Dynamic Behaviour of Selective Laser Melted 316L Steel - Mechanical Properties and Microstructure Changes

316L steel specimens with three different shear zones made by SLM (Selective Laser Melting) were subjected to dynamic tests using the Split Hopkinson Pressure Bar method. The effect of high-speed deformation on changes in microstructure was analyzed. In addition, the stress-strain relationship was determined from the SHPB results. To visualize the deformation process of the specimens during the tests, a camera with a high frame rate was used. It was shown that as the plastic deformation increases, the hardness of the material increases. Microstructural analysis of dynamically loaded areas revealed numerous defects. Twinning was found to be the main deformation mechanism. Large plastic deformation and many other microstructural changes such as shear bands, cracks and martensite nucleation were also observed

High strain rate effect on tensile ductility and fracture of AM fabricated Inconel 718 with voided microstructures

The paper describes Electromagnetic Ring Expansion Tests (ERET) performed on Laser Melting Powder Bed Fusion (LPBF) Inconel 718 stress relieved test pieces, to establish the effect of a randomly dispersed spherically voided microstructure on tensile ductility, fracture, and fragmentation at high strain rate (10-3 < e < 104 s-1). An empirical model to predict porosity type and growth rates as a function of laser energy density was established, to select the LPBF process parameters to fabricate test pieces under stable conduction and keyhole melting. The size, shape, distribution of macro and keyhole pores in the test pieces obtained for ERET testing were characterised. At high strain rate the number of ring fragments for the highest porosity doubled, accompanied by a reduction in true strain at maximum uniform elongation and fracture strain. The trend for reducing fracture strain with increasing porosity at high strain rate was described by a decaying power law. Overall, there was a significant positive strain rate effect on tensile ductility at lower porosities attributed strain rate hardening (Hart, 1967) [1]. Fracture surfaces containing the highest porosity identified four different void coalescence mechanisms that helped explain the influence of larger pores on the stress state in the alloy.The AM of IN718 and tensile testing was funded by the UoD, College of Science and Engineering Research Excellence Framework (REF) funding for the Director of IISE (P. Wood) and AM Researcher (U. Gunputh). The support of G. Williams for IN718 sample preparation and M. Pawlik for tensile testing is acknowledged. A. Rusinek acknowledges the program UC3M-Santander Chair of Excellence in additive manufacturing. The expanding ring tests investigations were funded by the Polish Ministry of Science and Higher Education, Centre for Research and Development under research grant No. TECHMATSTRATEG2/410049/12/NCBR/2019

Quasi-static and dynamic compressive behaviorof Gum Metal: experiment and constitutive model

The quasi-static and high strain rate compressive behavior of Gum Metal with composition Ti-36Nb-Ta-3Zr-0.3O (wt pct) has been investigated using an electromechanical testing machine and a split Hopkinson pressure bar, respectively. The stress–strain curves obtained for Gum Metal tested under monotonic and dynamic loadings revealed a strain-softening effect which intensified with increasing strain rate. Moreover, the plastic flow stress was observed to increase for both static and dynamic loading conditions with increasing strain rate. The microstructural characterization of the tested Gum Metal specimens showed particular deformation mechanisms regulating the phenomena of strain hardening and strain softening, namely an adiabatic shear band formed at ~ 45 deg with respect to the loading direction as well as widely spaced deformation bands (kink bands). Dislocations within the channels intersecting with twins may cause strain hardening while recrystallized grains and kink bands with crystal rotation inside the grains may lead to strain softening. A constitutive description of the compressive behavior of Gum Metal was proposed using a modified Johnson-Cook model. Good agreement between the experimental and the numerical data obtained in the work was achieved

