A comparison of two frameworks for kinematic hardening in hyperelasto-plasticity

In this work we compare two frameworks for thermodynamically consistent hyperelasto-plasticity with kinematic hardening. The first was formulated by Dettmer and Reese (2004), inspired by Lion (2000), and has been used to model sheet metal forming. The second, formulated by Wallin et al. (2003), has been used to model large shear strains and cyclic ratcheting behavior of pearlitic steel (Johansson et al. 2006). In this paper we show that these frameworks can result in equivalent models for certain choices of free energies. Furthermore, it is shown that the choices of free energy found in the literature only result in minor differences. These differences are discussed theoretically and investigated numerically

Robust templates for domain boundary engineering in ErMnO<inf>3</inf>

Emerging properties of domain boundaries define the emerging field of domain boundary engineering. For many applications, the domain boundary acts as template onto which the desired properties, such as (super-) conductivity, polarity, ferroelectricity, magnetism, are imposed. This requires for most applications that the domain structures remain unchanged under appropriate chemical doping. Hassanpour et al (2016 New J. Phys. 18 043015) have now shown, for the first time, that the magnetic and electric domain structures remain indeed robust against charge carrier doping (Ca2+ and Zr4+) of the workbench multi-ferroic ErMnO3. This opens the way into novel functionalities based on the nanostructure of ErMnO3.This is the final version of the article. It first appeared from IOP Publishing via http://dx.doi.org/10.1088/1367-2630/18/5/05100

On the Prediction of Anisotropy Evolution in Polycrystalline Multiphase Materials

In this contribution a multiscale modeling (MSM) framework is used to model the behavior of a multi-phase polycrystalline material. The use of MSM is motivated by the interest in how mechanisms occuring at different length scales contribute to the macroscopic behavior

Flicker vortex structures in multiferroic materials

Computer simulation of ferroelastic materials reveals dynamic polar vortex structures related to flexo-electricity between cation and anion lattices. At finite temperatures, the vortices are found to flicker in time and space. Widely spaced ferroelastic twin boundaries nucleate vortices while dense twin boundaries suppress them. The time averaged number of vortices at any site decays exponentially, indicating the highly mobile dynamics of the vortex lattice. Applied electric fields break the rotational symmetry of vortices and finally destroy them. The total number density of vortices follows a field and temperature dependence as N(E)=N0/[1+A exp(E/k(T−TVF))] with TVF &amp;lt; 0. The observed vortex structures are akin to those observed in magnetic and superconducting disordered vortex lattices.This is the author's accepted version. The final version is available from AIP at http://scitation.aip.org/content/aip/journal/apl/105/11/10.1063/1.4896143?showFTTab=true&containerItemId=content/aip/journal/ap

Elastic softening of leucite and the lack of polar domain boundaries

Elastic properties of leucite have been investigated using resonant ultrasound spectroscopy over a temperature range from 300 K to 1400 K. According to these measurements, elastic moduli soften by ~50% at the Ia3d-I41/acd ferroelastic transition temperature Tc1 = 940 K relative to the value at 1400 K. A second softening is observed at Tc2 = 920 K, corresponding to the structural change from the space group I41/acd to I41/a. These elastic anomalies are analyzed in a simple model of a pseudoproper ferroelastic transition under the assumption that the transitions observed at Tc1 and Tc2 can be approximated by a single pseudoproper ferroelastic transition. The two phase transitions are accompanied by a single peak in mechanical damping attributed to the high mobility of twin walls in the intermediate phase followed by pinning in the low temperature phase. To determine whether twin walls in tetragonal leucite are polar, resonant piezoelectric spectroscopy and second harmonic generation measurements were performed but no evidence of polarity was found.E.K.H.S. is grateful to EPSRC (EP/K009702/1) and the Leverhulme Foundation (RPG-2012-564) for support. M.A.C. acknowledges NERC grants (NER/A/S/2000/01055 and NE/F017081/1).This is the final version of the article. It first appeared from De Gruyter via http://dx.doi.org/10.2138/am-2015-5313ccb

On the Prediction of Macroscopic Yield Surfaces of a Pearlitic Steel using Multiscale Modeling

