Browsing by Author "Taşdemirci, Alper"

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Advanced Material Characterization and Modeling the Foreign Body Impact Damage Initiation and Progression of a Laminated Carbon Composite
(01. Izmir Institute of Technology, 2023-07) Bayhan, Mesut; Güden, Mustafa; Taşdemirci, Alper; Taşdemirci, Alper; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The coupon level composite sample tests and the accompanying numerical models were carried out to predict the response of woven carbon fiber composite structures against impact. The numerical models of the coupon-level tests were implemented in LSDYNA software using the MAT_162 and MAT_58 composite material models. The results obtained by both quasi-static and dynamic tests were used to determine their constants. In addition to the tests that were used for the determination and calibration of the material model parameters, separate tests and their models were performed for the validation, including punch shear tests and low-velocity impact tests. It could be said that the material models examined were considered comprehensive and precise as the experimental results were well predicted by the numerical models. Also, the rate sensitivity of the woven carbon composite in the in-plane and thickness directions was investigated experimentally and numerically. In the tests, the DIC method was employed in the determination of the displacement and strain of the specimen. Based on the results obtained, it was concluded that the in-plane tensile properties are rate insensitive. Besides, the simulations of the component level tests, such as bird strike and drone impact, were established to investigate the damage initiation and propagation within the composite. It was found that the drone impact results in more severe damage compared to the bird impact. It is worth noting that the development of such precise composite material models to simulate dynamic loadings will definitely shorten the time between the beginning of designing and the component testing.
Alüminyum Oksit Uzun Fiber Destekli Mg Matris Kompozitlerin Statik ve Yüksek Hız Basma Davranışı
(Pamukkale Üniversitesi, 2004) Akil, Övünç; Çiftçioğlu, Muhsin; Güden, Mustafa; Güden, Mustafa; Çiftçioğlu, Muhsin; Taşdemirci, Alper; Hall, Ian W.; Taşdemirci, Alper; 03.02. Department of Chemical Engineering; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Bu çalışmada uzun alüminyum oksit (FP™) fiber destekli magnezyum matris kompozitlerin enine basma davranışının deformasyon hızına bağlı değişimi araştırılmıştır. Silindirik numuneler fiber doğrultusuna dik yönde değişik uzama oranlarında Split Hopkinson basınç çubuğu ve statik mekanik test cihazı kullanılarak test edilmiş uzama-gerilme ilişkileri incelenmiştir. Bunun yanında optik mikroskop ve SEM kullanılarak kırılma mekaniği belirlenmeye çalışılmıştır. Çalışma sonucunda malzemenin enine basma mukavemetinin deformasyon hızı ile arttığı tespit edilmiş olup mikro-yapı incelemesinde deformasyonun ikizlenme ve kayma ile gerçekleştiği belirlenmiştir.
Citation - WoS: 67
Citation - Scopus: 89
Ballistic Behavior of High Hardness Perforated Armor Plates Against 7.62 Mm Armor Piercing Projectile
(Elsevier Ltd., 2014) Kılıç, Namık; Taşdemirci, Alper; Bedir, Said; Güden, Mustafa; Erdik, Atıl; Ekici, Bülent; Taşdemirci, Alper; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
In this paper, some of the important defeating mechanisms of the high hardness perforated plates against 7.62 x 54 armor piercing ammunition were investigated. The experimental and numerical results identified three defeating mechanisms effective on perforated armor plates which are the asymmetric forces deviates the bullet from its incident trajectory, the bullet core fracture and the bullet core nose erosion. The initial tests were performed on the monolithic armor plates of 9 and 20 mm thickness to verify the fidelity of the simulation and material model parameters. The stochastic nature of the ballistic tests on perforated armor plates was analyzed based on the bullet impact zone with respect to holes. Various scenarios including without and with bullet failure models were further investigated to determine the mechanisms of the bullet failure. The agreement between numerical and experimental results had significantly increased with including the bullet failure criterion and the bullet nose erosion threshold into the simulation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved and the defeating mechanism of perforated plates was clearly demonstrated.
Citation - WoS: 19
Citation - Scopus: 20
Calcined and Natural Frustules Filled Epoxy Matrices: the Effect of Volume Fraction on the Tensile and Compression Behavior
(Elsevier Ltd., 2013-01) Gültürk, Elif; Taşdemirci, Alper; Güden, Mustafa; Güden, Mustafa; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0–12 vol.%) on the quasistatic tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix.
