Papers by Keyword: Constitutive Model

Abstract: Based on the characteristic of cyclic softening of the quenched and tempered Carbon steel 45, a cyclic plastic constitutive model was proposed to describe the cyclic behavior under symmetrical and unsymmetrical strain cycling with different strain amplitudes. In this model, the phenomenon of the decrease of the up yield limit stress with the increase of strain in the initial 1/4 cycle was taken into account. The proposed evolution equations of the yield size and backstress can simulate the cycling softening under symmetrical and unsymmetrical strain cycling well. The results indicated that either the simulated shape of the cyclic softening hysteresis loops or the evolution of stress amplitude with the increase of the cyclic number during the low cycle fatigue coincides with the experimental ones very well.

Abstract: Finite element models with a constitutive material behavior that represents the non-linear response of fiber composites are used to simulate the compressive failure mechanism i.e. kinkband formation. A constitutive material law in framework of micromechanical modeling containing comprehensive constitutive equations for the constituent materials is adopted to model the non-linear behavior of the unidirectional layered materials. This material law is implemented as UMAT user subroutine in ABAQUS/Standard to study kinkband formation. The methodology provides a procedure to investigate the kinkband formation due to fiber misalignment for various complex structures having voids and material discontinuities that occur normally during the manufacture of these unidirectional fiber composites.

Abstract: This paper attempts to simulate the stress-strain relations of Pontida silty clay under triaxial tests in accordance with the latest theory of geotechnical nonlinear deformation analysis-breakage mechanics of geomaterials. The result proves that the binary medium model of over-consolidated clayey soil can effectively reflect the deformation mechanism of soil mass and the brittle break phenomenon, thus possessing good suitability and effectiveness. This also lays down the foundation and provides new ways for the further discussion of establishing the elastic-plastic constitutive model of clayey soil softening properties and intensity attenuation effects with the consideration of large shear displacement.

Abstract: In the process of deep tunnel excavation, the surrounding rock mass, which often endures high initial geo-stress, is in the state of typical unloading. As the adjustment of stress induced by excavation, rock mass behaves a peculiar kind of mechanical deformation characteristics, different from those in loading conditions. As thus, a series of representative unloading tests on hard granite from DaGangShan power station in China, which is being excavation at 1500 meters deep below earth surface, are carried out to simulate dynamically excavation process for studying the peculiar mechanical deformation characteristics. On the basis of unloading tests, a series of research results are acquired as follows： (1) Under unloading condition, lateral deformation occurs in the unloading direction and volumetric strain changes from compression deformation to dilation deformation. (2) Under unloading condition, hard granites behave brittle failure and Mogi-coulomb criterion can well describe the failure characteristics. (3) According to curves of unloading tests, the constitutive model is deduced for simulation analysis.

Abstract: Based on the creep testing results of geogrids, a three-parameters viscoelastic constitutive model of the geogrids is established, and their applicabilities and reliabilities are evaluated by using the utmost optimization theory. It is illustrated that the three-parameters viscoelastic model of geogrids established can relatively accurately reflect the two-stage attenuation creep properties of geogrids at a low stress. Then, a constitutive model of reinforced soil considering viscoelasticity of geogrids is established, and the constitutive model parameters of reinforced soil are solved based on the utmost optimization theory. Finally, the variation regularities of stress-strain characteristics of reinforced soil with the changes of different influencing factors is studied.

Abstract: Quantities AZ80 and AZ31 magnesium alloy billets were compressed with 60% height reduction on hot process simulator at 150,200,250,300,350,400,450°C under strain rates of 0.001, 0.01, 0.1,1 and 10s^-1.A constitutive model with a few parameters is used to characterize the dynamic recrystallization strain softening of AZ80 and AZ31 alloy, which comprehensively reflect the effects of the deformation temperature, strain and strain rate on flow stress.

Abstract: Hot deformation tests were carried out on Al5083 – 2 %(vol) TiC nanocomposite in a temperature range of 250 – 450°C at varying strain rate of 0.01 – 1.0 sec^-1. Constitutive models were developed for the prediction of peak flow stress relating strain rate, true stress, temperature and activation energy. The percentage error between measured flow stress and constitutive model values were calculated to analyse the efficacy of the model in the prediction of peak stress. Finally, a window of working of the selected nanocomposite is established for finding out the safer region of working.

Abstract: With the Superplastic forming technology, the problem that the forming of the complex titanium alloy parts is difficult has been solved. The high temperature forming characteristics of the titanium alloy material and the establishment of the constitutive model of material that will be used as the material model of the simulation of the material forming (the minimum thickness is larger than 0.8 mm) about the negative Angle parts are based on high-temperature tensile test. The influence of the thickness of the parts is analyzed from three different SPF schemes, which are simulated by the MSC.MARC software. The results demonstrate the parts taking advantage of two-stage SPF, which is consisted of concave die SPF method and convex die SPF method can meet the requirement of minimum thickness and improve the thickness distribution on the die draft sides. Furthermore, the thickness distribution of the parts is more uniform with the convex die SPF method.

Abstract: Abstract: It had been put forward that a new method to establish material constitutive model based on extrusion test, which was that the material constitutive model was determined with the Arrhenius equation according to the extrusion test data. The tube extruding test of supper-alloy Inconel625(IN625) had been done on 16300kN extrusion machine. According to the extrusion test data and the Arrhenius equation, it had been determined that the constitutive model of supper-alloy IN625 based on extrusion test, and the relative errors between calculation results of the model and experiment results are less than 7.8%. The suitable conditions of the constitutive model of supper-alloy IN625 are that the temperature being 1150°C～1200°C, and extrusion speed being 15～60mm/s, and strain-rate being 1.86～7.44.

Abstract: In order to achieve the numerical calculating rheological forming process of materials, a series of tension experiments under the different temperatures and different strain rates were done on the standard samples of sheet TC1 titanium alloy. The experimental results were analyzed theoretically and the rheological stress constitutive models of TC1 titanium alloy are built combining the strong points of the Perzyna model and Johnson-Cook model. Comparing the calculation results conducted from the model with the experimental results, it proves that the model can reflect the temperature effect and strain rate effect of TC1 titanium alloy.