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Purpose is the formulation, numerical implementation, identification and application of a material model for ductile damage and failure during cyclic and non-proportional loading. The authors combined a hyperelasticity-based elasto-plastic model for non-linear isotropic as well as kinematic hardening with a modified Gurson model. Evolution strategy helped identify the model parameters for the high-strength steel 10MnMoNi5-5. The simulation of ductile failure in fracture mechanics specimens verified the model with respect to cyclic loading at two temperatures. The simulation of additional fracture mechanics applications validated the model as to the development of residual stresses at the crack tip under cyclic loads. [ABSTRACT FROM AUTHOR]

The purpose of the current work is the investigation and comparison of aspects of the material behavior predicted by two models for anisotropic, and in particular cross, hardening in bcc sheet steels subject to non-proportional loading. The first model is the modified form (Wang et al., 2008) of that due to Teodosiu and Hu (1995, 1998). In this (modified) Teodosiu-Hu model (THM), cross hardening is assumed to affect the yield stress and the saturation value of the back stress. The second model is due to Levkovitch and Svendsen (2007) and Noman et al. (2010). In the Levkovitch-Svendsen model (LSM), cross hardening is assumed to affect the flow anisotropy. As clearly demonstrated in a number of works applying the THM (e.g., Boers et al., 2010; Bouvier et al., 2005, 2003; Hiwatashi et al., 1997; Li et al., 2003; Thuillier et al., 2010; Wang et al., 2008) and the LSM (e.g., Clausmeyer et al., 2014, 2011b; Noman et al., 2010), both of these are capable of predicting the effect of cross hardening on the stress-deformation behavior observed experimentally in sheet steels. As shown in the current work, however, these two models differ significantly in other aspects, in particular with respect to the development of the yield stress, the back stress, and the yield surface. For example, the THM predicts no change in the shape of the yield surface upon change of loading path, in contrast to the LSM and crystal plasticity modeling of bcc sheet steels (Peeters et al., 2002). On the other hand, the LSM predicts no hardening stagnation after cross hardening as observed in experiments, in contrast to the THM. Examples are given. [ABSTRACT FROM AUTHOR]

TLQP-21 is a VGF-derived neuropeptide proposed to be involved in regulation of metabolism. More specifically it has been suggested that TLQP-21 has the ability to enhance glucose stimulated insulin secretion, making it a candidate for treatment of patients with type 2 diabetes. In this study, we investigated the impact of TLQP- 21 on insulin, glucagon, and somatostatin secretion in the perfused rat pancreas. We found that administration of 5 and 50 nM TLQP-21 had no impact on pancreatic hormone secretion at 3.5 or 8 mM glucose levels. Increasing TLQP-21 (200 nM) and glucose concentration (3.5 and 16 mM) led to a nonsignificant decrease in glucagon secretion, though insulin and somatostatin secretory patterns remained unaffected. In a final set of experiments, perfusions were performed with infusion of 50 and 1 000 nM TLQP-21 to ensure sufficient stimulation. However, administration of TLQP-21 under this setup showed no impact on the pancreatic hormone secretion either. In conclusion, the outcome of this study does not concur with previous findings, suggesting that the effect of TLQP-21 does not directly involve silent hormone secretion. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this paper is to introduce a homogenization method for the material behavior of two-phase composites characterized by a thin-layer-type microstructure. Such microstructures can be found for example in thermally-sprayed coating materials like WC/Fe in which the phase morphology takes the form of interpenetrating layers. The basic idea here is to idealize the thin-layered microstructure as a first-order laminate. Comparison of the methods with existing homogenization schemes as well as with the reference finite-element model for idealized composites demonstrates the advantage of the current approach for such microstructures. Further an extension of the approach to a variable interface orientation is presented. In the end the current method is compared to results based on FE-models of real micrographs. [Copyright &y& Elsevier]

Abstract: In this work, a thermodynamic approach to the modeling and simulation of induced elastic and inelastic material behaviour in the phenomenological realm as based on the concept of evolving structure tensors is discussed. From the constitutive point of view, these quantities determine the material symmetry properties. In addition, the stress and other dependent constitutive fields are isotropic functions of these by definition. The evolution of these during loading then results in an evolution of the anisotropy of the material. From an algorithmic point of view, the current approach leads to constitutive models which are quite amenable to numerical implementation. To demonstrate the applicability of the resulting constitutive formulation, we apply it to the cases of (i) metal plasticity with combined hardening involving both deformation- and permanently induced anisotropy relevant to the modeling of processes such as metal forming, and to (ii) deformation-induced anisotropy in an initially orthotropic pneumatic membrane consisting of a rubber matrix and nylon fibres. [Copyright &y& Elsevier]

