Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Novel Strut-Based Mechanical Analysis: Flow Stress Determination of Electron Beam Melt (EBM) Lattice Structures(Springernature, 2025) Bin Riaz, Muhammad Arslan; Erten, Hacer Irem; Guden, MustafaIn modeling lattices, the material flow stress equation, such as the Johnson and Cook (JC) equation, is usually determined from the mechanical tests conducted on bulk, relatively large test size specimens which were manufactured using the same process parameters with the lattices. However, the flow stresses of struts were shown in several studies to be significantly lower than those of large size test specimens. To overcome this discrepancy, a novel approach that combined the strut compression test, the strut double shear test (DST) and the numerical model of the strut DST using the JC equation was proposed. The study confirmed that the flow stress determined from the machined bulk tension test specimens overestimated the experimental compression stress-strain behavior of a body centered cubic (BCC) Ti6Al4V lattice. The flow stress parameters determined from the compression stress-strain curves of the as-printed strut specimens, on the other side, showed the best match to the experimental compression stress-strain behavior of the BCC lattice. The fidelity of the determined parameters of the JC equation was further verified with the experimental and numerical DSTs. It was also shown that the numerical iterations of DST model could be used for the fine-tuning the flow stress parameters.Article The Johnson and Cook Damage and Flow Stress Model Parameters of a Rolled Stainless Steel 304 Alloy(Elsevier, 2026) Akdogan, Ibrahim Berk; Davut, Kemal; Gueden, Mustafa; Erten, Hacer Irem; Tasdemirci, Alper; Maleki, Farshid Khosravi; Gok, Mustafa SabriPrevious studies on stainless steel 304 alloy (SS 304) have mostly focused on the stress-strain behavior as function of the volume fraction of deformation induced martensite and the applied strain and strain rate. Although equally important, the failure/fracture of this alloy has not been thoroughly investigated so far. In the present study, the Johnson and Cook (JC) damage model parameters of a rolled-SS 304 alloy, valid at a high strain rate (2900 s-1), were experimentally determined and numerically validated along with the JC flow stress parameters. The tensile failure strain of the alloy decreased as the strain rate increased from 10-3 to 10-1 s-1 and to 2900 s-1. Experimentally lower flow stresses at 2900 s-1 than at 1x10-3 s-1 were also found at the strains above 0.2, which was attributed to the adiabatic heating that declined the extend of the martensitic transformation at increasing strains. The determined damage and flow stress model parameters were further calibrated with the results of the numerical models of the quasi-static and high strain rate tension tests. Microscopic analyses and the hardness measurements on the untested and tested specimens confirmed the martensitic transformation and the highest hardness values were found in the specimens tested at 1x10-3 s-1. The martensite volume fraction as function strain rate until about necking strain (homogeneous deformation) was calculated and also microscopically determined using the electron back-scatter diffraction (EBSD) for the specimens tested at different strain rates. The results indicated the highest martensite volume fraction in the specimens tested at 10-3 s-1 (0.55-0.6) and the lowest in the specimens tested at the high strain rate (0.27-0.30). An agreement between the calculated and the EBSD determined martensite volume fractions was shown for the studied alloy.