Collaborative Research: In situ Diffraction and Cohesive-Zone Studies of the Fatigue-Crack-Growth Behavior in Mg Alloys

非技术摘要：镁合金在汽车和航空航天工业中作为结构部件的加速采用是由其低密度、高强度重量比和高比刚度的独特性能驱动的。然而，镁合金的疲劳性能和相关的失效机制尚未得到很好的表征，这严重限制了这些轻质合金的技术可行性。该奖项支持基础研究，以提供对最终决定镁合金疲劳寿命的失效过程的微观结构水平的理解。该研究将为智能设计先进的轻质结构合金铺平道路，提高疲劳寿命。从更广泛的意义上说，这项研究将影响航空航天和汽车工业，并将有助于美国提高其制造业的竞争力。独特的实验和建模工具将有助于丰富田纳西大学和伊利诺伊大学目前的力学和材料课程。一个演示工具包将暴露在这两所大学的高中生断裂和故障的概念，以及如何裂纹停止机制可以引入到提高fatigue lifes.Technical摘要：本研究的目标是耦合镁合金的疲劳裂纹扩展研究，与原位无损测量和微观力学建模调查，这将建立微观故障过程和宏观疲劳裂纹扩展性能之间的连接。主要目的是确定周围的塑性和裂纹尖端过程区的镁合金的疲劳裂纹扩展阻力的作用。在周围的塑性区，在现场中子衍射测量和高能同步辐射X射线衍射技术将提供前所未有的信息塑性各向异性，双极性，流动的非正常性，在任意应力多轴下的镁合金的织构演变。在过程区，这是无法访问的实验测量，一种新的非线性场投影计划将被用来逆重建的凝聚力区的法律，唯一的疲劳裂纹生长从周围的变形场，由衍射实验测量。通过在颗粒间和颗粒内尺度上将自上而下的应力分析与自下而上的破坏机制联系起来，这一基础研究可以导致基于微观结构理解的预测模型，材料科学家可以利用这些模型来提高先进结构合金的疲劳寿命。该奖项反映了NSF的法定使命，并通过利用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

Non-Technical Abstract: The accelerated adoption of magnesium alloys as structural components in the automobile and aerospace industry is driven by their unique properties of low density, high strength-to-weight ratio, and high specific stiffness. However, the fatigue properties of magnesium alloys and associated failure mechanisms have not been well-characterized, which severely limits the technological viability of these lightweight alloys. This award supports the fundamental research to provide the microstructural-level understanding of the failure processes, which ultimately govern the fatigue life of magnesium alloys. The research will pave the way towards the intelligent design of advanced, lightweight structural alloys with the improved fatigue life. In the broader sense, this research will impact the aerospace and automotive industries and would help U.S. improve its manufacturing competitiveness. The unique experimental and modeling tools will help enrich the current course curriculum on mechanics and materials at both the University of Tennessee and University of Illinois. A demonstrative toolkit will expose high school students at both universities to concepts of fracture and failure, and how crack stopping mechanisms can be introduced to improve fatigue life.Technical Abstract:The goal of this research is to couple fatigue-crack-growth studies of magnesium alloys, with in situ nondestructive measurements and micromechanical modeling investigations, which will establish the connection between microscopic failure processes and macroscopic fatigue-crack-growth properties. The primary objective is to identify the roles of the surrounding plasticity and crack-tip process zones in the resistance to fatigue-crack growth of magnesium alloys. Within the surrounding plastic zone, in situ neutron-diffraction measurements and high-energy synchrotron X-ray diffraction techniques will provide the unprecedented information on plastic anisotropy, twin polarity, flow non-normality, and texture evolution in magnesium alloys under the arbitrary stress multiaxiality. Within the process zone, which is inaccessible to experimental measurements, a novel nonlinear field projection scheme will be used to inversely reconstruct the cohesive zone laws for fatigue-crack growth uniquely from the surrounding deformation fields that are measured by the diffraction experiments. By linking top-down stress analyses with bottom-up failure mechanisms at inter- and intra-granular scales, this fundamental research can lead to predictive models based on microstructural understanding with which materials scientists can utilize to improve the fatigue life of advanced structural alloys.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.