聚氨酯注浆材料在循环压缩加载下疲劳性能与微观结构演化

应用于基础设施维修加固的聚氨酯注浆材料通常承受反复荷载作用,对聚氨酯注浆材料进行循环压缩加载试验以测试其压缩疲劳性能,全程记录材料的应变响应,并在SEM下观测材料泡孔结构疲劳破坏的微观形貌特征。试验结果表明:材料在循环荷载下的响应分为三个阶段,第一阶段持续数十次,弹性应变递次增大;第二阶段应变值稳定;第三阶段在高应力水平下表现为疲劳破坏,在低应力水平下表现为循环硬化。对于0.3g/cm3的试件,导致疲劳破坏的应力阈值α在0.7~0.8之间;而0.5g/cm3试件的阈值在0.6~0.7之间。发生疲劳破坏时,材料的宏观表现为垂直于荷载方向的鼓出,微观表现为泡壁裂纹扩张和棱边屈曲。此外,提出疲劳损伤参数D表征材料模量在循环荷载下的演化,D可以敏感地捕捉低应力水平下第三阶段材料的循环硬化。

Fatigue resistant and microstructure evolution of polyurethane grout materials under uniaxial compression

The comprehensive experimental investigations are conducted on the compressive fatigue resistant of polyurethane grout materials, which are widely used in maintenance of infrastructure and subjected to repeated loads.SEM and compression fatigue tests were applied to the specimens with different densities.The variation of strain under the cyclic compressive load is recorded.The test results show that strain development under load cycles can be divided into three stages: the first stage lasts for decades of cycles and elastic strain increases gradually;the strain at second stage is relative stable;while at third stage, specimen would be fatigue failure at higher stress level and behave as cyclic hardening at lower stress level.The stress threshold of fatigue, α ,is between 0.7 and 0.8 for the specimen of 0.3 g/cm3, and it is between 0.6 and 0.7 for the specimen of 0.5 g/cm3.When fatigue failure happens, the specimen will be bulging perpendicular of the load.Developing of micro cracks in polymer walls and bulking of polymer struts can be observed in microscope images.Besides, a parameter D based on the variation of elastic modulus under cycle loading is proposed to quantify the fatigue failure, and D is more pronounced than strain index when materials undergo cyclic hardening at the third stage at low level.