Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 1Citation - Scopus: 1Investigation of Penetration Behavior of Combined Geometry Shells at Quasi-Static and Intermediate Strain Rates: an Experimental and Numerical Study(Elsevier, 2023) Turan, Ali Kıvanç; Taşdemirci, Alper; Kara, Ali; Şahin, Selim; Güden, MustafaIn this study, the penetration/perforation behavior of a core material with previously determined static and dynamic crushing characteristics was investigated both experimentally and numerically. Penetration/perforation problems occur due to shrapnel effect when sandwich structures containing energy-absorbing core materials by crushing are exposed to blast loads. The penetration behavior of combined geometry shells consisting of a hemispherical cap and a cylindrical segment was investigated experimentally using blunt, conical and hemispherical penetrator tips. The quasi-static penetration tests were performed in a universal test machine, and the intermediate strain rate penetration tests were performed in a drop weight test device. The numerical models of penetration tests were implemented in LS-DYNA at the test strain rates as well as at the higher strain rates. Results showed that different penetrator geometries induced damage forms of symmetrical tearing, petaling, plugging and inversely formed hemispherical domed cone. The increase in the thickness of core geometry resulted in a decent increase in force–displacement curves, as average of force levels increased around 140%, 200% and 220% for blunt, conical and hemispherical tip penetrators, respectively. Numerical results indicated very good correlation with experimental work and enabled to investigate effect of strain rate and micro-inertia over numerical models at elevated penetrator velocities. Penetration behavior was found to be affected from micro-inertia effects up to a threshold displacement of 4 mm for thicker and 5 mm for thinner core units and strain rate effects were found to be dominant beyond that point.Article Citation - WoS: 28Citation - Scopus: 34The Strain Rate Sensitive Flow Stresses and Constitutive Equations of a Selective-Laser and an Annealed-Rolled 316l Stainless Steel: a Comparative Study(Elsevier, 2022) Güden, Mustafa; Enser, Samed; Bayhan, Mesut; Taşdemirci, Alper; Yavaş, HakanThe strain rate dependent compressive flow stresses of a Selective-Laser-Melt 316L (SLM-316L) alloy and a commercial (annealed-extruded) 316L (C-316L) alloy were determined, for comparison, between 1x10-4 and ∼2500 s-1 and between 1x10-4 and ∼2800 s-1, respectively. The Johnson and Cook flow stress material model parameters of both alloys were also determined. The microstructural examinations of the deformed cross-sections of tested specimens (interrupted tests) showed a twinning-induced-plasticity in SLM-316L alloy and a martensitic transformation-induced-plasticity in C-316L alloy. Twin and martensite formations were detected microscopically higher in the dynamically tested specimens until about 0.22 strain, while the twin and martensite formations decreased at increasing strains due to adiabatic heating. The rate sensitivity of SLM-316L was determined slightly higher than that of C-316L within the quasi-static strain rate range (1x10-4 and 1x10-2 s-1), while the rate sensitivities of both alloys were similar in the quasi-static-high strain rate range (1x10-4 and ∼2500-2800 s-1) at low strains. A more rapid decrease in the rate sensitivity of C-316L at increasing strains was found in the quasi-static-high strain rate range. The similar activation volumes of both alloys, corresponding to the dislocation intersections, indicated a similar thermally activated deformation process involvement in both alloys.Article Citation - WoS: 3Citation - Scopus: 5The Effect of Strain Rate on the Mechanical Behavior of Teflon Foam(Elsevier Ltd., 2012) Taşdemirci, Alper; Turan, Ali Kıvanç; Güden, MustafaThe quasi-static (1 × 10−3, 1 × 10−2 and 1 × 10−1 s−1) and high strain rate (7200 and 9500 s−1) experimental and high strain rate numerical compression deformation of a Gore Polarchip™ CP7003 heat insulating Teflon foam was investigated. High strain rate tests were conducted with the insertion of quartz crystal piezoelectric transducers at the end of the transmitter bar of a compression Split Hopkinson Pressure Bar (SHPB) set-up in order to measure the force at the back face of the specimen. A fully developed numerical model of the SHPB test on Teflon was also implemented using LS-DYNA. The simulation stresses showed close correlations with the experimentally measured stresses on the bars. The developed model successfully simulated the high strain rate loading. The damage initiation and progression of experimental high strain rate tests were further recorded using a high speed camera and found to be very similar to those of the simulation high strain rate tests.