The purpose of this work is the formulation and application of a continuum thermodynamic approach to the phenomenological modeling of a class of engineering materials which can be dynamically formed using strong magnetic fields. This is carried out in the framework of a thermodynamic, internal-variable-based formulation in which the deformation, temperature and magnetic fields are in general coupled. This coupling takes the form of the Lorentz force as an additional supply of momentum, and the electromotive power as an additional supply of energy, in the material. In the current approach, the basic thermomechanical field relations for mass, momentum and moment of momentum are obtained from the total energy balance via invariance, and completed by Maxwell’s field equations. The constitutive formulation is based on the exploitation of the Müller-Liu entropy principle, here for the case of isotropic thermoelastic, viscoplastic material behaviour. The resulting reduced constitutive and field relations and restrictions are then applied to the modeling and simulation of high-speed electromagnetic forming of metal tubes and sheet metal. In this context, scaling arguments show that, over the relevant length- and timescales of engineering interest, the evolution of the magnetic field is diffusive in nature, and thermal conduction is negligible. Comparison of the simulation and experimental results for the final sheet metal form shows very good agreement. [ABSTRACT FROM AUTHOR]

The purpose of this work is the development and numerical implementation of a non-local extension of existing Gurson-based modeling for isotropic ductile damage and attendant crack growth. In the current work, this extension is based on a generalization of Gurson-based ductile damage modeling formally analogous to that of Needleman and Tvergaard as based on a (local) effective damage parameter f* which accounts in their case in an effective fashion for the effect of void coalescence on yield behaviour. Here, the corresponding generalized effective damage parameter ν is introduced in order to delocalize the model damage process. To this end, ν is modeled in this work as a scalar-valued continuum microstructural field or generalized phase field via a recent thermodynamic approach to the modeling of such fields. In the last part of the work, the complete model for coupled damage-deformation is implemented numerically using the finite element method and utilized to investigate the damage behaviour of an inhomogeneous steel block in simple tension. The corresponding simulation results demonstrate in particular that delocalization of the model damage process also leads to minimization of mesh-dependence. For simplicity, the current formulation is restricted to the case of small strain and isothermal conditions. [Copyright &y& Elsevier]

In this work, a phenomenological field-based approach to the formulation of models for structured materials or continua is presented. The corresponding results are in particular relevant to that class of such materials for which the distribution of (micro)structure at each material point and the evolution of this distribution may influence the behavior of the material as a whole (e.g., in nematic liquid crystals with variable orientation). Essential to the underlying approach is the assumption or idealization that the structured continuum in question is characterized kinematically by additional degrees of freedom in comparison to standard continua. On this basis, the kinematics and balance relations for the structured continuum are formulated with respect to a (generalized) kinematic space via direct generalization of standard kinematics and balance relations. In particular, the formation of the latter for the structured continuum is based on the corresponding (total) energy balance. Indeed, analogous to the standard case, the assumed Euclidean frame-indifference of this balance, together with the transformation properties of the fields appearing in it, determine the forms of the remaining balance relations for the structured continuum. With these general results in hand, account is next taken of the fact that the degrees of freedom of the standard continuum constitute a subset of those of the structured continuum. As already established in previous work, this fact can be represented in a mathematically-precise fashion as a fibre bundle, with base space the standard kinematic space, i.e., three-dimensional Euclidean point space, and total space the kinematic space for the structured continuum. In this context, the kinematic space for the structure itself is represented by the typical fibre of the fibre bundle. Among other results, one obtains on this basis a split of the momentum balance for the structured continuum into momentum balances for the standard... [ABSTRACT FROM AUTHOR]

Examines on frame-indifference and form-invariance in constitutive theory. Usability of Euclidean frame-indifference and indifference; Concepts of Euclidean frame-indifference; Relationship between simple material and a kinetic gas.

The present contribution deals with the development of a laminate-based model designed to study the single and polycrystalline tetragonal ferroelectric material behaviour. Laminate-based models are micromechanically motivated and consider the volume fraction of the distinct ferroelectric variants directly in their formulation. At first, a single crystal laminate-based model is established by considering the average strain and polarisation compatibility conditions. A suitable thermodynamic electric Gibbs energy and a rate-dependent dissipation equation are postulated to capture the dissipative hysteretic material response. The update of the inequality constrained volume fractions is solved by adopting a Fischer–Burmeister-type algorithm in combination with a Newton–Raphson scheme. Following the single crystal formulation, a homogenisation procedure based on random orientation of the individual grains in a polycrystalline aggregate is considered. The material properties and the polarisation switching response of the randomly oriented individual grains are averaged using a finite element framework in order to study the macroscopic polycrystalline behaviour. A parameter fitting procedure based on experimental data for single crystalline response, taken from the literature, is detailed and the material model as well as the algorithmic scheme are verified by solving representative boundary value problems. Moreover, the finite element based simulation results are compared with newly generated experimental hysteresis data for a barium titanate piezoceramic. [ABSTRACT FROM AUTHOR]

