3D打印碳纤维混凝土断裂力学性能试验研究

Experimental study on fracture mechanical properties of 3D printed carbon-fiber-reinforced concrete

为研究打印碳纤维混凝土的断裂力学性能,开展劈裂和三点弯试验,分析了打印方式和纤维含量对其力学性能、断裂破坏机理和微观开裂特性的影响规律,从断面材料完整性角度阐释了其各向异性的成因,建立了打印碳纤维混凝土与浇筑混凝土力学性能指标之间的关系表达式。研究结果表明:打印碳纤维混凝土断裂过程与浇筑混凝土的相似,可分为弹性阶段、裂缝稳定扩展阶段和裂缝不稳定扩展阶段;打印方式会引起混凝土不同方向上断面材料完整性削弱程度的不同,相应地引起力学性能不同程度的降低,这是导致打印混凝土各向异性的本质原因;断面材料完整性削弱程度越大,剪切微裂缝数量比例越高,且随着纤维含量增加,纤维桥接作用的增强效果有所降低;由于纤维分布的随机性,力学性能指标衰减系数与剪切裂缝数量占比衰减系数之间的关系呈非线性。

In order to study the fracture mechanical behavior of the printed carbon-fiber-reinforced concrete,the splitting and three-point-bending tests were conducted.The effects of the printing method and fiber content on the fracture damage mechanism,fracture mechanical properties,and microscopic crack characteristics of the specimens were analyzed.The mechanism of the anisotropy origination was explained by the comparisons of the sectional material integrity.A fitting expression between the mechanical indicators of 3D printed carbon-fiber-reinforced concrete and conventionally cast concrete was proposed.The study results indicate that:compared to the cast concrete,the printed carbon-fiber-reinforced concrete has the similar fracture process which includes the elastic stage,cracking stable expansion stage and cracking unstable expansion stage;the printing method could lead to the different weakening of the sectional material integrity and the corresponding decrease of the mechanical indicators of different material direction,respectively;if the sectional material integrity is weakened more seriously,the proportion of shear micro-cracks will increase and the enhancement of fiber bridging action will decrease with the increasing of the fiber content;due to the random of the distribution of the fiber,the reduction factors of the mechanical indicators and the amount ratio of the shear cracks have the nonlinear relationships.