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通过不同钢纤维体积分数及不同试件尺寸的预制缺口三点弯曲梁断裂试验,研究了普通乱向及定向钢纤维增强水泥基复合材料的抗起裂特性。利用试验测得的荷载-裂缝口张开位移曲线,分析了钢纤维对水泥基复合材料断裂性能的影响,并基于线性相关系数陡降法计算了起裂韧度。结果表明,定向钢纤维增强水泥基复合材料的起裂韧度明显高于普通乱向钢纤维增强水泥基复合材料;起裂韧度随钢纤维体积分数的增加而逐渐增大,当钢纤维体积分数达到0.9%左右时,定向钢纤维增强水泥基复合材料的起裂韧度值趋于稳定;在本试件高度范围内(40~100mm),起裂韧度随试件尺寸增加而逐渐增大,且定向钢纤维增强水泥基复合材料的增长趋势较为平缓。此外,从裂缝尖端夹杂改变其应力强度因子的角度解释了钢纤维的掺入及定向对起裂韧度的提高作用。
The crack initiation characteristics of normal and oriented steel fiber reinforced cement-based composites were studied by three-point bending test of prefabricated notched beams with different steel fiber volume fractions and different specimen sizes. The effect of steel fiber on the fracture properties of cementitious composites was analyzed by using the load-crack opening displacement curve measured by the test. The fracture toughness was calculated based on the linear correlation coefficient steep descent method. The results show that the fracture toughness of the oriented steel fiber reinforced cement-based composites is obviously higher than that of the common random steel fiber reinforced cement-based composites. The fracture toughness increases with the increase of the volume fraction of the steel fibers. When the steel fiber volume The fracture toughness of the oriented steel fiber reinforced cement-based composites tends to be stable when the fraction reaches 0.9%. In the height range of the specimen (40 ~ 100mm), the fracture toughness increases gradually with the increase of specimen size Large, and the directional steel fiber reinforced cement-based composites, the growth trend is relatively flat. In addition, the effect of steel fiber incorporation and orientation on the initiation fracture toughness was explained from the point that the crack tip inclusions changed its stress intensity factor.