We present a multiscale dislocation density-based constitutive model for the strain-hardening behavior in twinning-induced plasticity (TWIP) steels. The approach is a physics-based strain rate- and ...temperature-sensitive model which reflects microstructural investigations of twins and dislocation structures in TWIP steels. One distinct advantage of the approach is that the model parameters, some of which are derived by ab initio predictions, are physics-based and known within an order of magnitude. This allows more complex microstructural information to be included in the model without losing the ability to identify reasonable initial values and bounds for all parameters. Dislocation cells, grain size and twin volume fraction evolution are included. Particular attention is placed on the mechanism by which new deformation twins are nucleated, and a new formulation for the critical twinning stress is presented. Various temperatures were included in the parameter optimization process. Dissipative heating is also considered. The use of physically justified parameters enables the identification of a universal parameter set for the example of an Fe–22Mn–0.6C TWIP steel.
A subregular solution thermodynamic model was used to calculate the stacking fault energies (SFEs) of high-manganese (10 to 35 wt pct) steels with carbon contents of 0 to 1.2 wt pct. Based on these ...calculations, composition-dependent diagrams were developed showing the regions of different SFE values for the mentioned composition range. These diagrams were called SFE maps. In addition, variations in the SFE maps were observed through increasing the temperature, aluminum content, and austenite grain size. These changes were seen either as an increasing trend of SFE caused by raising the temperature and aluminum content, or as a decreasing behavior caused by increasing the grain size. The SFE value of 20 mJ/m
2
within these diagrams was introduced as the upper limit for the strain-induced martensite formation. The variations in this limit caused by increasing the temperature and aluminum content were mathematically evaluated to find out the minimum amount of manganese that was required to avoid the martensitic transformation. By introducing the isocarbon and isomanganese diagrams of the SFE, it was seen that both temperature and aluminum had a greater effect on the SFE when added to the steels with the lower manganese contents. Moreover, by adding more aluminum to the composition of the high-manganese steels, its influence on the SFE decreased continuously.
Thermodynamic stacking fault energy (SFE) maps were developed using the subregular solution model for the Fe-Mn-Al-C system. These maps were used to explain the variations in the work-hardening ...behavior of high-manganese steels, both through experiments and by comparison with the published data. The suppression of the transformation induced plasticity (TRIP) mechanism, the similarity between the shape of the work-hardening rate diagrams for the produced iso-SFE materials, and an earlier onset of stage C of work hardening by decreasing SFE were shown to be efficiently predictable by the given mechanism maps. To overcome the limitations arising from studying the deformation response of high-manganese steels by SFE values alone, for example, the different work-hardening rate of iso-SFE materials, an empirical criterion for the occurrence of short-range ordering (SRO) and the consequently enhanced work-hardening, was proposed. The calculated values based on this criterion were superimposed on the thermodynamics-based mechanism maps to establish a more accurate basis for material design in high-manganese iron-based systems. Finally, the given methodology is able to clarify the work-hardening behavior of high-manganese twinning induced plasticity (TWIP) steels across an extensive range of chemical compositions.
Despite great progress in engineering functional tissues for organ repair, including the heart, an invasive surgical approach is still required for their implantation. Here, we designed an elastic ...and microfabricated scaffold using a biodegradable polymer (poly(octamethylene maleate (anhydride) citrate)) for functional tissue delivery via injection. The scaffold's shape memory was due to the microfabricated lattice design. Scaffolds and cardiac patches (1 cm × 1 cm) were delivered through an orifice as small as 1 mm, recovering their initial shape following injection without affecting cardiomyocyte viability and function. In a subcutaneous syngeneic rat model, injection of cardiac patches was equivalent to open surgery when comparing vascularization, macrophage recruitment and cell survival. The patches significantly improved cardiac function following myocardial infarction in a rat, compared with the untreated controls. Successful minimally invasive delivery of human cell-derived patches to the epicardium, aorta and liver in a large-animal (porcine) model was achieved.
Polymer flooding is an important enhanced oil recovery technology introduced in field projects since the late 1960s. The key to a successful polymer flood project depends upon proper estimation of ...polymer retention. The aims of this paper are twofold. First, to show the mechanism of polymer flooding and how this mechanism is affected by polymer retention. Based on the literature, the mobility ratio significantly increases as a result of the interactions between the injected polymer molecules and the reservoir rock. Secondly, to provide a better understanding of the polymer retention, we discussed polymer retention types, mechanisms, factors promoting or inhibiting polymer retention, methods and modeling techniques used for estimating polymer retention.
