梯度钛合金裂纹扩展速率测试及梯度对扩展寿命影响
Fatigue crack growth rate determination of graded titanium alloys and the influence of gradient for propagation life

为明确梯度材料中裂纹扩展速率分布情况，对含裂纹TC11-TC4以及TA15-TA2两种组合梯度钛合金进行标准三点弯疲劳试验。试验结果表明：梯度结构中不同部位的相同组分扩展性能相同，给出了4种3D打印组分钛合金的Paris公式；梯度材料组分弹性模量的变化会改变裂纹尖端应力强度因子，对位于模量较低一侧的裂纹扩展有抑制作用；过渡层影响厚度范围内裂纹扩展速率介于两种组分之间且连续过渡，表明梯度材料可以消除异种材料连接的界面效应，提出基于组分材料体积分量的混合率描述梯度层中扩展性能的分布规律；恒定载荷试验中仅扩展方向不同情况下寿命有显著差别，验证了合理安排梯度参数可提高结构出现裂纹后的生存能力，其中扩展性能以及模量的变化分布对扩展寿命均有影响。 To make sense of the crack growth rate distribution in graded material, a standard three-point bending fatigue test was performed on two groups of cracked graded titanium alloys TC11-TC4 and TA15-TA2. Test results show that the same components in different parts of graded structure shear an identical propagation property and the Paris formulas of the four kinds of 3D printing titanium alloy have been determined. The variation distribution of elastic modulus influences the stress intensity factor and inhibits the propagation of crack in the lower modulus side. During influence thickness of transition layer, propagation rate is between that of the two components and varies continuously, proving that gradient is able to eliminate the interface effect in the connection of dissimilar materials. A mixing law based on volume rate has been proposed to describe the distribution of crack propagation rate. In the test under constant periodic load, there was a remarkable difference in the propagation life of specimens only propagated along different directions. It means damage tolerance in graded structures can be improved with a reasonable arrangement of the gradient. The variation distribution of modulus and fatigue property both influence the propagation lives. 中央高校基本科研业务费专项资金（NS2016003）；机械结构力学及控制国家重点实验室（南京航空航天大学）自主研究课题（0213G01）