快速成形蜂窝结构的蠕变破坏
Creep failure of honeycombs made by rapid prototyping
摘要：
增材制造和快速成型是用于生成蠕变状态下应用的晶格材料的通用方法。然而，这些技术引入了可能降低宏观蠕变强度的缺陷。在本研究中，二维PMMA晶格的单轴拉伸响应测量的粘塑性制度：测试进行在100 C，这是略低于玻璃化转变温度Tg的PMMA。引入了制造缺陷（平台边界和支柱厚度变化）和设计缺陷（缺失单元壁、固体夹杂物和随机扰动接头）。对于在0.07至0.19范围内的相对密度，测量宏观强度的分散。据观察，最初的失败的晶格是扩散的性质：支柱失败在一些不相关的位置，其次是一个单一的宏观裂纹横向加载方向的发展。相比之下，相同的PMMA晶格在室温下以相关的脆性方式失效。进行有限元研究，以深入了解扩散失效模式和所发挥的作用，作为制造的缺陷，包括分散在拉伸强度的个别支柱的晶格。实验观察到对设计缺陷的高损伤容限：由于细胞壁的去除或固体夹杂物的存在，强度的击倒可以忽略不计。这些研究结果有助于设计和制造的损伤容限晶格在蠕变制度。
英文摘要：
Additive manufacture and rapid prototyping are versatile methods for the generation of lattice materials for applications in the creep regime. However, these techniques introduce defects that can degrade the macro-scopic creep strength. In the present study, the uniaxial tensile response of two-dimensional PMMA lattices is measured in the visco-plastic regime: tests are performed at 100C which is slightly below the glass transition temperature T g of PMMA. Both as-manufactured defects (Plateau borders and strut thickness variation) and as-designed defects (missing cell walls, solid inclusions, and randomly perturbed joints) are introduced. The dispersion in macroscopic strength is measured for relative densities in the range of 0.07 to 0.19. It is observed that initial failure of the lattice is diffuse in nature: struts fail at a number of uncorrelated locations, followed by the development of a single macroscopic crack transverse to the loading direction. In contrast, the same PMMA lattice fails in a correlated, brittle manner at room temperature. An FE study is performed to gain insight into the diffuse failure mode and the role played by as-manufactured defects, including the dispersion in tensile strength of individual struts of the lattice. A high damage tolerance to as-designed defects is observed experimentally: there is negligible knock-down in strength due to the removal of cell walls or to the presence of solid inclusions. These findings aid the design and manufacture of damage tolerant lattices in the creep regime.
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