In the present paper, the effects of process parameters on phase transformations during non-isothermal deformations are described and discussed. Non-isothermal high temperature compressive ...deformations were conducted on 22MnB5 boron steel by using deformation dilatometry. Cylindrical samples were uniaxially deformed at different strain rates ranging from 0.05 to 1.0
s
−1 to a maximum compressive strain of 50%. Qualitative and quantitative investigations were carried out using surface hardness mapping data as well as dilatation curves. It was observed that a higher initial deformation temperatures resulted in a higher martensite fraction of the microstructure, while a variation in the martensite start temperature was negligible. Another conclusion was that by applying larger amounts of strain as well as higher force levels, not only the martensite start temperature, but also the amount of martensite was reduced. Moreover, it was concluded that using surface hardness mapping technique and dilatometry experiments were very reliable methods to quantify and qualify the coexisting phases.
This article presents a coordinated operation model for energy management of a multi‐integrated energy system based on Mixed‐Integer Linear Programing (MILP). The power derived by trains from ...regenerative braking energy (RBE), during deceleration, is utilised to meet the interconnected energy hubs’ (IEHs) demand. The recovered energy is calculated by simulating the motion of the trains in MATLAB software. The electricity and heat demand response (DR) programs are integrated into the proposed model to study their impacts on the operating cost and the carbon emission of the IEH, considering several case studies. Furthermore, the uncertainties of the RBE, photovoltaic power generation, and loads of the IEH are considered by formulating the optimisation problem stochastically through a scenario‐based approach. Therefore, a scenario generation and reduction decision‐making technique is employed. Finally, the GAMS optimisation software is used to assess the efficiency of the presented MILP model. The simulation results indicate that the total operating cost of the IEH reduced 2.0% and 1.4% in the case studies. Also, the CO2 emission is decreased by about 0.3% by applying the coordination scheme besides the DR programs.
Nitrogen in austenitic stainless steels and its effect on the stacking fault energy (SFE) has been the subject of intense discussions in the literature. Until today, no generally accepted method for ...the SFE calculation exists that can be applied to a wide range of chemical compositions in these systems. Besides different types of models that are used from first-principle to thermodynamics-based approaches, one main reason is the general lack of experimentally measured SFE values for these steels. Moreover, in the respective studies, not only different alloying systems but also different domains of nitrogen contents were analyzed resulting in contrary conclusions on the effect of nitrogen on the SFE. This work gives a review on the current state of SFE calculation by computational thermodynamics for the Fe-Cr-Mn-N system. An assessment of the thermodynamic effective Gibbs free energy,
, model for the
phase transformation considering existing data from different literature and commercial databases is given. Furthermore, we introduce the application of a non-constant composition-dependent interfacial energy, б
γ/ε
, required to consider the effect of nitrogen on SFE in these systems.
In the current work, the effects of deformation temperature and strain rate on microstructure and mechanical properties of a boron-alloyed steel after being isothermally compressed and subsequently ...quenched are investigated. The results indicate that at a constant strain rate, the hardness and martensite start temperature (Ms) normally increase as the deformation temperature increases. It is also observed that higher strain rates increase the hardness and flow stress, although a clear effect of strain rate on Ms is not observed. It is concluded that while increase of deformation temperature reduces the work hardening rate, the effects of strain rate on work hardening rate is intricate. Additionally, some models to deal with the work hardening rate variations as a function of temperature and strain rate are represented. Finally, the changes of flow stress, Ms temperature, hardness, and martensite volume fraction are compared in terms of the applied process routes: isothermal deformation followed by cooling, and simultaneous deformation and cooling processes.
Schools are an ideal setting in which to measure and promote mental health difficulties. The aim of present study was to develop the Nemad Electronic Mental-Health Assessment Devices for Children ...(NEMAD-C) aged 6 to 12 years in Iran. A sample of parents and teachers (N = 10,163) were recruited to complete the parent and teacher reports. Totally, explorative and confirmatory factor analyses showed that the eight-factor model provides a better fit for both parental report and teacher report versions. Results revealed a screening tool consisting of eight dimensions: child abuse risk, self-harm, anxiety, depression, disruptive behavior disorders, attention deficit/hyperactivity disorders, academic achievement deficit, and self-regulation. Findings showed that the internal consistency coefficients of the subscales were high, and convergent validity was evidenced by significant correlations with theoretically related constructs. Therefore, the NEMAD-C has adequate reliability and validity and could be used for multi-dimensional assessment of mental health problems in Iran.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK, VSZLJ
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