T6 Type Research Articles

Influence of Heat Treatment on Stress Intensity Factor of Nano Boron Carbide Hybrid Al2219 Composites with MoS2

The current work emphasizes on study of influence of heat treatment on Stress Intensity factor (KIC) of Al alloy matrix hybrid composites. Hybrid composites with a constant Nano B4C content of 3 weight % and MoS2 of 4 weight % as reinforcements to Al2219 alloy matrix are fabricated by using two step stir casting technique and tested for Stress Intensity factor and fracture toughness as per ASTM standards. One set of composites are subjected to T6 type heat treatment. Compact Tension (CT) Specimen were prepared using wire EDM process and tested in BISS Axial Universal Testing Machine to find Stress Intensity factor (KIC). From this study stability of crack propagation under mode-I failure is analyzed. Results show generous increment in energy required to open the crack and crack propagation is delayed in heat treated composites when compared to non-heat treated composites and furthermore improvement in fracture toughness of the heat treated specimen over non-heat treated specimen.

Primary School Students’ Performance Orientation - The Czech Republic Research

Abstract Introduction: The current school is strongly focused on student performance. Each student faces a large number of learning tasks, which place considerable demands on them, arouse in them a different degree of interest, evoke a different degree of commitment to work, are associated with different expectations or have a different degree of attractiveness. Performance situations are associated with pleasant experiences but also with experiences of failure, which in their essence affect the activity or passivity of the student, and thereby affect the prioritization of the necessity to excel or the need to avoid failure. These needs are the basis of performance orientation, which is analysed in the paper. The aim is to verify whether the motivational orientation of students is related to their beneficial outcomes. Methods: The quantitative nature of the paper made it possible to use both indicators of descriptive statistics (mean, median, mode, standard deviation) and inductive statistics (Mann-Whitney U test, Pearson's Chi-square test, Shapiro-Wilk normality test). The surveyed sample of 363 respondents consisted of an available selection of students from 14 primary schools in five regions of the Czech Republic in 2019. The data were collected physically at schools using a standardized questionnaire. Students were acquainted with its purpose and content. Statistical analysis of the data was carried out electronically, both in terms of methodology in accordance with the research design of Hrabal and Pavelková (2011). Results: The analysis of the data of the sample of respondents revealed that the performance orientation of problem students differs statistically significantly from that of the performance motivation of non-problem students in two cases: 1) the need for successful performance, where differences were verified using hypothesis H1 and 2) in the ratio of performance needs, where the differences were verified using hypothesis H4. In other cases, no statistically significant difference was found between the two groups. Discussion: The presented findings correspond to current domestic (Krykorková & Váňová, 2010) and foreign research (Weiner, 2000). They draw attention to the importance of a positive motivation of the student in terms of his degree of involvement in the development of his own dispositions, which affects the benefit of the student. Positively motivated students achieve better results with a comparable intellect than non-motivated students (Man & Mareš, 2005). The role of the teacher and his knowledge of motivational types of students is of paramount importance in this respect. Limitations: The sample under examination of respondents does not bring a representative sample in terms of the representation of students according to school years, regions of the Czech Republic or according to the representation of so-called problem or non-problem students. The outcomes of the survey can thus be applied only to a given sample of respondents. Conclusion: The benefitting for students in the sample showed lower positive motivation than their intellectually comparable non-problem classmates. It is a question of reserves, the use of which is a challenge not only for themselves, but also for the school and parents. The largest differences between the two groups were recorded in the specific ratio of positive and negative motivation 4: 2 within the T1 type and in the ratio 1: 3 within the T6 type. The attempt to determine the causes of this fact, especially proposing a remedy, is a topic for further research in this area.

Geometry of massless scattering in integrable superstring

We consider the action of the q-deformed Poincaré superalgebra on the massless non-relativistic R-matrix in ordinary (undeformed) integrable AdS2 × S2 × T6 type IIB superstring theory. The boost generator acts non-trivially on the R-matrix, confirming the existence of a non-relativistic rapidity γ with respect to which the R-matrix must be of difference form. We conjecture that from a massless AdS/CFT integrable relativistic R-matrix one can obtain the parental massless non-relativistic R-matrix simply by replacing the relativistic rapidity with γ. We check our conjecture in ordinary (undeformed) AdSn × Sn × T10−2n, n = 2,3. In the case n = 3, we check that the matrix part and the dressing factor — up to numerical accuracy for real momenta — obey our prescription. In the n = 2 case, we check the matrix part and propose the non-relativistic dressing factor. We then start a programme of classifying R-matrices in terms of connections on fibre bundles. The conditions obtained for the connection are tested on a set of known integrable R-matrices.

