碳纤维复合泡沫铝冲击响应的各向异性及变形机理

The present proposal concentrates on the mechanical response and the mechanism of energy dissipation of closed-cell carbon fibers/aluminum composite foam under impact load. Combining materials science with mechanics based upon the establishment of structure-pproperties relation for fibers/metals composite foam, the high strain rate tests for closed-cell carbon fibers/aluminum composite foam will be conducted by split Hopkinson presure bar. The main emphasis of the project focuses on the effect of cell shape anisotropy, gas effect and the carbon fiber content on the dynamic behavior of carbon fibers/aluminum composite foam as well as the establishment of the ratio-related constitutive relation. The "Process Frozen" method will be used to investigate the deformation and damage mechanisms at various stages of dynamic response for carbon fibers/aluminum composite foam, to reveal the mechanism of energy dissipation of carbon fibers/aluminum composite foam under impact load. Through the analysis of the influence of orientation of cell and carbon fiber on the microstructure evolution of cell wall materials under impact load, especially the evolution of molten phase transition zone induced by impact load and the factors that infuence it, the present study attempt to clarify the thermoplastic instability mechanism of cell wall materials under varying strain ratio. On the basis of mentioned above, one can reveal the correlation between the macroscopic mechanical response and meso/micro-structure to give reliable theoretical guidance to the control of meso/micro-structure of cell wall materials and assessing the impact resistance of carbon fibers/aluminum composite foam.

本项目围绕碳纤维复合闭孔泡沫铝承受冲击载荷时的力学响应及变形机理，融合材料学和力学研究方法，以建立结构-性能关系为主线。利用分离式Hopkinson压杆对碳纤维复合铝泡沫进行动态压缩测试，着重研究孔形各向异性、气体效应、碳纤维含量对纤维复合铝泡沫动力学特性的影响，建立碳纤维复合铝泡沫率相关本构关系。通过"过程冻结"技术在细观孔/膜水平探讨碳纤维复合铝泡沫动态响应各阶段的变形模式和失效机理，从而揭示碳纤维复合铝泡沫在承受冲击载荷作用时的能量耗散机制。分析冲击载荷条件下孔取向和碳纤维对孔壁材料微结构演化的影响，探讨冲击诱发熔融相变区的演化过程及其影响因素，阐明不同应变率条件下孔壁材料的热塑失稳机制。在上述基础上，揭示碳纤维复合闭孔泡沫铝宏观动力学响应与细微观结构间的关系，为指导泡沫铝制备过程中细微观结构的控制和评价其耐撞性提供理论依据。

泡沫金属对高速冲击载荷的缓冲和有效的能量吸收特性使其在减震、碰撞过程中具有潜在的应用价值。本项目从闭孔泡沫铝金属的制备优化、精细表征和性能测试入手，结合材料学与力学研究手段，较为系统地研究了闭孔泡沫金属的宏观力学行为，并通过细观-微观表征揭示了闭孔泡沫金属的变形机理。首先，优化了熔体发泡法制备碳纤维复合铝基闭孔泡沫的制备工艺，改善了碳纤维在基体中的分布和泡孔的均匀性。对碳纤维复合闭孔泡沫铝的准静态压缩、高速压缩和冲击韧性进行了测试。详细表征了碳纤维复合泡沫铝材料压缩稳定性和能量吸收能力。证明了碳纤维复合闭孔泡沫铝材料具有明显的应变率效应，且基体材料的率敏感性是导致闭孔泡沫铝应变率效应的主要因素，其它如微惯量和气体压缩与气体粘滞流动均可忽略。提出了在高应变率条件下，闭孔泡沫铝以两种模式变形，剪切变形和端部局域化变形。明确了高应变率压缩能量耗散的主要机制：孔壁材料破碎产生大量新表面及碳纤维的拔出和断裂。对碳纤维复合闭孔泡沫铝材料的冲击韧性进行了测试并获得了冲击历程曲线。结果表明，密度仍然是首要影响因素，随着密度的增加平均峰值载荷、最大能量吸收、冲击韧性都增加，但对于中等密度泡沫材料，裂纹传播路径是影响冲击韧性的另一重要因素。由于裂纹传播的不确定性导致中等密度泡沫冲击韧性值具有较大的波动性。这可能与泡孔的尺寸、分布有很大关系，该方面的研究有待进一步深入。