剪切疲劳荷载下无砟轨道灌缝胶低温粘附特性

为研究无砟轨道聚氨酯灌缝胶在剪切疲劳荷载下粘附性能发展规律,依据灌缝胶工况开发了剪切疲劳试验及低温粘附特性直接拉伸试验,对经不同次数剪切疲劳加载的粘附性试件进行直接低温拉伸试验,分析剪切疲劳前后不同灌缝胶最大拉力、破坏位移指标的变化规律,及拉力-位移曲线的发展特性.结果表明:对未经疲劳加载的灌缝胶,材料异氰酸酯指数R与粘附强度呈正相关,与粘附抗变形能力呈负相关;疲劳加载后,R与材料抗疲劳性能呈负相关;疲劳加载初期,R较小的灌缝胶因体系内链段取向而出现粘附性能提高、离散性变大现象;疲劳加载过程中,由于材料内部介质不连续导致最大拉力指标稳定性优于破坏位移;随剪切疲劳加载次数增加,材料内部损伤累积破坏了粘附整体性,使失效模式由脆性破坏趋向于韧性破坏;基于试验结果,推荐抗剪切疲劳性能较好灌缝胶R宜在1.7~2.5之间.

Low-temperature adhesive properties of sealant applied in ballastless track under shear fatigue loading

To research the adhesive properties of polyurethane sealant under shear fatigue loading, a test method for evaluating the adhesive properties of sealants was developed based on the in-situ working condition. Direct tension tests at low temperature were conducted on the samples subjected to various shear fatigue cycles, the effects of various sealants on the maximum tensile force, failure displacement and force-displacement curves were analyzed and compared between experienced and un-experienced shear fatigue loading. The results show that the isocyanate index R of the samples un-experienced shear fatigue loading presents the positive correlation with bonding strength, and negative correlation with deformation resistivity. However, the R value presents a negative correlation with fatigue resistivity of sealants for the samples experienced shear fatigue loading. The adhesive properties and discreteness of sealants were improved due to chain orientation within sealants at the initial period of fatigue cycles. During the fatigue cycles, the stability of maximum force index is superior to the failure displacement due to the discontinuous medium of sealant body. As the increase of fatigue cycles, the accumulation of damage breaks the integrality of the bonding interface, which leads to the change of failure mode from brittle failure to ductile failure. Based on the test results, the sealants with R values between 1.7~2.5 could present better shear fatigue resistance performances.