通过机械疲劳试验,研究了单组分有机硅结构密封胶的力学性能随机械疲劳次数、应变幅度的变化.结果表明结构胶疲劳过程中的拉伸载荷在不同应变幅度时的变化趋势相同,均在第2次循环拉伸时出现明显下降,而后开始回升并达到一个最大值,超过一定范围后继续增加疲劳次数,拉伸载荷又开始缓慢下降,但载荷值变化的速度随应变幅度的增大而加快;当应变幅度为±12.5％时,结构胶的拉伸粘接强度在机械循环处理3万次～5万次时略有下降,5万次后强度又回升到初始值,10万次～ 180万次之间逐渐下降.结构胶最大拉伸强度时的伸长率在不同应变幅度下有着相似的变化趋势:先升再降,后再次上升最后下降,且随着应变幅度的增大,这种趋势变化由缓到急;结构胶经机械疲劳后的断裂位置会偏向基材一侧,且会产生一定程度的界面粘接破坏;取各应变幅度下不同疲劳次数后的粘接强度平均值,对机械疲劳次数作图并对曲线进行拟合可得结构胶拉伸粘接强度与机械循环次数的关系y=-0.0206x+1.0218,可预测一定机械疲劳次数时对应的拉伸粘接强度.%The changes of mechanical fatigue cycles and strain amplitude on the physical properties of one-component structural silicone sealant was researched by mechanical fatigue test.Results show that the stiffness of structural silicone sealant has the same trend under different strain amplitude,and it decreases obviously at the second cycles and then starts to rise and reaches a maximum value.When continuing increase the cycles,the stiffness decreases slowly.But the velocity of the stiffness changes becomes faster with the increase of the strain amplitude.When the strain amplitude is 12.5％,the tensile strength decreases slightly between 30,000 ～50,000 cycles,then the strength rises to the initial value after 50,000 cycles,at last decreases gradually between 100,000 ～ 1,800,000 cycles.The elongation at maximum tensile strength of the sealant has a similar varying trend at different strain amplitude,and it rises first then drops,then rises again and then decreases at last.The varying trend become faster with the increase of strain amplitude,and the fracture position of structural silicone sealant will be biased toward the side of base material after mechanical fatigue,and a certain degree of interfacial bonding failure will be produced.Draw the mechanical fatigue curves by getting the average value of the adhesive strength at different mechanical fatigue cycles.The relationship of y =-0.0206x + 1.0218 between the tensile bond strength of the structural silicone sealant and the number of mechanical fatigue cycles can be obtained by fitting the mechanical fatigue curves,which can predict the tensile bond strength corresponding to the number of mechanical fatigue cycles.
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