【作者】 李源；

【导师】 韩旭；

【作者基本信息】 湖南大学 ， 机械工程， 2013， 博士

【摘要】 通过传统的疲劳试验方法得到准确的高周疲劳参数，往往耗费大量的费用和时间。若干年来，探讨缩短试验时间、减少试验成本的快速预测高周疲劳性能的理论和实验方法，一直是研究人员关注的热点问题。能量方法是快速预测疲劳性能的一种重要手段，但现有方法在高周疲劳耗散能准确计算、宏观耗散能与内部微结构演化关系及储能测量等方面仍存在很多瓶颈和难点问题。为此，本文力求在基于耗散能的快速预测金属疲劳性能方法上做出一些较有价值的尝试和探索。首先针对高周疲劳过程中的微热变化，提出一种疲劳耗散能计算方法；其次，研究疲劳过程中宏观耗散能与内部微结构演化关系；最后，构建基于稳态耗散能和初始瞬态耗散能的疲劳性能快速预测方法。主要研究工作如下：（1）提出一种基于红外热像技术的疲劳耗散能计算方法。在热力学框架下，基于薄板假设，建立疲劳载荷下的材料的热传导方程。运用非接触式的红外热像技术和电液伺服疲劳实验机，构建一套观测疲劳微热变化的红外疲劳实验系统。通过设置参考试样和隔热装置以降低环境噪声的影响，分离出导致局部温升变化的耗散源、热弹性源和热辐射源，并推导出单循环疲劳耗散能计算公式及检测门限，最后通过实例验证耗散能计算方法的可行性和准确性。（2）通过不同载荷历程下的疲劳耗散能实验，验证了宏观疲劳耗散能可作为表征材料内部微结构演化的标识。基于疲劳过程中的能量平衡方程，推导出初始瞬态和稳定能量耗散阶段疲劳耗散能、塑性应变能和储能的理论计算方法，分析弹性迟滞区间内耗散能和塑性应变能的变化规律。通过全面对比分析拉伸损伤和疲劳损伤前后耗散能变化规律，可知宏观疲劳耗散能与内部微结构演化密切相关，可作为疲劳损伤评估的一个敏感指标，并应用于等变幅疲劳损伤实时监测中。（3）提出一种基于稳态耗散能的疲劳性能参数快速预测方法。当经历一定的疲劳寿命循环次数后，材料达到稳态能量耗散阶段后，内部微观结构演化达到准平衡态过程，单循环疲劳耗散能基本保持恒定。通过拟合对应不同疲劳载荷水平的稳态耗散能，提出预测疲劳极限的单线法和双线法。同时，拟合出疲劳耗散能-寿命曲线与应力-寿命曲线相同的规律，且耗散能-寿命曲线能够表征疲劳寿命的离散分布。推导出基于稳态耗散能的Miner累积损伤模型，将其用于预测剩余寿命预测和载荷次序效应研究中，所得结果与实验数据一致，具有较好的精度。（4）研究基于初始瞬态耗散能的高周超高周疲劳性能参数预测方法。在疲劳初始瞬态能量耗散阶段，耗散能迅速增加并逐渐稳定，对应于材料的初始微塑性效应。通过实时监测不同疲劳载荷作用下初始瞬态耗散能变化规律，研究基于初始累积塑性耗散能的疲劳性能参数预测方法，所得疲劳极限与稳态耗散能方法及实验确定的疲劳极限相近；拟合的初始塑性耗散能-寿命曲线也呈现出与应力-寿命和稳态耗散能-寿命曲线相同的规律。最后，基于安定理论和Dang-Van疲劳准则，探索基于初始累积耗散能的超高周疲劳极限预测方法，具有一定的合理性。更多还原

