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1
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The Influence of Tool Tilt Angle on 1050 Aluminum Lap Joint in Friction Stir Welding Process

100%
Barlas Z.
Acta Physica Polonica A
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2017
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vol. 132
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issue 3
679-681
EN
In this paper, the effect of tool tilt angle on tensile-shear failure load and weld zone properties for 1050 aluminum plates, welded by friction stir lap welding, were investigated. For this purpose, tool tilt angle was varied from 0° to 5° under the constant other parameters, such as tool geometry, tool rotation speed of 1200 rpm and tool travel speed of 30 mm/min. The tensile-shear test was employed to test the mechanical properties of the joint. Optical microscope examinations, microhardness and temperature measurements were also performed in weld zone of lap joints. According to overall results, the tool tilt angle has a reasonable influence on the joint soundness and weld defect formation. If the tool axis was perpendicular to plate surface or a larger tool tilt angle was used, such configurations had harmful effect for the weld zone. In such case the tensile-shear failure load dropped from 4853 N to 2799 N. Recorded peak temperatures varied from 381°C to 438°C in the weld center. The measured mean hardness values of the stir and heat-affected zones were 31.5 HV and 28.3 HV, respectively, which are lower than that of aluminum 1050 base metal (40.7 HV).
2
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Weldability of CuZn30 Brass/DP600 Steel Couple by Friction Stir Spot Welding

100%
Barlas Z.
Acta Physica Polonica A
|
2017
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vol. 132
|
issue 3
991-993
EN
This study deals with the weldability and assessment of the friction stir spot welding of dissimilar CuZn30 brass/DP600 steel couple. The effects of axial tool load and tool hold time were evaluated in the joining experiments. The tool load forces of 3.2-4.8 kN and the tool hold times of 8 s and 12 s were applied to brass/steel bimetal sheets. Tensile-shear test was employed to investigate the mechanical properties of the joint. Optical and scanning electron microscopies were utilized to characterize the microstructure of the joint having the better mechanical performance, as well as the microhardness test. Temperature measurements were also performed between the lapped sheet faces. The results show that the vertical tool load value has reached more significant influence than the tool hold time. Furthermore, the tensile-shear failure load has increased with increasing tool load and hold time and has reached the highest value of 4.6 kN. The EDS analyses on the fractured surface depict that the copper and zinc concentrations are similar to those of CuZn30 base metal. A peak temperature of 607°C was measured in the weld centre of this joint. No significant microstructural change was observed in the steel sheet, while the fine grains with onion rings were revealed in the brass. Different hardness values were measured depending on microstructural change in the weld zone. Although the onion rings made a contribution to the microhardness, a softened stir zone (129.8 HV), with regard to the brass base metal (149.1 HV), was observed.
3
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Energy Dissipation in the AFM Elasticity Measurements

80%
Klymenko O., Wiltowska-Zuber J., Lekka M., Kwiatek W.
Acta Physica Polonica A
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2009
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vol. 115
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issue 2
548-551
EN
Nowadays, it is well established that changes of cell stiffness observed by atomic force microscopy are linked with the cell cytoskeleton. Its structural and functional alterations are underlying major diseases such as cancer, inflammation or neurodegenerative disorders. So far, the use of atomic force microscopy is mostly focused on the determination of the Young modulus using the modified Hertz model. It can quantitatively describe the elastic properties of living cells, however, its value is burdened by the fact that cells are neither isotropic nor homogeneous material. Often, during the atomic force microscopy measurements, the hysteresis between the loading and unloading curves are observed which indicates the dissipation of an energy. In our studies, the index of plasticity was introduced to enumerate such effect during a single loading-unloading cycle. As the results show, such approach delivers an additional parameter describing the mechanical state of cell cytoskeleton. The analysis was performed on test samples where the mechanical properties of the melanoma cells were changed by glutaraldehyde and cytochalasin D treatments. The non-treated cells were compared with fibroblasts.
4
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ESR Studies of Paramagnetic Centers in Pharmaceutical Materials - Cefaclor and Clarithromycin as an Example

80%
Skowronska A., Wojciechowski M., Ramos P., Pilawa B., Kruk D.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
514-517
EN
Electron spin resonance (ESR) studies of two antibiotics, Cefaclor and Clarithromycin, have been performed in order to investigate concentration and dynamics of free radicals generated in these compounds due to thermal sterilization. For Cefaclor three combinations of temperature and heating time have been applied: 160°C, 170°C, 180°C for 120 min, 60 min, and 30 min, respectively, according to the pharmaceutical sterilization norm. Clarithromycin has been heated at 160°C for 120 min. The ESR lineshape has been investigated versus microwave power ranging from 2.2 mW to 70 mW. Electron spin-spin relaxation time has been estimated from the ESR lineshape analysis. Concentrations of radicals generated due to different sterilization procedures have been compared with the purpose to select the best sterilization scheme.
5
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The Increase in Protein Contour Length Depends on Mechanical Unfolding Conditions

80%
Dąbrowska A., Lebed K., Lekka M., Kulik A., Forró L.
Acta Physica Polonica A
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2008
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vol. 113
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issue 2
753-762
EN
Many proteins in alive organisms have a domain structure providing them the possibility to reversible unfolding, which seems to play an essential role in those processes occurring in tissues which are controlled by mechanical cellular tension. In this work the atomic force microscopy was applied to investigate the mechanical properties of the single molecules of fibronectin, a protein participating in the important mechanical processes in extracellular matrix. The results showed that the conditions of mechanical stretching influence not only the force required to unfolding of a domain but also the increase in protein contour length induced by such unfolding event. Two mean values of the increase in length (called shortly the unfolding length) L_1 and L_2, were obtained and ascribed to unfolding of either the whole fibronectin domain of type III (L_2) or its fragment (L_1). Both unfolding lengths revealed similar dependence on the stretching conditions. This experimental observation of increase in unfolding length with increasing loading rate was successfully described with a combination of two theoretical models (Bell model and the worm-like-chain model), previously used separately in the analysis of protein unfolding. The general mechanical property of fibronectin domains was emphasized and proposed as a potential determinant of the cellular adhesion.
6
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Investigation of Mechanical Properties of Fe-Based Metal Matrix Composites by Warm Compaction for Gear Production

