【作者】 陈伟；

【导师】 陈明和；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2008， 硕士

【摘要】 TC21钛合金是一种新型的损伤容限型两相(α+β)钛合金,在高性能航空及航天飞行器结构件制造中有着巨大的应用前景。为了适应飞机损伤容限设计准则的要求,必须对其损伤容限性能进行研究。断裂韧性、裂纹扩展速率和裂纹扩展门槛值是表征损伤容限性能的重要指标,尤其是微观组织对损伤容限性能的影响,值得开展深入的研究。本文针对TC21钛合金断裂韧性、裂纹扩展速率及裂纹扩展门槛值的定量模型进行研究。主要工作如下:首先,根据断裂力学的基本理论,在线弹性条件下将四个常用的断裂判据之间的关系联系了起来。通过定量金相技术测量了不同热处理制度下得到的网篮组织的特征参数。在分析特定组织参数对TC21钛合金的断裂韧性影响的基础上,建立了TC21钛合金断裂韧性依赖于其网篮组织α相宽度、α束域宽度和材料参数的数学模型,将为先进钛合金的创研和工业应用提供宝贵的理论基础和设计借鉴。其次,由于疲劳寿命公式是构件损伤容限设计、疲劳寿命估算的主要依据,且可由疲劳裂纹扩展速率公式通过积分变换得到。因此,选择合适的疲劳裂纹扩展速率公式是对构件进行损伤容限设计的关键。针对TC21钛合金的裂纹扩展数据,选择能够同时描述裂纹扩展三个阶段的模型,采用最小二乘法和回归分析拟合得到模型中的参数,为该合金构件的损伤容限设计提供依据。最后,在损伤容限设计中另一个不可或缺的参数是裂纹扩展门槛值。各种各样的裂纹闭合机制,如:裂纹偏转引起的闭合效应、粗糙度引起的闭合效应、裂纹尾迹塑性引起的闭合效应及氧化物引起的闭合效应等,是影响裂纹扩展门槛值的重要因素。定量地研究与分析这些因素对TC21钛合金裂纹扩展门槛值的影响,具有重要的理论价值和工程意义。更多还原

【Abstract】 TC21 titanium alloy is a new kind ofα+βtwo-phase titanium alloy with great application prospect in the manufacture of aeronautic and astronautic structural parts. The damage tolerance behaviour of TC21 titanium alloy must be researched in order to meet the demand of damage tolerance design rules. Fracture toughness, crack growth rate and crack growth threshold are three important indexes characterizing damage tolerance, and especially the influence of microsturecure on damage tolerance is worth of deeply researching. Based on the above reason, this paper conducted the research of models of fracture toughness, crack growth rate and crack growth threshold of TC21 titanium alloy. The main contents are as follows:Firstly, according to the theory of fracture mechanics, the relationship between four Fracture Criteria was integrated under linear elasticity. The characteristic parameters of basketweave microstructure attended under different heat treatments were measured through quantitative metallography technique. On the basis of analyzing the influence of microstructure on the fracture toughness of TC21 titanium alloy, the mathematical model that the fracture toughness depended on the width ofαphase, the width ofαbundle and material constants was constructed. The model will provide valuable theory basis and design reference for the research of new kind titanium alloy and industrial application.Secondly, in order to develop damage tolerance design on components of TC21 titanium alloy and estimate its fatigue lifetime, the main basis is fatigue life formula, which can be derived from the integration of the fatigue crack growth rate. Thereby, it is the key to choose a proper fatigue crack growth rate formula to develop damage tolerance design on components. According to the fatigue crack growth data of TC21 titanium alloy, the model which can describe the three stages of fatigue crack growth was chosen and the parameters of the model were fitted using least square method and regression analysis. The model will provide reference for damage tolerance of TC21 titanium alloy components.Lastly, the crack growth threshold is another important index of damage tolerance design. The kinds of crack closure mechanisms due to crack deflection and branching, plastic wake, fracture-surface asperity and roughness, as well as oxide wedging were important factors influencing fagitue crack growth threshold value. Researching and analyzing quantificationally the influence of above factors on fagiture crack growth threshold have important theory value and engineer significance.更多还原