【作者】 王琦；

【导师】 叶笃毅；

【作者基本信息】 浙江大学 ， 化工过程机械， 2019， 硕士

【摘要】 转子轮盘作为汽轮机的核心部件之一,在服役过程中,由于轮槽齿根存在应力集中,在交变服役条件下,往往发生疲劳失效。因此,对汽轮机转子轮槽进行疲劳寿命预测是汽轮机疲劳强度设计的重要内容之一。本文主要针对当前结构疲劳寿命预测中日益受到重视的能量方法,从疲劳损伤内应力及其塑性功的演化特征出发,并结合疲劳损伤能耗分析,来研究基于内应力塑性功的结构件疲劳寿命预测能量模型,并将其应用于汽轮机转子轮槽的疲劳裂纹萌生寿命预测研究。本文首先结合轮槽材料光滑试样在脉动载荷下的低周疲劳试验结果,采用Cottrell内应力理论(循环应力可分解为背应力和摩擦应力),从背应力/摩擦应力角度分析了轮槽材料的循环硬化/软化特征。基于疲劳损伤能耗结构,将循环过程中的塑性应变能分解为背应力塑性功和摩擦应力塑性功,本文进一步研究了循环加载下轮槽材料的背应力塑性功演化特征。结果表明:在一个循环内,背应力塑性功呈现涨落现象,其值仅占塑性应变能的一小部分,且与作用应变幅密切相关。上述疲劳过程中背应力塑性功的演化特征与循环加载下材料储能变化规律相一致。基于疲劳过程中轮槽材料的背应力塑性功演化特征,并结合疲劳损伤能耗分析,采用局部应变法,研究建立了一种以背应力塑性功为损伤参量的轮槽疲劳寿命预测能量模型。并将其应用于P8轮槽构件的疲劳裂纹萌生寿命预测。为了验证上述寿命预测能量模型的可靠性,本文开展了两种宽径比P8轮槽模拟件的低周疲劳试验,获得了不同载荷下轮槽构件最大应力集中齿根的疲劳裂纹萌生寿命(对应裂纹长度0.5 mm左右)。通过对比轮槽构件的预测寿命与试验寿命,证明了本文建立的轮槽构件寿命预测能量模型的预测精度完全满足工程需要(预测寿命与试验寿命比值总体位于1.5倍分散带以内)。此外,本文还将上述疲劳寿命预测能量模型与传统疲劳能量模型(基于塑性应变能和基于总应变能)的预测值进行了比较,结果表明:基于背应力塑性功的疲劳能量模型可显著提高疲劳寿命预测精度。由于该模型物理意义明确,因此,值得工程结构抗疲劳设计中重视。更多还原

【Abstract】 As one of the core components of a steam turbine,the rotor disc often suffers from fatigue failure due to the stress concentration in the tooth root of the wheel groove during service.Therefore,the prediction of the fatigue life of turbine rotor slots is one of the important contents in the design of turbine fatigue strength.In this paper,in view of the current structure of the energy is becoming more and more attention in the fatigue life prediction method,the fatigue damage evolution characteristics of stress and the plastic work,combined with the fatigue damage analysis of energy consumption,to study based on the stresses in the plastic work energy structure fatigue life prediction model,and applied to the steam turbine rotor wheel groove of fatigue crack initiation life prediction research.In this paper,based on the low cycle fatigue test results of smooth samples of wheel-groove materials under pulsating loads,Cottrell internal stress theory(cyclic stress can be decomposed into back stress and friction stress)was adopted to analyze the cyclic hardening/softening characteristics of wheel-groove materials from the perspective of back stress/friction stress.Based on the fatigue damage energy consumption structure,the plastic strain energy in the cyclic process is decomposed into back stress plastic work and friction stress plastic work.The results show that the plastic work of the back stress fluctuates in a cycle,and its value only accounts for a small part of the plastic strain energy,and is closely related to the strain amplitude.The evolution of plastic work of back stress in the fatigue process is consistent with the change law of material energy storage under cyclic loading.Based on the evolution characteristics of back stress plastic work of wheel groove materials during fatigue process,and combined with the analysis of fatigue damage energy consumption,a prediction energy model of wheel groove fatigue life with back stress plastic work as damage parameter was established by using local strain method.It is applied to the prediction of fatigue crack initiation life of P8 wheel groove components.In order to verify the reliability of the above life prediction energy model,this paper carried out two kinds of low-cycle fatigue tests of P8 wheel-groove simulator with width-diameter ratio,and obtained the fatigue crack initiation life of the tooth root with maximum stress concentration under different loads(corresponding to the crack length of about 0.5mm).By comparing the predicted life and test life of wheel-groove components,it is proved that the prediction accuracy of the prediction energy model of wheel-groove components established in this paper fully meets the engineering needs(the ratio of predicted life and test life is generally within 1.5 times of dispersion zone).In addition,the above fatigue life prediction energy model is compared with the traditional fatigue energy model(based on plastic strain energy and total strain energy).The results show that the fatigue energy model based on plastic work of back stress can significantly improve the accuracy of fatigue life prediction.Because the physical meaning of the model is clear,it is worth paying attention to in the anti-fatigue design of engineering structure.更多还原