充水保压蜗壳结构中钢衬的低周疲劳问题

Study on low-cycle fatigue of steel spiral cases embedded under pressurized conditions

鉴于抽水蓄能机组蜗壳通常采用充水保压技术埋入混凝土,在运行期钢蜗壳须要承受频繁的大幅值静水压力循环作用,面临一定程度的低周疲劳失效风险,以某实际充水保压蜗壳结构为例,首先基于ABAQUS有限元分析平台完成了该组合结构的施工-运行过程静力仿真分析,然后基于DesignLife疲劳分析平台,依据有限元静力分析结果采用常幅值荷载的循环方式预测了钢蜗壳的疲劳寿命,其中材料的S-N曲线(应力-寿命曲线)选取为Eurocode3-112.计算结果表明:运行期钢蜗壳的局部脱空现象会对其自身的受力产生不利影响,脱空区-高应力区-高疲劳失效风险区三者间存在显著的因果对应关系.从预测的疲劳寿命数量级(2×10~5以上)看,电站运行期内钢蜗壳无低周疲劳失效的风险.

Steel spiral cases in pumped storage hydroelectric power plants（HPPs）are in general filled with water and temporarily pressurized while encasement concrete is placed.A steel spiral case in a pumped storage HPP should bear high-amplitude cyclic internal water pressure.Hence the steel spiral case carries some degree of risk of low-cycle fatigue failure during the operating period of the HPP.In this context,a complete finite-element simulation of the construction-to-operation process of a spiral case structure was carried out using the ABAQUS code.The finite-element simulation results were then used to generate constant-amplitude fluctuating stresses for the fatigue life prediction of the steel spiral case,based on the DesignLife software.The Eurocode 3-112 S-N curve was employed for the definitions of the fatigue-related material properties.The simulation results show that the local gapping existing between the steel spiral case and its surrounding concrete adversely affects the structural performance of the steel component.The causal links between the gapping and the high-stress zones,and between the high-stress and the high-fatigue-failure-risk zones,are noteworthy.The predicted fatigue life of the steel spiral case is greater than 2×10~5 cycles.The findings suggest that the steel spiralcase should not undergo a low-cycle fatigue failure during the operating period of the HPP.