ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.753

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractIn the numerical treatment of thermal and transformation stresses produced during quenching, and of the resulting residual stresses, calculations carried out using computer programs are for economic reasons restricted to simple geometries such as infinite plates or cylinders. Difficulties arise when results so obtained are applied to real components. The effects of geometric discontinuities, for example near the top and bottom of a cylinder, need further systematic investigation. In this paper, stress distributions in steel cylinders of different diameters, quenched with and without transformation effects from different temperatures, are calculated using a finite–element program; the differences revealed in the local stress states are discussed. Results of special calculations making use of different boundary conditions are introduced, allowing the important mechanical and thermal factors that influence the final residual–stress states to be assessed. These results allow the validity of assumptions necessary in the analytical computations to be estimated realistically.MST/1

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.754

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThick parts of high–strength aluminium alloys usually undergo a drastic quench which gives rise to thermal stresses and may cause distortion of products. The control of complex phenomena involved during quenching is achieved by determining the temperature distribution, thermal strains, and residual stresses using the MARC finite element program. In this approach, the thermo mechanical problem is assumed to be uncoupled, i.e. the thermal and mechanical calculations are solved consecutively. First a non–linear heat transfer analysis is performed taking the temperature dependence of the thermophysical properties and transient conditions of convection at the surface of the plate into account. This is followed by a thermo–elastoplastic stress analysis using the predicted temperature distributions, assuming an isotropic behaviour of the material and taking the temperature dependence of its mechanical properties into account. The calculation of thermal stresses occurring during the cold and hot water quenching of a 70 mm thick plate of 7075 alloy using this method shows a good agreement between theoretical predictions and experimental values of residual stresses, as measured by the layer removal method.MST/2

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.765

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractSubstantial improvements have been made recently in the quality of the mathematical models used to represent the generation of thermal stress and strain during the quenching of steel components. However, viscous processes have received little attention in these models, even though there is frequently sufficient time for creep processes to occur during a quench. The inclusion of stress–relaxation and creep effects in one such model has led to a marked improvement in the degree of agreement between the experimental and predicted residual–stress distributions obtained after an oil quench, at the expense of a modest reduction in the corresponding level of agreement after a water quench. The best correlation is obtained by the representation of stress–relaxation and creep effects by means of a standard linear solid model at temperatures above 230°C, with stress–relaxation rates a function of temperature only. Since the isothermal stress–relaxation tests indicated significant viscous processes at temperatures above 130°C, it is possible that the model could be further refined by consideration of the interaction of viscous processes that occur at different stages in the quench. Results are also presented of the predicted relationship between stress and strain at the surface and centre of a plate during quenching in both water and oil.MST/3

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.770

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA finite–element technique has been used to examine the effect of the edge on the generation of thermal stress in a water–quenched circular plate of a steel of high hardenability. This allows results obtained using an infinite–plate model to be applied to finite bodies, where the stress distribution is influenced by the presence of a free edge. The radial residual stress begins to fall towards zero at a point about one–and–a–half plate thicknesses from the free edge. The variation in the stress in this part of the plate was complex and was accompanied by the development of an axial stress which was compressive up to a point close to the edge, where it became tensile. The variation in the hoop stress resembled that in the radial stress, but tensile values were always obtained at points on the edge. The mean value of the radial and hoop stresses in the edge–affected region was 75% of the stresses formed in the interior of the plate. This provides a suitable conversion factor when finite bodies are involved.MST/5

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.780

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractMethods of thermal stress relief such as stretching and compression are compared for different thermal and mechanical properties during quenching. The heat equation for a simple geometric model, such as an infinite plate, is solved with an experimental surface conductance and a step–by–step method of determining the temperature field in the thickness of the plate. This field is introduced as data for the uncoupled thermal elastic–plastic model for quenching. In the calculation of the plastic–strain path, the thermal and mechanical properties are considered as temperature dependent for a homogeneous and isotropic material. Good agreement is found between the calculated residual stresses and experimental values for an aluminium alloy and a stainless steel. The predicted residual–stress distributions and strain history are then used as data for the numerical simulation of stress–relief methods with an incremental integration of the Prandtl–Reuss equation. This analysis allows the observation of the effects of small variations in mechanical properties during quenching on the residual–stress field after mechanical stress relief and the theoretical comparison of different processes.MST/6

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.786

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe residual stresses in a pure iron cylinder 50 mm in diameter, after water quenching from 850°C were calculated using the finite element method. This rather simple case without phase changes was chosen so that the calculated results could be compared with those from experiments. The comparison, however, showed discrepancies which could not be explained solely by the inaccuracy of the data or by the mathematical approach used for the calculation. These differences were found to be the result of plastic deformations that occurred during measurement of the residual stresses by the boring–turning method. This was borne out by a numerical simulation of the experimental procedure. Beginning the calculation at the residual–stress state after quenching, the boring and turning steps were simulated by a stepwise elimination of the contributions of the removed material to the total stiffness matrix. Thus, the changes in the residual stresses and the corresponding changes in the measured strain at the surface due to removal of material could be calculated. The boring–turning technique assumes pure elastic stress states throughout the process of material removal. However, the calculated results revealed that this technique caused unanticipated plastic deformations which resulted in erroneous experimental results in this special case. Stress values measured by mechanical methods are therefore unreliable if the corresponding equivalent stress in parts of the cross–section of the cylinder approaches the yield point at room temperature.MST/7

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.793

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractIn order to predict residual stresses and distortion caused by quenching in a large low-alloy steel shaft, a computer program based on the finite element method was developed, and uniaxial restraint testing of the transient strain during cooling was carried out. Using the program, the transient stresses occurring during quenching are calculated by a step-by-step procedure, and the effects of transformational behaviour on residual stresses and distortion discussed. The results show that the transient stresses and the transformation affect each other, and that residual stresses and distortion are strongly related to the transformational behaviour.MST/8

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.798

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe two main effects of stress on phase transformation, kinetics modification and transformation plasticity, are reviewed for both diffusional and non-diffusional transformations. Results for these interactions during the pearlitic and martensitic transformation of steels under uniaxial tensile stress are analysed from a metallurgical point of view. These results are used to produce a model for a triaxial stress state, and in a finite element program for calculating internal stresses during quenching. Transformation plasticity is introduced in the calculation of internal stresses as an additional strain related to the stress state and to the progress of transformation, and the kinetics of martensitic transformation are also related to the stress state. The calculated results show that these phenomena have important consequences on the stress and plastic strain histories during quenching.MST/9

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.805

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

Abstractn this paper, the kinetics of anisothermal structural transformations are first discussed. Classical models are shown to raise difficulties because they do not take into account the existence of a temperature–dependent equilibrium proportion of the phases. A very simple model incorporating this factor is proposed and shown to lead to a good correlation between experimental and theoretical results it is also shown to be compatible with the thermodynamics of irreversible processes. The model can be extended to include the possibility of isothermal kinetics of the Johnson–Mehl type, as well as the influence of austenite grain size. The influence of the transformations on plastic behaviour (transformation plasticity) is next discussed. A simple model is described using first purely heuristic considerations, then a more microscopic and physical approach. Possible improvements to this model are suggested, especially the inclusion of the fact that the microscopic plasticity generated by volume differences between the phases must influence not only transformation plasticity (Greenwood–Johnson mechanism), but also ordinary plasticity, which must be present at all points on the stress–strain curve.MST/10

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.10.815

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor