An integrated approach for characterization and unification of short and long crack growth models for high cycle fatigue behavior of lightweight metals

高周疲劳（HCF）失效影响航空航天机车、汽车和核工业中主要由镁、铝和钛等轻金属合金制成的许多结构部件的安全性、可靠性、完好性和支持成本。HCF行为的确定对于这些行业中的安全和成本效益设计变得极其重要。已经提出了各种版本的疲劳寿命预测方法，以考虑短裂纹和长裂纹扩展机理。然而，这些方法缺乏机械系统的方法来充分解决小/短裂纹的行为。本研究的目的是进行实验和建模工作所需的扩展的短裂纹行为的理解在HCF制度，从而它奠定了基础的物理为基础的预测建模方法的发展，利用统一的微观和宏观疲劳损伤的方法在HCF应用。因此，将进行实验以测量试样的生长短裂纹附近的高分辨率全场位移场和应变场，使得诸如裂纹开口、局部应力分布、塑性区和许多关键参数（短裂纹阈值、裂纹尖端位移等）的力学场的全域被测量。可以得到这种高分辨率的裂纹尖端附近的变形和裂纹扩展数据在多个长度尺度上提供不仅是一个完整的力学领域，而且还提供洞察疲劳裂纹扩展机制在整个试样的寿命。将对实验数据进行广泛分析，以确定疲劳裂纹如何沿沿着各种长度尺度演变，以及这些控制参数如何在短裂纹扩展力学的驱动力中发挥作用，从而导致考虑到短裂纹和长裂纹扩展行为的统一裂纹扩展模型的发展。*深入分析实验数据将导致更可靠的疲劳损伤模型的发展，提高精度的基础上，提高基本的理解短裂纹扩展力学在HCF政权。PI的最近的建模研究的系统扩展将被用于沿着与数值建模技术，以开发一个新的统一的建模方法，合并短长裂纹损伤力学方法。* 该研究计划有可能为航空航天，汽车，国防和生物机械行业的结构部件的HCF设计提供显着改进。开发的模型将影响更多行业的设计实践，并导致基于模型的方法来设计安全和经济的产品。研究结果和成果将通过在同行评审期刊和学术会议上发表的出版物广泛传播。该研究还将旨在与其他机构的研究人员合作，并培训一批该领域的HPQ。

High cycle fatigue (HCF) failures affect safety, reliability, readiness and support cost for many structural components mainly made of light metallic alloys such as magnesium, aluminum, and titanium in the aerospace locomotive, automotive, and nuclear industries. Determination of HCF behavior becomes extremely important for safe and cost-effective designs in those industries. Various versions of fatigue life prediction approaches have been proposed to take into account short and long crack propagation mechanics. However, those methods lacked a mechanically systematic approach to fully address the behavior of small/short cracks.***This research aims to perform experimental and modeling works needed to expand understanding of short crack behavior in HCF regime, thus it lays the foundation for the development of physics based predictive modeling methods utilizing a unification of micro and macro fatigue damage approaches in HCF applications. Therefore, experiments will be conducted to measure high resolution full-field displacement and strain fields in the vicinity of a growing short crack for test specimens so that a full domain of mechanical fields such as crack openings, local stress distribution, plastic zone and many critical parameters (short crack thresholds, displacement at crack tip, etc.) can be obtained. Such high resolution near crack tip deformation and crack growth data at multiple length scales provide not only a full field of mechanics, but also give insights into fatigue crack growth mechanisms throughout the specimen lifetime. Experimental data will be extensively analyzed to determine how fatigue cracks evolve along various length scales and how those controlling parameters will play a role in the driving force of short crack growth mechanics, thus leading to the development of a unified crack growth model taking into account short and long crack growth behaviors.***In-depth analysis of experimental data will lead to development of more reliable fatigue damage models with increased accuracy based on improved fundamental understanding of short crack growth mechanics in HCF regime. The systematic extension of the PI's recent modeling study will be used along with numerical modeling techniques to develop a new unified modeling approach to merge short long crack damage mechanics approaches. ***This research program has the potential to offer significant improvement in HCF design of structural components in aerospace, automotive, defense and biomechanical industries. The developed model(s) will impact design practices in many more industries and lead to model-based approaches to design safe and economical products. Research findings and results will be disseminated broadly through publications in peer-reviewed journals and academic conferences. The research will also aim to collaboration with researchers from other institutions and train a group of HPQs in this field.