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Fatigue behaviour of friction stir welded AA2024‐T3 alloy: longitudinal and transverse crack growth
Author(s) -
MILAN M. T.,
BOSE FILHO W. W.,
RUCKERT C. O. F. T.,
TARPANI J. R.
Publication year - 2008
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.2008.01234.x
Subject(s) - materials science , crack closure , residual stress , paris' law , crack growth resistance curve , welding , fracture mechanics , composite material , ultimate tensile strength , structural engineering , engineering
ABSTRACT The fatigue crack growth properties of friction stir welded joints of 2024‐T3 aluminium alloy have been studied under constant load amplitude (increasing ‐ΔK ), with special emphasis on the residual stress (inverse weight function) effects on longitudinal and transverse crack growth rate predictions (Glinka's method). In general, welded joints were more resistant to longitudinally growing fatigue cracks than the parent material at threshold Δ K values, when beneficial thermal residual stresses decelerated crack growth rate, while the opposite behaviour was observed next to K C instability, basically due to monotonic fracture modes intercepting fatigue crack growth in weld microstructures. As a result, fatigue crack growth rate (FCGR) predictions were conservative at lower propagation rates and non‐conservative for faster cracks. Regarding transverse cracks, intense compressive residual stresses rendered welded plates more fatigue resistant than neat parent plate. However, once the crack tip entered the more brittle weld region substantial acceleration of FCGR occurred due to operative monotonic tensile modes of fracture, leading to non‐conservative crack growth rate predictions next to K C instability. At threshold Δ K values non‐conservative predictions values resulted from residual stress relaxation. Improvements on predicted FCGR values were strongly dependent on how the progressive plastic relaxation of the residual stress field was considered.