超高强钢丝斜拉索腐蚀疲劳性能评定

The effects of corrosion, fatigue and the coupling action generate the irreversible damage for stay cable, which should threaten the safety of Cable-Stayed Bridge and cause enormous losses to national economy. The damages caused by the corrosion and fatigue of stay cables are inevitable during the service periods. Therefore, the corrosion monitoring and corrosion fatigue properties assessment of super high strength parallel-wire stay cables are proposed in this proposal. The electrochemical properties and corrosion monitoring methods of super high strength steel wires are considered in this proposal. In addition, based on the corrosion fatigue of super high strength steel wires, the models of evaluation of corrosion fatigue for super high strength parallel-wire stay cables are established in this proposal. First, the electrochemical properties of plating and metal matrix for super high strength steel wires are studied; and the characteristics of pitting corrosion along the length of steel wires are obtained by using the accelerated corrosion tests. A novel corrosion monitoring method for steel wires is proposed based on the stress concentration in plane stress state caused by pitting corrosion. Subsequently, a multi-parameter Weibull model of the corrosion S-N relationship considering length effects for super high strength steel wires is established. The stress range and corrosion degree are regarded as the input variables for the proposed model. The expectation-maximization (EM) algorithm is used to deal with parameter estimation considering the censored data. In the proposed model, the weakest-link effect gradually becomes dominant and causes a decrease in fatigue life that increases along the dimension length. Especially, the auto-correlation length of the fatigue life can be estimated by the proposed model. Further, based on the statistic models in the macroscale and the mechanisms of corrosion fatigue in the microscale, the coupling effects of the corrosion and fatigue are evaluated and the damage model of corrosion fatigue for super high strength steel wires is established in the proposal. Finally, the damage evolution models of the broken wires considering the randomness of the corrosion and fatigue for super high strength steel wires are illustrated. The Monte Carlo simulation is conducted to simulate the fatigue life of stay cables considering the coupling effects of the corrosion and fatigue. The threshold fraction of broken wires would be determined for corrosion fatigue of stay cables based on the safety and economic requests. The final goal of this proposal is to establish the prediction model of the corrosion fatigue for super high strength parallel-wire stay cables, which is a general issue of the safety evaluation for parallel-wire stay cables.

斜拉索服役期内不可避免地遭受腐蚀、疲劳及其耦合作用产生不可逆损伤危及斜拉桥服役安全。本项目以超高强钢丝斜拉索为研究对象，从钢丝腐蚀电化学性质及腐蚀监测着手进而研究其腐蚀疲劳性能，兼顾腐蚀及腐蚀疲劳耦合作用下钢丝疲劳寿命评价，系统地构建斜拉索腐蚀疲劳性能评定解决方案。首先，研究超高强钢丝的电化学性质及腐蚀形貌特征，研究基于平面应力状态应力集中的腐蚀监测方法与腐蚀程度评价模型；其次，建立考虑长度效应、腐蚀程度的钢丝疲劳寿命统一多参数Weibull模型及参数EM估计算法，从统计模型与损伤机制角度研究腐蚀疲劳耦合作用下钢丝损伤演化，探究耦合作用对裂纹成核及裂纹扩展寿命的影响，建立腐蚀疲劳临界损伤限值。最后，研究变幅作用下钢丝损伤等效准则，构建斜拉索内钢丝损伤演化路径及其随机模拟方法，确定斜拉索腐蚀疲劳临界断丝率，建立超高强钢丝斜拉索腐蚀疲劳寿命预测模型，系统地解决斜拉索腐蚀疲劳评定面临的共性问题。

随着斜拉桥跨径不断增大超高强钢丝斜拉索开始获得工程应用，但斜拉索服役期内不可避免地遭受腐蚀、疲劳及其耦合作用产生不可逆损伤危及斜拉桥服役安全。本项目以超高强钢丝斜拉索为研究对象，从腐蚀特性着手研究超高强钢丝电化学性质，根据加速腐蚀试验研究钢丝表面腐蚀形貌特征及其随机模拟方法，提出平面应力状态应力集中的腐蚀原位定量监测方法；建立腐蚀钢丝疲劳寿命统一多参数Weibull模型及其参数EM估计算法，研究极限强度、腐蚀程度与应力幅对钢丝疲劳寿命的影响规律，采用腐蚀疲劳耦合试验研究腐蚀速率、疲劳荷载频率与应力幅对钢丝损伤演化的控制作用；考虑斜拉索内钢丝腐蚀与疲劳耦合作用的双重随机性及断丝导致的荷载重分布，提出钢丝腐蚀程度－疲劳寿命逆等秩准则，建立斜拉索内钢丝损伤演化路径模型并推导钢丝依次断裂时疲劳循环次数的递推关系，研究腐蚀斜拉索疲劳寿命的终止条件及其疲劳寿命的概率分布，研究腐蚀程度及其变异性与应力幅对斜拉索疲劳寿命的影响规律，系统地建立腐蚀斜拉索疲劳寿命随机模拟与预测评价方法。研究结果表明：疲劳寿命统一多参数Weibull模型可以较好地表征腐蚀程度0.18%–18.67%范围内不同概率保证率下钢丝的疲劳寿命，初始极限强度对腐蚀超高强钢丝疲劳性能的影响可以忽略不计，超高强钢丝斜拉索须采用更有效的腐蚀防护措施，否则超高强钢丝将更快地发生疲劳破坏；腐蚀疲劳耦合试验揭示出腐蚀速率与裂纹萌生存在竞争关系，特定情况下腐蚀会抑制疲劳裂纹萌生；斜拉索疲劳寿命由其内一小部分腐蚀程度大、疲劳寿命低的钢丝控制，以断丝率5%作为终止条件能充分利用钢丝疲劳性能且具有一定安全裕度，随腐蚀程度增大斜拉索疲劳寿命显著降低，低应力幅时疲劳寿命对腐蚀程度及其变异性更敏感。本项目取得的研究成果具有重要科学价值和应用前景，为超高强钢丝斜拉索设计及在役高强钢丝斜拉索安全评定提供理论依据，为保障斜拉索服役安全奠定基础。