Crystal nucleation is among the most important processes in the synthesis of materials. Here we study the competitive and multistep nucleation process of body centered cubic (bcc) and face centered cubic (fcc) crystals using phase-field crystal simulations. The initial state is a non-equilibrium liquid. This transforms into an amorphous phase composed of clusters with short-range order (SRO) and medium-range order (MRO). Crystal nucleation begins with the formation of MRO clusters structurally similar to the subsequently nucleated crystal. The formation of bcc and fcc nuclei from MRO clusters involves the following steps: (1) formation of a small thin platelet with MRO; (2) its subsequent growth into 3D MRO clusters; (3) development of crystal embryos from MRO clusters; and (4) crystal embryos transformation into a stable crystal nuclei. In addition, the role of bcc precursors in the formation of fcc nuclei is clarified. In particular, {112} surfaces and steps on {110} surfaces of bcc precursors serve as energetically favorable sites for fcc nucleation. This is also reflected in the resulting orientation relationships, i.e., Pitsch, Nishiyama-Wassermann and Kurdjumov-Sachs, between the bcc precursor and fcc nucleus. [ABSTRACT FROM AUTHOR]

A moving bed biofilm reactor (MBBR) pilot plant, using Kaldnes type K1 biofilm carriers, was tested for nitrogen removal at the FREVAR wastewater treatment plant. The pilot plant was fed primary treated municipal wastewater, at temperatures from 4.8 to about 20 deg. C. The results showed that a reasonable design nitrification rate will be 190g TKN/m3d, at 10 deg. C and a reactor pH=/>7.0. Pre-denitrification was very dependent on the concentration of readily biodegradable organic matter and the amount of oxygen in the influent to thefirst anoxic MBBR. It was found that a MBBR process for nitrogen removal at FREVAR will require a total reactor volume corresponding to an empty bed hydraulic retention time of 4-5 hours at average design influent flow. This was based on an influent concentration of 25 mg total N/l, 70% annual average removal of total N and a treatment process consisting of primary treatment, MBBRs with combined pre- and post-denitrification, and followed by coagulation/flocculation and a finalsolids separation stage. [ABSTRACT FROM AUTHOR]

A phase field method for brittle fracture is formulated for a finite strain elasto-viscoplastic material using a novel obstacle phase field energy model. The obstacle energy model results in a crack profile with compact support, and thus gives a physically realistic description of the material behaviour at the vicinity of the crack tip. The resulting variational inequality is discretised by a finite element method, and is efficiently solved using a reduced space Newton method. The solution accuracy and numerical performance of this method is compared with a conventional phase field energy model for brittle fracture through representative examples, and a significant reduction in the numerical solution cost is demonstrated. [ABSTRACT FROM AUTHOR]

Background and Purpose: Specific, high potency receptor antagonists are valuable tools when evaluating animal and human physiology. Within the glucose-dependent, insulinotropic polypeptide (GIP) system, considerable attention has been given to the presumed GIP receptor antagonist, (Pro3)GIP, and its effect in murine studies. We conducted a pharmacological analysis of this ligand including interspecies differences between the rodent and human GIP system.Experimental Approach: Transiently transfected COS-7 cells were assessed for cAMP accumulation upon ligand stimulation and assayed in competition binding using (125) I-human GIP. Using isolated perfused pancreata both from wild type and GIP receptor-deficient rodents, insulin-releasing, glucagon-releasing and somatostatin-releasing properties in response to species-specific GIP and (Pro3)GIP analogues were evaluated.Key Results: Human (Pro3)GIP is a full agonist at human GIP receptors with similar efficacy (Emax ) for cAMP production as human GIP, while both rat and mouse(Pro3)GIP were partial agonists on their corresponding receptors. Rodent GIPs are more potent and efficacious at their receptors than human GIP. In perfused pancreata in the presence of 7 mM glucose, both rodent (Pro3)GIP analogues induced modest insulin, glucagon and somatostatin secretion, corresponding to the partial agonist activities observed in cAMP production.Conclusions and Implications: When evaluating new compounds, it is important to consider interspecies differences both at the receptor and ligand level. Thus, in rodent models, human GIP is a comparatively weak partial agonist. Human (Pro3)GIP was not an antagonist at human GIP receptors, so there is still a need for a potent antagonist in order to elucidate the physiology of human GIP. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is comparing three strategies for dealing with inhomogeneities of non-elliptical shape in the context of homogenization methods. First, classical mean-field methods and two relatively new approaches, IDD and ESCS, are used in combination with analytical expressions for the Eshelby tensor based on its irreducible decomposition. The second strategy to be investigated is the Mori-Tanaka method in combination with the replacement tensor approach, which uses numerical models of dilute inhomogeneities embedded in large matrix regions. The third approach consists of the direct Finite Element discretization of microstructures. The elasticity tensors and directional Young’s moduli are first studied for arrangements of aligned inhomogeneities of three different shapes and of combinations of these shapes. Subsequently the three modeling strategies are applied to a real microstructure. Comparisons are not only carried out with respect to phase volume fractions, but also with respect to the contrast in the elastic phase properties. All calculations are restricted to plane strain conditions and to isotropic material behavior. [Copyright &y& Elsevier]

