Papers by Keyword: Rheological Model

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Authors: Keum Oh Lee, Seong Gu Hong, Soon Bok Lee
Abstract: Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and flow stress. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the bi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of 350-500oC and it was due to the enhanced dynamic recovery effect.
Authors: Gaetano M. Pittalà, Michele Monno
Abstract: The machining of titanium alloys is critical also because of high temperature reached at the tool nose. The temperature of the cutting tool affects the tool life and, in order to decrease the temperature, cutting speed is reduced. The prediction of temperature can allow designing the cutting process, in terms of cutting parameters, or make the best selection of the cutting tool, with reduced experimental effort. The rheological model is an important issue in the FEM simulation of cutting in order to achieve a good accuracy, In this paper the milling operation will be considered. This is very common in manufacturing and, often, it represents the last operation, determining the final product quality. Cutting forces, measured by dynamometer table, and temperature, measured by infrared camera, have been recorded during milling tests. The infrared camera captures a part of the workpiece close to the cutting edge. First the material model has been set up considering only cutting forces; next, a sensitivity analysis about the material model parameters has been performed in order to assess the influence of temperature in the determination of the material parameters.
Authors: You Yun Li, Xin Bo Zheng, Zhen Yi
Abstract: In this paper, based on the essential attribute of the asphalt mixture, the characteristics of the asphalt mixture creep deformation were analyzed. With the comparison of the theoretical and experimental results, the advantages and disadvantages of the common rheological models used as the reaction of asphalt mixture creep characteristics were studied. The characteristics of of the asphalt mixture deformation have been analyzed. For the accurate response of nonlinear viscous elasticity model of asphalt mixtures must be a reasonable combination of the characterization of deformation characteristics of various components, this paper reveals the rheological deformation of asphalt mixture of components and parts of correspondence with the proper models. Finally, the experimental data were given to verify the correctness of the proposed model.
Authors: Ekaterina Astafyeva
Abstract: Soft soils are well represented as the foundation of buildings all over the world. Settlements of buildings that are built on soft soils are developing over decades and often uneven. This can cause structural damages to constructions and as consequence unplanned repairs or even collapses of buildings in general. To justify the use of different models of soil mechanics it is necessary to carry out their verification. Verification of the model consists of compliance to the simple laboratory experiments and of the adequacy of the field tests description. And the most important thing is that the results of calculations should be based on comparison between series of field observations. The principal difficulty of comparing calculation results with field observations is that the actual soil deformation is developing over a long time, and most of the calculation methods are aimed to obtain finite values of deformations. Comparison between data of finite deformations and data of field observations is not quite correct, because, as a rule, in-situ (field) observations recorded incomplete development process of deformations but not only the final result of settlement. Therefore, to compare these calculations and observations we should select calculation models that can examine the development of deformations in time. Based on the above, it is interesting to analyze the applicability of the most common engineering methods and calculation models of the soils that underlie different calculation programs used in practice.
Authors: Carlo Bruni, Lorenzo Donati, Mohamad El Mehtedi, M. Simoncini
Abstract: The present investigation aims at studying and modelling the flow behaviour of the AZ31 magnesium alloy by means of torsion tests performed in extended ranges of temperature and strain rates. Two types of rheological models were considered. The former is based on the power law equation, whilst the latter is based on the Sellars and Tegart approach. The effectiveness of the two constitutive models in describing the flow behaviour of the AZ31 magnesium alloy under investigation was evaluated. It was observed that both the equations are able to predict the flow behaviour of the material at different temperatures and strain rates. In particular, the former is very effective in predicting the hardening stage of the flow curve, whilst the latter allows to fit the softening stage. The models were used for the finite element analysis of a complex extrusion process and the results, in terms of the load-stroke curves, compared to each other.
Authors: Shi Lin Yan, Wen Tao Li, Shao Peng Wu, Ling Pang
Abstract: The research on the conductive asphalt concrete(CAC) is to melt snow and ice on the pavement and improve the property of skid resistance. However, research at present mainly focuses on the electrical property not on the fatigue behavior which is also important to the application of CAC in the future. The specific rheological model is developed and the relation between creep and fatigue is investigated in this paper. By the single axial static creep test, the existed rheological model (Burgers model) and method of regression, the creep deformation of asphalt concrete is measured with time and parameters of the model are obtained. The results indicate that strain increases quickly with increasing time at initial loading phase, and then the change of strain tend to a stable value in a constant load. At unloading phase, strain decreases immediately and then keep another stable value which was greater than zero. The addition of conductive fillers improves the elastic properties and has no significant influence to the viscosity of asphalt concrete. In addition, the fatigue life can be predicted by the parameters of the Burgers model. The addition of conductive fillers improves energy dissipated, which leads to shorter fatigue life of conductive asphalt concrete compared to the control at levels of longer fatigue life.
Authors: Li Hong Chen, Shu Yu, Hong Tao Zhang
Abstract: Shear strength reduction finite element method (SSRFEM) has been a main technique for stability analysis of slope. Although SSRFEM has advantages to deal with complex geometry and nonlinear material, the criteria for failure is still argued. Ideal elastoplastic model and rheological model were both adopted, and the results of computation showed that using the intersection of two straight lines as failure point was more appropriate. The usage and advantage of two different material models was compared.
Authors: Jan Pěnčík, Libor Matějka
Abstract: Use of waste materials is an actual topic that corresponds to current trends associated with the decreasing of power exigency and sustainable development. The possibility to reduce depletion of natural resources and decrease the produced waste lies in an efficient and possibly repeated use of resources. An important subgroup of waste is formed by materials from petroleum derivatives - polymers (PP, PE, HDPE etc.). Polymers and their composite materials can be used as a base material for most products including products used in civil engineering. One of these products is an insulation block for elimination of thermal bridges in wall footing. During design of this product the MAP method (modelling-analysis-prediction) has been used together with experimental testing. This paper deals with the description of long term behaviour of an insulation block made of recycled polymers using full scale testing. Experimental data is compared to different rheological models.
Authors: Marcel Horák, František Novotný
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.
Authors: Fu Ting Sun, Cheng Xue She, Kun Li
Abstract: The creep property of cement grouted joint is studied based on creep test and theoretical analysis. Firstly, the multi-stage shear creep test under constant normal stress, joint roughness and cement filled thickness is carried out to obtain the creep deformation. Then the conventional linear Nishihara model is used to fit the test results. Due to the big deviation of the theoretical results from the test, the instantaneous elastic shear stiffnesses under different loading stages are calculated. It is found that they vary with the shear stress. The reasons for the nonlinearity are analyzed. Finally the parameters of the Nishihara model are modified to be nonlinear and fit with the test results showing good coincidence between them. These researches release the creep property of the cement grouted joint, and will provide a good basis for further research considering more influencing factors such as normal stress, joint roughness and cement filled thickness.
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