Efficient Design of Fiber Reinforced Cementitious Composites Through Interface Tailoring

本文主要研究了一种新型的增韧机制--主裂纹尖端周围的广泛扩散损伤。这项研究的动机是最近发现了1-4%聚乙烯纤维增强的应变硬化脆性水泥基复合材料(SHBMC)的延性断裂模式。观察到裂纹扩展伴随着裂纹尖端周围广泛的体积非弹性变形，以及裂纹尾迹中传统的纤维桥联和拔出。有些试件的离面能量吸收甚至高于纤维桥连能，总断裂能达到34kJ/m2。这大约相当于不含纤维的原始基质断裂能的3400倍。作为参考，铝合金的断裂能在8-30kJ/m2之间。基于J-BASE断裂测试技术，将进行R曲线行为的实验研究，以及裂纹面上和面外断裂能分配的实验研究。单轴试验中的伪应变硬化过程与缺口试件延性断裂过程中损伤的空间演化之间的相关性将被用来建立延性断裂模式的详细微观机制。

The present work focuses on a new type of toughening mechanism -- extensive diffused damage surrounding in the main crack-tip. The proposed research is motivated by a recent discovery of a ductile fracture mode in strain hardening brittle cement matrix composites (SHBMC) reinforced with 1-4 % polyethylene fibers. Crack propagation is observed to be accompanied by extensive volumetric inelastic deformation surrounding the crack tip, in addition to conventional fiber bridging and pull-out in the crack wake. The off-crack-plane energy absorption is found to be even higher than the fiber bridging energy in some specimens we have tested so far, with total fracture energy reaching 34 kJ/m2. This represents roughly 3400 times the fracture energy of the virgin matrix without fibers. As reference, the fracture energy of aluminum alloys is between 8 - 30 kJ/m2. Experimental investigations on R-curve behavior, and on- and off-crack-plane fracture energy partitioning will be conducted based on the J-based fracture testing technique. Correlation between pseudo strain-hardening processes in uniaxial testing and the spatial evolution of damage during the ductile fracture process in notched specimens will be used to establish the detail micromechanisms of the ductile fracture mode.