宫伟伟. 泡沫铝动态力学性能的物质点法研究. 清华大学博士学位论文，2012.5

近年来,随着航天技术的不断发展,空间碎片日益增多,对航天器的安全运 行造成了很大的威胁。空间碎片运行的速度很高,在千米每秒的量级,数值模拟 成为了这种极端问题的经济有效的研究手段。本文采用物质点法研究防护材料泡 沫铝的动态力学行为,给出了一种研究具有复杂形状材料的动态力学行为的思路 和手段。
某些情况泡沫铝可以看作均匀的实体材料,但此时需要选择合适的本构模型 来很好地描述泡沫铝的力学行为。Deshpande-Fleck泡沫模型以其形式简单,依赖 实验给出的参数较少,而且方便在模型中考虑相对密度对力学性能的影响,以及 容易引入失效模型等优势得到了广泛的应用。本文将Deshpande-Fleck泡沫模型和 体积应变失效模式引入到物质点法中,推导了完整的应力更新迭代公式并通过 了Taylor杆实验验证,实现了对泡沫铝材料动态压缩性能的三维仿真模拟。通过 与实验对比,表明物质点法在模拟此类问题时比有限元法更具有优势。
欧空局指出泡沫铝是非常好的航天器防护材料之一,将其应用于Whipple防 护结构可以设计出更为有效的抗撞击防护方案。在超高速撞击中,碎片撞击到泡 沫铝孔壁时引起的材料失效破碎等现象都是在微尺度上进行的,此时需要考虑泡 沫铝的微观结构。本文提出了基于Micro-CT扫描图片来重构三维真实泡沫铝微观 物质点模型的方法,采用物质点法模拟了两种含有泡沫铝的Whipple防护结构, 通过与实验验证,表明物质点法及生成的微观模型能够很好地再现实验,给出合 理的结论。并对两种防护结构适用的防护情况进行了分析比较。
作为吸能材料,泡沫铝平台应力段的高低及长短决定了它的吸能能力,相对 密度是表征泡沫铝性能的重要参数,基体材料的性质也会影响其力学性能。本文 基于泡沫铝微观模型,采用物质点法和动态hopkinson杆实验分析了应变率和相对 密度对泡沫铝平台应力的影响。
为扩展物质点法的适用范围,在物质点法程序中引入了损伤模型,该模型能 够很好地模拟金属材料发生失效破坏时的力学行为。其中本构模型的推导适用于 在物质点法中添加一般的基于Mises准则的非线性本构模型的应力更新迭代方法, 为进一步添加各种模型给出了参考。

Recently, with the rapid development of aerospace technology, the number of space debrises keeps growing, which is a great threat for the safety of the spacecrafts. The velocity of space debris is in the order of 103m/s. Numerical simulation is an efficient research tool to investigate this kind of high-velocity impact problems. In this paper, we study the dynamical properties of aluminum foam, which is an important protective material for the spacecraft, using material point method (MPM). This work is of certain reference value for the investigation of dynamical behaviors of materials with complex shapes and microstructures.
In some cases, the aluminum foam can be approximately consider as the solid bulk material, but the suitable constitutive model should be used instead. Deshpande Fleck foam model is a widely used constitutive model with simple form, failure models and few empirical parameters. The influences of relative density to the dynamical properties can also be easily modified in this model. The Deshpande Fleck foam model is used in this paper considering material failure of volume strain. A complete formula of improved stress iteration has been developed and verified by the experimental data of Taylor bar test. 3D simulation of aluminum foam compression process has been performed for estimating the dynamical properties. The simulation results agree well with the experimental data, and the advantages of MPM over finite element method (FEM) have been addressed.
The European Space Agency (ESA) pointed out that the aluminum foam is an ex- cellent material for protection of spacecrafts. Using aluminum foam, some more efficient Whipple protection structures can be designed. During the hypervelocity impact with debris, the material failure occurs at the microscales inside the aluminum foam, thus the microstructures should be considered. In this paper, the real microstructure model of aluminum foam is reconstructed based on the micro-CT scanned images. Two kinds of Whipple protection structures have been investigated using MPM simulation. The nu- merical results agree well with the experimental results.
Furthermore, the application fields of these two kinds of structures are compared and analyzed. In the energy-absorption materials, the length and height of platform stress de- cide their performances. Relative density and base material are all important in deciding the form properties. Based on the microstructure model of aluminum foam, we studied the influences of strain rate and relative density using MPM simulation and Hopkinson bar experiment. A quantitative relation between platform stress, strain rate and relative density has been developed. A dynamic damage model has been added in the MPM to extend its application field, describing the dynamical behaviors of metals when failure occurs.