High‐stress fatigue crack propagation in thin AA2024‐T3 sheet material

Abstract

Fatigue crack growth in 1.6-mm-thick sheets of aluminium alloy AA2024-T3 was investigated under very high-stress conditions using 950-mm-wide middle tension (MT) specimens. Experiments were conducted by applying uniaxial load ratios R (0.1, 0.3 and 0.5) with the maximum nominal stress of 120 MPa following conditions relevant for aircraft fuselage structures. The experiments were conducted with digital image correlation to determine loading conditions acting on the crack tip. Stable crack growth rates of up to da/dN > 4 mm/cycle and ΔK > 100 MPa√m were reached, and final crack lengths 2a > 500 mm were obtained. High-stress intensity factors cause plastic zone sizes that extend up to approximately 100 mm from the crack tip. The da/dN-ΔK data obtained in this study provide crucial information about the fatigue crack growth and damage tolerance of very long cracks under high-stress conditions in thin lightweight structures.

Automatic detection of fatigue crack paths using digital image correlation and convolutional neural networks

“…In contrast to the previous data set, the spatial resolution of the DIC system was about 4.8 mm (1 pixel = 0.32 mm) with a facet size of 19 × 19 pixels and a facet distance of 15 pixels. Further details of the fcp experiment can be found in Breitbarth et al 42 A new training data set that includes the existing training data train S4.7 and new FEA training data was used. The FEA simulations took into account the higher load range applied to this large specimen.…”

The application of digital image correlation (DIC) in fatigue experimentation: A review

“…Recent advancements in experimental mechanics have been achieved by the application of DIC in fracture mechanics experiments, because full-field information about the displacements and strains provides access to local crack tip field data. 80 Nowell et al 81 note how the availability of low cost digital cameras, combined with commercial or open-source software, has made DIC a popular means of measuring displacements in fracture mechanics experiments.…”

“…Full-field digital image correlation (DIC) strain output on the relatively large surface of a middle tension (MT) fatigue specimen. The DIC method provided information about the entire deformation field of the specimen, including the stress dead zone in the center of the MT specimen between the crack tips 80 [Colour figure can be viewed at wileyonlinelibrary. com] electron channel contrast imaging was carried out.…”

“…The topic of fracture mechanics concerns the study of items related to FCG such as fracture mechanics parameters (FMP)―for example, stress intensity factor (SIF), crack closure, energy release rate―crack tip position, crack growth rate, and crack growth laws. Recent advancements in experimental mechanics have been achieved by the application of DIC in fracture mechanics experiments, because full‐field information about the displacements and strains provides access to local crack tip field data 80 . Nowell et al 81 note how the availability of low cost digital cameras, combined with commercial or open‐source software, has made DIC a popular means of measuring displacements in fracture mechanics experiments.…”

“…Of the publications surveyed for this review, the largest ROI used with a DIC system was Breitbarth et al 80 who―in an effort to fill the gap between classical FCG and stable crack extension data―studied the growth of long fatigue cracks under high‐stress conditions. To create the necessary conditions, middle tension (MT) plate specimens (MT specimens are notched at center) of dimensions 1250 × 950 × 1.6 mm 3 were tested.…”