Comparison of results of dynamic recrystallization research of HC420lA steel by two types of tests on Gleeble 3800
The article shows an influence of kind of tests on material hot defamation behaviour during physical modelling on
Gleeble 3800. As material, high-strength low-alloy automobile steel HC420LA was used. Stress-strain curves and material constants based on results of flow stress and plain strain tests were calculated and compared. Besides finite-element modeling of rolling round bar on a smooth barrel was performed taking into account the calculated mechanical characteristics.
Plane strain and uniaxial compression tests are generally used for characterization of a material constitutive behavior during hot forming. Interpretation of the results obtained by such tests is complicated by flow inhomogeneity occurring in a specimen volume and temperature variations. Inverse analysis is an effective instrument allowing one to take these factors into account and obtain more accurate constitutive equations of a material. In this study the constitutive behavior of HC420LA steel was examined by plane strain and uniaxial compression testing on Gleeble 3800. Finite element simulation of the tests was performed in order to evaluate the flow inhomogeneity and its effect on stress-strain curves obtained as a result of testing. Inverse analysis was used to correct the initial Gleeble data and obtain accurate constitutive equations of the material.
Binary Al–Ni, Al–Mg and ternary Al–Mg–Ni alloys containing various dispersions and volume fraction of second-phase particles of crystallisation origin were compressed in a temperature range of 200–500 °C and at strain rates of 0.1, 1, 10, 30 s−1 using the Gleeble 3800 thermomechanical simulator. Verification of axisymmetric compression tests was made by finite-element modelling. Constitutive models of hot deformation were constructed and effective activation energy of hot deformation was determined. It was found that the flow stress is lowered by decreasing the Al3Ni particle size in case of a low 0.03 volume fraction of particles in binary Al–Ni alloys. Intensive softening at large strains was achieved in the alloy with a 0.1 volume fraction of fine Al3Ni particles. Microstructure investigations confirmed that softening is a result of the dynamic restoration processes which were accelerated by fine particles. In contrast, the size of the particles had no influence on the flow stress of ternary Al–Mg–Ni alloy due to significant work hardening of the aluminium solid solution. Atoms of Mg in the aluminium solid solution significantly affect the deformation process and lead to the growth of the effective activation energy from 130–150 kJ/mol in the binary Al–Ni alloys to 170–190 kJ/mol in the ternary Al–Mg–Ni alloy.
The simulation of metal behavior using hot deformation is hard, complex problem. That behavior depends on temperature, strain and strain rate. In the hot deformation processes, such as uniaxial compression test, the material inner structure is changing, one could see hardernin, dynamic recovery and, for some speciments, dynamic recristallization. The main aim of this work is constraction of initial forming model of a high-strength automotive steel HC420LA under hot deformation.
The increasing of the efficiency of technological modes of steel products manufacturing requires simulation of metal forming during hot deformation. To obtain correct results, one should set the correct initial and boundary conditions, including the mechanical properties of materials, which represent the dependence of the stress-strain and strain rate at maintained temperature. In the experiments one must reveal the mechanical properties and constants of the steels according to strain rate, predetermined temperature and chemical composition. So, the type of test is usually dependents on the technology process, which simulation will be using the obtained information. One can identify four main types of tests used in the hot deformation: compression, tension, torsion and rupture tests. The simplest tests are considered as uniaxial compression or tension tests. The results of these tests are the curves of <<flow stress -- strain>>. The present study describes an approximation method of test results for uniaxial compression of cylindrical samples made from AISI304 steel. During this work a mathematical model of the <<stress -- strain>> relation has been described. An algorithm that determines the necessary numerical coefficients for this model was developed. As a result, the equation of the material state, which is characterized by the stress relation on the strain, strain rate (0.15, 0.5, 1.5, 5 and 15 inverse seconds) and temperature (800, 950, 1080 and 1200 degree Celsius) was found. Also the approximation comparison with the experimental results were obtained.
The high-strength steels (HSLA) used in such fields, which require light and reliable design. First of all, it's machine-building industry. The aim of this paper – on the basis of obtained data, after carried out a tests using hot deformation of steel HC420LA, obtain parameters which describe its mechanical properties. This is necessary to determine the optimal technological production regimes.
Hot forming behavior of high-strength automotive steel HC420LA is the main objective of this work. Uniaxial and plane strain compression tests were performed at Gleeble 3800 testing machine. A comparison of these types of tests was realized. The material constitutive constants were found as well as the dependences of peak and stady-state stresses on strain rate and temperature. It is shown that the testing technique have an impact on the stress-strain curves obtained by its implementation, this can lead to a mismatch of results of computer simulation of metal forming technologies. In order to evaluate such mismatches a finite element simulation of bar rolling process using the material properties obtained by different testing methods is considered.
The application of mathematical modeling methods (with subsequent computer sales) to determine the parameters of accuracy geometry bands obtained with the new equipment and process the step deformation bands of hard alloys based on copper
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.