Simulation of the structure and electronic properties of fluorographene polymorphs formed on the basis of 4-8 graphene

As a result of a theoretical analysis of the possible structure of polymorphic varieties of compounds obtained from the fluorination of L4-8 graphene, the possibility of existence of 6 main structural varieties of CF-L4-8 layers is established (T1-T6 structural types). Ab initio calculations of these layers were performed by the density functional theory method using the generalized gradient approximation. As a result of the calculations, it was established that only five polytypes have a stable structure except for the T3 type layer. The crystal lattices of CF-L4-8 compounds are tetragonal for the T1 - T5 types, and for the T6 type crystal lattice is orthorhombic. The sublimation energies of CF-L4-8 polymorphs of fluorographene vary in the range of 13.36 to 14.09 eV/(CF), which is slightly less than the calculated value of this parameter (14.32 eV/(CF)) for experimentally synthesized CF-L6 fluorographene of T1-type. The maximum band gap, equal to 4.96 eV, is observed for the T2 type layer, and the minimum value (3.05 eV) corresponds to the fluorographene layer of the T3 type.

Black horizons and integrability in string theory.

This thesis is devoted to the study of geometric aspects of black holes and integrable structures in string theory. In the first part, symmetries of the horizon and its bulk extension will be investigated. We investigate the horizon conjecture beyond the supergravity approximation, by considering alpha prime corrections of heterotic supergravity in perturbation theory, and show that standard global techniques can no longer be applied. A sufficient condition to establish the horizon conjecture will be identified. As a consequence of our analysis, we find a no-go theorem for AdS2 backgrounds in heterotic theory. The bulk extension of a prescribed near-horizon geometry will then be considered in various theories. The horizon fields will be expanded at first order in the radial coordinate. The moduli space of radial deformations will be proved to be finite dimensional, by showing that the moduli must satisfy elliptic PDEs. In the second part, geometric aspects and spectral properties of integrable anti-de Sitter backgrounds will be discussed. We formulate a Bethe ansatz in AdS2 x S2 x T6 type IIB superstring, overcoming the problem of the lack of pseudo-vacuum state affecting this background. In AdS3 x S3 x T4 type IIB superstring, we show that the S-matrix is annihilated by the boost generator of the q-deformed Poincare superalgebra, and interpret this condition as a parallel equation for the S-matrix with respect to a connection on a fibre bundle. This hints that the algebraic problem associated with the scattering process can be geometrically rewritten. This allows us to propose a Universal S-matrix.

Investigation of Ballistic Impact Response of Aluminum Alloys Hybridized with Kevlar/Epoxy Composites

In this comparative study, ballistic impact responses of various aluminum alloys hybridized with Kevlar/Epoxy composite is investigated numerically. The numerical models were developed using the explicit finite element module of ANSYS. 50 caliber projectile with an initial velocity of 400 m/s is used during the analyses. In the first part of the study, 7075, 6061 and 2024 aluminum alloys are compared for their ballistic impact resistance. Amount of perforation energies (energy absorbing capacity of target) and projectile residual velocities of these alloys are compared. Also, thicknesses of plates are increased up to the point at which the plates don't exhibit full perforations for the used projectile and initial velocity. It is seen that that residual velocity of the Al 7075 T6 is the smallest among the used aluminum alloys which means that 7075 T6 type of aluminum has the higher ballistic impact resistance. In the second part of the study, six different hybrid models that have different combinations of Al 7075 and Kevlar29/Epoxy are proposed. Perforation energies and projectile residual velocities of these proposed models are compared under ballistic impact loadings. It was shown that the hybrid model with 6AL-6KEV orientation, was the optimum structure to resist the ballistic impact loading among the proposed models. Which means that the plate with this orientation has exhibited the maximum energy absorbing characteristics.

High Temperature Wear Properties of Artificially Aged 6061Al-B4CpMetal Matrix Composite

In the present work, 6061Al matrix reinforced with 9wt. % B4C particle size of 88 microns is produced by liquid metallurgy method. During processing, K2TiF6 and B4C in the ratios of 0.2 were preheated and added to Al melt at 750°C with continuous stirring to obtain uniform distribution of B4C in 6061Al matrix. The casted composites were subjected T4 and T6 type heat treatments with quenching medium as water at room temperature. Microstructure characterization was done for both the heat treated and un-heat treated specimens using optical microscope/XRD. The presence of Mg2Si was confirmed through XRD studies. High temperature wear tests were conducted using Pin-On-Disc apparatus. Wear test samples were prepared as per ASTM G99 standards and slide against stainless steel disc (32HRC) with constant sliding velocity of 2.51m/sand constant sliding distance of 1000m by varying the load ranging from 9.81N to 39.24N at test temperatures of 150°C. Results of wear tests suggest that wear resistance increases in the order of matrix, composite without aging and composite with aging. The worn surface morphology showed that heat treated Al-B4C composites have more wear resistance capacity than as cast 6061Al.

