A constitutive model of the deformation behaviour of twinning induced plasticity (TWIP) steel at different temperatures

The mechanical behaviour of Fe-18Mn-0.6C-1Al (wt%) TWIP steel was modelled in the temperature range from room temperature to 400°C. The proposed constitutive model was based on the Kocks-Mecking-Estrin (KME) model. The model parameters were determined using extensive experimental measurements of the physical parameters such as the dislocation mean free path and the volume fraction of twinned grains. More than 100 grains with a total area of ~300μm2 were examined at different strain levels over the entire stress-strain curve. Uniaxial tensile deformation of the TWIP steel was modelled for different deformation temperatures using a modelling approach which considers two distinct populations of grains: twinned and twin-free ones. A key point of the work was a meticulous experimental determination of the evolution of the volume fraction of twinned grains during uniaxial tensile deformation. This information was implemented in a phase-mixture model that yielded a very good agreement with the experimental tensile behaviour for the tested range of deformation temperatures. © 2014 Elsevier B.V.

Forming behaviour analysis and constitutive modelling of Ti-6Al-4V at room temperature.

 A constitutive model was proposed in this thesis and a promising approach for accurate prediction of forming behaviour of high strength titanium alloy sheet metal forming at room temperature is presented. Outcomes showed a potential solution of cold roll forming of this material for aerospace and automotive structural applications.

Constitutive analysis of hot deformation behavior of a Ti6Al4V alloy using physical based model

The effect of deformation parameters on the flow behavior of a Ti6Al4V alloy has been studied to understand the deformation mechanisms during hot compression. Cylindrical samples with partially equiaxed grains were deformed in the α+β phase region at different thermo-mechanical conditions. To develop components with tailored properties, the physically based Estrin and Mecking (EM) model for the work hardening/dynamic recovery combined with the Avrami equation for dynamic recrystallization was used to predict the flow stress at varying process conditions. The EM model revealed good predictability up to the peak strain, however, at strain rates below 0.01s^-1, a higher B value was observed due to the reduced density of dislocation tangles. In contrast, the flow softening model revealed higher value of constants a and b at high strain rates due to the reduction in the volume fraction of dynamic recrystallization and larger peak strain. The predicted flow stress using the combined EM+Avrami model revealed good agreement with the measured flow stress resulted in very low average absolute relative error value. The microstructural analysis of the samples suggests the formation of coarse equiaxed grains together with the increased β phase fraction at low strain rate leads to a higher flow softening.

Constitutive overexpression of the OsNAS gene family reveals single-gene strategies for effective iron- and zinc-biofortification of rice endosperm

Background
Rice is the primary source of food for billions of people in developing countries, yet the commonly consumed polished grain contains insufficient levels of the key micronutrients iron (Fe), zinc (Zn) and Vitamin A to meet daily dietary requirements. Experts estimate that a rice-based diet should contain 14.5 µg g−1 Fe in endosperm, the main constituent of polished grain, but breeding programs have failed to achieve even half of that value. Transgenic efforts to increase the Fe concentration of rice endosperm include expression of ferritin genes, nicotianamine synthase genes (NAS) or ferritin in conjunction with NAS genes, with results ranging from two-fold increases via single-gene approaches to six-fold increases via multi-gene approaches, yet no approach has reported 14.5 µg g−1 Fe in endosperm.

Methodology/Principal Findings
Three populations of rice were generated to constitutively overexpress OsNAS1, OsNAS2 or OsNAS3, respectively. Nicotianamine, Fe and Zn concentrations were significantly increased in unpolished grain of all three of the overexpression populations, relative to controls, with the highest concentrations in the OsNAS2 and OsNAS3 overexpression populations. Selected lines from each population had at least 10 µg g−1 Fe in polished grain and two OsNAS2 overexpression lines had 14 and 19 µg g−1 Fe in polished grain, representing up to four-fold increases in Fe concentration. Two-fold increases of Zn concentration were also observed in the OsNAS2 population. Synchrotron X-ray fluorescence spectroscopy demonstrated that OsNAS2 overexpression leads to significant enrichment of Fe and Zn in phosphorus-free regions of rice endosperm.