Constitutive Equation Determination and Dynamic Numerical Modelling of the Compression Deformation of Concrete
(Wiley, 2021) Seven, Semih Berk; Saatcı, Selçuk; Çankaya, M. Alper; Güden, Mustafa; Uysal, Çetin; Taşdemirci, Alper; Taşdemirci, Alper; Saatci, Selçuk; Güden, Mustafa; 03.03. Department of Civil Engineering; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2-2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values.
Citation - WoS: 30
Citation - Scopus: 36
Crushing and Energy Absorption Characteristics of Combined Geometry Shells at Quasi-Static and Dynamic Strain Rates: Experimental and Numerical Study
(Elsevier Ltd., 2015-01) Taşdemirci, Alper; Kara, Ali; Şahin, Selim; Taşdemirci, Alper; Kara, Ali; Turan, Ali Kıvanç; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The quasi-static and dynamic crushing response and the energy absorption characteristics of combined geometry shells composed of a hemispherical cap and a cylindrical segment were investigated both experimentally and numerically. The inelastic deformation of the shells initiated with the inversion of the hemisphere cap and followed by the axisymmetric or diamond folding of the cylindrical segment depending on the loading rate and dimensions. The fracture of the thinner specimens in dynamic tests was ascribed to the rise of the flow stress to the fracture stress with increasing strain rate. The hemisphere cap absorbed more energy at dynamic rates than at quasi-static rates, while it exhibited lower strain rate and inertia sensitivities than the cylinder segment. For both the hemisphere cap and the cylinder segment, the inertial effect was shown to be more pronounced than strain rate effect at increasing impact velocities. © 2014 Elsevier Ltd.
Citation - WoS: 25
Citation - Scopus: 26
Crushing Behavior and Energy Absorption Performance of a Bio-Inspired Metallic Structure: Experimental and Numerical Study
(Elsevier Ltd., 2018-10) Taşdemirci, Alper; Taşdemirci, Alper; Akbulut, Emine Fulya; Güden, Mustafa; Güzel, Erkan; Tüzgel, Fırat; Yücesoy, Atacan; Şahin, Selim; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
A 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.
The Deformation Behavior of a Multi-Layered Aluminum Corrugated Structure at Increasing Impact Velocities
(Izmir Institute of Technology, 2017-12) Sarıkaya, Mustafa Kemal; Taşdemirci, Alper; Güden, Mustafa; Güden, Mustafa; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The compression impact deformation of a layered 1050 H14 aluminum corrugated sandwich structure was determined both experimentally and numerically under low, intermediate and high velocities to investigate the validity of the perfect and imperfect models. Three-dimensional finite element models of the tested specimens were developed using the LS-DYNA. At increasing velocities from quasi-static velocity to 200 m s-1, the tested corrugated structures showed three distinct deformation modes: between 0.0048 and 22 m s-1 the deformation was quasi-static homogenous mode; between 22 and 60 m s-1 a transition mode and above 90 m s-1 a shock mode. These observations were also confirmed by the camera records and model layer strain profiles. The imperfect models predicted the deformation behavior in homogeneous and transition modes, while the imperfect and perfect models both well predicted the shock mode. Layer strain profiles showed that as the velocity increased, the crushed layer densification strains increased. The numerical models and experiments of direct impact tests showed that distal end crushing stress increased with increasing velocity. The increase of the stress within the homogeneous and transient mode velocities was ascribed to the micro-inertia effect and the tested corrugated structure showed a Type II behavior. The rigid perfectly plastic locking (r-p-p-l) model prediction using quasi-static plateau stress and densification strain and quasi-static plateau stress and numerically determined densification strain at that specific velocity resulted higher velocities and full densification, while the r-p-p-l model based on varying plateau stress and densification strain well predicted in the shock mode.
