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Evaluation of thermal and mechanical filler gas influence on honeycomb structures behaviour
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, izvirni znanstveni članek

Opis: In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions.
Ključne besede: mechanics, cellular materials, honeycomb structure, gas filler, thermal properties, mechanical properties, dynamic loading, LS-DYNA, computational simulations
Objavljeno: 31.05.2012; Ogledov: 1225; Prenosov: 31
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Charpy toughness and microstructure of vibrated weld metal
Bogdan Pučko, Vladimir Gliha, 2006, izvirni znanstveni članek

Opis: Vibration during welding can be used to obtain certain changes in mechanical properties of weld metal. Research work on the influence of vibration on the secondary microstructure of welds and hence on the Charpy toughness was performed. Vibration during welding exhibits positive effects on the microstructure constituent formation. Multipass welding was simulated with reheating of the original single pass weld in order to obtain similar microstructure to multipass welds. Microstructures were examined with an optical microscope. Additionally, fractographic examination of the rupture of Charpy specimens was performed. Changes in the microstructure according to vibration were observed which affect toughness of the weld metal. Vibration during welding was rated more effective in the case of reheating the weld metal, which is the case in multipass welding.
Ključne besede: welding, welded joints, mechanical properties of metals, ferrite, vibration, microstructure, toughness, notched bar testing, weld metal
Objavljeno: 31.05.2012; Ogledov: 1667; Prenosov: 80
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The influence of thread twist on alterations in fibers` mechanucl properties
Andreja Rudolf, Jelka Geršak, 2006, izvirni znanstveni članek

Opis: In order to design high-quality threads, it is necessary to know the properties of threads and fibers, as well as the loadings and deformations which may occur during the sewing process. Thread properties depend on the mechanical properties of the fiber and the constructional parameters of the thread and its surface treatment, which directly influence sewing performance.The mechanical properties of a thread primarily depend on the fiber mechanical properties and the amount of twist. Knowledge of the thread dynamic loadings during the sewing process, depending on the number of turns and the lubrication method, is important for planning the required processing properties of the thread. This paper presents research into the influence of thread twist and the lubrication method on the mechanical properties and dynamic load of PES core-spun thread and its fibers. Research into the mechanical properties of the different twisted and surface treated threads, and separated fibers was carried out for this purpose. The influence of threaddynamic load during a sewing process was also researched regarding any alterations in the mechanical properties of the threads and separated fibers. Analyses of the results show that the amount of twist depends on the mechanical properties of the thread and its constituent fibers, whilst the method of surface treatment is based on the specific mechanical properties of the thread. A dynamic load causes greater or smaller thread deformations, which is reflected in changes in the thread and fiber mechanical properties. The occurred changes depend on dynamic load, amount of twist, and the lubrication method, which is confirmed with statistical analysis of the measured results.
Ključne besede: garment manufacturing, sewing, threads, textile fibres, surface treatment, dynamic loads, mechanical properties, amount of twist
Objavljeno: 30.05.2012; Ogledov: 1733; Prenosov: 24
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Characterization of open-cell cellular material structures with pore fillers
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2008, izvirni znanstveni članek

Opis: Due to their mechanical properties, cellular material structures are often used in automotive, aerospace, ship and railway industries, as elements for deformational energy absorption. New advanced cellular material structures have been evaluated and characterised in the scope of this study in order to determine their energy absorption capability through the deformation process. Parametric computational simulations in the framework of the finite element method have been used for this purpose. Newly developed computational models of regular open-cell cellular material structures considering viscous pore fillers have been developed and their response under impact conditions was analysed using the explicit code LS-DYNA. The results of the performed study show that introduction of viscous fillers indeed increases the energy absorption capability of open-cellular material structures. Additionally, it was determined that the size of the cellular material (number of cells) dramatically influences the cellular structure response and that the filler influence is stronger in cellular structures with higher relative density.
Ključne besede: cellular materials, computer simulation, deformation, mechanical properties
Objavljeno: 31.05.2012; Ogledov: 1100; Prenosov: 62
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Structure-properties relations of the drawn poly(ethylene terephthalate) filament sewing thread
Andreja Rudolf, Majda Sfiligoj-Smole, 2008, izvirni znanstveni članek

