环境腐蚀下斜拉索钢丝多尺度疲劳损伤演化机理研究

Due to natural aging and cracking of stay cable sheath, stay cable wires exposed to the natural environment are prone to corrosion damage and subjected to an alternating load. It is necessary to investigate the evolution mechanism of multi-scale fatigue damage of wires under environmental corrosion. According to the indoor accelerated corrosion test of wires, the distribution characteristics of corrosion pits are studied. The time-varying probability model of corrosion pits is established based on fractal theory. The evaluation method of corrosion degree of wires is discussed. Multi-group and multi-series corrosion fatigue tests are conducted. The relationship between fatigue life of wires and cyclic stress is established under different corrosion degrees. The S-N curves of wires are modified by the Goodman criterion. The effect of corrosion pits on fatigue life is analyzed. A new method of corrosion fatigue life prediction based on fractal dimension is proposed. A new multi-scale corrosion fatigue crack growth model is created. The three-dimensional corrosion fatigue crack growth of steel wires is analyzed and the validity is verified. The appropriate damage variable is selected to establish the nonlinear evolution equation of corrosion fatigue damage of wires. The assessment method on corrosion fatigue reliability and the durability of stay cables will be carried out when random factors on loading condition, working environment, structure system, material properties and wire fracture are taken into account. The whole life design theory of cable-stayed bridge is improved, and it provides the theoretical basis for damage diagnosis of cable-stayed bridges.

由于斜拉索护套自然老化和受损破裂等原因，暴露在自然环境中的斜拉索钢丝容易发生腐蚀破坏，并且承受交变荷载作用，因此有必要对环境腐蚀下钢丝多尺度疲劳损伤演化机理展开研究。通过钢丝室内加速腐蚀试验研究腐蚀坑分布特性，采用分形理论建立钢丝腐蚀坑时变概率模型，探讨钢丝锈蚀程度评定方法。开展多组多系列钢丝腐蚀疲劳试验，确定不同锈蚀程度下钢丝疲劳寿命与循环应力之间的关系，基于Goodman准则对S-N曲线进行修正，分析腐蚀坑对疲劳寿命的影响，提出基于分形维数的腐蚀疲劳寿命预测新方法；建立一种新的多尺度腐蚀疲劳裂纹扩展模型，对钢丝三维腐蚀疲劳裂纹扩展进行分析并验证模型有效性；选取合适的损伤变量建立钢丝腐蚀疲劳损伤非线性演化方程。综合考虑受载状况、工作环境、结构体系、材料特性、钢丝断裂等随机性因素，提出斜拉索腐蚀疲劳可靠度及耐久性评估方法，完善斜拉桥全寿命设计理论，为在役斜拉桥的损伤诊断提供理论依据。

现有的斜拉索高强钢丝由于护套开裂和锚固区长期积水会产生环境腐蚀现象，在外界往复荷载作用下很容易出现疲劳破坏。本项目采用试验和数值模拟相结合的方法研究环境腐蚀下高强钢丝疲劳损伤演化机理。首先通过室内加速腐蚀试验研究三种不同大气环境（工业酸雨环境、乡村大气环境和海洋大气环境）下腐蚀退化规律，采用临界距离法和应变能密度法对疲劳寿命进行预测，为了模拟实际腐蚀情况下的多蚀坑问题，开展了不同锈蚀程度下（单蚀坑以及双蚀坑）高强钢丝疲劳试验研究。结果表明：（1）海洋大气环境的腐蚀程度最高，工业酸雨环境和乡村大气环境的腐蚀程度相当；（2）提出了一种可以考虑钢丝直径影响的蚀坑缺口应力集中系数计算公式，通过疲劳试验数据验证了临界距离法和应变能密度法在锈蚀高强钢丝疲劳评估中的准确性，相比较于传统名义应力法离散性较小；（3）建立了不同腐蚀程度下含单蚀坑和多蚀坑高强钢丝的名义应力和疲劳寿命之间的关系，还有待于进一步验证不同蚀坑当量化裂纹方法。因此，本项目对斜拉索的耐久性和全寿命评估打下坚实基础，完善了现有的疲劳评估方法。