【Abstract】 The conventional fatigue tests need lots of cost and time to obtain the accurate high-cycle fatigue parameters. Therefore, the theoretical and experimental rapid predictionmethods became the focus problem of the researchers. Energy theory is an importantmethod for rapid prediction of fatigue properties. However, there are many bottlenecks anddifficult problems in the existing methods, such as the computational accuracy of the high-cycle fatigue dissipated energy, the relationship between the macro dissipated energy andthe internal microstructure evolution and the stored energy measurements, etc. To this end,this dissertation aims to establish some valuable method to predict the fatigue properties inbasis of dissipation energy computation. First, a dissipated energy computation method wasproposed for the small thermal changes during high-cycle fatigue process. Secondly, therelationship between dissipation energy in macroscopic scale and the internal micro-structure evolution in microscopic scale was studied during fatigue process. Finally, tworapid prediction methods of high-cycle fatigue properties were established based on stable-state dissipated energy and initial transient dissipated energy. The major research works ofthis dissertation are as follows:(1) A fatigue dissipated energy computational technique for fatigue loadings based oninfrared thermal imaging technology is developed. In the thermodynamics framework, aheat conduction equation was established under fatigue loadings based on thin-planeassumption. An infrared fatigue test system was set to observe the small thermal changesusing the non-contact infrared thermal imaging technology and fatigue test machine. In thesystem, the environmental noise was reduced by setting the reference specimen and thethermal insulation equipment. The dissipation source, thermo-elastic source and thermalradiation source causing local temperature changes were isolated. A dissipated energy per-cycle computational equation then derived from the dissipation source, and the detectionthreshold was determined by dissipated energy measurements. The feasibility and accuracyof the dissipated energy computational technique was finally verified by a fatigue test.(2) Through fatigue dissipated energy measurements under different load history, themacro-dissipated energy can be used as a marker of the internal microstructure evolution.Based on energy balance equation in fatigue process, the dissipated energy, plastic strainenergy and stored energy per-cycle theoretical calculation method were developed underthe initial transient and steady state stages. The variation of dissipated energy and plastic strain energy were analyzed in elastic hysteresis domain. Through a comprehensivecomparative analysis of dissipated energy variations during tensile damage, fatigue damagethe results show that the fatigue dissipated energy is closed related with the internalmicrostructure evolution, and it could be used as a sensitive indicator to fatigue damageassessment. Fially, the constant and variable amplitude fatigue damage was in-stiumonitored by fatigue dissipated energy.(3) Based on the steady state dissipated energy, a rapid prediction method for fatigueproperties was developed. After a certain number of fatigue lifetime cycles, the materialreaches a steady state dissipation energy stage, and the internal microstructure evolutionreached a quasi-equilibrium state. The dissipated energy was remained constant duringfatigue process. One curve method and dual curve method of fatigue limit predictionwere proposed by fitting dissipated energy under different levels of fatigue loadings insteady-state stage. Meanwhile, the dissipated energy versus lifetime curves derived showsthe same rule with the stress versus lifetime curve, and the dissipated energy versus lifetimecurve was also characterized the discrete distribution of fatigue lifetime. A Miner’scumulative damage model was deduced from dissipated energy measurements. The modelwas used to predict the residual lifetime and to study the load sequence effects. The resultswere consistent with the experimental data with good accracy.(4) A high-cycle and very high-cycle fatigue lifetime prediction was studiedconsidering with initial micro-plasticity effects. The dissipated energy per-cycle wasrapidly increasing and then gradually stabilized, corresponding to the initial micro-plasticeffects at the initial transient dissipated energy stage. Variations of the initial dissipatedenergy were monitored under different levels of fatigue loadings at the initial transient andsteady state stages. A new prediction method was studied based on the initial plasticdissipated energy. The fatigue limit according to this method was close to the one predictedby the steady-state dissipated method and the experimental test. The initial plasticdissipated energy versus lifetime curve fitting was also similar to stress versus lifetime andsteady-state dissipated energy versus lifetime curve. Based on the shakedown theory ofplasticity and Dang-Van fatigue criteria, a new fatigue limit prediction method of veryhigh-cycle fatigue was studied based on the initial cumulative dissipated energy. Theexperimental results proved that the method has certain rationality.更多还原