Opis: This article presents research into draw ratio influence on the structure-properties relationship of drawn PET filament threads. Structural modification influence due to the drawing conditions, i.e., the birefringence and filament crystallinity, on the mechanical properties was investigated, as well as the shrinkage and dynamic mechanical properties of the drawn threads. Increasing draw ratio causes a linear increase in the birefringence, degree of crystallinity, filament shrinkage, and a decrease in the loss modulus. In addition, loss tangent and glass transition temperature, determined at the loss modulus peak, were increased by drawing. The observed structural changes influence the thread's mechanical properties, i.e., the breaking tenacity, elasticity modulus, and tension at the yield point increase, while breaking extension decreases by a higher draw ratio.
Ključne besede: PET sewing thread, drawing, birefringence, DSC, DMA, mechanical properties
Objavljeno: 31.05.2012; Ogledov: 1336; Prenosov: 76
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Dependence of material characteristics on lubrication in bulk forming process
Leo Gusel, 2009, objavljeni znanstveni prispevek na konferenci

Opis: In the paper the influence of coefficient of friction (lubricant) on different properties of cold formed material has been examined. Tensile tests, hardness measurements and electrical conductivity measurements were performed.In the frame of the experimental work the process of cold forward extrusion of a cylinder made from copper alloy was investigated. The specimens were extruded at four different lubricants coefficients of friction. The results have shown that use of different lubricators with different coefficients of friction can have effects on the material properties during and after cold forming process.
Ključne besede: lubrication, cold forming, copper alloy, mechanical properties
Objavljeno: 31.05.2012; Ogledov: 1099; Prenosov: 13
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Tensile test models for low-carbon microalloyed steels with high niobium contents
Marcos Pérez-Bahillo, Nenad Gubeljak, David A. Porter, Beatriz López, Jožef Predan, Antonio Martín-Meizoso, 2011, izvirni znanstveni članek

Opis: In the present investigation, the effect of both: rolling parameters (2 reduction rates and 3 cooling rates) and chemical elements such as: C, Mn, Nb,Ti, Mo, Ni, Cr, Cu and B, has been studied in relation to strength properties in low-carbon microalloyed steels with high niobium contents (up to 0,12 wt. % Nb). For this purpose, an experimental set-up was designed based on an intelligent design of experiments (DoE), resulting in 26 casts (laboratory casts).Acombination of metallography, Electron Back-Scattered Diffraction (EBSD) and tensile tests have been performed to study how processing parameters and chemical composition affect the strength. The results, where the proof stress, tensile strength, uniform and fracture elongations are the response variables, have been analysed statistically by means of multiple linear regression technique, leading to response equations. From the results, it was found that the effectiveness of niobium increasing the strength is reduced as carbon content increases.
Ključne besede: microalloyed steels, mechanical properties, niobium
Objavljeno: 01.06.2012; Ogledov: 1063; Prenosov: 76
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Evaluating the bending rigidity of flat textiles with the use of an Instron tensile tester
Mirosława Kocik, Witold Żurek, Izabella Krucinska, Jelka Geršak, Jan Jakubczyk, 2005, izvirni znanstveni članek

Opis: The purpose of this work is to verify the possibility of using an Instron tensile tester for evaluating those mechanical properties of flat textile fabrics which are responsible for their handle properties. A method of evaluating the bending rigidity of woven fabrics was developed. The method consists in axially compressing samples fixed at both ends and placed in a vertical position, which leads to their buckling. The bending rigidity was determined on the basis of the critical maximum force occurring at buckling, and the curvature of the buckled sample which appears as result of the action of this force. The results obtained by this method were compared with those obtained with the use of the FAST system. The good compatibility of both these methods was proved by the correlation coefficients.
Ključne besede: flat textiles, mechanical properties, measurements, fabric handle, bending rigidity, bending moment, curvature, buckling, buckling length
Objavljeno: 01.06.2012; Ogledov: 1180; Prenosov: 33
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Flax fibres sorption properties influenced by different pretreatment processes
Tatjana Kreže, Severina Iskrač, Majda Sfiligoj-Smole, Karin Stana-Kleinschek, Simona Strnad, Darinka Fakin, 2005, izvirni znanstveni članek

Opis: The sorption behavior of raw and treated flax fibers was investigated. This paper presents the effect of conventional pretreatment processes (alkaline, acid) in comparison to environment-friendly enzymatic processes on the sorption ability of flax fibers. Weight-loss, moisture sorption, water retention value and contact angle were determined in order to interpret the pretreatment results. In addition, the influence of the process on the fibers' mechanical properties was studied. The ecological parameters of the treatment wastewaters were analyzed.
Ključne besede: textile fibres, flax, flax fibre properties, pretreatments, sorption properties, mechanical properties, ecological parameters
Objavljeno: 01.06.2012; Ogledov: 1400; Prenosov: 24
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