Papers by Keyword: Initial State

Abstract: In order to investigate the effect of rolling on microstructure and mechanical properties of different initial states, cast and extruded magnesium alloy AZ80 bars were rolled in calibre. The microstructural characterization was done by light microscopy. As a result, the initial grain size of the cast AZ80 (66 μm) clearly differs from the extruded bar (13 μm). After 14 passes of hot rolling in calibre, a significant grain refining effect was achieved resulting in grain sizes of 5 μm for the cast and 3 μm for the extruded material. To investigate the mechanical properties in the initial and rolled state, tensile tests of both conditions were conducted at room temperature. Due to grain refining, the tensile strength (162 MPa) and the elongation (3 %) of cast AZ80 increased remarkably during 14 passes of calibre rolling (360 MPa and 19 %). The strengthening effect was also evident for the rolled extruded AZ80. However, the cast material exhibited cracks during calibre rolling due to its inexpedient microstructure for a high deformation calibre. On the contrary, the extruded AZ80 was easily deformable. This shows the clear impact of initial states on aspired end properties of processed materials. Future investigations will deal with developing a suitable calibration for cast AZ80.

Abstract: The article is focused on the design of spatially curved cable - supported footbridges, which represent a simple and elegant solution for bridging longer spans. It can be used independently or in a combination with other structural arrangements, e.g. with the arch structures.To verify the behavior of the structure, a several testing models were created. At first only simple, plan – straight models were created so the results could be checked by manual calculations. Latter, the more complex, curved models were tested. All models were designed and analyzed with the Ansys software using geometrically nonlinear calculations. The analysis consisted in the searching for ideal geometry of the supporting cable, cross section geometry of the bridge deck and other parameters, which are necessary to find a correct initial state of the structure. The main criterion for finding the initial state was a demand of minimal deformations in the strut - supporting nodes, which leads to the minimal redistribution of the internal forces during the design lifetime. The result of the paper is a detailed analysis of the construction’s behavior. The main emphasis is on methodology of search for the initial state. Further, the buckling analysis of the struts and cable were performed and it’s resistance to buckling was determined using various live load configurations.

Abstract: A new sliding mode variable structure controller is proposed. First, aiming at improving the convergence speed, a new nonlinear sliding mode surface is proposed. Then, the initial error speed is designed to make the initial state of the system to be just on the sliding mode surface which is to impair the chattering and improve the robustness of the controller. Finally, a mobile manipulator with two arms is taken as an example to simulate the trajectory tracking with the proposed controller. It is found that system shows high convergence speed and strong robustness against disturbance. The chattering is also impaired greatly.

Abstract: A state-dependent critical state model is employed to analyze strain localization of sand in this paper. The sand model is developed based on the concept of the state-dependent critical state for sands, and an analysis of strain localization is performed on the drained plane strain tests of Hostun sand. The results show that the state-dependent critical state model is capable of simulating the effect of initial state on strain localization compatibly.

Abstract: The swelling behaviour of compacted expansive soils have been studied with variation in initial state. For comparison, a series of swell and shrinkage capacity laboratory tests with different initial dry densities，moisture contents and pressures have also been made with three different consistency state. Both percent swell and shrinkage are significantly influenced by the consistency state index. There is an unique relationship between percent swell and consistency state index of the soil. The percent swell-load relationship could be identified as a logarithmic relationship facilitating the prediction of ultimate percent swell under different load with a few initial results.

Abstract: Titanium was subjected to hydrostatic extrusion, a method of producing Severe Plastic Deformation (SPD). The experiments were aimed at refining the microstructure of the titanium in order to improve some of its mechanical properties. The effect of the initial state of titanium on the process of extrusion process and the final product was investigated. The results of these investigations are used to establish the optimum conditions for the hydrostatic extrusion process and more easily selecting the initial condition of the material according to the intended application of the extruded product.