基于微观力学模型应变硬化水泥基复合材料强韧化设计与动态力学行为

Normal concrete with the remarkable characteristics of brittle material subjected to earthquake, impact and explosion, high speed impacting and blasting, will be seriously damage or destructed. Fiber reinforced cement matrix composites with high ductility is used to promote coordinated deformation capability and safety of civil engineering structure. Existed strain-hardening cementitious composites restricted by their level of strength, are difficult to meet the demand for structural materials with high strength and high ductility under the action of strong dynamic load. This topic attempts to abandon the traditional materials testing method by trial and error. Based on the theory of micromechanics design, the theoretical calculation will firstly adopt to obtain characteristic parameters of matrix, fiber and interface to realize multiple cracking and steady state cracking of high strength strain-hardening cementitious composite. With reference to the design values of the theoretical calculation, the methods of the choice of cementitious materials system, the incorporation of artificial flaw particles, polymer and mixed fibers, are to realize the design of cementitious composite materials with high strength and high ductility. Combined with material static mechanical test and microstructure analysis, the strengthening and toughing mechanism of material are further defined. Using microcomputer control drop hammer impact test machine, Hopkinson pressure bar (SHPB) and MTS investigate tensile and compressive mechanical properties evolution law of the material under high and low strain rate impacting, and then the material constitutive relation of dynamic mechanics model and the dynamic mechanical damage model are established.

具有显著脆性材料特征的普通混凝土在遭受地震、冲击、高速撞击及爆炸等高应变速率荷载作用下会发生毁灭性破坏。高延性的纤维增强水泥基复合材料是提升土木工程结构协同变形能力和安全性的重要措施。现有的应变硬化水泥基复合材料受其强度等级的限制，很难满足强动载荷作用下对高强高延性结构材料的需求。本课题摒弃传统材料制备中常用的尝试法，以微观力学设计理论为基础，通过模拟计算，获得基于稳态开裂、多缝开裂模式的高强应变硬化水泥基复合材料基体、纤维及界面等特征参数的取值范围。参照理论计算的设计取值，通过胶凝材料体系的选择、引入人工缺陷粒子、高分子聚合物及混杂纤维等方法，实现水泥基复合材料高强高延性的设计。结合材料力学测试和微结构分析，进一步明确材料强韧化机理。利用落锤冲击试验机、霍普金森压杆和MTS研究高、低应变率下材料动态拉伸、压缩力学性能演变规律，建立该材料的动态力学本构关系模型及动态力学损伤模型。

混凝土材料因其塑性变形能力很差，在一些自然灾害或人为破坏行为如地震、爆炸、冲击震动等高速动载条件作用下往往会发生毁灭性破坏，从而造成极大的安全隐患和人类生命财产损失。纤维增强使水泥基复合材料的抗压强度、抗裂性、抗拉(弯)强度、韧性、抗冲击性能、抗疲劳性能以及耐久性等有着不同程度的提高。本研究基于断裂力学、细观力学和统计学的SHCC微观力学模型的建立和相关的计算程序的编写，实现了单丝拉拔力学行为、纤维桥接应力以及SHCC材料单轴拉伸行为的模拟计算，为高延性纤维增强水泥基复合材料设计与性能优化提供了分析方法。通过纤维的选择，基体强度的提高，引入人工缺陷粒子及高分子聚合物改性基体及纤维/基体界面，成功地制备了性能稳定的高强应变硬化水泥基复合材料，揭示高强应变硬化水泥基复合材料的强韧化机理。将超细钢纤维与PE纤维混杂可获得抗压强度175MPa、抗折强度33MPa，拉伸应变5%的超高强高延性的水泥基复合材料，并提出了一种基于饱和开裂的高强混杂纤维SHCC的设计方法。获得了低速冲击和高速压缩载荷作用下高强SHCC冲击强度、峰值应变、断裂韧性等动力学参数的演化规律及断裂损伤、裂纹扩展特征，建立该类材料动态力学损伤本构关系模型。