In this study, the residual stresses in a thermal-sprayed tungsten carbide-cobalt coating are numerically investigated after a plasma-spraying process and after a subsequent roller-burnishing process. The results from the simulations are compared to the first experimental results obtained by a classical hole-drilling method. First, effective material parameters are identified by a detailed microstructure FE model based on scanning electron microscope (SEM) images of the coating. Then, two types of simulations are performed with regard to thermally induced residual stresses as well as the rolling process. In the first model, the microstructural details like pores, interface, and surface roughness are modeled in detail based on light microscope (LM) images. In the second model, the coating and substrate are assumed to be ideal homogeneous, and the interface and surface to be as planar. Furthermore, two types of boundary conditions are investigated: (1), the periodic boundary conditions for the left and right faces, and, (2) when these faces are free. It is shown that, for large sample sizes, the results nearly coincide. The simulation results show increasing compressive residual stresses in thickness direction after the rolling process, which is in qualitative agreement with the experiment. A layer of tensile stresses is obtained at the surface in the simulation which could not be captured by the hole-drilling method. Furthermore, an investigation with homogeneous material behavior is performed in 3D. [ABSTRACT FROM AUTHOR]

Abstract: Electromagnetic metal forming is a contact-free high-speed forming process in which strain rates of more than 103 s−1 are achieved. The deformation of the workpiece is driven by the Lorentz force, a material body force, that results from the interaction of a pulsed magnetic field with eddy currents induced in the workpiece by the magnetic field itself. In this work, a coupled 3D simulation of this process is presented. For the mechanical structure a thermoelastic, viscoplastic, electromagnetic material model is relevant, which is incorporated in a large-deformation dynamic formulation. The evolution of the electromagnetic fields is governed by Maxwell’s equations under quasi-static conditions. Their numerical solution in 3D requires particular arrangements due to problems connected with an adequate gauging of the fields. Hence, Nédélec elements are employed. Coupling between the thermomechanical and electromagnetic subsystems takes the form of the Lorentz force, the electromotive intensity, and the current geometry of the workpiece. A staggered scheme based on a Lagrangian mesh for the workpiece and an ALE formulation for the electromagnetic field is utilized to solve the coupled system, guaranteeing the efficiency and accuracy of the data transfer between the two meshes. [Copyright &y& Elsevier]

Abstract: The purpose of this work is the formulation of a thermo-magneto-mechanical multifield model and presentation of the numerical strategies applied. In particular, this model is used to simulate electromagnetic sheet metal forming processes (EMF). In this process, deformation of the workpiece is driven by the interaction of a current generated in the workpiece by a magnetic field generated by a coil adjacent to the workpiece. The interaction of these two fields results in a material body force known as Lorentz force. Up to now, modeling approaches found for EMF in the literature are restricted to the axisymmetric case. For real industrial applications however, the modeling of three-dimensional forming operations becomes crucial for an effective process design. The implementation of such a 3D model still represents work in progress. Results shown in this paper are restricted to the axisymmetric case. [Copyright &y& Elsevier]

Investigates the use of maternal provisioning of offspring during ontogeny within Atlantic Salmon families. Attributes to the variation in the size and proximate composition of eggs and alevins; Activity of alevins to store lipids between hatching and first feeding; Conflict of goals between mother and offsprings for mazimizing fitness.

The article presents a study which demonstrated that glucose-dependent insulinotropic polypeptide (GIP) potentiates amino acid-stimulated glucagon secretion, documenting a similar nutrient-dependent action to that described in β cells. Topics discussed include role of α cell GIP receptor (GIPR) activity in insulin secretion, glucose and metal tolerance tests, and plasma analysis.

Abstract: In this paper, the formulation and numerical implementation of a phenomenological model which accounts for directional hardening effects in metals subjected to non-proportional loading is outlined. This model generalizes that of Teodosiu and Hu [C. Teodosiu, Z. Hu, Microstructure in the continuum modelling of plastic anisotropy, in: Proceedings of the 19th Risø International Symposium on Material''s Science: Modelling of Structure and Mechanics of Materials from Microscale to Product, Risø National Laboratory, Roskilde, Denmark, 1998, pp. 149–168] to general strain-path changes. Indeed, as discussed briefly here, this model predicts directional hardening only for strain-path changes involving unloading and reloading. After demonstrating the ability of the current model to predict directional hardening for general loading path changes, it is applied to the simulation of springback after deep drawing and ring splitting. [Copyright &y& Elsevier]

