Diffusion Maintaining the type and number of phases e. Alteration of phase composition e. Atoms are displaced by random walk.
Acta Materialia 58 The elastic—plastic deformation of crystalline aggregates depends on the direction of loading, i.
This phenomenon is due to the anisotropy of the elastic tensor and to the orientation dependence of the activation of the crystallographic deformation mechanisms dislocations, twins, martensitic transformations.
A consequence of crystalline anisotropy is that the associated mechanical phenomena such as shape change, crystallographic texture, strength, strain hardening, deformation-induced surface roughening and damage are also orientation dependent.
This is not a trivial statement as it implies that mechanical parameters of crystalline matter are tensor quantities. An example is the uniaxial stress—strain curve, which is the most important mechanical measure in structural materials design.
Another consequence of this statement is that the crystallographic texture orientation distribution and its evolution during forming is a quantity that is inherently connected with plasticity theory. Texture can hence be used to describe the integral anisotropy of polycrystals in terms of the individual tensorial behavior of each grain and the orientation-dependent boundary conditions among the crystals.
Formally, the connection between shear and texture evolution becomes clear from the fact that any deformation gradient can be expressed as the combination of its skew-symmetric portion, which represents a pure rotation leading to texture changes if not matched by the rotation implied by plastic shear, and a symmetric tensor that is a measure of pure stretching.
Plastic shear hence creates both shape and orientation changes, except for certain highly symmetric shears.
However, these approaches were neither designed for considering explicitly the mechanical interactions among the crystals in a polycrystal nor for responding to complex internal or external boundary conditions Fig. Instead, they are built on certain simplifying assumptions of strain or stress homogeneity to cope with the intricate interactions within a polycrystal.
For that reason variational methods in the form of finite-element FE approximations have gained enormous momentum in this field.
The entire sample volume under consideration is discretized into such elements. The essential step which renders the deformation kinematics of this approach a crystal plasticity formulation is the fact that the velocity gradient is written in dyadic form.
The general framework supplied by variational crystal plasticity formulations provides an attractive vehicle for developing a comprehensive theory of plasticity that incorporates existing knowledge of the physics of deformation processes [8—10] into the computational tools of continuum mechanics [11,12] with the aim of developing advanced and physically based design methods for engineering applications .
This is not only essential to study in-grain or grain cluster mechanical problems but also to better understand the often quite abrupt mechanical transitions at interfaces . However, the success of CPFE methods is not only built on their efficiency in dealing with complicated boundary conditions.
They also offer great flexibility with respect to including various constitutive formulations for plastic flow and hardening at the elementary shear system level. The constitutive flow laws that were suggested during the last decades have gradually developed from empirical viscoplastic formulations [16,17] into physics-based multiscale internal-variable models of plasticity, including a variety of size-dependent effects and interface mechanisms [9,18— 26].
In this context it should be emphasized that the FE method itself is not the actual model but the variational solver for the underlying constitutive equations that map the anisotropy of elastic—plastic shears associated with the various types of lattice defects e.
Since its first introduction by Peirce et al. These approaches, commonly referred to as crystal plasticity finite-element models, are important both for basic microstructure-based mechanical predictions as well as for engineering design and performance simulations involving anisotropic media.
Besides the discussion of the constitutive laws, kinematics, homogenization schemes and multiscale approaches behind these methods, we also present some examples, including, in particular, comparisons of the predictions with experiments.
The applications stem from such diverse fields as orientation stability, microbeam bending, single-crystal and bicrystal deformation, nanoindentation, recrystallization, multiphase steel TRIP deformation, and damage prediction for the microscopic and mesoscopic scales and multiscale predictions of rolling textures, cup drawing, Lankfort r values and stamping simulations for the macroscopic scale.
The crystal plasticity finite element constitutive methods have increasingly gained momentum in the field of materials modeling and particularly multicsale mechanical and micromechanical modeling. In these approaches one typically assumes the stress response at each macroscopic continuum material point to be potentially given by one crystal or by a volume-averaged response of a set of grains comprising the respective material point.
The latter method naturally involves local homogenization. Compared to isotropic J2 approaches the crystal plasticity finite element method reduces the degrees of freedom for the displacement field at each integration point to the crystallographic slip dyades transformed according to the local grain orientation.
Representing and updating the crystallographic orientation at each Gauss point renders crystallographically discrete plasticity simulations powerful tools for investigating anisotropy and the evolution of deformation textures. Adequate coarse graining methods allow us to design polycrystal models for commercial and large-scale applications.
These different crystal homogenization methods use sub-clusters of grains and multi-phase material within crystal plasticity finite element solvers. Polycrystal forming simulations in the crystal plasticity finite element method Using texture components in crystal plasticity finite element simulations PDF-Dokument [ Lamination microstructure in shear deformed copper single crystals Lamination microstructure in shear deformed copper single crystals Olga Dmitrieva, Patrick W.
Digital image correlation allows us to exactly determine the macroscopic state of deformation of the sample.Dr Henning Prommer is a Winthrop Research Professor at the University of Western Australia and a Principal Research Scientist and Team Leader in the Environmental Contaminant Mitigation and Technologies Program at CSIRO Land and Water, Australia.
The microstructure evolution of pure Mg and two Mg–rare-earth alloys (Mg–3 wt.% Dy and Mg–3 wt.% Er) was studied during in situ compression tests by electron backscatter diffraction and .
Phase Transformation in Metals Development of microstructure in both single- and two-phase alloys involves phase transformations-which involves the alteration in the number and character of the phases.
Phase transformations take time and this allows the definition of transformation rate or kinetics. The authors, part of the International Consortium on Innovation and Quality in Pharmaceutical Development (IQ Consortium), explore and define common industry approaches and practices when applying GMPs in early development.
- - Annex 10 GUIDANCE ON TRANSFORMATION/DISSOLUTION OF METALS AND METAL COMPOUNDS IN AQUEOUS MEDIA1 A Introduction A This Test Guidance is designed to. Waste discharges during the offshore oil and gas activity.
by Stanislav Patin, translation by Elena Cascio based on "Environmental Impact of the Offshore Oil and Gas Industry".