Magnesium alloys have poor deformation properties at room temperature, and the application of an electric pulse current during deformation can improve the plastic-forming ability. In this study, the ...electric pulse rolling of AZ91D magnesium alloy specimens has been examined by changing the pulse output voltage. The results demonstrate that the best surface quality and lowest content (8.4 %) of the β-Mg17Al12 phase are achieved at an output voltage of 300 V. EBSD tests have revealed the lowest weave strength on {0002} and {100} at a pulse output voltage of 300 V, as well as the greatest enhancement of twinning. The maximum tensile strength was 165 MPa at an output voltage of 300 V, with a maximum elongation of 4.1 % at an output voltage of 200 V.
Initial shear stress is inevitable in actual engineering slopes, subgrades and foundations. The soils exhibit different dynamic characteristics under an initial shear stress. The dynamic strength ...characteristics of saturated clay under cyclic loading were studied through a dynamic triaxial test of remoulded clay in the Wenchuan area. The effects of the failure criterion, initial shear stress and vibration frequency on the dynamic strength characteristics of saturated clay were also analysed. The results showed that the strain failure criterion with a strain value of 2.5 % or the transitional strain εtp can reflect the soil damage realistically and evaluate the dynamic strength of the soil objectively. εp = 2.5 % can be used to replace εp = εtp when the dynamic strength parameter of the saturated clay was calculated under seismic loading equivalent failure vibration times. The dynamic strength parameters of the saturated clay under different earthquake magnitudes were calculated by introducing the equivalent failure vibration times of the soil under seismic loading, thereby providing data support for the stability analysis of the clay foundation under seismic loading. The initial shear stress and vibration frequency have a considerable effect on the dynamic strength of saturated clay. Under the same vibration frequency, the larger the initial shear stress is, the smaller the required dynamic stress is for the soil to break, and the smaller the dynamic strength parameter is. The existence of the initial shear stress reduces the dynamic strength of the soil. Under the same vibration times, the higher the vibration frequency is, the greater the required dynamic stress is for the soil to break, the larger the dynamic strength parameter is, and the greater the dynamic strength of the soil is.
Initial shear stress is inevitable in actual engineering slopes, subgrades and foundations, and soils exhibit different dynamic characteristics under the influence of initial shear stress. Using a ...dynamic triaxial test system, this study explores the dynamic shear modulus and damping ratio of saturated sand from Wenchuan, investigates the effects of the initial shear stress and vibration frequencies on the dynamic shear modulus and damping ratio of saturated sand and proposes a normalised dynamic shear modulus formula that considers the initial shear stress and vibration frequency. Results show a threshold dynamic shear strain of the saturated sand. When the dynamic shear strain is below this threshold, the dynamic shear modulus significantly increases with the initial shear stress and vibration frequency. Otherwise, the influence of the initial shear stress and vibration frequency gradually decreases and eventually stabilises. The initial shear stress significantly affects the normalised dynamic shear modulus/strain curves where a larger initial shear stress corresponds to a higher curve. Meanwhile, the vibration frequency only exerts a slight influence. The curves under different frequencies are generally within the same band and fall near the Seed upper envelope. The initial shear stress also has a significant influence on the damping ratio where a larger initial shear stress corresponds to a smaller damping ratio. On the basis of the experimental results, a normalised dynamic shear modulus/shear strain formula that considers the influence of the initial shear stress and vibration frequency is established. Fitting results indicate that this formula shows good agreement with the test data.
In order to achieve high efficiency, energy saving and high quality of welding, it is necessary to carry out research on cable-type wire TIG-MIG hybrid welding. In this study, voltage and current ...influences on the arc shape in cable-type wire TIG-MIG hybrid welding were studied. The results showed that in cable-type wire TIG-MIG hybrid welding, with an increase in the TIG current, the MIG current increased at first and then remained constant, while the MIG basic voltage remained unchanged. With an increase in the MIG voltage, the TIG current produced small changes, but overall, it remained stable. The TIG current of different droplet-transfer modes had different effects.
We study theoretically the biaxial bending of symmetric, flat layered ceramic composites (laminates) due to external loading. We focus on three-layered alumina/zirconia laminates. We compare the ...principal stresses in the samples in the case of static and harmonic dynamic loading. The dynamic equation within the Kirchhoff theory for thin homogeneous plates is first generalized to the case of multilayered plates. It is solved numerically with the relaxation method, which we have developed for this purpose.