To study the nanoscopic interaction between edge dislocations and a phase boundary within a two-phase microstructure the effect of the phase contrast on the internal stress field due to the dislocations needs to be taken into account. For this purpose a 2D semi-discrete model is proposed in this paper. It consists of two distinct phases, each with its specific material properties, separated by a fully coherent and non-damaging phase boundary. Each phase is modelled as a continuum enriched with a Peierls–Nabarro (PN) dislocation region, confining dislocation motion to a discrete plane, the glide plane. In this paper, a single glide plane perpendicular to and continuous across the phase boundary is considered. Along the glide plane bulk induced shear tractions are balanced by glide plane shear tractions based on the classical PN model. The model's ability to capture dislocation obstruction at phase boundaries, dislocation pile-ups and dislocation transmission is studied. Results show that the phase contrast in material properties (e.g. elastic stiffness, glide plane properties) alone creates a barrier to the motion of dislocations from a soft to a hard phase. The proposed model accounts for the interplay between dislocations, external boundaries and phase boundary and thus represents a suitable tool for studying edge dislocation–phase boundary interaction in two-phase microstructures. [ABSTRACT FROM AUTHOR]

This contribution deals with investigations on enhanced Fischer–Burmeister nonlinear complementarity problem (NCP) functions applied to a rate-dependent laminate-based material model for ferroelectrics. The framework is based on the modelling and parametrisation of the material's microstructure via laminates together with the respective volume fractions. These volume fractions are treated as internal-state variables and are subject to several inequality constraints which can be treated in terms of Karush–Kuhn–Tucker conditions. The Fischer–Burmeister NCP function provides a sophisticated scheme to incorporate Karush–Kuhn–Tucker-type conditions into calculations of internal-state variables. However, these functions are prone to numerical instabilities in their original form. Therefore, some enhanced formulations of the Fischer–Burmeister ansatz are discussed and compared to each other in this contribution. [ABSTRACT FROM AUTHOR]

Alternative processing of the precursor protein pro-GIP results in endogenously produced GIP(1–30)NH 2 , that by DPP-4 cleavage in vivo results in the metabolite GIP(3–30)NH 2 . We showed previously that GIP(3–30)NH 2 is a high affinity antagonist of the human GIPR in vitro . Here we determine whether it is suitable for studies of GIP physiology in rats since effects of GIP agonists and antagonists are strictly species-dependent. Transiently transfected COS-7 cells were assessed for cAMP accumulation upon ligand stimulation or assayed in competition binding using human 125 I-GIP(1–42) as radioligand. In isolated perfused rat pancreata, insulin, glucagon, and somatostatin-releasing properties were evaluated. Competition binding demonstrated that on the rat GIP receptor (GIPR), rat GIP(3–30)NH 2 bound with high affinity (K i of 17 nM), in contrast to human GIP(3–30)NH 2 (K i of 250 nM). In cAMP studies, rat GIP(3–30)NH 2 inhibited GIP(1–42)-induced rat GIPR activation and schild-plot analysis showed competitive antagonism with a pA 2 of 13 nM and a slope of 0.9 ± 0.09. Alone, rat GIP(3–30)NH 2 displayed weak, low-potent partial agonistic properties (EC 50 > 1 μM) with an efficacy of 9.4% at 0.32 μM compared to GIP(1–42). In perfused rat pancreata, rat GIP(3–30)NH 2 efficiently antagonized rat GIP(1–42)-induced insulin, somatostatin, and glucagon secretion. In summary, rat GIP(3–30)NH 2 is a high affinity competitive GIPR antagonist and effectively antagonizes GIP-mediated G protein-signaling as well as pancreatic hormone release, while human GIP(3–30)NH 2 , despite a difference of only one amino acid between the two (arginine in position 18 in rat GIP(3–30)NH 2 ; histidine in human), is unsuitable in the rat system. This underlines the importance of species differences in the GIP system, and the limitations of testing human peptides in rodent systems. [ABSTRACT FROM AUTHOR]

An electro-mechanically coupled phase field model for ferroelectric domain evolution is introduced. Based on Gurtin's concept of a microforce balance, a generalized Ginzburg-Landau evolution equation is derived from the second law of thermodynamics. The thermodynamic potential is formulated for transversely isotropic material behavior by adopting a coordinateinvariant formulation. The model is reduced to 2D and implemented into a finite element framework. The numerical simulations concern the microstructure evolution in mechanically clamped BaTiO3 single-crystals. In the second part of this contribution Keip et al. [1], the poling behavior of ferroelectric composites and polycrystals is investigated with regard to size effects and the influence of a discontinuous order parameter field across grain boundaries. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