Influence of T6-heat treatment on mechanical properties of Al7075 alloy reinforced with Cenosphere

Cenospheres are light weight, inert and hollow spheres filled with air with main constituents of silica and alumina. It is a by-product obtained after combustion of pulverized coal in thermal power plants. Due to its light weight and hollow in nature, Cenospheres are used as reinforcement in metal matrix composites to enhance the mechanical and microstructural properties. The 7xxx series are heat treatable aluminium alloys used in high performance structural, aerospace and transportation applications. The present paper reports the effect of heat treatment on mechanical properties of Cenosphere incorporated Al-7075 composites produced by stir casting technique. The composites were subjected to T6 type heat treatment , subsequently the heat treated specimen of different composition and different heat treatment duration were tested for evaluation of mechanical properties and same has been compared with the results of as cast (un heat-treated) composite specimens. The mechanical properties such as ultimate tensile strength, compression strength and hardness are analyzed as a function of heat treatment duration. The results of heat treated samples are then compared with as cast samples.

WISE J061213.85-303612.5: a new T-dwarf binary candidate

T and Y-dwarfs are among the coolest and least luminous objects detected, and they can help to understand the properties of giant planets. Their multiplicity properties can shed light on the formation process. We observed a sample six T dwarfs and one L9 dwarf with the Laser Guide Star (LGS) and NAOS-CONICA, the adaptive optics (AO) facility, and the near infrared camera at the ESO Very Large Telescope. From the seven observed objects, we have identified a subarcsecond binary system, WISE J0612-3036, composed of two similar components with spectral types of T6. We measure a separation of $\rho$ = 350$\pm$5 mas and a position angle of $PA = 235\pm1^{\circ}$. Using the mean absolute magnitudes of T6 dwarfs in the 2MASS $JHK_s$ bands, we estimate a distance of $d$=31$\pm$6 pc and derive a projected separation of $\rho$ = 11$\pm$2 au. Another target, WISE J2255-3118, shows a very faint object at 1.3 arcsec in the $K_{\rm s}$ image. The object is marginally detected in $H$, and we derive a near infrared color of $H-K_{\rm s}$$>$ 0.1\,mag. $HST/WFC3$ public archival data reveals that the companion candidate is an extended source.Together with the derived color, this suggests that the source is most probably a background galaxy. The five other sources are apparently single, with 3-$\sigma$ sensitivity limits between $H$=19-21 for companions at separations $\geq$ 0.5 arcsec. WISE 0612-3036 is probably a new T-dwarf binary composed of two T6 dwarfs. As in the case of other late T-dwarf binaries, it shows a mass ratio close to 1, although its projected separation, $\sim$11 au, is larger than the average ($\sim$ 5 au). Additional observations are needed to confirm that the system is bound.

Wear and corrosion performance of two different tempers (T6 and T73) of AA7075 aluminium alloy after nitrogen implantation

The present work reports the improvements in corrosion resistance and tribological properties achieved after Nitrogen ion implantation into aluminium alloy AA7075 subjected to two different tempers, T6 and T73.Nitrogen implantation at a nominal dose of 2×1017ions/cm2 and at an accelerating voltage of 50keV produced an increase of the surface hardness of the alloys up to a 130% in T6 samples and to 190% in T73 samples.The increase in hardness has a very positive effect on wear resistance as indicate the significant reduction of specific wear rate on both tempers (about −75% for T6 and −90% for T73 samples).Similarly, an improvement in corrosion properties of both tempers is confirmed by DC techniques, showing a decrease of the registered current density on potentiodynamic curves, and by the increase of impedance shown by AC techniques.This overall improvement in the alloy performance has been mainly attributed to the formation of a stoichiometric aluminium nitride layer (AlN), identified by XPS and GIXRD.The combination of EXCO immersion tests and electrochemical measurements allowed explaining the effect of AlN layer, which behave as a barrier delaying the onset of corrosion and slowing its progress. However, the implantation do not modified the corrosion morphology which seems to be determined mainly by the heat treating conditions. Thereby, in both tempers the localized attack starts at the intermetallic/matrix interface, but in T6 type specimens the progress of corrosion is clearly intergranular, while T73 specimens show the formation of clusters of small geometrical pits, probably related to the biggest MgZn2 strengthening precipitates.

