Fatigue and deformation aspects of lightweight materials

在当今迅速演变的能源危机中，提高燃油效率和减少温室气体排放是汽车和航空航天工业需要解决的首要问题和紧迫问题。轻量化是最重要的策略之一，重量每减少10%，燃油效率就会提高6.6%至8%。镁是最轻的结构金属——它比钢轻75%，比铝轻三分之一。它现在被视为汽车和航空航天领域的战略轻质材料。然而，镁合金的广泛应用存在许多问题，包括疲劳和可靠性、焊接和连接、耐腐蚀性和成形性。在循环变形过程中孪晶和去孪晶是如何发生的，以及变形镁合金的各向异性和强拉压屈服不对称性是否可以减少或消除。申请研究的目标是解决这些关键问题和障碍，建立在申请人在该领域广泛和开创性的研究经验和知识的基础上，并发展对镁合金和其他类型轻质材料的疲劳和断裂的基本理解。具体而言，将审查以下主题：i)将阐明和模拟变形镁合金的潜在疲劳变形和孪生-失孪生机制，ii)将使用一种独特的高温x射线衍射仪分析和评估织构和残余应力，该衍射仪允许现场测量温度的函数，iii)将检查焊接和保护涂层对抗疲劳变形的影响。Iv)将开发新的处理方法和模型来减弱纹理和降低各向异性。这些项目将提高对镁合金长期性能的基本理解，为进一步开发用于航空航天、汽车和电子应用的轻质合金提供基础，并培养工业、学术界和政府实验室急需的博士和硕士学生。

In today's rapidly evolving energy crisis, improvements in fuel efficiency and reductions in greenhouse gas emissions are prime concerns and urgent topics to be solved in the automotive and aerospace industries. Lightweighting is one of the most important strategies, with every 10% reduction in weight leading to a 6.6% to 8% increase in fuel efficiency. Magnesium is the lightest of structural metals - it weighs 75% less than steel and is about one third lighter than aluminum. It is now regarded as a strategic lightweight material in the automotive and aerospace sector. However, there exist a number of issues that severely limit the widespread applications of magnesium alloys, including fatigue and reliability, welding and joining, corrosion resistance, and formability. Other issues remain as to how the twinning and detwinning occur during cyclic deformation, and if the anisotropy and strong tension-compression yield asymmetry in wrought magnesium alloys can be reduced or eliminated. The objectives of the proposed research are to address these critical issues and barriers building upon the applicant's extensive and pioneering research experience and knowledge in this area, and develop a fundamental understanding of fatigue and fracture of magnesium alloys and other types of lightweight materials. Specifically, the following topics will be examined: i) the underlying fatigue deformation and twinning-detwinning mechanisms in wrought magnesium alloys will be elucidated and modeled, ii) the texture and residual stresses will be analyzed and evaluated using a unique high-temperature X-ray diffractometer which permits in-situ measurements as a function of temperatures, iii) the effect of welding and protective coatings on fatigue deformation resistance will be examined, iv) new processing approach and models will be developed to weaken textures and reduce anisotropy. These projects will improve fundamental understanding of long-term performance in magnesium alloys, provide a basis for further development of lightweight alloys for aerospace, automotive and electronic applications, and lead to the training of Ph.D. and master's students who are in high demand from industry, academe, and government laboratories.