冲击载荷下多尺度碳纤维增强镁合金层合板动态力学行为与损伤机理研究

To improve impact damage resistance of fiber reinforced lightweight alloy laminates and to provide important theoretical basis for the design and application of the composite structure, the present study will be focused on the dynamic response of carbon fiber reinforced magnesium alloy laminates under impact loading by experimental, theoretical and simulation studies. In the experiment, multi-scale carbon fibers reinforced magnesium alloy laminates are fabricated by using hot-pressing method, in which graded nano-crystalline magnesium alloy sheet as the base materials and low melting point magnesium alloy reinforced by graphene nanoplatelets as the solder between the matrix and carbon fiber woven cloth. Quasi static and impact tensile mechanical properties as well as the low and high velocity impact response of the composite laminates with different fiber volume fractions and numbers of plies are investigated. Effect laws of different factors such as the gradient nanocrystalline structure of magnesium alloy sheet, graphene nanoplatelets/carbon fiber hybrid reinforcements, and their interfacial adhesion with magnesium alloy matrix on overall performance and damage evolution and failure mechanism under impact loading are discussed, and the rate dependent anisotropic constitutive equation and mechanical property parameters of the laminated composites are determined. On the aspects of theory and numerical simulation, the multi-level computational model of the laminated composites is established based on the laminated plate theory, damage and fracture mechanics methods as well as the constitutive equation obtained by the experiment. Impact resistance properties and damage evolution characteristics of the laminates with different patterning parameters under various impact conditions are numerically investigated. Finally, the strengthening and toughening mechanics mechanism for the multi-scale fiber/magnesium laminate interfaces are also analyzed.

为了提高纤维增强轻质合金层合板的抗冲击损伤能力，以便为复合材料结构设计与应用提供重要的理论依据，本项目拟采用新型碳纤维镁合金层合板试件开展冲击加载下动态响应的实验、理论及模拟研究。在实验上，通过热压法制备镁合金钎料粘结的纳米石墨烯/碳纤维增强梯度纳米晶镁合金板层合材料，研究不同层数和体分比纤维镁合金层板的准静态、冲击拉伸力学性能及不同冲击速度下的动力学响应，探讨镁合金梯度纳米晶结构、镁合金与石墨烯/碳纤维混杂增强体的界面相互作用及微观力学行为等对该层板在冲击载荷作用下的整体性能与损伤演化规律及破坏机理的影响，确定其应变率相关的各向异性动态本构及力学性能参数。在理论和数值模拟方面，基于层合板理论、损伤力学及断裂力学方法，将通过实验建立的本构关系赋予多尺度层合板力学模型，模拟不同碳纤维镁合金层板在不同冲击条件下的抗冲击性能和损伤演化特征, 分析多尺度碳纤维镁合金层板结构界面强韧化的力学机理。

作为一种新型轻质纤维金属层合板结构(FMLs)，碳纤维聚合物复合材料增强镁合金层合板有可能成为冲击载荷下汽车和航空航天部件及船舶装甲军事装置的潜在运用复合材料，但由于镁合金板强韧性及纤维镁合金层板层间性能较差，抗冲击纤维镁合金层合板的动态力学行为及变形损伤机理问题在纤维金属复合材料宏细观力学及其多尺度分析中受到了国内外学者的高度重视。实验方面，我们采用超声表面纳米晶化和振动辅助热压技术制备了纳米石墨烯增强层间混杂粘结的新型碳纤维聚合物复合材料/梯度纳米化AZ31B 镁合金层合板，对其进行了静动态拉伸、抗弹冲击及动态断裂性能实验研究，获得了该种复合材料动态力学性能的统一Johnson-Cook模型，并基于数字图像相关(DIC)技术从变形局部化的生成速度成功地解释了材料动态响应的特征；此外，实验测试得到了碳纤维镁合金层板的静动态断裂韧性，通过改进的优化算法反演得到了层间内聚力模型(cohesive zone model, CZM)参数，并用于冲击模拟分析中；还对AZ31B镁合金板及不同构象碳纤维镁合金层板的抗弹性能进行了抗弹冲击性能对比，得到了层板构象及加载条件对其动态响应的影响规律。理论和数值分析方面，一方面基于分子动力学和细观力学理论对纳米复合粘结剂动态力学性能进行了多尺度分析，建立了定量控制石墨烯团聚分布的算法，得到了优化的纳米复合粘结剂力学性能参数，并用于指导实验和验证；另一方面，基于改进的镁合金板各向异性屈服损伤本构、界面指数型CZM模型、纤维复合材料层的3D Hashin失效准则及引入渐进刚度折减，开发了纤维镁合金层合板反复冲击和抗弹冲击子程序，采用该子程序进行的抗弹冲击模拟结果与实验数据吻合得较好。与已有发表同类纤维镁合金层合板相比，本文开发的新型多尺度纤维镁合金层板具有较高的静动态力学性能，其冲击失效模式主要由其界面脱粘控制，伴随着镁合金薄板与纤维/树脂复合材料层之间的分层以及其断裂破坏，增强增韧界面使得梯度纳米化镁合金板与纤维/树脂复合层之间产生协同增强。