Conclusions
The OsNAS genes, particularly OsNAS2, show enormous potential for Fe and Zn biofortification of rice endosperm. The results demonstrate that rice cultivars overexpressing single rice OsNAS genes could provide a sustainable and genetically simple solution to Fe and Zn deficiency disorders affecting billions of people throughout the world.

Wavelet-Galerkin method for one-dimensional elastoplasticity and damage problems: Constitutive modeling and computational aspects

This work presents an analysis of the wavelet-Galerkin method for one-dimensional elastoplastic-damage problems. Time-stepping algorithm for non-linear dynamics is presented. Numerical treatment of the constitutive models is developed by the use of return-mapping algorithm. For spacial discretization we can use wavelet-Galerkin method instead of standard finite element method. This approach allows to locate singularities. The discrete formulation developed can be applied to the simulation of one-dimensional problems for elastic-plastic-damage models. (C) 2007 Elsevier B.V. All rights reserved.

Karyotype characterization, constitutive heterochromatin and nucleolus organizer regions of Paranaita opima (Coleoptera, Chrysomelidae, Alticinae)

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CHROMOSOME-STUDIES IN HYPOPTOPOMATINAE (PISCES, SILURIFORMES, LORICARIIDAE) .2. ZZ ZW SEX-CHROMOSOME SYSTEM, B-CHROMOSOMES, AND CONSTITUTIVE HETEROCHROMATIN DIFFERENTIATION IN MICROLEPIDOGASTER-LEUCOFRENATUS

Cytogenetic analysis of two local populations of microlepidogaster leucofrenatus showed a basic diploid chromosome number (2N) of 54 in both populations. Some fishes were found to have a 2N = 55 or 56 chromosomes due to the presence of one or two large heterochromatic B chromosomes. Specimens of M. leucofrenatus from the Poco Grande stream had 24 metacentrics, 24 submetacentrics, four subtelocentrics, and one submetacentric homomorphic pair in males and one submetacentric/subtelocentric heteromorphic pair in females, whereas individuals of this species from the Marumbi River had 22 metacentrics, 24 submetacentrics, four subtelocentrics, two acrocentrics, and one submetacentric/subtelocentric heteromorphic pair in females. The occurrence of the heteromorphic pair in the females was due to the presence of an extra C-banded segment on the W chromosome. Ag-NORs in both populations were located interstitially on the short arm of the largest metacentric pair. The Poco Grande population had less constitutive heterochromatin than did the Marumbi River population. The speciation process in this fish species is discussed on the basis of heterochromatin distribution.

On a regular convex solver potential for an elastic-damage constitutive model: a theoretical analysis

This work is related with the proposition of a so-called regular or convex solver potential to be used in numerical simulations involving a certain class of constitutive elastic-damage models. All the mathematical aspects involved are based on convex analysis, which is employed aiming a consistent variational formulation of the potential and its conjugate one. It is shown that the constitutive relations for the class of damage models here considered can be derived from the solver potentials by means of sub-differentials sets. The optimality conditions of the resulting minimisation problem represent in particular a linear complementarity problem. Finally, a simple example is present in order to illustrate the possible integration errors that can be generated when finite step analysis is performed. (C) 2003 Elsevier Ltd. All rights reserved.

Constitutive heterochromatin, G-bands and nucleolus-organizer regions in four species of Didelphidae (Marsupialia)

Chromosomes of Didelphis albiventris, D. marsupialis, Philander opossum and Lutreolina crassicaudata, four species of marsupials with very similar karyotypes and 2n=22 were studied. All the chromosomes were acrocentrics except the X in L. crassicaudata, which is a metacentric. The G-band patterns of these species are similar but the distribution of constitutive heterochromatin differs among them as shown by C-banding. The hypothesis that the X in L. crassicaudata might be an isochromosome derived from the acrocentric X in the other species is discarded since G-and C-banding patterns differ in the two arms. In D. marsupialis the Ag-NORs are terminal and located in both arms of one pair and in the long arms of two pairs of medium-sized autosomes. In P. opossum the NOR-bearing chromosomes could be precisely identified through simultaneous silver staining and G-banding. The Ag-NORs are terminal and located at the short arm of pair 5 and the long arm of pair 7. © 1982 Dr W. Junk Publishers.