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[en] We prove a static shakedown theorem for viscoplastic and plastic workhardening materials which satisfy a constitutive inequality similar to the principle of maximum plastic work for perfectly plastic materials. Then we are allowed to define a static and a kinematic shakedown safety factor for a loading domain. It is shown that for a certain class of workhardening plastic and viscoplastic materials, including most of well-known models, the two shakedown safety factors are equal and define a true safety factor. Finally we prove a partial shakedown theorem, which can be used to analyse the shakedown possibilities of a structure of which the elastic response contains singularities. (orig.)
[en] This work aims to characterize the 36 NiCrMo 6 steel in monotic traction. The tested samples were subjected to mechanical surface treatment (MST) by diamond ball burnishing. This process allow it possible to modify the physical and geometrical properties of the material. The stress-strain diagram obtained were processed and digitalised. The hardening domain was modelled and rational curves were established, taking into account the stresses triaxiality. Thus, the work hardening exponent of material considered was evaluated. The effect of ball burnishing on this exponent has studied in proceeding a comparative manner between burnished and machined surface. The results obtained show that by applying the optimal parameters for burnishing, the work hardening exponent of pre-machined surface layer can be increased by 10%, where nB = 0.407 (nT = 0.312 machined surface). (paper)
[en] This paper reviews the work hardening, recovery and recrystallization mechanisms in alloys containing dispersed precipitates. In the section on work hardening, the influence od spacing, particle size and shape on the density and distribution of dislocations have been discussed. They represent a large part of the energy stored in the material following drformation, which in turn is driving force for recrystallization. Next, the role of precipitates on recovery, on the formation and the growth of recrystallized regions has been discussed in detail. The competition between recovery and recrystallization and recrystallization of supersaturated solid solutions have also been mentioned. Finally, the technological relevance of the aspects treated in this paper has been discussed. (author)
[pt]Este trabalho faz uma revisao dos mecanismos de encruamento, recuperacao e recristalizacao de ligas contendo dispersao de precipitados. No topico referente ao encruamento sao discutidos os efeitos do espacamento, tamanho e forma das particulas de densidade e distribuicao das discordancias, as quais representam a parcela principal da energia armazenada no material apos a deformacao, que por sua vez e o potencial termodinamico para a recristalizacao. Em seguida o papel dos precipitados na recuperacao, na formacao e no crescimento das regioes recristalizadas e discutido em detalhes. A competicao entre recuperacao e recristalizacao e a recristalizacao de solucoes solidas supersaturadas sao tambem abordadas. Finalmente e discutida a relevancia tecnologica dos fenomenos tratados. (autor)
[en] The hot deformation behavior of as-cast hypoeutectic Al-Si-Mg alloy has been investigated through hot compression tests at temperatures between 573 and 773 K and the strain rate of 0.001-1 s−1. A modified Hansel-Spittel constitutive model is proposed, which takes the effect of strain rate on strain hardening into account. The processing maps are established based on the dynamic material model and the Murty criterion. Microstructure observations show that dynamic recovery dominates the dynamic softening behavior, and recrystallized grains are found in the sample tested at 773 K with strain rate of 0.01 and 0.001 s−1. The size of Si particles decreases by about 64.73% with the effective strain increasing from 0 to 1.2. The optimal hot processing parameters of as-cast hypoeutectic Al-Si-Mg alloy are established based on the processing maps.
[en] Highlights: • The rate-dependent behavior of 42CrMo steel exists at a wide range of strain rates. • Due to the adiabatic temperature increase, the thermal softening effect exists. • An improved Z-A model taking account of the thermal softening is proposed. 42CrMo steel used in high-speed train axles withstands complex loading conditions. To study the mechanical properties and the stress-strain relationship of 42CrMo steel, it was subjected to quasi-static and dynamic compression experiments. Experiments at eight different strain rates, ranging from 10− 3 to 4500 s− 1, demonstrate that it exhibits rate-dependent plastic behavior, thermal softening, and work-hardening behaviors. The dislocation theory explains the deformation mechanism of 42CrMo steel. Furthermore, a new constitutive model, which includes the thermal softening effect, based on the Zerilli–Armstrong constitutive model, is proposed to describe the dynamic mechanical behavior of 42CrMo steel. The model results are in good agreement with the experimental data, demonstrating that the proposed constitutive model describes the mechanical behavior of 42CrMo steel at various strain rates very well.
[en] A novel constitutive model of cyclic plasticity under general states of loading is developed. A proportional and a non-proportional non-hardening region in plastic strain space is introduced to describe the characteristic features of cyclic hardening behaviour; proportional or non-proportional cycles are assumed to induce no isotropic hardening in these non-hardening regions. Then, by incorporating the hardening parameters defined by these regions, the stress-plastic strain relation is formulated by modifying the two surface model in advanced flow theories of plasticity. The proposed model described the cyclic behavior for proportional and circular cycles of constant and of different strain amplitudes. (orig./RF)
[en] Highlights: • Studied wear behavior of rheocast Mg–Sn based alloys under ambient temperature. • The volumetric wear was found to be increased with increasing applied load. • Different wear micro-mechanism was observed under electron micro-scope. • Plastic deformation and work hardening took place for all the alloys mainly at the higher loads. - Abstract: Present paper focuses on the dry sliding wear behavior of rheocast Mg–Sn based alloys under ambient temperature. The alloys were studied through pin-on-disc wear experiments under four different loading conditions, namely, 9.8, 19.6, 29.4 and 39.2 N. Present investigations highlight the influence of load on the cumulative wear loss, volumetric wear loss, dry sliding wear rate and co-efficient of friction of the different alloys under study. The volumetric wear was found to be increased with increasing applied load. Different wear micro-mechanisms were observed under electron micro-scope. The wear occurs mainly by ploughing mechanism and by delamination also. During wear, extensive plastic deformation and work hardening took place for all the alloys mainly at the higher loads. Micro-structural analysis has been performed for all the alloys at different loading conditions
[en] In order to clarify the competition between work hardening (WH) caused by dislocation movements and the dynamic softening result from dynamic recovery (DRV) and dynamic recrystallization (DRX), a new two-stage flow stress model of X12CrMoWVNbN10-1-1 (X12) ferrite heat-resistant steel was established to describe the whole hot deformation behavior. And the parameters were determined by the experimental data operated on a Gleeble-3800 thermo- mechanical simulation. In this constitutive model, a single internal variable dislocation density evolution model is used to describe the influence of WH and DRV to flow stress. The DRX kinetic dynamic model can express accurately the contribution of DRX to the decline of flow stress, which was established on the Avrami equation. Furthermore, The established new model was compared with Fields-Bachofen (F-B) model and experimental data. The results indicate the new two-stage flow stress model can more accurately represent the hot deformation behavior of X12 ferrite heat-resistant steel, and the average error is only 0.0995. (paper)