多轴动静态加载条件下泡沫金属的宏细观参数对其破坏面的影响研究

Metallic foams offer significant performance gains in light, stiff structures, for efficient absorption of energy. In practical applications, metallic foams are usually subjected to dynamic multi-axial loading and exhibit failure behaviors. Hence, a constitutive law describing the failure behavior of foams is essential..This project aims to characterize the failure surface and to reveal failure mechanism of foams under multi-axial loading. Several dynamic and quasi-static uniaxial and multi-axial experiments will be conducted to verify the numerical simulation and to preliminary characterize the failure surface in principal stress (or strain) space. Numerical multi-axial simulation experiments will be conducted based on 3D Voronoi. The characterization of failure surface will be perfect. Statistical analysis of deformations and failure mode of cells will be conducted. Employing theories of plasticity, fracture, plate and shell, theoretical models will be explored to explain the failure mechanism of foams. The anisotropic 3D Voronoi meso-structures are constructed to investigate to effects of the irregularity gradient, the thickness distribution gradient and relative density gradient on failure properties. Effects of macro- and meso-structural parameters on failure properties will be explored quantitively. A failure surface characterization will be proposed including parameters such as strain rate, anisotropy, relative density, irregularities and thickness distribution..These studies will contribute to constitutive law of foams, offer reliable failure data for numerical simulations based on macroscopic structures and assist in mechanical properties of cellular materials under dynamic and quasi-static multi-axial loading.

泡沫金属具有质轻、吸能效率高等优良性能，在航空航天和吸能减震等领域有广阔的应用前景。泡沫金属及其复合结构应用时，承受多轴动荷载并发生破坏，多轴加载条件下泡沫金属破坏力学性能研究是迫切需要解决的科学问题。本项目以确定泡沫金属的破坏面表征和破坏机理为目标，采用实验、数值仿真实验和理论分析相结合的方法，定量研究应变率、相对密度、不规则度和胞壁厚度分布参数对破坏面的影响。拟开展单、双轴和三轴动静态试验，初步表征破坏面；基于3D Voronoi细观模型，开展多轴动静态数值仿真实验，丰富破坏面数据，完善破坏面表征；统计分析胞孔变形特征，研究破坏机理并建立理论模型；研究尺寸不规则度、胞壁厚度分布梯度变化的各向异性模型破坏面性能。本项目研究有助于完善泡沫金属的本构关系，为泡沫金属宏观结构数值分析提供可靠的破坏参数；本项目研究方法可促进其它多胞材料多轴动静态加载条件下的力学性能研究。

本项目采用理论、实验和数值模拟相结合的方法，完成了高应变率动态拉伸条件下泡沫金属多轴动态测试技术研究、尺寸不规则度梯度分布的泡沫金属单轴动态冲击吸能和多轴加载破坏特性研究、泡沫金属多轴动态加载条件下破坏特性和破坏机理研究以及多轴拉伸和拉压组合加载条件下泡沫金属本构关系理论研究等一系列研究内容，表征多轴动静态加载条件下泡沫金属破坏面特性表征，阐明了变形机理，发展了本构关系理论。本项目实现了5000 /s应变率的泡沫金属单轴动态拉伸实验，结果表明，中低应变率时泡沫金属拉伸性能表现出率无关特性，高应变率时泡沫金属拉伸强度与应变率线性正相关；提出了合理的中低应变率（不大于500 /s）多轴动态拉伸以及高应变率带围压的动态拉伸/冲击实验测试方案，结果表明中低应变率时泡沫金属破坏面呈现出率无关的特性；应力平面内泡沫金属破坏面形状类似椭圆，相对密度和不规则度参数不影响归一化的破坏面，应变平面内泡沫金属破坏面无规则形状；泡沫金属破坏主要有压缩失稳、拉伸断裂和混合破坏模式；拉伸和拉压组合工况下泡沫金属的后继屈服面归一化后与相对密度和不规则度无关，后继演化规律符合关联流动发展，提出了表征了泡沫金属拉伸和拉压组合工况下宏观力学行为的本构关系理论模型，模型预测的结果与实验结果吻合。本项目系统研究加载速率、相对密度和不规则度细观结构参数对泡沫金属多轴动静态宏观力学性能的影响，促进了泡沫金属多轴动态拉伸测试技术的发展，完善了本构关系理论研究，有助于指导泡沫金属及其复合结构的优化设计。