usually anisotropic in stiffness, namely having different Young's moduli along different lattice directions. To reduce the elastic anisotropy, we propose a family of variable thickness TPMS shell lattices with isotropic stiffness designed by a strain energy-based optimization algorithm. The optimization results show that all the six selected types of TPMS lattices can be made to achieve isotropic stiffness by varying the shell thickness, among which N14 can maintain over 90% of the Hashin-Shtrikman upper bound of bulk modulus. All the optimized shell lattices exhibit superior stiffness properties and significantly outperform elastically-isotropic truss lattices of equal relative densities. Both uniform and optimized types of N14 shell lattices along [100], [110] and [111] directions are fabricated by the micro laser powder bed fusion techniques with stainless steel 316L and tested under quasi-static compression loads. Experimental results show that the elastic anisotropy of the optimized N14 lattices is reduced compared to that of the uniform ones. Large deformation compression results reveal different failure deformation behaviors along different directions. The [100] direction shows a layer-by-layer plastic buckling failure mode, while the failures along [110] and [111] directions are related to the shear deformation. The optimized N14 lattices possess a reduced anisotropy of plateau stresses and can even attain nearly isotropic energy absorption capacity.
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