含不连续界面钛合金扩散连接层合板的疲劳裂纹扩展减缓机理及寿命预测方法研究

Diffusion-bonded titanium alloy laminates with discontinuous interfaces are newly developed long-life metallic structures comprising macroscopic interface defects. As for the fatigue-crack-growth-retardation effect of discontinuous interfaces, marking load will be firstly developed, which is subsequently used in surface crack growth tests of single-layer TC4 titanium alloy plates and diffusion-bonded laminates with continuous/discontinuous interfaces. With quantitative fractography, complete information on crack growth can be obtained. Secondly, the influence of interlayer on crack growth will be illustrated through crack growth behavior analysis, microstructure study and in situ observation of fatigue crack growth, based on which, the influence of residual stress will be separated and an intrinsic crack growth rate model is to be developed for the interlayer. Thirdly, a multi-scale study will be performed on the crack growth behavior of the diffusion-bonded titanium alloy laminate with discontinuous interfaces. Both theoretical and numerical methods will be employed to explore the reason for the crack growth retardation around the boundary of discontinuous interfaces, and the mechanism of discontinuous interface-related crack growth retardation is to be revealed. Finally, a crack-growth-life-prediction approach will be developed for the diffusion-bonded laminate with discontinuous interfaces. The effect of multiple design parameters on fatigue life will also be discussed. This research aims to provide damage tolerance analysis method for diffusion-bonded titanium alloy laminated structures, and to lay a theoretical foundation for the optimal design of diffusion-bonded titanium alloy laminates to meet the design requirements of light weight and long life.

界面不连续的钛合金扩散连接层合板是一种含宏观界面缺陷的新型长寿命结构。针对不连续界面的疲劳裂纹扩展减缓效应，本研究拟首先构建标识载荷方法，进行TC4钛合金单层板、扩散连接层合板和含不连续界面的扩散连接层合板的表面裂纹扩展试验，通过断口判读，获得裂纹扩展全过程信息。其次，通过裂纹扩展行为分析、材料微结构研究及疲劳裂纹扩展原位观测，阐明界面层对裂纹扩展的影响。在此基础上，剥离残余应力的影响，建立界面层本征裂纹扩展速率模型。第三，进行含不连续界面扩散连接层合板裂纹扩展行为的多尺度研究，采用理论分析和数值模拟方法，分析不连续界面边界附近裂纹扩展速率降低的原因，阐明不连续界面减缓裂纹扩展的机理。最后，建立含不连续界面扩散连接层合板的裂纹扩展寿命预测方法，探讨多种设计参数对寿命的影响。此研究旨在为钛合金扩散连接层合结构的损伤容限分析提供方法，为其优化设计奠定理论基础，以满足低重量、长寿命的设计要求。

含不连续界面钛合金扩散连接层合板是一种新型结构，为阐明其损伤容限特性。本项目开展了界面层对TC4钛合金DB层合板裂纹扩展影响、不连续界面的裂纹扩展减缓机理和含不连续界面钛合金DB层合板的裂纹扩展寿命预测方法研究，提出了能再现三维复杂裂纹扩展全过程信息的标识载荷参数确定方法，发展了标识载荷技术，再现了扩散连接层合板和含不连续界面的扩散连接层合板的裂纹扩展全过程信息；阐明了扩散连接界面层对裂纹扩展行为的影响规律，分析给出了界面层裂纹扩展速率公式；阐明了不连续界面附近的三维裂纹扩展行为，揭示了不连续界面减缓裂纹扩展的机理；引入T应力修正，构建了考虑裂纹约束的裂纹扩展速率统一公式，建立了含不连续界面的裂纹扩展寿命分析方法，探讨了设计参数对裂纹扩展寿命的影响。.本项目发现了不连续界面疲劳裂纹扩展减缓效应、揭示了减缓机理，建立了裂纹扩展寿命预测方法，为含不连续界面的扩散连接层合板优化设计奠定了理论基础。