Određivanje naprezanja tečenja hidrauličnim pokusom dubokog izvlačenja

In sheet metal forming operations the mechanical properties of the sheet metal (stress-strain curve, flow stress) greatly influence metal flow and product quality. Accurate determination of the stress-strain relationship is important in process simulation by finite element method. In this paper the sheet thickness gradation in different points of the hemisphere formed in the bulge test is analysed, both theoretically and experimentally. A precise determination of sheet thickness at the pole is very important in the precise determination of stress-strain relationship. The use of the hydraulic bulge test for estimation of flow stress under biaxial stress-strain state is discussed.U oblikovanju trake mehanička svojstva trake (σ–ε dijagram, naprezanje tečenjem) značajno utječu na tečenje i kakvoću proizvoda. Točno određivanje odnosa naprezanje-istezanje je važno u procesu simulacije metodom konačnih elemenata. Na pokusu dobivenim dubokim izvlačenjem analiziralo se i teoretski i eksperimentalno, po debljini trake i polukugli. Precizno određivanje po debljini trake je važno za odnos naprezanje-istezanje. Raspravljeno je rabljenje hidrauličkog pokusa dubokog izvlačenja za procjenu naprezanja tečenja za dvoosno stanje naprezanje-istezanje

Change of ears creation of AHSS steels after heat treatment of zinc coating

The article deals with the normal anisotropy, the earring evaluation of deep-drawing steels DC06, micro-alloyed steel H220 and steel with transformation induced plasticity TRIP RAK 40/70 and deals with the influence of annealing temperature to ears creation of H220 steel and TRIP RAK 40/70 steel. The evaluation of normal anisotropy has been made by tensile test on TIRA test 2300 according standards STN EN 10002-1+AC1 and STN 42 0321. The evaluation of earring degree has been carried out on the cups, which have been drawn on a hydraulic press Fritz Muller 100

Influence of plastic deformation inhomogeneity on corrosion resistance of TIN plates

Thin steel sheets are used in the production of food packaging, especially for long-term storage. Reducing the thickness of steel sheets and increasing the speed of the drawing process in the manufacture of packaging often decrements its plastic deformation stability. These changes bring about the need to use evaluation methods able to determine mechanical and plastic properties of steel sheets quickly and at a low cost. Two types of tin-plated steel sheets were used for experimental research into the influence of plastic deformation on their corrosion resistance. The paper compares the results of the uniaxial tension test and the biaxial tension test of tin-plated sheet properties

The Influence of Tandem Mill Reduction on Double Reduced (DR) Tinplates Anisotropy

In this paper, influence of tandem mill reduction on double reduced tinplates anisotropy is presented. In order to achieve favourable anisotropy properties (deformation texture) of tinplates for deep drawing operations, optimal percentage reduction on tandem mill is important. The experiment was carried out in laboratory conditions and three sorts of materials (T 57, T 61 and T 65) were used. The anisotropy was classified by earing test determining the ear height of tinplate after deep drawing by measuring the height of any ear. Percentage reduction on tandem mill and final earing relationships of tinplates are researched

Usporedba oblikovno - graničnog dijagrama (FLD) modela izvlačenja čeličnih limova

U ovom radu je provedeno usporedno ispitivanje tri matematička modela (model Marciniak - Kuczynskog, Hill-Swiftov i Sing-Rao) kao i empirijskih modela kojeg je predložila Sjeverno američka grupa za istraživanje dubokog izvlačenja (NADDRG). Granični kriterij (1993.) koji je nedavno predložio Hill koristi se za izračun graničnih deformacija u vezi s Swiftovim uvjetom nestabilnosti difuzije pri sužavanju i korištenjem analize Marciniak - Kuczynski. Naglasak ovog istraživanja je u različitim pristupima predmnjevanja FLD. Dobiveni su eksperimentalni rezultati za različite niskougljične čelične limove za izvlačenje u kakvoći limova FeP06 G i ZStE 220P kao i refosforiziranih i mikrolegiranih čelika. Usporedbom, teorijski model je bio u dobroj podudarnosti s praksom.In this paper a comparative investigation of three mathematical models (Marciniak - Kuczynski model, Hill - Swift model and Sing - Rao model) as well as an empirical model proposed by the North American Deep Drawing Research Group (NADDRG) has been carried out. The yield criterion (1993), recently proposed by Hill, is used for the calculation of the limit strains in connection with the Swift’s instability condition for diffuse necking and with the Marciniak - Kuczynski analysis. The emphasis of this investigation is to consider these different approaches to predicting the FLD. Experimental results have been obtained for different low carbon steel sheets of drawing quality - FeP06 G and ZStE 220P as well as rephosphorised and micro-alloyed steel. It was compared, which theoretical model showing good correlation with experiment is suitable for materials mentioned above