This paper deals with the application of the model presented in the first part Schrade et al. [1] to ferroelectric composites filled with electrically conducting inclusions as well as to ferroelectric polycrystals. Composites are analyzed through the use of a computational homogenization framework for phase field methods proposed in Zäh & Miehe [2]. This will give insights into the coupled phenomena taking place on the microscale and on their relation to the overall behavior. Both will be of special interest for the development of advanced composite materials with tailored properties like, for example, particulate magneto-electric composites, which are composed of a ferroelectric matrix and magnetic rare-earth elements or metals. Furthermore, we analyze the behavior of ferroelectric polycrystals with a focus on size effects. This will enable us to reveal preferred microstructure configurations depending on the system and grain size. In addition to that, it will serve as basis for the extraction of the directional properties of polycrystals with respect to their switching behavior in the different grains of the polycrystal. Associated simulations could then be used to supply coarser models with the needed directional informations. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A recent material model considering the evolution of plastic anisotropy in interstitial free steels is validated for the forming process of the channel die, a complex part. In the model the evolution of the intra-granular microstructure is represented by tensor-valued internal variables. The model accounts for the cross hardening behavior observed in rheological tests of interstitial free steels. A novel cross hardening indicator which is directly derived from the constitutive model is proposed. This cross hardening indicator is a quantitative measure for the occurrence of cross hardening in the forming process of complex parts. A correlation between the occurrence of cross hardening and larger values of the stored (elastic) energy is observed. The influence of cross hardening on the forming process is investigated, in particular, the drawing forces and the geometric deviations due to springback. The influence of cross hardening on the forming process of the channel die geometry is small. The influence of cross hardening on the more complex S-Rail geometry is larger due to larger plastic deformation and more severe loading path changes. The concept of the proposed transient hardening indicator should be applicable to other models for the evolution of plastic anisotropy. A possible use of the cross hardening indicator would be the efficient choice of the material model in the context of sheet metal forming simulations. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is the development, identification and validation of a model for the simulation of a thermomechanical multistage production process chain for sheet steels. The process of interest consists of forming (in particular deep-drawing) followed by cutting and heat treatment. For the forming and cutting stages, the complete model is based in particular on a model for thermoelastic, viscoplastic (i.e., rate-dependent) material behavior in sheet steels accounting for isotropic and anisotropic (i.e., kinematic and cross) hardening. This is combined with a model for thermally induced phase transformations in order to model heat treatment. The particular material modeled here is the sheet steel . This steel has an initially ferritic microstructure which is maintained during forming and cutting. Heating of the workpiece after forming and cutting during heat treatment phase results in transformation of ferrite to austenite. Subsequent air-cooling back to room temperature is accompanied by a second transformation from austenite to martensite. Model predictions for the workpiece behavior during forming and cutting show quite good agreement with corresponding experimental results. In contrast, small discrepancies between the model predictions and experimental results for the change in workpiece geometry during cooling imply that the phase transformation from austenite to martensite in is not purely volumetric in nature as assumed in the model. Rather, it results in change in the deviatoric state of stress in the material and a corresponding change in shape of the workpiece. [Copyright &y& Elsevier]

Magnesium-yttrium alloys show significantly improved room temperature ductility when compared with pure Mg. We study this interesting phenomenon theoretically at the atomic scale employing quantum-mechanical (so-called ab initio) and atomistic modeling methods. Specifically, we have calculated generalized stacking fault energies for five slip systems in both elemental magnesium (Mg) and Mg—Y alloys using (i) density functional theory and (ii) a set of embedded-atom-method (EAM) potentials. These calculations predict that the addition of yttrium results in a reduction in the unstable stacking fault energy of basal slip systems. Specifically in the case of an I2 stacking fault, the predicted reduction of the stacking fault energy due to Y atoms was verified by experimental measurements. We find a similar reduction for the stable stacking fault energy of the {1122} {1123} non-basal slip system. On the other hand, other energies along this particular γ-surface profile increase with the addition of Y. In parallel to our quantum-mechanical calculations, we have also developed a new EAM Mg-Y potential and thoroughly tested its performance. The comparison of quantum-mechanical and atomistic results indicates that the new potential is suitable for future large-scale atomistic simulations. [ABSTRACT FROM AUTHOR]

