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)失效影响了航空航天、机车、汽车和核工业中以镁、铝、钛等轻金属合金为主的许多结构部件的安全性、可靠性、完好性和支撑成本。HCF行为的确定对于这些行业的安全和经济有效的设计来说变得极其重要。为了考虑短裂纹和长裂纹的扩展机理，已经提出了各种版本的疲劳寿命预测方法。然而，这些方法缺乏一种机械系统的方法来全面解决小裂纹/短裂纹的行为。本研究旨在进行实验和建模工作，以扩大对HCF区短裂纹行为的理解，从而为在HCF应用中利用微观和宏观疲劳损伤方法的统一开发基于物理的预测建模方法奠定基础。为此，将对试件进行高分辨率的扩展短裂纹附近的全场位移和应变场的测量，以获得裂纹张开、局部应力分布、塑性区和许多关键参数(短裂纹门槛值、裂纹尖端位移等)的全域机械场。可以获得。这些高分辨率的裂纹尖端附近变形和多个长度尺度上的裂纹扩展数据不仅提供了完整的力学领域，而且还提供了对整个试件寿命过程中疲劳裂纹扩展机制的深入了解。将对实验数据进行广泛的分析，以确定疲劳裂纹是如何沿不同的长度尺度演化的，以及这些控制参数将如何在短裂纹扩展力学的驱动力中发挥作用，从而导致建立考虑短裂纹和长裂纹扩展行为的统一的裂纹扩展模型。对实验数据的深入分析将导致基于对HCF机制下短裂纹扩展机制的基本理解，开发出更可靠的、精度更高的疲劳损伤模型。系统地扩展了PI最近的建模研究，并结合数值建模技术，开发了一种新的统一建模方法，以合并短、长裂纹损伤力学方法。这项研究计划有可能在航空航天、汽车、国防和生物机械行业的结构部件的HCF设计方面提供重大改进。开发的模型(S)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。研究成果和成果将通过同行评议期刊和学术会议上的出版物广泛传播。这项研究还将致力于与其他机构的研究人员合作，培训一批这一领域的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.