Uncoupled Damage Models for Ductile Failure in Flow Forming Processes H. Vural1,∗, T. O. Fenercioğlu2, T. Yalçinkaya1 1 Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Türkiye 2 Repkon Machine and Tool Industry and Trade Inc., Istanbul 34980, Türkiye ∗ vural.hande@metu.edu.tr Keywords: Flow forming process, Inconel 718, Formability limits. Flow forming (FF) is an incremental forming process in which the thickness of the material is thinned. During this process, the material undergoes complex stresses and substantial plastic deformation, often leading to cracks due to exceeding its formability limits. It is crucial to predict the forming limit accurately to improve the efficiency and quality of the process. Ductile failure analyses are carried out with finite element (FE) simulations to compare the damage prediction capacities of different ductile failure criteria in the literature. The FF process is studied using different criteria with titanium alloys [1,2], but the results obtained from FE simulations have not aligned well with experimental tests. In contrast, our previous study [3] on FF failure analysis with the nickel-based superalloy Inconel 718 (IN718) showed that the Cockcroft-Latham (CL) damage criterion outperformed the Johnson-Cook (JC) and modified Mohr-Coulomb (MMC) models in predicting damage locations and fracture limits when compared to experimental tests. In this study, the aim is to extend this research by developing several damage criteria modeled for IN718, which then is compared in terms of predicting damage locations and formability limits in the FF process, considering various thinning ratios. Ayada, Ayada-m, Ko-Huh (KH), Le-Roy (LR), McClintock (MC), Oh and Rice-Trace (RC) failure criteria are implemented as a user-defined field subroutine (VUSDFLD) in commercial FE analysis software Abaqus/Explicit. Four distinct tensile test specimens, each characterized by a varied range of stress triaxiality, are employed to calibrate the criteria, and evaluate their capabilities in different stress triaxiality. Then, FE simulations of FF are performed at 37.5%, 50% and 70% reduction ratios using the calibrated models. The obtained results from different models are compared and their performance in predicting the formability limit and crack initiation location is discussed in detail. References [1] Ma, H., Xu, W., Jin, B.C., Shan, D., Nutt, S.R. (2015). Damage evaluation in tube spinnability test with ductile fracture criteria. International Journal of Mechanical Sciences 100, 99–111. [2] Xu, W., Wu, H., Ma, H., Shan, D. (2018). Damage evolution and ductile fracture prediction during tube spinning of titanium alloy. International Journal of Mechanical Sciences 135, 226–239. [3] Erdogan, C., Vural, H., Karakaş, A., Fenercioğlu, T. O., and Yalçinkaya, T., (2023). Ductile failure of Inconel 718 during flow forming process and its numerical investigation. Engineering Failure Analysis, vol. 152, p. 107424. 57
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