Interstitial free sheet steels show transient work hardening behavior, i.e., the Bauschinger effect and cross hardening, after changes in the loading path. This behavior affects sheet forming processes and the properties of the final part. The transient work hardening behavior is attributed to changes in the dislocation structure. In this work, the morphology of the dislocation microstructure is investigated for uniaxial and plane strain tension, monotonic and forward to reverse shear, and plane strain tension to shear. Characteristic features such as the thickness of cell walls and the shape of cells are used to distinguish microstructural patterns corresponding to different loading paths. The influence of the crystallographic texture on the dislocation structure is analyzed. Digital image processing is used to create a 'library' of schematic representations of the dislocation microstructure. The dislocation microstructures corresponding to uniaxial tension, plane strain tension, monotonic shear, forward to reverse shear, and plane strain tension to shear can be distinguished from each other based on the thickness of cell walls and the shape of cells. A statistical analysis of the wall thickness distribution shows that the wall thickness decreases with increasing deformation and that there are differences between simple shear and uniaxial tension. A change in loading path leads to changes in the dislocation structure. The knowledge of the specific features of the dislocation structure corresponding to a loading path may be used for two purposes: (i) the analysis of the homogeneity of deformation in a test sample and (ii) the analysis of a formed part. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of the present work is the experimental investigation of the nucleation of PLC deformation bands in the aluminium alloy AA5754. The PLC bands are investigated using both mechanical methods and infrared (IR) thermography. The latter employs a high-speed IR camera which captures local changes of radiated power resulting from mechanical dissipation and heating due to the nucleation of PLC bands. The resulting IR images are used to determine spatio-temporal power field variations via image subtraction. Furthermore, band trajectories obtained from the IR images are used to study possible correlations between the spatio-temporal evolution of stress and radiated power in the specimens and PLC band development. [Copyright &y& Elsevier]

Abstract: In this paper, a new method for analyzing the microstructure evolution of aluminum during deformation at elevated temperatures by extrusion is presented, which is entirely separated from secondary restoration effects viz. static recrystallization and grain growth. In order to observe the development of grains and their orientation under severe plastic deformation, a small-scale forward extrusion setup was designed which allows quenching the extrusion butt together with the die and the container immediately after extrusion to preserve the grain structure evolved during the deformation. The forming path and the forming history of a selected material point were calculated by numerical simulation. The evolution of the microstructure along the forming path was analyzed using electron backscatter diffraction. A database for the development of physically based phenomenological models for predicting and simulating the evolution of microstructure during the hot deformation of EN AW-6082 alloy is provided. [Copyright &y& Elsevier]

Glucagon secretion plays an essential role in the regulation of hepatic glucose production, and elevated fasting and postprandial plasma glucagon concentrations in patients with type 2 diabetes (T2DM) contribute to their hyperglycaemia. The reason for the hyperglucagonaemia is unclear, but recent studies have shown lack of suppression after oral but preserved suppression after isoglycaemic intravenous glucose, pointing to factors from the gut. Gastrointestinal hormones that are secreted in response to oral glucose include glucagon-like peptide-1 (GLP-1) that strongly inhibits glucagon secretion, and GLP-2 and GIP, both of which stimulate secretion. When the three hormones are given together on top of isoglycaemic intravenous glucose, glucagon suppression is delayed in a manner similar to that observed after oral glucose. Studies with the GLP-1 receptor antagonist, exendin 9-39, suggest that endogenous GLP-1 plays an important role in regulation of glucagon secretion during fasting as well as postprandially. The mechanisms whereby GLP-1 regulates glucagon secretion are debated, but studies in isolated perfused rat pancreas point to an important role for a paracrine regulation by somatostatin from neighbouring D cells. Clinical studies of the antidiabetic effect of GLP-1 in T2DM suggest that the inhibition of glucagon secretion is as important as the stimulation of insulin secretion. [ABSTRACT FROM AUTHOR]

Abstract: Using thermal spraying various surface coatings consisting of different material compositions can be manufactured. Besides different solid phases the resulting coating microstructure often contains a non-negligible amount of pores. In this context a roller burnishing process with a hydrostatic ball-point-tool is examined to compact the thermally sprayed coating, thereby reducing porosity. The rolling process is performed by a robot on free-formed workpieces. A simulation concept for the prediction of forces in a robot-guided roller burnishing process based on a series of detailed ABAQUS simulations is presented. It is shown that, based on these test configurations, the process forces can be calculated much faster and with sufficient precision. Thereby an optimal rolling path, which requires the least amount of normal force to be applied, can be determined efficiently leading to the decision whether a specific robot is equipped to handle the path. Furthermore, the described approach may be used as a pattern to apply similar methods to other engineering problems where accurate simulative solutions exist, but cannot be applied to problems of realistic size due to their expenditure of time. [Copyright &y& Elsevier]

Abstract: The aim of this work is to present briefly a model for predicting and simulating the evolution of microstructure, in particular the evolution of grains, during hot forming processes of aluminum alloy EN AW-6082 and give a comparison with the experimental results. The model is a physically motivated phenomenological model based on internal state dependent variables. The microstructure evolution is a temperature dependent process and is simulated in a fully coupled thermo-mechanical process by help of Finite Element software Abaqus. The results are compared and verified with experimental results obtained by EBSD measurement of a small-scale extrusion process established for scientific purposes. The simulation results are in reasonable agreement with experiment. [ABSTRACT FROM AUTHOR]

