Numerical and experimental analyses of the stress field ahead of fatigue cracks in laser-treated AA2198-T851

icaf2023 Tracking Number 72

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Laser heating treatment (LHT) is a residual-stress-based approach exhibiting successful results in reducing fatigue crack propagation rates in laboratory specimens. Although its effect is usually related to the original residual stress field, it is known that cyclic loading and crack growth can cause relaxation and redistribution of residual stresses. In this work, M(T) specimens made of 2.0 mm thick AA2198-T851 alloy sheets with L-T and T-L crack orientations were treated with a fibre laser (power 200 W, displacement speed 1 mm/s) to produce two heating lines ahead of each crack front on one of each specimens’ face. Constant-amplitude loading tests were conducted on treated and untreated specimens at a zero-to-tension condition (R = 0). In addition, electrical resistance strain gauges bonded 4 mm away from the notch tip along the crack path were employed to measure the deformation behaviour ahead of the approaching crack tip. A numerical model was developed for the stress-strain state ahead of the crack, including plane stress condition, linear elastic response, the anisotropic Gurson-Tvergaard-Needleman (GTN) yield criterion coupled with damage, associative plastic flow rule and nonlinear isotropic hardening Swift model. The mesh refinement was concentrated around the crack path direction from the notch tip until the specimen’s edge. The experimental results showed significant fatigue crack growth (FCG) retardation experienced by the laser-treated specimens; this effect was more pronounced in the L-T orientation. Numerical simulations could depict the stress field distribution in the treated specimen. Numerical simulations of damage increment under monotonic loading were adopted for a preliminary evaluation of the effect of LHT on the strain behaviour of the specimens. Keywords: Laser heating; Fatigue crack growth; Numerical analyses; AA2198-T851