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

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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.