Determination of the Equivalent Stress-Strain Curves of Ductile Metals Through Image Analysis
(01. Izmir Institute of Technology, 2024) Taşdemirci, Alper; Güden, Mustafa; Güden, Mustafa; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
This thesis presents a methodology for determining the equivalent stress-strain and the failure strain-stress triaxiality curves of ductile metallic materials using the advanced computing and image analysis methods. The determined curves were then used to calculate the parameters of the Johnson and Cook (JC) flow stress and damage models. A code was developed in Python to perform the numerical calculations and image analysis using the Python's libraries and image analysis tools. The main entries to the code were the experimental force-displacement curves at different strain rates, the experimental failure strain-stress triaxiality curve at a reference quasi-static strain rate, the experimental failure strain-strain rate curve at a constant stress triaxiality and the video images of the deforming test specimens. The correctness and reliability of the developed code in predicting the equivalent stress-strain curves and the parameters of the JC flow stress and damage models were clearly demonstrated for the selected 316L and AISI 4340 alloys. The code could also be easily adopted to other well-now constitutive equations commonly used in the finite element software. Finally, the results of present study contribute to the field of mechanical engineering by providing a robust tool for the materials characterization essential for designing and optimizing engineering components subjected to complex states of stresses.
Development and Design of Closed-Cell Aluminum Foam-Based Lightweight Sandwich Structures for Blast Protection
(Izmir Institute of Technology, 2008) Ergönenç, Çağrı; Taşdemirci, Alper; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Blast performance and energy absorption capability of closed-cell aluminum foam based lightweight sandwich structures were investigated by a coupled experimental and numerical technique to find out the effect of face and core material on the blast response. Split Hopkinson Pressure Bar Testing Method (SHPB) was used to characterize the mechanical properties of constituents of the sandwich structures at high strain rates. A SHPB set-up, a high strain rate testing apparatus which can successfully create blast load at laboratory scales, was built at IZTECH on behalf of a TUBITAK project (106M353). The high strain rate test data were used as an input for the numerical models. Closed-cell aluminum foam was chosen as core material for sandwich structures owing to its high energy absorption characteristic while deforming plastically. Finite element modeling of sandwich structures subjected to blast loading were performed for different core and face thicknesses and face materials in order to investigate their effects on the blast load mitigation.Experimentally and numerically revealed conclusions are; sandwich structures absorbed more energies than the bulk materials from %50 to %150 when appropriate combinations of core and face materials are used. Numerical simulations showed that 6.3 and 7.2 cm thick foam interlayer are the most efficient foam thicknesses for a 9 cm sandwich plate against 10 kg TNT blast load. Another important conclusion is for the same blast threat i.e. 10 kg of TNT, AISI 4340 Steel is the most effective face material.
The Development of a New Testing Methodology in Dynamic Mechanical Chracterization of Concrete
(Izmir Institute of Technology, 2018-07) Seven, Semih Berk; Güden, Mustafa; Taşdemirci, Alper; Taşdemirci, Alper; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Concrete is one of the most used material types in the world. Due to its structural complexity and insufficient testing techniques, the dynamic mechanical behavior of concrete has not yet been revealed sufficiently. This thesis aims to develop reliable and accurate mechanical characterization methodology for concrete using the combination of experimental and numerical methods together. The dynamic mechanical characterization of concrete at quasi-static and high strain rates was performed implementing unique techniques for both experimental and numerical studies. In quasi-static testing, universal compression test machine was used with strain gage mounted specimen for better strain measurements. In high strain rate tests, two modifications were implemented on the conventional Split Hopkinson Pressure Bar (SHPB) test apparatus. The first modification is the usage of pulse shaper to obtain nearly constant strain rate and dynamic stress equilibrium in the specimen. Second, piezo-electric quartz crystal force transducers were implemented on the specimen-bar interfaces to increase accuracy and sensitivity of the force measurement on the front and back forces of the specimen. Experimental results were validated constituting numerical study using finite element tool LS-DYNA. Concrete was modeled using Holmquist-Johnson-Cook (MAT_111) material model. HJC material model parameters were determined using experimental results coupling with the numerical analysis and the mechanical behavior of concrete was constituted. It was concluded that using pulse shaper and quartz crystals pretty useful when testing concrete and other brittle materials at high strain rates. Modification of new specimen geometries on numerical analysis showed better understandings of the effect of geometry on the dynamic stress equilibrium.
