Microstructure-Sensitive Investigations of Fatigue of Magnesium Alloys

材料的疲劳是一个重要的工程科学课题，因为它是在从航空航天到汽车、船舶和工业领域的应用中观察到的机械失效的主要原因之一。该奖项支持基础研究，以提供了解疲劳损伤孵化，启动和演变所需的知识。在这项研究中特别感兴趣的是镁的情况，因为它的合金具有可以导致重量减轻和节能方面的显着进步的特性。 因此，这项研究的结果预计将有利于美国经济和社会，因为它有可能改善这种非常轻的金属合金的使用。这项研究的更广泛影响针对学术代表性不足的群体参与STEM研究和培训。具体而言，费城社区学院的学生是该市最大的公共机构，人口以少数民族为主，他们将被选中与调查小组一起进行研究，利用全面的推广计划，重点是使用多尺度力学和基于模拟的工程。该奖项支持的研究方法是基于使用多尺度实验力学与基于物理的计算建模相结合。 具体而言，识别可靠的疲劳损伤的前兆的问题是通过执行实验的规模在晶粒水平的信息是重要的，并链接到机械领域，如变形，以及微观结构参数和它们的演变，包括孪晶，脱孪晶，位错活动，开裂和它们的相互作用。在晶粒尺度上的实验测量将包括全场光学和声学无损数据集，这些数据集可以与宏观尺度上的机械行为和类似的无损测量直接相关。这样的实验信息可以提供一个微观结构敏感的解释宏观观察到的疲劳行为的影响，包括塑性各向异性，拉压不对称和变形条带。实验信息也将被用来形成新的计算程序，能够模拟疲劳引起的材料微观结构的变化。具体而言，分子动力学将被用来研究在单晶水平上的孪生成核和增厚。此外，晶体塑性模拟将用于模拟空间分辨的孪晶及其与滑移系和晶界的相互作用，以验证在镁多晶体中进行的观察。此外，晶体塑性和连续相场模型将被用来模拟实验观察到的和疲劳引起的局部应变的形成，这是相关的损伤启动。

Fatigue of materials is an important engineering science topic since it is one of the predominant causes of mechanical failure observed in applications ranging from aerospace to automotive, marine and industrial fields. This award supports fundamental research to provide needed knowledge to understand fatigue damage incubation, initiation and evolution. Of particular interest in this research is the case of magnesium since its alloys have properties that could lead to significant advances in weight reduction and energy savings. Therefore, results of this research are expected to benefit the U.S. economy and society as it has the potential to improve the use of this very light metal alloys. The broader impact of this research targets the participation of academically underrepresented groups in STEM research and training. Specifically, students in the Community College of Philadelphia, which is the largest public institution in the city with a predominantly minority-based population, will be selected to conduct research with the investigators' group leveraging a comprehensive outreach plan focusing on the use of multiscale mechanics and simulation-based engineering. The research approach supported by this award is based on the use of multiscale experimental mechanics coupled with physics-based computational modeling. Specifically, the problem of identifying reliable precursors to fatigue damage is addressed by performing experiments at a scale at which grain level information is important and is linked to mechanical fields such as deformation, as well as to microstructural parameters and their evolution including twinning-detwinning, dislocation activity, cracking and their interactions. Experimental measurements at the grain scale will include full field optical as well as acoustic nondestructive datasets, which can be directly correlated with the mechanical behavior and similar nondestructive measurements made at the macroscale. Such experimental information could provide a microstructure-sensitive explanation of macroscopically observed fatigue behavior effects including plastic anisotropy, tension-compression asymmetry and deformation banding. The experimental information will be also used to form novel computational procedures capable to model fatigue-induced changes in the material microstructure. Specifically, molecular dynamics will be used to study twin nucleation and thickening at the single crystal level. Furthermore, crystal plasticity simulations will be used to simulate spatially resolved twins and their interactions with slip systems and grain boundaries to validate observations made in magnesium polycrystals. Furthermore, crystal plasticity and continuum phase field models will be used to model experimentally observed and fatigue-induced localized strain formations which are related to damage initiation.