Winter Bird Assemblages in Rural and Urban Environments: A National Survey

Urban development has a marked effect on the ecological and behavioural traits of many living organisms, including birds. In this paper, we analysed differences in the numbers of wintering birds between rural and urban areas in Poland. We also analysed species richness and abundance in relation to longitude, latitude, human population size, and landscape structure. All these parameters were analysed using modern statistical techniques incorporating species detectability. We counted birds in 156 squares (0.25 km2 each) in December 2012 and again in January 2013 in locations in and around 26 urban areas across Poland (in each urban area we surveyed 3 squares and 3 squares in nearby rural areas). The influence of twelve potential environmental variables on species abundance and richness was assessed with Generalized Linear Mixed Models, Principal Components and Detrended Correspondence Analyses. Totals of 72 bird species and 89,710 individual birds were recorded in this study. On average (±SE) 13.3 ± 0.3 species and 288 ± 14 individuals were recorded in each square in each survey. A formal comparison of rural and urban areas revealed that 27 species had a significant preference; 17 to rural areas and 10 to urban areas. Moreover, overall abundance in urban areas was more than double that of rural areas. There was almost a complete separation of rural and urban bird communities. Significantly more birds and more bird species were recorded in January compared to December. We conclude that differences between rural and urban areas in terms of winter conditions and the availability of resources are reflected in different bird communities in the two environments

Urban and rural habitats differ in number and type of bird feeders and in bird species consuming supplementary food

Bird feeding is one of the most widespread direct interactions between man and nature, and this has important social and environmental consequences. However, this activity can differ between rural and urban habitats, due to inter alia habitat structure, human behaviour and the composition of wintering bird communities. We counted birds in 156 squares (0.25 km(2) each) in December 2012 and again in January 2013 in locations in and around 26 towns and cities across Poland (in each urban area, we surveyed 3 squares and also 3 squares in nearby rural areas). At each count, we noted the number of bird feeders, the number of bird feeders with food, the type of feeders, additional food supplies potentially available for birds (bread offered by people, bins) and finally the birds themselves. In winter, urban and rural areas differ in the availability of food offered intentionally and unintentionally to birds by humans. Both types of food availability are higher in urban areas. Our findings suggest that different types of bird feeder support only those species specialized for that particular food type and this relationship is similar in urban and rural areas. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11356-015-4723-0) contains supplementary material, which is available to authorized users

Problem professional ethics

A man, In order to obtain something which makes him Or Her happy, Has to per form action which are – In the opinion of others – valuable and Worth to be paid for. Already from the previous sentence we can deduce a Simple truth that there is nothing for free, each thing service Has its price. Or in other words, sometimes you have to be a giver In order to be given something later. A work is a noble act, although many May become indignant about this statement. By working we multiply things we already have, Or we Get New ones. A human activity which makes us richer, is the one which is attributable to the human nature, and an inactivity or a satisfaction with things we already have is in contradiction with this nature. Taking into account a job ethics, as moral we can consider only such an activity of an individual which has won recognition in somebody else’s eyes, the highest manifestation of which is a remuneration. Not elsewhere, but on the ground of job ethics we ecounter a dissatisfaction of some people with actions of others, e.g. with an employer’s behavior who evades the obligation to pay work. The job ethics, since of became a part of a social discussion served politicians, as well a philisophers, or clerics to fight aversion to this organization of everyday live, which is indicated by the clock and operating hours of a factory. This aversion was based on an aspiration to satisfy one’s own needs, and nothing more. A 19 th – century labourer, having been given a remuneration, which enabled him or her a poor existence – poor but existence, did not see a reason why he or she should work more. After all, outside work there were so many interesting things to do, so it was not worth to waste time for moneygrubbing

Rewolucja jako przejaw zmiany społecznej

Rewolucję można uznać za najbardziej spektakularny przejaw reform społecznych. Rewolucja budzi powszechny entuzjazm, daje nadzieję, tworzy wizję przyszłości, którą często sobie wyobrażamy. Przez wieki człowiek buntował się przeciwko czemukolwiek, tylko grecki umysł to zmienił. Wielu socjologów uważa, że ​​nieodłączny wiek należy nazwać rewolucją. Powszechny sukces rewolucji zależy od mobilizacji społecznej i zauważenia, że ​​może ona dać szansę na zmianę formalnej pozycji społecznej