The Development of Constitutive Equations of Polycarbonate and Modeling the Impact Behavior
(01. Izmir Institute of Technology, 2023-07) Sarıkaya, Mustafa Kemal; Taşdemirci, Alper; Güden, Mustafa; Güden, Mustafa; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The Johnson and Cook (JC) flow stress and damage parameters of a polycarbonate were determined by the mechanical tests and numerical simulations. 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). The flow stress equation 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, Allen-Rule and Jones, Cowper-Symonds and the nonlinear rate approach. No strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at intermediate strain rates and large strains. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types in the PI tests, except the Cowper-Symonds relation which predicted the fracture of the polycarbonate plate at 140 m s-1. The absorbed energy at 160 m s-1 test was determined 1.6 times that of the QSI test, proving an increased energy absorption of the tested polycarbonate at the investigated impact velocities. The verified parameters were finally used to model the damages formed on a canopy against bird strike.
The Development of Forming Simulation Methodology of a Plate Type Heat Exchanger
(01. Izmir Institute of Technology, 2023-07) Şimşek, İbrahim; Taşdemirci, Alper; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
In this study, the production process of plate type heat exchangers was developed as a simulation methodology. Within the scope of the study, first, the parameters in the production process were determined. Then, mechanical characterization studies were planned with the AISI 316L stainless steel material used during production and the alternative AISI 304 stainless steel material, and the tests were completed with the support of the relevant stakeholders. The tests were determined according to the requirements of the simulation methodology. In this context, uniaxial tensile test, biaxial hydraulic bulge test and Split Hopkinson tensile tests were performed to obtain the necessary inputs for the mechanical characterization of the material and creating the material model. The material models established with the information obtained from the tests were validated with the modeling of the test setups in the numerical environment. The simulation methodology was developed in the LS-DYNA environment in the light of the process parameters obtained from the production and the data obtained from the mechanical characterization tests. The simulation model created with the developed methodology was verified because of comparison with the sample produced from AISI 316L stainless steel material taken from production. After the verified model was obtained, a simulation model was created with AISI 304 stainless steel. In addition, for the model formed with AISI 316L stainless steel, process parameters optimization study was carried out, and preliminary work activities related to reducing production times were carried out in numerical environment. After these modeling activities, the knowledge of the license plate was increased. In addition, effective plastic stress during the process, springback effect, residual stress values after springback, effective plastic strain, thickness distribution and thickness reduction values were obtained for the plate. By using the forming limit diagram of AISI 316L stainless steel, information about the final formability behavior was obtained.
Citation - WoS: 33
Citation - Scopus: 41
Development of Novel Multilayer Materials for Impact Applications: a Combined Numerical and Experimental Approach
(Elsevier Ltd., 2009-05) Taşdemirci, Alper; Taşdemirci, Alper; Hall, Ian W.; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
A well-verified and validated numerical model was used to investigate stress wave propagation in a multilayer material subjected to impact loading. The baseline material consisted of a ceramic faceplate and composite backing plate separated by a rubber or teflon foam interlayer: several variants were investigated in which the number, type, and total thicknesses of the interlayers were altered. Comparison of the variants showed that the use of multiple teflon foam interlayers could drastically reduce the average stress in the multilayer material. Based on the numerical results, further experimental work was undertaken upon one of the variants. Very large and unexpected tensile stress oscillations were observed in the ceramic layers, leading to a refinement of the numerical model which successfully reproduced the oscillations and also demonstrated that separation of the sample layers led to trapping of the stress wave within the layers. Use of the validated numerical model allowed detailed analysis of the processes of wave transmission and demonstrates the important synergy that can exist between experimental and modeling studies. The current study provides a valuable starting point for designing future multilayer materials with specific, controlled properties.
Citation - WoS: 10
Citation - Scopus: 14
Development 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; Güden, Mustafa; Taşdemirci, Alper; Kambur, Çağdaş; Çankaya Özbek, Sevim; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The 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.
Citation - WoS: 23
Citation - Scopus: 25
Diatom Frustule-Filled Epoxy: Experimental and Numerical Study of the Quasi-Static and High Strain Rate Compression Behavior
(Elsevier Ltd., 2008) Taşdemirci, Alper; Taşdemirci, Alper; Yüksel, Sinan; Güden, Mustafa; Karsu, Deniz; Gültürk, Elif; Hall, Ian W.; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
In this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress–time response and deformation sequence of the samples in high strain rate testing.
