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: 18Citation - Scopus: 19The Impact Response of a Nomex® Honeycomb Core/E-glass Composite Sandwich Structure To Increasing Velocities: Experimental and Numerical Analysis(Elsevier, 2023) Çelik, Muhammet; Güden, Mustafa; Sarıkaya, Mustafa; Taşdemirci, Alper; Genç, Cem; Ersoy, Kurtuluş; Serin, ÖzgürThe impact response of an E-glass fiber reinforced epoxy/Nomex® honeycomb core sandwich was investigated both experimentally and numerically at increasing velocities through concentrated quasi-static indentation force (CQIF), low velocity impact (LVI) and high velocity impact (HVI) tests. The composite face sheets and core were modelled using MAT_162 and MAT_026 homogenized material model in LS-DYNA, respectively. The experimental and numerical LVI test forces corresponding to core crushing and face sheet penetration were shown to be higher than those of the CQIF tests and increased as the impactor velocity increased. The increase of the impact forces at increasing velocities was largely ascribed to the inertia and the strain rate sensitive fracture strength of the composite sheets. The core shearing was detected in the CQIF and LVI tests both experimentally and numerically. It was also detected in the HVI tests at the velocities less than 20 m s?1. The deformation in the HVI tests at and above ? 29.4 m s?1 was highly localized in the impact area with no core shearing and a large delamination damage area at the front face sheet. The force enhancement due to the micro-inertia of the core deformation was shown to be not significant at the studied velocities. © 2023 Elsevier LtdArticle Citation - WoS: 12Citation - Scopus: 17Development of the Johnson-Cook Flow Stress and Damage Parameters for the Impact Response of Polycarbonate: Experimental and Numerical Approach(Elsevier, 2023) Sarıkaya, Mustafa; Güden, Mustafa; Kambur, Çağdaş; Çankaya Özbek, Sevim; Taşdemirci, AlperThe Johnson and Cook (JC) flow stress and damage model parameters of a polycarbonate (PC) plate were determined by the mechanical tests and numerical simulations of the tests. The experimental tests included quasi-static and high strain rate tension and compression, quasi-static notched-specimen tension, quasi-static indentation (QSI), low velocity impact (LVI) and projectile impact (PI). Initially, five different quasi-static flow stress-strain equations were extracted from the experimental and numerical tests. The flow stress equa-tion determined from the experimental average true stress-true strain curve well agreed with the effective stress -strain obtained from the quasi-static numerical tension test. The numerical QSI force-displacement curve based on the experimental average true stress-true strain equation was further shown to be very similar to that of the experiment. The LVI and PI test simulations were then continued with the experimental average true stress-true strain equation using five different flow stress-strain rate relations: JC, Huh and Kang (HK), Allen-Rule and Jones (ARJ), Cowper-Symonds (CS) and the nonlinear rate approach (NLA). The rate sensitivity parameters of these relations were extracted from the quasi-static and high strain rate tests. The LVI test simulations using the stress -strain rate relations exhibited force-displacement curves higher than those of the experiments. The detected almost no strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at these intermediate strain rates and large strains involved. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types: dishing at 100 and 140 m s-1 and petalling at 160 m s- 1, except the CS relation which predicted the fracture of the plate at 140 m s-1. The experimental average projectile exit velocity at 160 m s- 1 was further well predicted by the used stress-strain rate relations while the experimental average petal thicknesses were under estimated by the models. The absorbed energy at 160 m s-1 PI test was determined 1.6 times that of the QSI test, which proved an increased energy absorption capability of the tested PC at the investigated impact velocities.Article Citation - WoS: 9Citation - Scopus: 9The Strain Rate History Effect in a Selective-Laser 316l Stainless Steel(Elsevier, 2023) Enser, Samed; Güden, Mustafa; Taşdemirci, Alper; Davut, KemalThe strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi-static (10−3 s−1) and high strain rate (1600-3200 s−1) interrupted and reloading compression tests. The specimens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was ∼70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in ∼60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher fraction of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains.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: 39Citation - Scopus: 40Impact Loading of Functionally Graded Metal Syntactic Foams(Elsevier, 2022) Movahedi, Nima; Fiedler, Thomas; Taşdemirci, Alper; Murch, Graeme E.; Belova, Irina V.; Güden, MustafaThe present study addresses the impact loading of functionally graded metal syntactic foams (FG-MSF). For comparison, samples of the same material were also compression loaded at quasi-static velocities. Samples of A356 aluminium FG-MSF were produced using counter-gravity infiltration casting with combination of equal-sized layers of expanded perlite (EP) and activated carbon (AC) particles. A modified Split Hopkinson Pressure Bar test set-up was used to impact the FG-MSFs from their EP or AC layers at 55 m/s or 175 m/s impact velocities. A high-speed camera captured the deformation of the samples during testing. It was shown that increasing the loading velocity enhanced both the compressive proof strength and energy absorption of the impacted FG-MSF from both layers, confirming a dynamic strengthening effect of the foam. The samples impacted from both layers at 55 and 175 m/s showed a transition and a shock mode of deformation, respectively. The impacted samples at 55 m/s experienced lower final average strain values compared to 175 m/s.