Mechanical Property and Intergranular Corrosion Sensitivity of Zn-Free and Zn-Microalloyed Al-2.7Cu-1.7Li-0.3Mg Alloys

The influence of 0.72 pct Zn addition on the tensile properties of Al-2.7Cu-1.7Li-0.3Mg alloys was investigated. Their intergranular corrosion (IGC) dependence on aging [T6 type at 423 K (150 °C) and 448 K (175 °C) and T8 type at 423 K (150 °C)] time was studied. An IGC diagram associated with aging process was established. The addition of 0.72 pct Zn enhanced the strength of the Al-Li alloy with T6 type aging at 448 K (175 °C). With aging process, the corrosion mode of the T6-aged Al-Li alloys was changed in the following order: pitting and local IGC (initial aging stage), general IGC (underaging stage), local IGC (near peak-aging stage), and pitting (overaging stage) again. The IGC depth was increased first and then decreased with aging time extension. The corrosion potential change of grains and the microstructure variation were used to explain the IGC sensitivity of the Al-Li alloy with different tempers. Meanwhile, 0.72 pct Zn addition decreased the IGC sensitivity of the Al-Li alloy, especially the T6-aged Al-Li alloy.

Influence of Magnesium Addition on Mechanical Properties and Microstructure of Al-Cu-Mg Alloy

The influence of Mg addition on mechanical properties and microstructure of Al-Cu-Mg alloy was investigated. Cast Al - Cu- Mg alloys have widely been used in aircraft, aerospace, industrial and architectural applications for their good mechanical properties, high strength-to-weight ratio. An intensive study of these cast aluminium family has been found in many literature as a source for enhancing the mechanical properties and microstructure of aluminium alloys. The main objective of this paper was to investigate the effect of magnesium on mechanical properties and microstructural changes of Al4Cu alloys. The modifications of Al4Cu by adding Mg of 0.5 to 2.5 % in the interval of 0.5% mixing with stirrer and casted by gravity die casting, subsequently the specimens were subjected T6 type heat treatment for 6 hr at 180 0 C. The effect of Mg and ageing on microstructure was studied by using optical microscope. The mechanical properties such as tensile strength and hardness were studied using universal tensile testing machine and Brinell hardness tester respectively. It was observed that the tensile strength and hardness increased with increase of percentage of Mg. The addition of 2.5% Mg increases the tensile strength by 69.9% while hardness increased by 22%. Samples that were aged showed that with addition of 1% of Mg had effect on grain refinement and mechanical properties of the alloy because of smaller grain size.

Identifying nearby field T dwarfs in the UKIDSS Galactic Clusters Survey

We present the discovery of two new late-T dwarfs identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 2 (DR2). These T dwarfs are nearby old T dwarfs along the line of sight to star-forming regions and open clusters targeted by the UKIDSS GCS. They are found towards the Alpha Per cluster and Orion complex, respectively, from a search in 54 square degrees surveyed in five filters. Photometric candidates were picked up in two-colour diagrams, in a very similar manner to candidates extracted from the UKIDSS Large Area Survey (LAS) but taking advantage of the Z filter employed by the GCS. Both candidates exhibit near-infrared J-band spectra with strong methane and water absorption bands characteristic of late-T dwarfs. We derive spectral types of T6.5+/-0.5 and T7+/-1 and estimate photometric distances less than 50 pc for UGCS J030013.86+490142.5 and UGCS J053022.52-052447.4, respectively. The space density of T dwarfs found in the GCS seems consistent with discoveries in the larger areal coverage of the UKIDSS Large Area Survey, indicating one T dwarf in 6-11 square degrees. The final area surveyed by the GCS, 1000 square degrees in five passbands, will allow expansion of the LAS search area by 25%, increase the probability of finding ultracool brown dwarfs, and provide optimal estimates of contamination by old field brown dwarfs in deep surveys to identify such objects in open clusters and star-forming regions.

Effect of weld metal microstructure on the monotonic and cyclic mechanical behavior of tig welded 2091 Al–Li alloy joints

The effect of TIG welding on the mechanical behavior of Al–Li alloy 2091-T851 has been investigated by means of tensile and fatigue testing. Compared to the base alloy, as-welded joints were found to display significant reductions in both tensile and fatigue strengths and to suffer a drastic degradation in ductility. Such behavior is primarily related to the presence of large elongated R phase precipitates at the weld metal grain boundaries, which leads to intergranular crack propagation through that part of the joint. Substantial microstructural changes, though, can be induced in the weld metal by subjecting the welded joints to a post-weld T6 type heat treatment. This promotes dissolution of the R phase, thus enhancing the tensile properties as well as the fatigue strength, consistent with the predominance of transgranular fracture of the weld metal in the heat treated joints. Finally, the microstructural aspects presented above indicate that the weld metal is plastically more heterogeneous than the base alloy and therefore is expected to work-harden faster, which is borne out by the tensile test results.

