Load partitioning and evidence of deformation twinning in dual-phase fine-grained zr-2.5%Nb alloy.

In situ neutron diffraction loading experiments were carried out on a cold-rolled dual-phase (a-phase, '"' 10% b-phase) Zr–2.5%Nb alloy at room temperature. The specimens were cut at different angles from the rolling direction (RD) towards the transverse direction (TD), thus the loading axis changes gradually from the rolling to transverse direction. Due to the strong texture of the studied alloy, and unidirectional nature of deformation twinning, the changing loading direction with respect to initial texture has a significant impact on the collaborative slip-twinning deformation mode in the hexagonal close-packed (hcp) a-phase. The present neutron diffraction results provide direct evidence of {1 - 1.2}/1 - 1. - 1S ‘‘tensile’’ twins in the a-phase of dual-phase Zr–2.5%Nb alloy at room temperature. Additionally, TEM analysis was employed to confirm the presence of ‘‘tensile’’ twins, and determine if other type of twins were present. It is further clear from the neutron diffraction results that applied load is gradually transferred from the plastically softer a-phase to the plastically harder b-phase which acts as a reinforcing phase having a yield strength in the range 750–900 MPa depending on the loading direction

Micromechanical modelling of twinning in polycrystalline materials: Application to magnesium

In this work, a crystal plasticity constitutive model is proposed to describe the mechanical behavior of metallic materials for which twinning plays a significant role in the deformation process. Constitutive relations are obtained from a micromechanical approach that explicitly considers the interactions between twinned and untwinned domains. Then, based on a thermodynamical analysis of the problem, a new expression for the driving force for the expansion of twinned domains is proposed. Finally, to account for the polycrystalline nature of metallic materials, the constitutive model is implemented in a FFT spectral solver. In the second part of this paper, the model is used to study the mechanical behavior of a AZ31 magnesium alloy under compression, for which a significant amount of experimental data is available in the literature. The comparison between numerical and experimental data allows for discussion of the influence of the different deformation modes on the development of both crystallographic texture and lattice strains. The evolution of lattice strains is found to be largely influenced by the internal stress redistribution process associated with the expansion of twinned domains. Also, the polycrystalline plasticity model provides a correct description of how the morphological texture is strongly altered during the deformation process due to the important activity of twinning systems.The authors wish to thank Bjørn Clausen from LANSCE-LC for providing the experimental dataset for magnesium. This work was financed by Nu-Tech Precision metals, NSERC, COG, and OPG under the Industrial Research Chair program in Nuclear Materials at Queen's University

A set of moment tensor potentials for zirconium with increasing complexity

Machine learning force fields (MLFFs) are an increasingly popular choice for atomistic simulations due to their high fidelity and improvable nature. Here, we propose a hybrid small-cell approach that combines attributes of both offline and active learning to systematically expand a quantum mechanical (QM) database while constructing MLFFs with increasing model complexity. Our MLFFs employ the moment tensor potential formalism. During this process, we quantitatively assessed structural properties, elastic properties, dimer potential energies, melting temperatures, phase stability, point defect formation energies, point defect migration energies, free surface energies, and generalized stacking fault (GSF) energies of Zr as predicted by our MLFFs. Unsurprisingly, model complexity has a positive correlation with prediction accuracy. We also find that the MLFFs wee able to predict the properties of out-of-sample configurations without directly including these specific configurations in the training dataset. Additionally, we generated 100 MLFFs of high complexity (1513 parameters each) that reached different local optima during training. Their predictions cluster around the benchmark DFT values, but subtle physical features such as the location of local minima on the GSFE surface are washed out by statistical noise

Strategic sustainable development in the UK construction industry, through the Framework of Strategic Sustainable Development, using Building Information Modelling

The UK Government has set out ambitious plans for all new domestic and commercial buildings to be zero carbon rated by 2016 and 2020 respectively. These are some of the most progressive environmental targets for the built environment in the western world. There are also sustainability principles (SP) that need to be addressed by the UK construction industry, particularly negative impacts such as waste and pollution. Currently, 100 million tonnes of construction waste, including 13 million tonnes of unused materials, is generated each year, with only 20% currently capable of being recycled. The majority of this waste ends up in landfill, contributing to further pollution of the biosphere. The literature suggests that these negative impacts result from a variety of causes, including ineffective leadership, ingrained cultures, outdated technologies and poor logistics. There are a number of innovative projects within the UK, particularly at a local level, that pose the question as to whether bottom up approaches may be more successful than top down policies, as set by national and local government. This paper presents a case study demonstrating the former approach within the construction industry. Research and consultancy has been undertaken collaboratively between industry, academia and professional practice in the production of 15 individually designed sustainable dwellings in the North East of England. This project has employed Building Information Modelling (BIM) as a new collaborative working platform, aligned to the Modern Method of Construction (MMC). By situating this inquiry within an authentic case study it has highlighted currently ineffective strategies, policies and leadership which have prevented full exploitation of the potential of BIM and MMC towards sustainable production. This inquiry supports the integration of the Framework of Sustainable Strategic Development (FSSD) into construction procurement, as a method for implementing bottom up leadership in a value driven project

Intergranular stresses in polycrystalline fatigue: diffraction measurement and self-consistent modelling

Time of flight neutron diffraction is a highly versatile and truly non-destructive technique that can be used for quantitative analysis of grain level deformation. In the present study neutron diffraction is employed to collect information about the evolution of elastic lattice trains during in-situ fatigue cycling of stainless steel. The measured strains are interpreted through the comparison with a self-consistent polycrystal deformation model. The implications of this analysis for fatigue lifting procedures are discussed

Intergranular and interphase strains during loading of duplex steel

Duplex stainless steels, consisting of approximately equal amounts of austenite and ferrite, are typically designed to combine the best features of these constituent phases. Such a two phase material is inhomogeneous, and the phases have different elastic and plastic responses under an applied load. We thus need to understand the stress state of the individual phases during deformation. Neutron diffraction provides a phase specific probe of the elastic strain in bulk material. In situ tensile tests have been carried out at the ISIS pulsed neutron source on rolled duplex steel, with samples cut parallel, perpendicular and 45° to the rolling direction. Elasto-plastic self consistent models have proved highly successful in modelling the phase and grain level response of austenitic and ferritic steels. We have apply the model to the behaviour of duplex steel, selecting a population of grains in the self consistent model including both austenite and ferrite grains. The model successfully describes some features of the load sharing between phases as well as the strain distribution between differently oriented grain families within each phase

Intergranular and interphase strains during loading of duplex steel

Duplex stainless steels, consisting of approximately equal amounts of austenite and ferrite, are typically designed to combine the best features of these constituent phases. Such a two phase material is inhomogeneous, and the phases have different elastic and plastic responses under an applied load. We thus need to understand the stress state of the individual phases during deformation. Neutron diffraction provides a phase specific probe of the elastic strain in bulk material. In situ tensile tests have been carried out at the ISIS pulsed neutron source on rolled duplex steel, with samples cut parallel, perpendicular and 45° to the rolling direction. Elasto-plastic self consistent models have proved highly successful in modelling the phase and grain level response of austenitic and ferritic steels. We have apply the model to the behaviour of duplex steel, selecting a population of grains in the self consistent model including both austenite and ferrite grains. The model successfully describes some features of the load sharing between phases as well as the strain distribution between differently oriented grain families within each phase