基于裂纹扩展的锈蚀拉索疲劳寿命评估

Fatigue Life Assessment of Corroded Cables Based on Crack Propagation

将平行钢丝索视为一个多裂纹竞争的串-并联模型,通过点蚀不均匀系数确定锈蚀钢丝的初始裂纹尺寸.基于疲劳裂纹扩展速率模型各参数的概率分布,采用疲劳失效全过程Monte-Carlo模拟法计算了不同断丝率下拉索的疲劳寿命,并通过试验数据对计算结果进行了验证.结果表明:拉索断丝率随疲劳次数增加符合幂级数的增长规律,当拉索的断丝率达到10%之后,拉索的断丝率迅速增长而失去抵抗疲劳荷载的能力.纤维束模型中串联钢丝单元划分越多,拉索的疲劳寿命越短,但这种趋势会随着钢丝单元数的增加而逐渐趋于稳定.锈蚀拉索的疲劳寿命服从Weibull分布,点蚀效应缩短了钢丝裂纹萌生寿命,随锈蚀程度的增加,拉索疲劳寿命均值大幅下降,变异性减小,其抗疲劳性能快速劣化.通过雨流计数法将随机荷载历程转化为疲劳荷载谱块的重复作用,基于钢丝的腐蚀发展规律计算了不同腐蚀程度拉索的疲劳寿命,建立了随机荷载作用下拉索腐蚀程度与疲劳寿命劣化之间的关系模型.根据P-dcN曲线可对锈蚀拉索服役期的疲劳可靠性进行评估,应用时需要准确掌握拉索钢丝的缺陷或腐蚀细节信息.

The parallel wire cable is regarded as a series-parallel model with multi-crack competition,and the initial crack size of corroded steel wire is determined by a pitting non-uniformity coefficient.Based on the probability distribution of the parameters of the fatigue crack growth rate model,the fatigue life of the cable under different wire breakage rates is calculated by using the Monte Carlo simulation method of the whole process of fatigue failure,and the calculated results are verified by the test data.The results show that the wire breaking rate of the cable conforms to the growth law of the power series with the increase in fatigue times.When the wire-breaking rate of cable reaches about 10%,the wire-breaking rate of cable increases rapidly and loses the ability to resist fatigue load.The more the series steel wire elements are divided in the fiber bundle model,the shorter the fatigue life of the cable,but this trend gradually stabilizes with the increase of the number of steel wire elements.The fatigue life of the corroded cable follows the Weibull distribution,and the pitting effect shortens the crack initiation life of the steel wire,resulting in a significant decrease in both the average fatigue life and variability of the cable with the increase of the degree of corrosion,as well as a rapid deterioration of its anti-fatigue performance.The random load history is transformed into the repeated action of fatigue load spectrum block by the rain flow counting method.Based on the corrosion development law of steel wire,the fatigue life of cables with different corrosion degrees is calculated,and the relationship model between cable corrosion degree and fatigue life degradation under random load is established.According to the P-dc-N curve,the fatigue reliability of corroded cables can be evaluated.It is necessary to accurately grasp the defect or corrosion details of cable steel wire in the application.