Revolution as symptoms social change

Revolution can be judged as the most spectacular sign of social reforms. Revolution gives rise to common enthusiasm, gives hope, creates the vision of the future, which is often imaginated. For centuries man rebelled against anything, only the Greek mind changed it. A lot of sociologist consider that inherent century should be called the revolution. The widespread success of the revolution is dependent on social mobilization and notice that it can give a chance to change the formal social position

Metodyka badania materiałów wysokoenergetycznych w warunkach obniżonej temperatury

The methodology developed for testing gun propellants at low temperatures according to PN-EN ISO 604:2006 is presented in the paper. Brief characteristics are given of the materials tested and the most important static compression test conditions, such as specimen dimensions, deformation velocity and temperature range for selected propellants, i.e. JA-2 and SC. To verify the methodology developed, preliminary strength tests were performed at selected temperatures (25, 0, -25 and -50°C). Tests were carried out on specimens fabricated by shortening the propellant grain to the dimensions required by the reference standard. The results obtained confirmed the expected strength properties for both propellants (tensile strength and brittleness). Due to its chemical composition, the JA-2 propellant is a material of low brittleness even at -50°C. It does not crack completely and only its yield point increases. The results obtained for the JA-2 propellant were consistent with those published in reference literature. The SC propellant proved to be very brittle even at room temperature. At temperatures below 0°C, it fractures completely after reaching the desired deformation. The results obtained confirm that the adopted strength test conditions and the way the tests were prepared and performed enable acquisition of comparable and reliable results. It can be seen by analysing the results for the JA-2 propellant, which are consistent with the data in the available references. In contrast, the tests on the SC propellant proved the validity of strength tests on this type of material. Brittleness of propellant grains is a very undesirable phenomenon. A change in the combustion surface of low explosives caused by the process of propellant grain fracturing can adversely affect the magnitude and course of the pressure pulse, leading to failure of a cartridge chamber or gun barrel.W artykule przedstawiono opracowaną metodykę badania prochów w obniżonej temperaturze na podstawie normy PN-EN ISO 604:2006. Opisano krótką charakterystykę badanych materiałów oraz najważniejsze warunki przeprowadzania statycznej próby ściskania takie, jak: wymiary próbek, prędkość deformacji oraz zakres temperatur dla wybranych gatunków prochu, tj.: JA-2 oraz SC. W celu weryfikacji opracowanej metodyki wykonano wstępne badania wytrzymałościowe w wybranych temperaturach (25, 0, -25 i -50 °C). Testy przeprowadzono dla próbek powstałych poprzez skrócenie ziarna do wymiarów zgodnych z normą. Uzyskane wyniki potwierdziły oczekiwane właściwości wytrzymałościowe dla obu gatunków prochu (kruchość, wytrzymałość na rozciąganie). Proch JA-2 ze względu na skład chemiczny jest materiałem o niskiej kruchości nawet w temperaturze -50 °C. Nie ulega całkowitemu skruszeniu, rośnie jedynie jego granica plastyczności. Wyniki uzyskane dla prochu JA-2 są zbieżne z wynikami opublikowanymi w literaturze. Proch SC okazał się materiałem bardzo kruchym już w temperaturze pokojowej. W temperaturach poniżej 0 °C ulegał całkowitemu skruszeniu po osiągnięciu zakładanego odkształcenia. Uzyskane wyniki potwierdzają, że przyjęte warunki testu wytrzymałościowego oraz sposób przygotowania i przeprowadzenia badań umożliwia uzyskanie porównywalnych i wiarygodnych wyników. Można to zauważyć analizując wyniki dla prochu JA-2, który są zgodne z danymi zamieszczonymi w dostępnej literaturze. Badania prochu SC udowadniają natomiast zasadność badań wytrzymałościowych tego typu materiałów. Kruchość ziaren prochowych jest zjawiskiem bardzo niepożądanym. Zmiana powierzchni spalania prochu wynikająca z procesu pękania ziaren prochowych może wpłynąć negatywnie na wielkość i przebieg impulsu ciśnienia i doprowadzić do zniszczenia komory nabojowej lub lufy działa