The characterization of thermal-sprayed coatings is often limited to microstructural analysis to evaluate the coatings morphology. Indentation is commonly used to determine the mechanical properties of different kinds of engineering materials. However, due to the complex structure of thermal-sprayed coatings, few results have been obtained so far. In this article, experimental nanoindentation tests and simulation results are compared. The experimental indentation tests show scattering in the force-deformation data due to the complex structure of the arc-sprayed coating which is investigated by means of an indentation test simulation. Based on the results for single constituent parts of the coating, the Young's modulus as well as further mechanical properties are identified. A general procedure is presented to predict the effective mechanical properties based on the microstructure, porosity, chemical composition, and properties of the coating after thermal spraying. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is the experimental investigation and statistical characterization of the grain microstructure and its development in aluminum alloys during hot extrusion. To this end, electron backscatter diffraction (EBSD) data are utilized. Based on this data, properties like the grain morphology, mean grain size, or mean grain misorientation, can be derived with the help of data analysis and processing methods. In the current work, these are applied to the investigation and quantitative determination of the microstructural development in the aluminum alloy EN AW-6060 along a path in the center of a partly extruded billet. With increasing deformation, it is observed that the mean grain size continually decreases due to dynamic recrystallization (CRX). As expected, grain alignment along the extrusion direction tends toward 〈111〉 with increasing deformation, and misorientation tends to decrease. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of the current work is the development and application of a new experimental technique and testing device for investigating the complex behavior of sheet metals during non-proportional loading. The method is based on plain strain pure bending, enabling the investigation of large deformation cyclic reversed loading, orthogonal pure bending, as well as springback. The key feature of the pure bending experiment is the absence of contact forces, material slip and friction. Furthermore, during the pure bending test, the strain gradient through the thickness is kinematically prescribed because the specimen is subjected to a plane strain condition in de direction parallel to the rotational axis (), which allows for a straightforward comparison of the pure bending experiments and parallel simulations. The latter is used here via the identification of a recent model for directional hardening effects and arbitrary strain path changes, (). The current method facilitates experimental investigation of hardening stagnation after reverse loading and cross hardening going well beyond that which is possible with existing methods based on the cyclic shear or tension-shear of sheet metal strips (.), or pure and three-point bending (). [Copyright &y& Elsevier]

Abstract: In complex forming processes, sheet metal undergoes large plastic deformations involving significant induced flow anisotropy resulting from the development of persistent oriented (planar) dislocation structures. The aim of the present work is the formulation and identification of a phenomenological model which accounts for the effect of the evolution of this oriented dislocation microstructure on the anisotropic hardening behavior. The model accounts for changes in the size, center, and shape, of the yield surface associated with isotropic, kinematic, and cross hardening, respectively. Identification of the model for the ferritic sheet metal steel LH800 is carried out with the help of shear, reverse shear, and tension–shear tests. The identified model has been validated using it to predict the stress–strain behavior of the material along different tension–shear loading paths and comparison with analogous experimental results. The results and in particular the comparison of theoretical predictions with experimental results clearly demonstrate the need of including cross hardening effects in the modeling of sheet metals like LH800. [Copyright &y& Elsevier]

Abstract: Using thermal spraying various surface coatings consisting of different material compositions can be manufactured. Besides different solid phases the resulting coating microstructure often contains a non-negligible amount of pores altering their mechanical properties. A common practice to analyze the porosity and composition of a coating is to create cross section images using standard light microscopy equipment or a scanning electron microscope. In this paper a method is presented to construct a three-dimensional multiphase model of the coating from a number of such cross section images by means of an image morphing technique. The resulting model can then be used for visualization purposes or further analysis e.g. within a finite element simulation. The described method has been applied to the construction of a finite element model of a porous coating sample which is used in a compaction simulation to determine its behavior in a rolling process. The required cross section images were obtained using a successive grinding and microscopy procedure. The material behavior of the porous material is modeled by using a modified Johnson–Cook material model formulation for an elasto-viscoplastic material. Comparison of 2D and 3D-simulation results are shown. [Copyright &y& Elsevier]

The article presents a study which emphasizes on the computation of electromagnetic fields for the speed up of the modelling and the numerical simulation of electromagnetic metal forming (EMF). It mentions that EMF is a high speed forming process where the rate of strain reaches over to 10³ s-1 and is induced by the Lorentz force. Among the techniques to speed up the simulation of EMF processes include the use of arbitrary Lagrangian Eulerian (ALE) and Maxwell's equations.

Abstract: The purpose of this work is the modeling and simulation of aluminum alloys during extrusion processes. In particular, attention is focused here on aluminum alloys of the 6000 series (Alph name="sbnd" /> Si) and 7000 series (Alyph name="sbnd" /> Mg). In the current paper, a number of aspects of the structural simulation as well as that of extrusion as a thermomechanical process are considered. These aspects include contact and adaptive mesh refinement, heat transfer inside the billet, heat transfer between the workpiece and the container, frictional dissipation, mechanical energy and surface radiation. The friction is considered to model the so called “dead material zone”. The radiation constant has been estimated so that the results are close to the experimental results. [Copyright &y& Elsevier]