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: 10Citation - Scopus: 12Testing and Modeling Blast Loading of a Sandwich Structure Cored With a Bio-Inspired (balanus) Core(Elsevier, 2022) Tüzgel, Fırat; Akbulut, Emine Fulya; Güzel, Erkan; Yücesoy, Atacan; Şahin, Selim; Taşdemirci, Alper; Güden, MustafaThe blast loading response of a sandwich structure consisted of bio-inspired (balanus) cores/units was investigated experimentally and numerically. A Direct Pressure Pulse (DPP) set-up was used to impose a blast-like loading. The equivalent blast conditions corresponding to the used impact velocities were implemented in the models. A benchmark study was performed by using three different methods namely pure Lagrangian, Arbitrary Lagrangian Eulerian, and hybrid. Dynamic crushing behavior was analyzed and exhibited a higher specific energy absorption capacity than its constituents (core and shell). Among the core configurations, all-front configuration was found the most efficient configuration regarding the specific energy absorption.Article Citation - WoS: 54Citation - Scopus: 59Orientation Dependent Tensile Properties of a Selective-Laser 316l Stainless Steel(Elsevier, 2021) Güden, Mustafa; Yavaş, Hakan; Tanrıkulu, Ahmet Alptuğ; Taşdemirci, Alper; Akın, Barış; Enser, Samed; Karakuş, Ayberk; Arslan Hamat, BurcuThe effect of specimen inclination angle with respect to building direction on the tensile properties of a selective laser melt 316L alloy was investigated. Tensile test specimens were fabricated with the angles between 0 degrees to 90 degrees at 15 degrees intervals using a rotation scanning. In addition, 316L alloy test specimens were generated in the ANSYS 2020R1 additive module and tensile tested in LS-DYNA in order to determine the effect of residual stresses on the tensile strengths. The microscopic analysis revealed a strong < 110 > fiber texture orientation along the building direction (the loading axis of 0 degrees inclined specimens) and a weak 111 texture or nearly random distribution of directions in the normal to the building direction (tensile loading axis of 90 degrees inclined specimens). The yield and tensile strength increased and ductility decreased with increasing inclination angle. The strength variation with the inclination angle was shown well-fitted with the Tsai-Hill failure criterion. Although, the used numerical models indicated an inclination-dependent residual stress, the difference in the residual stresses was much lower than the difference in the strengths between 0 degrees and 90 degrees inclined specimens. Predictions showed a lower twinning stress in 0 degrees inclined specimens due to < 110 > fiber texture orientation in the tensile axis. The fiber texture resulted in extensive twinning; hence, higher ductility and tension-compression asymmetry in 0 degrees inclined specimens. Based on these results, the variations in the strength and ductility of tested SLM-316L specimens with the inclination angle was ascribed to the variations in the angle between the fiber texture orientation and loading axis.Article Citation - WoS: 19Citation - Scopus: 21Dynamic Crushing Behavior of a Multilayer Thin-Walled Aluminum Corrugated Core: the Effect of Velocity and Imperfection(Elsevier Ltd., 2018) Sarıyaka, Mustafa; Taşdemirci, Alper; Güden, MustafaThe crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s−1. The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s−1, a transition mode between 22 and 60 m s−1 and a shock mode at 90 m s−1. Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s−1, respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s−1; thereafter, it saturated at ~2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid-perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations.Article Citation - WoS: 28Citation - Scopus: 28Crushing Behavior and Energy Absorption Performance of a Bio-Inspired Metallic Structure: Experimental and Numerical Study(Elsevier Ltd., 2018) Taşdemirci, Alper; Akbulut, Emine Fulya; Güzel, Erkan; Tüzgel, Fırat; Yücesoy, Atacan; Şahin, Selim; Güden, MustafaA thin-walled structure inspired from a biologic creature known as balanus was investigated experimentally and numerically under quasi-static and dynamic loads for load-carrying and energy absorption properties. The structure was composed of an inner conical core with a hemispherical cap and an outer shell in frusto-conical shape and formed by deep drawing. The applied deep drawing process was modelled using nonlinear finite element code LS-DYNA to determine the residual stress/strain and the non-linear thickness distribution after the forming process. It was also shown that the load carried by the balanus structure was greater than the arithmetic sum of the load carried by the inner core and by the outer shell separately. Although the mean force increase due to interaction effect at quasi-static strain rate was approximately 5%, while it increased to roughly 26% at dynamic strain rates in drop weight experiments. The numerical models also showed that the outer shell absorbed more energy than the inner core while the difference between the energy absorbing performance of the core and shell decreased with increasing deformation rate. The effect of strain rate and inertia on the increase in crush load increased with increasing impact velocity, while the strain rate effect had greater influence than the inertia on the crush load. The increased load carrying capacity of the balanus at quasi-static and dynamic strain rates was ascribed to the interaction between the core and shell and the confinement effect of the outer shell particularly at dynamic strain rate.