钢纤维对水泥基复合材料抗起裂特性的影响

摘要

The three-point bending tests on notched beams with different steel fibre volume fractions and different specimen sizes were conducted.The resistances to crack initiation of randomly distributed steel fibre reinforced cementitious composite (SFRC) and aligned steel fibre reinforced cementitious composite (ASFRC) were studied.Based on the load-crack mouth opening displacement curves,the influence of steel fibres on fracture properties of cementitious composites was disscussed,and the initial fracture toughness was determined by sudden reduction of linearly related coefficient.The results show that the initial fracture toughness of ASFRC is significantly greater than that of SFRC.The initial fracture toughness increases with the steel fibre volume fraction,and the increasing tendency of ASFRC tends to be stable when the steel fibre volume fraction is higher than 0.9％.The initial fracture toughnesses of SFRC and ASFRC all increase with the specimen sizes varying from 40 mm to 100 mm,and the in creasing tendency is slower in ASFRC.In addition,the enhancement of ASFRC to initial fracture toughness was explained by taking into account the fact that the inclusion embedded at the crack tip of composite would change the crack tip stress intensity factor.%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(40～100 mm),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.