Citation - WoS: 1
Citation - Scopus: 1
Dynamic Compression of Metal Syntactic Foam-Filled Aluminum Tubes
(Springer, 2024) Movahedi, Nima; Güden, Mustafa; Fiedler, Thomas; Taşdemirci, Alper; Sarikaya, Mustafa; Tasdemirci, Alper; Murch, Graeme E.; Belova, Irina V.; Guden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The current research investigates the compressive properties of metal syntactic foam (MSF)-filled tubes at dynamic loads with an impact velocity of 4 m/s. For this purpose, A356 aluminum alloy syntactic foams were prepared using an infiltration casting technique with an incorporation of expanded perlite (EP) filler particles. The study involves the testing and comparison of both MSF samples and MSF-filled tubes under dynamic loading scenarios. In the case of MSF-filled tubes, aluminum tubes are either fully filled (FFT) or half-filled (HFT) with MSFs. The manufactured foams and foam cores have a similar macroscopic density across all tested samples. Under dynamic loading, the MSF, HFT, and FFT samples exhibit distinct and different deformation mechanisms. In MSFs, dynamic compression is controlled by shearing of the sample, whereas in HFTs and FFTs, dynamic deformation occurs through the folding and buckling of the tubes, accompanied by partial deformation of the MSF cores.
Citation - WoS: 14
Citation - Scopus: 18
Dynamic Crushing and Energy Absorption of Sandwich Structures With Combined Geometry Shell Cores
(Elsevier Ltd., 2015-06) Taşdemirci, Alper; Kara, Ali; Kara, Ali; Taşdemirci, Alper; Turan, Kıvanç; Şahin, Selim; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
Dynamic crushing and energy absorption characteristics of sandwich structures with combined geometry shell cores were investigated experimentally and numerically. The effect of strain rate on the crushing behavior was presented by the crushing tests at quasi-static, intermediate and high strain rate regimes. It was shown that absorbed energy increased with increasing impact velocity. The effect of confinement on crushing behavior was shown by conducting confined experiments at quasi-static and dynamic rates. Higher buckling loads at lower deformation were observed in confined quasi-static crushing due to additional lateral support and friction provided by confinement wall. By using fictitious numerical models with strain rate insensitive material models, the effect of inertia and strain rate on crushing were shown. It was observed that, increase in impact velocity caused increase in inertial effects and strain rate effects were nearly independent from the impact velocity. The effects of multilayering were also investigated numerically.
Citation - WoS: 17
Citation - Scopus: 19
Dynamic Crushing Behavior of a Multilayer Thin-Walled Aluminum Corrugated Core: the Effect of Velocity and Imperfection
(Elsevier Ltd., 2018-11) Sarıyaka, Mustafa; Güden, Mustafa; Taşdemirci, Alper; Taşdemirci, Alper; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
The 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.
Dynamic Crushing Behavior of Sandwich Panels With Bio-Inspired Cores
(Izmir Institute of Technology, 2017-07) Güzel, Erkan; Güden, Mustafa; Taşdemirci, Alper; Taşdemirci, Alper; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
In the current study, a new approach was shown to develop an innovative loadcarrying and energy absorbing structure which can fulfill the requirements in the fields of automotive, defense and aerospace. Two different topics which have been in great demand in the recent times were combined: sandwich structures and bio-inspiration. Balanus which is a barnacle living along the seashores and on the ships’ surfaces was taken under examination to design a novel sandwich structure core geometry. The designed geometry was manufactured with deep drawing process. The sandwich structures were produced with different face sheets using a pattern to ensure the repeatability of the crushing tests. Firstly, the advantage of the bio-inspired core over the conventional core geometries was shown with a numerical study. Then, the crushing tests were conducted at both quasi-static and dynamic loading rates. Further, the effects of foam filling, confinement, inertia and strain rate sensitivity on the crashworthiness performance of the proposed structure were investigated. In addition to the experimental studies, numerical analyses were also performed using LS-DYNA 971. In the numerical studies, manufacturing process of the core geometry was also modeled to count in the residual stress/strain so that a good proximity was obtained between the experimental and numerical results. Moreover, the penetration and perforation behaviors were inspected. Utility of the proposed geometry where a high resistance is needed against dynamic crushing was demonstrated. Finally, several suggestions were proposed for the future works to elaborate the present study.