Identification of aerothermal heating for thermal protection systems taking into account the thermal resistance between layers

In this paper the aerothermal heating of a reusable launch vehicle is reconstructed on the basis of temperature measurements taken in the thermal protection system of this vehicle. The discussed integrated thermal protection system is composed of three layers. Mathematical model, describing the problem, takes into account the dependence on temperature of the material parameters as well as the thermal resistances occurring in the contact zones of the layers, which is a novelty in the proposed approach. For solving the direct problem, the implicit scheme of the finite difference method is applied. Next, by using the solution of the direct problem, the Tikhonov functional is created, which describes the error of the current approximate solution. Whereas for determining the solution of the inverse problem the Levenberg-Marquardt method, modified and adapted to the Tikhonov functional, is used. The paper presents the mathematical model of the problem and the method of solution together with the selected examples illustrating its exactness and stability. In order to better examination of the solution method some various values of parameters are taken in the demonstrated examples

Membrane-based torque magnetometer: enhanced sensitivity by optical readout of the membrane displacement

The design and realization of a torque magnetometer is reported that reads the deflection of a membrane by optical interferometry. The compact instrument allows for low-temperature measurements of tiny crystals less than a microgram with a significant improvement in sensitivity, signal-to-noise ratio as well as data acquisition time compared with conventional magnetometry and offers an enormous potential for further improvements and future applications in different fields. Magnetic measurements on single-molecule magnets demonstrate the applicability of the membrane-based torque magnetometer

Characteristics and comparative clinical outcomes of prisoner versus non-prisoner populations hospitalized with COVID-19

Prisons in the United States have become a hotbed for spreading COVID-19 among incarcerated individuals. COVID-19 cases among prisoners are on the rise, with more than 143,000 confirmed cases to date. However, there is paucity of data addressing clinical outcomes and mortality in prisoners hospitalized with COVID-19. An observational study of all patients hospitalized with COVID-19 between March 10 and May 10, 2020 at two Henry Ford Health System hospitals in Michigan. Clinical outcomes were compared amongst hospitalized prisoners and non-prisoner patients. The primary outcomes were intubation rates, in-hospital mortality, and 30-day mortality. Multivariable logistic regression and Cox-regression models were used to investigate primary outcomes. Of the 706 hospitalized COVID-19 patients (mean age 66.7 ± 16.1 years, 57% males, and 44% black), 108 were prisoners and 598 were non-prisoners. Compared to non-prisoners, prisoners were more likely to present with fever, tachypnea, hypoxemia, and markedly elevated inflammatory markers. Prisoners were more commonly admitted to the intensive care unit (ICU) (26.9% vs. 18.7%), required vasopressors (24.1% vs. 9.9%), and intubated (25.0% vs. 15.2%). Prisoners had higher unadjusted inpatient mortality (29.6% vs. 20.1%) and 30-day mortality (34.3% vs. 24.6%). In the adjusted models, prisoner status was associated with higher in-hospital death (odds ratio, 2.32; 95% confidence interval (CI), 1.33 to 4.05) and 30-day mortality (hazard ratio, 2.00; 95% CI, 1.33 to 3.00). In this cohort of hospitalized COVID-19 patients, prisoner status was associated with more severe clinical presentation, higher rates of ICU admissions, vasopressors requirement, intubation, in-hospital mortality, and 30-day mortality

Face Mask Use and Control of Respiratory Virus Transmission in Households

Mask use is associated with low adherence, but adherent mask users are significantly protected against seasonal disease