On the microscale, pearlite consists of hard and brittle cementite lamellae embedded in a ductile ferrite matrix. The cementite lamellae are arranged in colonies within which the lamella orientation is ideally constant. This composite-like constitution, on the microscale, makes pearlitic steels ideally suited for multiscale modeling. In this contribution a three-scale multiscale modeling setup is used to describe the mechanical behav- ior of a pearlitic steel. The macroscale represents the engineering scale on which a typical structural component would be analyzed. The mesoscale comprises colonies, with varying orientations (both mor- phological and crystallographic), thereby enabling the interactions between colonies to be taken into account. On the microscale a model representing the lamellar structure of pearlite is used. This model accounts for the behavior of the constituents but also the interactions between them. A cornerstone in this contribution is the formulation of a macroscopic, energy based, yield criterion based on homogenized quantities (cf. e.g. [1, 2, 3]). With such a criterion macroscopic yield surfaces can be predicted. The impact of altering the prolongation condition on the resulting yield surface is studied. Furthermore, the effect of adding a pre-loading before carrying out the yield surface prediction is investigated. Regarding the topic of how to identify the correct values of the parameters in a multiscale model several possibilities exists. This topic will be discussed briefly

Simulating acoustic emission: The noise of collapsing domains

EPSRCThis is the accepted version of an article which is published in 'Physical Review B' at https://journals.aps.org/prb/ - the link to the published version is http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.06410

Effect of pores and grain size on the elastic and piezoelectric properties of quartz-based materials

The role of grain size and porosity in the piezoelectric and elastic properties of SiO2-based materials was investigated using resonant piezoelectric spectroscopy, RPS, and resonant ultrasound spectroscopy, RUS. RPS performed on agate revealed a piezoelectric effect comparable in magnitude to that in single crystal quartz. The observed strong piezoelectricity in agate requires preferential orientation of SiO2 during crystal growth. Similarly, in novaculite and sandstone finite (but weak) RPS signals were evident, suggesting that the expected randomization of the piezoelectric quartz grains is incomplete. On the other hand, Vycor, a silica glass with a porosity of 40%, showed no evidence of the piezoelectric effect. According to temperature dependent RPS and RUS measurements, the α-β transition temperature in quartz does not change in polycrystalline samples. Finally, the temperature dependence under heating of the elastic constants is reversible in quartz and agate and irreversible in sandstone and vycor.RUS facilities in Cambridge were established through grant no. NE/B505738/1 to MAC from the Natural Environment Research Council. EKHS is grateful to the Leverhulme Foundation (RPG-2012-564) and EPSRC (EP/K009702/1) for financial support.This is the final version. It was first published by De Gruyter at http://www.degruyter.com/view/j/ammin.2015.100.issue-5-6/am-2015-5180ccby/am-2015-5180ccby.xm

First-principles reinvestigation of bulk WO3_{3}

Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO$_{3}$. Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which provides very good agreement with experimental data. We show that the hypothetical high-symmetry cubic reference structure combines several ferroelectric and antiferrodistortive (antipolar cation motions, rotations, and tilts of oxygen octahedra) structural instabilities. Although the ferroelectric instability is the largest, the instability related to antipolar W motions combines with those associated to oxygen rotations and tilts to produce the biggest energy reduction, yielding a $\textit{P}$2$_{1}$/$\textit{c}$ ground state. This nonpolar $\textit{P}$2$_{1}$/$\textit{c}$ phase is only different from the experimentally reported $\textit{Pc}$ ground state by the absence of a very tiny additional ferroelectric distortion. The calculations performed on a stoichiometric compound so suggest that the low-temperature phase of WO$_{3}$ is not intrinsically ferroelectric and that the experimentally observed ferroelectric character might arise from extrinsic defects such as oxygen vacancies. Independently, we also identify never observed $\textit{R3m}$ and $\textit{R3c}$ ferroelectric metastable phases with large polarizations and low energies close to the $\textit{P}$2$_{1}$/$\textit{c}$ ground state, which makes WO$_{3}$ $\textbf{a}$ potential antiferroelectric material. The relative stability of various phases is discussed in terms of the anharmonic couplings between different structural distortions, highlighting a very complex interplay.The work was supported by the ARC project AIMED and the F.R.S-FNRS PDR projects HiT4FiT and MaRePeThe. Calculations have been performed within the PRACE project TheDeNoMo and relied on the Céci facilities funded by F.R.S-FNRS (Grant No. 2.5020.1) and Tier-1 supercomputer of the Fédération Wallonie-Bruxelles funded by the Walloon Region (Grant No. 1117545). E.K.H.S. is grateful for support to EPSRC and the Leverhulme trust. H.H. thanks the AVERROES-ERASMUS Mundus project