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Fatigue crack propagation in laser peened materials: A holistic simu lation approach

B. Klusemann 1 , 2 , ∗ , S. Keller 1 , N. Kashaev 1

1 Institute of Materials Mechanics, Helmholtz-Zentrum Hereon, Geesthacht, Germany 2 Institute for Production Technology and Systems, Leuphana University Lüneburg, Luneburg, Germany

∗ benjamin.klusemann@hereon.de

Keywords: laser shock peening, fatigue crack growth, simulation

Laser shock peening (LSP) is known as efficient modification technique to generate deep com pressive residual stresses in metallic structures. These compressive residual stresses are capable to reduce the fatigue crack propagation (FCP) rate, which results in an extension of the structural lifetime and/or maintenance intervals in terms of a damage tolerant design philosophy. Con sidering that residual stresses are also in equilibrium, it is obvious that generated compressive residual stresses are accompanied by balancing tensile residual stresses. However, as tensile resid ual stresses are supposed to accelerate the FCP rate, the overall residual stress field has to be known, when modification techniques, such as LSP, are applied. To support our understanding of these phenomena, a holistic virtual twin [1] from LSP process simulation [2] to the prediction of FCP rate is set-up and used in a close linking with experiments. The underlying multi-step simulation approach consists of four steps: (i) LSP process simulation for a representative volume to predict resulting plastic strains; (ii) transfer and extrapolations of these plastic strains to a relatively large LSP-treated area; (iii) calculation of the overall residual stress field as well as the stress intensity factor (SIF) range and rate; (iv) estimation of the FCP rate based on FCP equations. An ‘experimental simulation’ validates the simulation chain, where calculated SIFs are applied to untreated material. The FCP rate of the untreated material and experimentally determined FCP rate of LSP-treated material agree well, which indicates the calculation of real istic SIFs. The study reveals also the contribution of crack closure [3] in terms of FCP retarding mechanism. References [1] S. Keller, M. Horstmann, N. Kashaev, B. Klusemann, “Experimentally validated multi-step simulation strategy to predict the fatigue crack propagation rate in residual stress fields after laser shock peening”, Int. J. Fatigue, vol. 124, pp. 265-267, 2019. [2] S. Keller, S. Chupakhin, P. Staron, E. Maawad, N. Kashaev, B. Klusemann, “Experimental and numerical investigation of residual stresses in laser shock peened AA2198”, J. Mater. Process. Tech., vol. 255, pp. 294-307, 2018. [3] S. Keller, M. Horstmann, V. Ventzke, N. Kashaev, B. Klusemann, “Experimental and numerical investigation of crack closure in residual stress fields generated by laser shock peening”, Eng. Fract. Mech., vol 221, 106630, 2019.

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