Sredinom 15. stoljeća platno kao nosilac postalo je alternativa drvu. Počele su se izrađivati slike na platnu, a slijedio ih je razvoj podokvira. Polovicom 18. stoljeća uvode se podokviri s kajlama, ...a nedugo zatim i podokviri s kutnim rastezačima. Obje vrste podokvira stvaraju prekomjernu silu u kutovima, što dovodi do raznovrsnih oštećenja slika. Pedesetih godina 20. stoljeća osmišljen je sustav elastičnog napinjanja, čime su odvojene mehanička potpora i napinjanje slike, koje su do tada bile „povjerene“ isključivo podokviru. Godine 1957. taj se sustav primjenjuje u Restauratorskom zavodu u Zadru, a potkraj osamdesetih godina prošloga stoljeća usvaja se u Hrvatskom restauratorskom zavodu i otada se kontinuirano primjenjuje. Takvim načinom do sada je napeto više od dvadeset slika, uglavnom velikih formata. Način izvedbe podokvira i napinjanja prilagođen je svakoj slici, ovisno o njihovu stanju očuvanosti, dimenzijama, obliku i uvjetima smještaja. Dugogodišnjim praćenjem stanja očuvanosti napetih slika, nisu primijećene deformacije podokvira, nosioca i slojeva boje. Napetost slika je zadovoljavajuća pa se može zaključiti da sustav dobro funkcionira, iako se može razvijati i modernizirati primjenom novih materijala te praćenjem i proučavanjem inozemnih iskustava.
In the mid-15th century, oil paintings began to be painted on canvas, so the development of the stretcher followed the use of canvas as a carrier. The first stretching on the stretcher bars is performed together with setting up the canvas through impregnation and preparation, and cannot be corrected. If paintings stretched on a fixed stretcher are exposed to adverse microclimatic conditions, the forces of the material resist each other, which often leads to deformation and damage to the paintings, as well as excessive loss of tension on the stretcher. The situation is often exacerbated by the decay of the wooden frame, often at the same time as the loss of elasticity of the canvas. Throughout history, various stretchers have been created, from the simplest to those with keys. In the late 18th century, expansion-bolt stretchers came to be used in order to resolve the issue of continuous stretching of paintings. Excessive and constant tension in the corners leads to the same effect as in fixed stretchers: that is, stress is concentrated in the corners, leading to various damage to the canvas. Stretchers were considered to perform two functions: mechanical support and provision of tension for the painting. In reality, due to its structure, the stretcher is only able to properly perform mechanical support of the canvas. In the early 1950s, Roberto Carità separated mechanical support and tension of the canvas, which had previously been left to the stretcher. He devised the method of elastic tension for canvases at the Istituto Superiore per la Conservazione ed il Restauro, in Rome, which sparked a real revolution. With this method, and using different elastic springs and regulating their force, we get elastic tensioning that allows equal continuous tension of the canvas in all directions, regardless of the mechanical support exerted by the stretcher. Gustav Berger also worked on this system, as did many Italian restorers who systematically conducted research, the most prominent being Antonio Iaccarino Idelson. In Croatia, this system was first used in 1957 at the Conservation Institute in Zadar. At the end of the 1980s, the practice was adopted at the Institute for Restoration of Works of Art, in Zagreb, and has been continuously used ever since. Over twenty paintings, mostly with large-format canvases, have been stretched using this method. The method of constructing the stretcher and the tensioning is adapted to each painting, depending on its state of preservation, dimensions, shape and conditions of accommodation. The paper describes two examples of tensioning in more detail.
U ovoj studiji su za procjenu razdiobe napetosti smicanja u vodotocima korištene umjetne neuronske mreže (ANNs) i prilagodljivi neizraziti sustav zaključivanja (ANFIS). Metode su primijenjene na 145 ...nizova podataka prikupljenih na četiri različite postaje na vodotocima Sarimsakli i Sosun u Turskoj. Točnost primijenjenih modela uspoređena je s točnošću modela višestruke linearne regresije (MLR). Rezultati su pokazali da su oba modela (ANNs i ANFIS) bili bolji u modeliranju raspodjele napetosti smicanja od MLR modela. Pri korištenju ANFIS modela za procjenu raspodjele napetosti smicanja u testnom razdoblju srednje kvadratne pogreške (RMSE) i srednje apsolutne pogreške (MAE) su u odnosu na MLR model bile smanjene za 47%, odnosno 50%. Utvrđeno je da se za testno razdoblje najbolji ANFIS model, s RMSE = 3.85, MAE = 2.85 i koeficijentom određenosti R2 = 0.921, pokazao superiornim u procjeni napetosti smicanja u odnosu na MLR model, s RMSE = 7.30, MAE = 5.75 i R2 = 0.794.
Klasičnim postupkom predenja na prstenastoj predilici ispredene su pređe iz egipatskog pamuka Giza 75 FG finoća 14,3, 16,7, 20,0 i 25,0 tex. Svaka od navedenih pređa ispredena je sa većim ...koeficijentom uvijanja i različitim postotkom isčeska 14, 16, 18 i 20 %. Na kružnopletaćem jednoigleničnom stroju malog promjera iz navedenih pređa izrađene su dvije grupe glatko kulirnih desno-lijevih pletiva s različitom napetosti pređe pri njenom ulasku u pletaći sistem. Prva je grupa uzoraka izrađena s uobičajenom napetosti pređe koja se koristi kod izrade ovakvih pletiva (0,15 cN/tex), dok je druga grupa uzoraka izrađena s većom napetosti (0,40 cN/tex). Dobivena mjerenja statistički su obrađena i testirana.
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