基于能量耗散镁合金非均质接头微区疲劳裂纹扩展机制及多尺度分析与表征

Magnesium alloys have broad application prospects in “the land, the sea, the air and the aerospace fields”, with the advantages of light-weight, high-strength and easy recovery. But their characteristics of low melting point and fast heat conduction make the heterogeneity characteristics of the joint more obvious, and lead to complicated deformation behavior, which limits the safe use of magnesium alloy components. This project studies the fatigue crack propagation mechanism of magnesium alloy welded joint with heterogeneous organization, and multi-scale analysis and characterization. In the project, the deformation behavior of the crack tip in welded joint micro heterogeneity (grain size, grain boundarycond phase particles, dislocation/twin, etc.) area will be investigated, and the cumulative damage and energy evolution process will be modeled. Based on the micro/nano mechanics method, it measures the micro zone mechanical properties evolution regularity of the crack tip, and explores the characterization of the fatigue crack propagation mechanism and the energy dissipation law. Meanwhile, it discusses the effect of defects (porosity, inclusions, etc.) on the fatigue crack tip deformation behavior and the energy dissipation evolution law. The multi-scale fatigue crack growth behavior and the residual life assessment method will be studied. Research results will enrich the fatigue fracture theory of magnesium alloy components, and have large scientific significance and application value for the reliability analysis of their use.

镁合金具有轻质、高强、可循环再生等优点，在“陆、海、空、天”等领域有着广泛的应用前景。但因其熔点低、导热快等特点，使其焊接接头的非均质特征更加明显，加载时的断裂行为更加复杂，限制了镁合金构件的安全使用。本项目提出利用能量耗散理论，研究镁合金焊接接头非均质组织的疲劳裂纹扩展机制及多尺度分析与表征。分析裂纹尖端在焊接接头非均质微区（晶粒尺寸、晶界/第二相粒子、位错/孪晶等）的变形行为，建立疲劳裂纹尖端微区累积损伤与能量演化模型。采用微/纳力学方法，测试疲劳裂纹尖端的微区力学性能演变规律，探索疲劳裂纹扩展机制及能量耗散规律的表征。同时探讨缺陷（气孔、夹杂等）对疲劳裂纹尖端变形行为及能量耗散演变规律的影响。探索多尺度下的疲劳裂纹扩展行为及剩余寿命评定方法。研究成果将丰富镁合金构件的疲劳断裂理论，对构件的使用可靠性能评价具有较大科学意义和应用价值。

镁合金具有熔点低、导热快等物理特性，其焊接后接头的非均质特征更加明显，导致其承载后的断裂行为更加复杂，使镁合金构件的安全使用受到了限制。本项目利用能量耗散理论，研究了镁合金焊接接头非均质组织的疲劳裂纹萌生与扩展机制；并对镁合金及其焊接接头进行了疲劳寿命评定。项目对镁合金焊接接头在承受循环载荷作用下的变形了进行测试分析，建立了循环变形曲线与变形及断裂过程的本构关系；探讨了疲劳裂纹扩展过程中的能量耗散机制，探索裂纹萌生、扩展过程中的能量演变与不可逆损伤的关系，建立了温度、声能演变速率与尖端应力强度因子之间的联系；基于镁合金焊接接头的非均质特性，对微裂纹萌生、扩展、断裂失效过程中的能量耗散进行分析，建立微观与宏观裂纹尖端变形、能量耗散之间的关系，对镁合金疲劳裂纹扩展变形机制进行多尺度分析与表征；基于循环载荷下的变形非均质特性，利用循环载荷下的变形、能量耗散量、微观组织演变等特征参数，对镁合金及其焊接接头疲劳裂纹萌生与扩展寿命进行了评定。研究成果将丰富镁合金构件的疲劳断裂理论，对构件的使用可靠性能评价具有较大科学意义和应用价值。