The computation of loads, torques and power consumption of hot rolling processes conducted at industrial scale requires a detailed analysis of the work-hardening rate of the material, as well as a ...precise description of the changes in flow stress with microstructure and deformation conditions. The present work describes two rational experimental methodologies that can be applied in order to accomplish this analysis, which encompasses the determination of the athermal stress, as well as the temperature and strain rate dependence of both the yield and saturation stresses of the material. The evolution of the flow stress in the course of plastic deformation is determined by means of the numerical integration of the phenomenological exponential-saturation work-hardening law advanced by Sah, J.P., Richardson, G., Sellars, C.M., 1969. Recrystallization during hot deformation of nickel. J. Aust. Inst. Met. 14, 292-297 expressed in differential form. In this way, it is possible to compute the current value of the flow stress in terms of its previous value and to update the changes in deformation temperature and strain rate that occur after each strain interval during the course of plastic deformation, as expected in industrial hot working processes. In the present work, these methodologies are applied to the analysis of the work-hardening transients of a number of stress-strain curves obtained for a C-Mn steel deformed under plane strain compression conditions, in the temperature range of 1123-1373 K, at strain rates in the range of 0.4-24 s super(-1). The results indicate that both the work-hardening rate and flow stress of the material can be satisfactorily described for most deformation conditions. It is shown that by employing the Sellars-Tegart-Garofalo model and the Zener-Hollomon parameter, in order to account for the temperature and strain rate dependencies of the stress parameters, the accuracy in the description of the experimental flow stress can be improved, but at the expense of an increase in the number of material parameters involved in the analysis. The limitations of employing a single internal state variable for the computation of the work-hardening rate and flow stress have also been discussed.
To study the deformation and failure mechanism of hard rocks, true triaxial compression tests were conducted on four types of hard rocks to obtain the complete stress–strain curves and failure modes. ...Under true triaxial compression conditions, the shapes of the complete stress–strain curves can be divided into three types: elastic–brittle (EB), elastic–plastic–brittle (EPB), and elastic–plastic–ductile (EPD) types. According to the different post-peak deformation behaviours, the stress–strain curves of EPB type can be subdivided into three sub-categories: post-peak instantaneous brittle (EPB-I), post-peak multi-stage brittle (EPB-M), and post-peak delayed brittle (EPB-D). The stress–strain curves change from EPD to EPB-D, EPB-M, EPB-I, and finally EB with increasing differential stress (σ
2
– σ
3
). The deformation characteristics are dependent on intermediate principal stress σ
2
, minimum principal stress σ
3
, mineral compositions, and mineral textures of rock samples. An increase in σ
3
leads to an increased ductility, while an increase in σ
2
leads to an increased brittleness. Moreover, rocks with regular mineral textures and low mineral hardness are more prone to ductility. When the deformation curve is transformed from EPD to EPB and then to EB, the tensile crack gradually predominates, and the macroscopic failure angle gradually becomes steeper.
Hot deformation is a key method of processing metallic materials and controlling their final properties through structure-forming processes. The ability to exploit the structural potentiality of both ...traditional alloys and new progressive materials is crucial in terms of sustainable development and economic growth. This reprint focuses not only on conventional technologies (e.g., rolling or forging) but also on modern procedures, such as various types of complex thermomechanical processing and controlled cooling. Most papers are based on the application of advanced hot deformation simulators and structural analysis methods, as well as computer simulations of bulk-forming processes.
The main regularities of deformation and loading of the stook during creation of the developed space with the great area of a side job are considered in the article. The possibility of formation of ...the set of balance among the stook barriers is estimated. The assessment of influence of rock "bridge" on the stook loading is given.
The dynamic mechanical behaviour of Mg-2Y-0.6Nd-0.6Zr alloys with different grain sizes at a high strain rate (1100 s-1) was investigated in this study, and the effect of grain size on the ...microstructure and deformation mechanism was analysed. In the process of dynamic compression, fine grains (3 μm) can inhibit the formation of twinning, the majority of twins in coarse grains are {101(—)2} tensile twins, and the number of {101(—)2} tensile twins increases with increasing grain size. The accumulation of dislocations is more obvious in fine grains. Under dynamic conditions, <c+a> dislocations more easily move in the samples with smaller grain sizes. With increasing grain size, the main deformation mechanism change from dislocation and <c+a> dislocation slip to {101(—)2} tensile twin and dislocation slip.
Multi-stage plastic deformation of metallic sheets for fabrication of complex micro structures with high aspect ratio features in different industrial clusters has been prevailing due to product ...miniaturization and integrated manufacturing. Owning to the varying strain path and the miniaturized scale of work pieces, both the strain path change (SPC) and size effect (SE) significantly affect the micro-scale deformation behaviors. To have a scientific insight and understanding of the influences of SPC and SE, two-stage tensile tests were conducted using the 0.1 mm thick SS 316L sheets with different grain sizes and EBSD was employed to characterize the microstructure evolutions. The results showed that the yield stress and elongation rate in the second tensile stage were decreased with the increase of pre-strain and the intersection angle between two tensile directions, while the hardening rate was found to be solely dependent on pre-strain. Changing the tensile direction in the second stage reversed the orientation distribution preference and raises the percentage of high Schmid factors, resulting in lowering the yield stress and hardening rate. On the other hand, more intra-granular mismatching boundaries accumulate in the coarsened grains, which impedes the dislocation movement and increases the deformation resistance. These two confronted mechanisms of SPC and SE interactively influence the deformation behaviors. A constitutive model for describing the flow stress affected by SPC and SE was established based on the micro-mechanism, which provided a basis to support the multi-stage microforming.
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•Interactive influences of strain path change and size effect were first explored.•Ultra-thin sheets' multi-stage deformation behaviors were thoroughly studied.•Microstructure evolution affected by both effects was investigated in-depth.•Intrinsic correlation between Schmid factor and both effects was obtained.•A physical-based constitutive model incorporating both effects was established.
Bulk nanostructured (NS) materials processed by severe plastic deformation (SPD) have received considerable attention for several decades. The physical origin of this processing philosophy is to ...enable substantial grain refinement from a micrometer to a nanoscale level mainly through the activation of fundamental deformation mechanisms: dislocation glide, deformation twinning, and their sophisticated interactions. The formation of nanostructures in NS metallic materials is significantly governed by the quintessential dominance of these two plasticity carriers during SPD, and their mechanical properties are thereby correspondingly affected. According to conventional crystal plasticity, the stacking fault energy (SFE) of materials is one of the most crucial factors primarily controlling which deformation mechanism plays an overwhelming role in accommodating the plasticity. Therefore, a profound understanding of the vital significance of SFE in NS materials can extend and enrich our comprehension of their structure-property relationship, lead to the design of NS metallic materials with superior properties, and pave the path for their perspective applications. Choosing Cu and its binary alloys as model systems, this review extensively surveys the principal influences of SFE on the preferred choice of deformation mechanisms during SPD, microstructural evolution, grain refinement, deformation behavior, and mechanical properties of NS material including tensile properties and cyclic deformation responses.
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