BCC Polycrystals Research Articles

Local Segregation at the Grain Junction: Elastic Singularity and its Effect on Radiation Embrittlement

Under consideration are the long-range stress field generated in deformed polycrystals by grain boundaries and junction lines and corresponding re-distribution of impurity atoms due to their elastic interaction with this stress field. Evaluation of the effect is made for deformed bcc polycrystals at 270°C containing the phosphorus impurity. It is assumed that under neutron irradiation the impurity atoms are in interstitial positions and form mixed P-Fe dumb-bells having a relaxation volume of about an atomic volume of host crystal. Corresponding re-distribution results in the impurity conglomeration around grain junction lines; in the areas as wide as 10% of the grain size the local P concentration is more than 50% higher then its mean concentration. Respective local segregations are considered to facilitate the brittle fracture origination, and the impurity-dependent component of radiation embrittlement is discussed within this framework.

Simulation of the Texture Evolution During Annealing of Cold Rolled Bcc and Fcc Metals Using a Cellular Automation Approach

In this study both primary static recrystallization and static recovery of cold rolled bcc and fcc metals and alloys are numerically simulated using a three‐dimensional model that is based on a modified cellular automaton approach. The model considers the influence of the initial deformation texture and microstructure on both static recovery and primary static recrystallization with a high spatial resolution. The cellular automat technique provides both local and statistical information about the kinetics, the morphology and the texture change during annealing. The influence of nucleation and growth can be studied in detail. The simulations are compared to experimental results obtained on fcc and bcc polycrystals.

Consequences of surface effects on the microcracking processes and the fatigue damage in fcc and bcc polycrystals

The present critical evaluation of the characterization of fatigue damage gives attention to the mesoscopic scale and notes the appropriateness of the analysis of surface microcracking processes in descriptions of polycrystals' damage mechanisms; the transition from LFC to HCF is thereby definable from the standpoint of the relationship between the surface and bulk modes of damage. A review is made of different approaches to the quantification of fatigue damage on the basis of surface microcrack evolution, noting evident points of controversy and likely means toward their experimental resolution. 18 refs.

Recent results concerning the modelling of polycrystalline plasticity at large strains

The general method which works for the case of linear properties of heterogeneous materials is taken as a pattern for the derivation of the local strain field in time-independent plasticity of polycrystals. The localization procedure leads to an integral equation solved by the self-consistent scheme approximation. Significant results concerning elastoplastic tangent moduli, initial and subsequent yield surfaces, residual stresses and stored energy and texture development for FCC and BCC polycrystals are reported.

Low-cycle fatigue damage mechanisms of FCC and BCC polycrystals: homologous behaviour?: Magnin, T., Ramade, C., Lepinoux, J. and Kubin, L. P. Mater. Sci. Eng. A Oct. 1989 A118, (1–2), 41–51

In this study, the effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK) was investigated. Due to the versatility of its material properties, the semi-crystralline PEEK polymer has been increasingly adopted in a wide range of applications particularly as a biomaterial for orthopedic, trauma, and spinal implants. To obtain the cyclic behavior of PEEK, uniaxial fully-reversed strain-controlled fatigue tests were conducted at ambient temperature and at 0.02 mm/mm to 0.04 mm/mm strain amplitudes. The microstructure of PEEK was obtained using the optical and the scanning electron microscope (SEM) to determine the microstructural inclusion properties in PEEK specimen such as inclusion size, type, and nearest neighbor distance. SEM analysis was also conducted on the fracture surface of fatigue specimens to observe microstructural inclusions that served as the crack incubation sites. Based on the experimental strain-life results and the observed microstructure of fatigue specimens, a microstructure-sensitive fatigue model was used to predict the fatigue life of PEEK that includes both crack incubation and small crack growth regimes. Results show that the employed model is applicable to capture microstructural effects on fatigue behavior of PEEK.

Poisson Ratios of Polycrystals

Poisson ratios of fee and bcc polycrystals are calculated for a variety of atomic models and the theoretical results are compared with experiment. In contrast with previously reported results, it is found that an accurate description of polycrystalline Poisson ratios of metals is obtained from the model in which the binding energy Ebind consists of a structure dependent part Estr and a volume dependent part Evol. Investigations are made of the general, inherent abilities of various subsets of this model to describe experimental polycrystalline Poisson ratios; these subsets include the Cauchy model (i.e. Evol is neglected in Ebind) and the Milstein-Rasky model (i.e. the volume dependent contribution to the bulk modulus χvol is neglected). In addition, specific com putations of polycrystalline Poisson ratios are made for the complete families of bcc and fcc Morse function (Cauchy) crystals and for (non-Cauchy) models (simplified forms of which are suggested by pseudopotential theory for the noble metals).

A Detailed Interpretation of Stress — Strain Curves of bcc Polycrystals

A Detailed Interpretation of Stress — Strain Curves of bcc Polycrystals

Individual collision cascades in static bcc polycrystals.

Collision cascades induced by self-irradiation of polycrystalline tungsten are calculated with the simulation program marlowe. Component analysis is used to describe their spatial configuration. The method is explained and the concepts derived from it enable one to characterize the individual cascades. The influence of the primary energy on their configuration as well as on the point defect and energy densities is shown. Cascades generated by channeled primaries are markedly different from those which undergo no dominant aligned scattering. Subcascade formation in polycrystals results from the channeling of secondary recoils and the probability of its occurrence is found to be greater as the primary energy increases. This contrasts with cascades simulated in random targets where no subcascade formation is observed. In addition, the analysis method reveals strong fluctuations in local point-defect-density distributions. It is suggested that these fluctuations are associated with nonuniformities in the deposited energy-density distributions. Finally, isotropic recombination is shown to affect individual cascade configurations as well as vacancy and interstitial densities in the core of the cascades. The aspects of the individual cascade development studied concur to show that the component analysis brings out specific characteristics that do not appear when the usual statistical approaches are used.

Static and dynamic simulation of texture: development in rolled metal of FCC and BCC polycrystals

Static and dynamic simulation of texture: development in rolled metal of FCC and BCC polycrystals