Sintering behaviour and mechanical properties of PM Al-Zn-Mg-Cu alloy containing elemental Mg additions

A commercially available PM Al-5.5Zn-2.5Mg-1.6Cu (wt-%) alloy has been used to study the effect of elemental Mg additions, ranging from 0 to 4.5 wt-%, on its sinterability and mechanical properties after sintering and heat treatment of the W and T6 type. DSC experiments were performed to study the chemical reactions occurring during sintering. Results obtained from dilatometry and DSC experiments were used to aid determination of the optimum sintering cycles under nitrogen. DSC experiments performed on as sintered samples were used for the determination of the solution treatment temperature. The microstructure obtained after sintering of the experimental Al alloys was characterised by SEM and XRD. The mechanical properties of the alloys, both, in the as sintered and heat treated states were obtained from tensile testing and hardness measurements. Additional theoretical calculations, using the THERMOCALC programme, along with the experimental observations, were carried out as an alloy design method to suggest an alternative chemical composition and alloying strategy aimed at upgrading the sintering behaviour and mechanical properties of the present alloy.

Influence of Retrogressing and Reaging on the Stress Corrosion Cracking Resistance of 7010

The Al-Zn-Mg-Cu alloy 7010 is known to respond well to retrogression and reaging (RRA) thermal treatments. Tensile properties and levels of fracture toughness comparable to the T6 type condition can be achieved by retrogressing for 40 minutes at 200°C and then reaging 24 h at 120°C. The improvement in stress corrosion cracking (SCC) is more difficult to quantify and constant crack opening displacement SCC can be prone to large scatter at the low crack velocities associated with T7x and RRA treated material. The results of SCC testing by constant load smooth bar testing and precracked constant crack opening displacement double cantilever beam testing are reported and correlated with microstructural observations.

Effect of Heat Treatment on Tensile Properties of Zinc-37.5 mass%Aluminium Alloy Containing Nickel or Silicon

Attention has been focussed in this study to understand the influence of microstructural changes brought about through T6 type heat treatment on the tensile strength and elongation of some zinc-37.5 mass%aluminium based alloys comprising nickel/silicon. Other (test) variables whose effects were studied include strain rate (at room temperature) and test temperature (at a typical strain rate). The study indicates that heat treatment and test conditions (strain rate and test temperature) affect the tensile properties of the zinc-based alloys to varying extents. The response of the alloys under different test conditions has been explained on the basis of specific characteristics of their various microconstituents. It has been observed that factors like microcracking tendency and thermal stability greatly control the mechanical properties of the samples. The predominance of the parameters over each other depends on the test conditions. Accordingly, the alloys exhibit changing properties as the condition of testing alters.

Defined In Situ Enumeration of T6 and HLA-DR Expressing Epidermal Langerhans Cells: Morphologic and Methodologic Aspects

An essential prerequisite for the in situ enumeration of epidermal Langerhans cells (LCs) is the unequivocal identification of the desired cell type. We have examined over 250 cryostat sections of normal human skin to analyze morphologic and methodologic problems underlying the quantification of epidermal LCs, defined by anti-T6 (OKT6) and anti-HLA-DR (OKIal) immunoperoxidase staining. Our findings show that OKT6 reactivity of dendritic processes in cross-sectioned epidermis yields microscopic images which are not easy to analyze objectively. The morphology that we find leads us to categorize dendritic cells into 3 arbitrary types of T6+ LC profiles. In addition we describe criteria for the assessment of OKT6 staining patterns relating to the dendritic state of epidermal LCs. Preliminary quantitative data on this issue are discussed in relation to: epidermal thickness; the thickness of skin tissue sections; and the discrepancy between the number of T6+ and HLA-DR+ LCs. We hope that the principles outlined in this report may serve to overcome potential methodologic problems with quantitation of T6+ epidermal LCs in skin sections.

High-Strength Aluminum Alloys

The room temperature properties of commercial, high-strength aluminum alloys are reviewed. In addition, the properties of experimental aluminum alloys of the —T6 type are discussed with respect to tensile, tear, and fracture toughness properties. Both the commercial and experimental aluminum alloys are compared with a maraged 18Ni-7Co-5Mo steel alloy and a beta-titanium (Ti-3Al-13V-llCr) cold-rolled alloy.