Papers by Keyword: Rheological Model

Abstract: The briquetted material and pressing surfaces force interaction is considered in the deformation center pressing zone. The investigated material is considered as an elastoplastic medium, described by rheological model: Bingham's body, which most fully reflects the physical medium under study properties. The material stress-strain state is divided into two stages: ideal-elastic and elastoplastic, each described by the obtained equation. Parameters of the force impact of the material on the pressure rolls depending on material physicomechanical characteristics and a press geometrical parameters are obtained.

Abstract: The results of physical simulation of hot compression of semi-finished products, selected from a cast ingot and hot-rolled plate from aluminum-lithium alloy V-1461, in the temperature range of 400-460°C and strain rates of 1-60 s^-1 are presented. It is established that at a constant strain rate the flow stresses decrease with increasing test temperature, an increase in the strain rate leads to an increase in flow stresses at a constant temperature. The parameters of the hot deformation rheological model, including the Zener-Hollomon parameter and the hyperbolic sine law, are determined. It is established that the parameters of the rheological model for the cast and hot-rolled state differ insignificantly.

Abstract: The paper is based on dynamic modeling research and experimental results obtained for freshly compacted concrete under stationary vibration. Thus, computational relationships and laws for vibration parameters and dissipated energy will be presented. In correlation with the dissipated energy, it will be evidenced by the evolution of the compaction degree and the resistance of the concrete depending on the vibration duration. It is noted that significant correlations have been established between the displacement curve of the dissipated energy and the loop hysteresis area for several vibration frequencies specific to the dynamic compaction regime

Abstract: The selection of the flow stress model of materials has a great influence on the plastic forming simulation of metal. For closed extrusion fine blanking, selecting the accurate and appropriate material flow stress model can make the finite element simulation closer to the real situation, and the simulation data is more reliable. In order to solve the accuracy problem of finite element simulation closed-extruding fine blanking, 5 types of flow stress fitting curve equations were obtained based on the data of sheet metal tensile test. With the secondary development of finite element software Deform-2D, the circular piece of closed-extruding fine blanking forming process was simulated, whose diameter is 14 mm and thickness is 30 mm. The simulation results of different rheological models were compared after physical experiment being carried out.The results show that Ludwik extrapolation rheological model is suitable for finite element simulation of closed-extruding fine blanking technology, which effectively improves closed-extruding fine blanking simulation accuracy. Lay the foundation for the application of closed-extrusion fine blanking in industry.

Abstract: Rheological model for crumb rubber modified bitumen (CRMB) by the rheological testing and model analyzer was investigated in this paper. The effects of crumb rubber content and temperature on rheological model and viscoelasticity of CRMB were conducted. The results illustrate that rheological model of bitumen is transformed from Dashpot into Burgers at 60°C after bitumen has been modified by crumb rubber. And the elasticity of CRMB is increased and the viscosity is decreased with crumb rubber content rising. For the modified bitumen with 20% crumb rubber (CRMB-20), its rheological model is Burgers among 20°C~80°C, but the model is translated into Maxwell at 100°C. As the temperature increases, both viscosity and elasticity of CRMB-20 are increased. Compared with 20°C, the instantaneous elastic and viscous deformation of CRMB-20 at 100°C are increased by 14.2 times and 80.5 times, respectively.

Abstract: The rheological properties of cement-based materials can be used to guide its construction. In this paper, rheological characteristics of fresh cement mortar (FCM) were investigated. The rheological model and its parameters of the FCM under different hydration time, different water to cement ratio (w/c) and sand to cement ratio (s/c) were obtained by the rheological testing and model analyzer. The result indicated that rheological model of the FCM is transformed from Burgers model to Bingham model with the extension of hydration time. And the model transformed from Burgers model to five component model with the decrease of w/c and the increase of s/c. However, the superplasticizer has little effect on the rheological model of cement mortar. The plastic deformation of the fresh cement mortar increased gradually with the prolongation of the hydration time, and the plastic yield value increased gradually from 50Pa to 250Pa with the increase of s/c. The change rate of plasticity of mortar is reduced from 422Pa/h to 107Pa/h with the increase of superplasticizer’s dosage, which shows the addition of superplasticizer retards the hydration rate.

Abstract: A two-continua model is constructed which allows one to describe the kinetics of hydrogen in metals. The developed rheological model is appropriate for estimation of the hydrogen transition from mobile to bonded state depending on the stress-state relation and description of the localization of the connected hydrogen that results in the material fracture.

Abstract: Based on the results of confined rheological compression test of unsaturated soil samples, some important characteristics and its effective factors have been discussed by using three-dimensional model. At first, the curves of lateral stress relaxation show the process of correspondence with vertical creep. Secondly, it is lateral total stress, and not effective stress, that is relaxed with time because of the volume viscidity of pore water and the shear viscidity of soil skeleton. At last, the limited steady rheological state of soil is controlled by stress strength.

Abstract: The main goal of investigations on semi-solid metal processing is to produce complex parts with enhanced mechanical properties. Flow behavior and die filling in semi-solid processing is an intrest area of researchers. A comprehensive understanding of the behavior of the under investigation metallic slurry is the design key of a successful manufacturing process. In this way the material’s transient response is very important for understanding of the rheological properties and also further commercial development of the process. The material used in this research is an Al-Si alloy which is widely used in automotive and aerospace applications. The experiments were conducted using a Searl rheometer which is specially designed for high temperature rheological measurements. For rheological tests of semi-solid alloy in different solid fractions, the isothermal holding and shear rate step change experiments were examined. Using practical rheological results, a single phase thixotropic model has been derived and adopted with measurements. The investigated alloy behavior was obviously thixotropic which is quantified in a theoretic model. Also instantaneous rheopectic behavior was observed for this alloy. The state of the microstructure has been applied through a structural parameter. The presented model for A356 alloy fits well with the experiments.

Abstract: The paper analyses one of possibilities to use new materials based on polyurethane, polypropylene or silicone having highly adhesive contact surfaces for gripping elements designing. In concrete terms, it is a case of an alternative approach to the solution of designing standard multi-elements vacuum gripping heads with an active control system (vacuum level control) controlling gripping forces in processes of automatic handling flat objects of the plate type. The aim of this new design solution is to replace individual gripping elements (suction cups) by elements, the surfaces of which coming to the contact with the object handled are provided with adhesion materials. The system minimizing energy demands stemmed from this solution, namely in the way that it decreases or even eliminates the pressure air consumption when combined vacuum-adhesive or only adhesive gripping elements are used. Moreover, it is possible to use the adhesive gripping principle profitably in technological processes susceptible to the environment contamination with airflow when manufacturing new products with many functional layers. Besides a general analysis of problems, the paper presents outputs of laboratory tests. Also a computer model of the contact respecting rheological behaviour of the adhesive material basic matrix is given.