80%
Gun T., Simsir M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 3
443-447
EN
In this study, mechanical behavior of iron-based (Fe-0.8C-2.0Cu-4.5Ni-1.8Mo-1.0B (wt.%)) metal matrix composite synthesized by powder metallurgy was investigated for gear production. Metal matrix composite has been produced by warm compaction, followed by free sintering in controlled Ar gas atmosphere. Green composite was produced under pressure of 650 MPa at 160°C. The green products have been sintered at various temperatures (1050, 1150 and 1250°C) and for various time periods (30, 60 and 90 min). Mechanical tests (hardness and wear tests) have been conducted. The microstructure and the worn surfaces of the samples have been examined under scanning electron microscope and analyzed by energy dispersive spectroscopy and X-ray diffraction method. The results have shown that hardness and wear resistance of the samples increase with increasing sintering temperature and time. Effect of sintering temperature is greater than that of sintering time. The highest hardness and wear resistance have been obtained in the composite sample produced at 1250°C for 90 min.
7
Content available remote

Parametric and Structural Analysis of Dynamic Anterior Cervical Biomaterial Plate Implant by Computer Aided Virtual Engineering

80%
Karaçalı Ö.
|
EN
The main objective of this study was to examine the convenience of an accurate model of placement of dynamic anterior cervical plate, made of poly (methl-methacrylate) biomaterial, for testing spinal implants, and to determine the maximum fatigue values of differently surfaced Ti-5Al-2.55n spinal screw-rods, by finite element modeling. Anterior cervical biomaterial plates reduce the hazard for spinal cord injury and provide outstanding fixation for the anterior column to stop the relocation and slackening of screws-rods, using a cross-split screw crown that may be fastened into the biomaterial plate. This article reports about the hollow Ti-5Al-2.55n screw and cervical biomaterial plate system. The flexion movement of the spine implant was modeled, using finite elements method, to control the stresses and strains of the bone and screw interfaces to external forces, as well as motion of the vertebras. This computational engineering analysis was aimed to support patients suffering anterior cervical arthrodesis after a degenerative disease or trauma. The obtained data from this research may provide an essential base to estimate the stabilization quality and mechanical properties of biomaterial selection. Model of the region between C4 and C6 segments of vertebrae of cervical spine was produced to correct the stabilization of implant with non-linear material properties. Study of the cervical biomaterial implant has provided instantaneous virtual experiment of secure fixation with minimal complications before a real implant surgery, using computer aided virtual engineering.
8
Content available remote

A Study of the Dynamic Anterior Cervical Plate Implant by Computer Aided Virtual Engineering Method

80%
Karaçalı Ö.
|
EN
The convenience of dynamic anterior cervical PMMA biomaterial placement of spinal implants is considered by finite element modeling. The maximum fatigue behavior was also studied in surface coated Ti-5Al-2.55n spinal screw-rods. Anterior cervical biomaterial plates reduce the hazard for spinal cord injury and provide outstanding fixation for the anterior column, to stop the relocation and slackening of screws-rods by a cross-split screw crown that may be fastened into the biomaterial plate. This article reports about the hollow Ti-5Al-2.55n screw and cervical biomaterial PMMA plate system. The flexion movement of the spine implant was modeled to control the stresses and strains of the bone and screw interfaces under the external forces, as well as motion of the vertebrae by finite element modeling. This computational engineering analysis is aimed to support patients suffering anterior cervical arthrodesis after degenerative disease or trauma. The data from this research may provide an essential base to estimate the stabilization quality. A model for the biomaterial between C4 and C6 segments of vertebrae of cervical spine was obtained. Study of the cervical biomaterial implant provides instantaneous secure fixation virtual experiment with minimal complications, before the real implant surgery, using computer aided virtual engineering.
9
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Content available

^1H NMR and Rheological Studies of the Calcium Induced Gelation Process in Aqueous Low Methoxyl Pectin Solutions

61%
Dobies M., Kuśmia S., Jurga S.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
33-46
EN
The ^1H NMR relaxometry in combination with water proton spin-spin relaxation time measurements and rheometry have been applied to study the ionic gelation of 1% w/w aqueous low methoxyl pectin solution induced by divalent Ca^{2+} cations from a calcium chloride solution. The model-free approach to the analysis of ^1H NMR relaxometry data has been used to separate the information on the static (β) and dynamic (〈τ_c〉) behaviour of the systems tested. The ^1H NMR results confirm that the average mobility of both water and the pectin molecules is largely dependent on the concentration of the cross-linking agent. The character of this dependency (β,〈τ_c〉 and T_2 vs. CaCl_2 concentration) is consistent with the two-stage gelation process of low methoxyl pectin, in which the formation of strongly linked dimer associations (in the range of 0-2.5 mM CaCl_2) is followed by the appearance of weak inter-dimer aggregations (for CaCl_2 ≥ 3.5 mM). The presence of the weak gel structure for the sample with 3.5 mM CaCl_2 has been confirmed by rheological measurements. Apart from that, the T_1 and T_2 relaxation times have been found to be highly sensitive to the syneresis phenomenon, which can be useful to monitor the low methoxyl pectin gel network stability.
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