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TY  - THES
AU  - Paysan, Florian
TI  - Über die bruchmechanische Charakterisierung mikroskopischer Ermüdungsrissphänomene in AA2024-T3 mittels Roboter-gestützter HR-DIC Mikroskopie
PB  - Rheinisch-Westfälische Technische Hochschule Aachen
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2025-04934
SP  - XVI, 167 Seiten : Illustrationen
PY  - 2025
N1  - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2025
AB  - The aluminum alloy AA2024-T3 is employed in the outer skin of aircraft fuselages. Despite decades of research, the damage tolerance and fatigue crack behavior of AA2024-T3 in thin sheets is not yet fully understood. For a deterministic life prediction of aviation components, it is imperative to understand the underlying fatigue crack phenomena throughout the entire crack growth process and their interaction with the material microstructure. This is complicated due to the microscopic scale of the phenomena. Furthermore, phenomena such as crack branching, crack deflection, or crack closure occur in a time-limited manner and can thus only be studied in terms of their impact on crack progression behavior or correlated to the da/dN − ∆K curve through time-series data. This work introduces an innovative method for conducting crack propagation experiments utilizing an automated, robot-assisted, high-resolution digital image correlation (HR-DIC) measurement system. A robotic arm moves a microscope across the sample surface to collect precise DIC data during crack growth. With this experimental setup, the crack propagation behavior of AA2024-T3 under various load ratios R ∈ 0.1, 0.3, 0.5 is investigated. Each experiment generates approximately 350 GB of data—a significant advancement over the conventional method according to ASTM E647-15, which is limited to the a − N curve. Analysing the extensive data sets requires the adoption of new, advanced data- and algorithmbased evaluation methods. In this context, the study develops novel HR-DIC-based crack propagation curves, which relate the crack growth rate (da/dN) to the cyclic crack tip stress intensity (∆Kcp). The stress intensity factor ∆Kcp is determined using the interaction integral J(a,b) based on HR-DIC displacement field data. Here, influencing factors that affect the results of the line integral, especially with HR-DIC data, are identified. Moreover, the work characterizes local crack closure behavior and compares the experimental results to those from 3D finite element (FE) crack propagation simulations. The excellent agreement enables the identification of plasticity-induced crack closure as the dominant crack closure mechanism and the derivation of new evaluation strategies for characterizing crack closure. Finally, the study demonstrates that fatigue crack growth in L-T orientation progresses slower than in T-L orientation, attributable to a higher frequency of crack deflections and branching in L-T orientation. The effect of crack deflections or branching can be correlated to characteristics in the HR-DIC-based crack growth curves, elucidating the link between multi-scale data. Consequently, this work makes a significant contribution to the digitalization of fracture mechanics.
LB  - PUB:(DE-HGF)11
UR  - https://publications.rwth-aachen.de/record/1012234
ER  -