A Multi-Scale Approach for Prediction of Irradiation Effect on RPV Steel Toughness

2005 ◽  
Author(s):  
O. Diard
Keyword(s):  
Shear Stress ◽  
Nuclear Reactor ◽  
Homogenization Method ◽  
Plastic Behavior ◽  
Irradiation Effect ◽  
Slip Systems ◽  
Local Approach ◽  
Stress Strain ◽  
Crystallographic Slip ◽  
Critical Resolved Shear Stress

Nuclear reactor pressure vessel steels are subjected to an irradiation-induced embrittlement in service and this may lead to a shift of the ductile-to-brittle transition temperature. The prediction of irradiation effect on toughness requires an accurate description of the elasto-visco-plastic behavior of irradiated steels. Recent progresses have been done to describe microstructural evolutions induced by irradiation. Ab-initio computations, molecular dynamics and discrete dislocations dynamics can predict the defects formation and the hardening induced by the dislocations – defects interactions. At this level, the irradiation effect is essentially reported as an increase of the critical resolved shear stress on the crystallographic slip systems. A numerical homogenization method is proposed to predict stress-strain curves of irradiated steels from the computed critical resolved shear stress evolution. Computations of realistic 3D aggregates and classical homogenization are performed with a Finite Element code [1]. Each grain is described as a single crystal with a crystal plasticity law, which naturally introduces the irradiation effect on the slip systems activity. The resulting average response over the whole aggregate corresponds to classical stress-strain curves. A Beremin type local approach is then applied to compute the fracture toughness of irradiated CT specimens. Assuming that the local approach parameters do not depend on the irradiation level, this methodology is able to take benefits of MD and DDD results to predict the irradiation effect on RPV steels toughness.

Effect of Temperature and Crystal Orientation on the Plasticity (SLIP) Evolution in Single Crystal Nickel Base Superalloy Notched Specimens

2007 ◽  
Author(s):  
Shadab Siddiqui ◽  
Nagaraj K. Arakere ◽  
Fereshteh Ebrahimi
Keyword(s):  
Shear Stress ◽  
Single Crystal ◽  
Element Model ◽  
Effect Of Temperature ◽  
Nickel Base Superalloy ◽  
Shear Stresses ◽  
Slip Systems ◽  
Slip Planes ◽  
Nickel Base ◽  
Critical Resolved Shear Stress

A comprehensive numerical investigation of plasticity (slip) evolution near notches was conducted at 28°C and 927°C, for two crystallographic orientations of double-notched single crystal nickel base superalloys (SCNBS) specimens. The two specimens have a common loading orientation of <001> and have notches parallel to the <010> (specimen I) and <110> (specimen II) orientation, respectively. A three dimensional anisotropic linear elastic finite element model was employed to calculate the stress field near the notch of these samples. Resolved shear stress values were obtained near the notch for the primary octahedral slip systems ({111} <110>) and cube slip systems ({100} <110>). The effect of temperature was incorporated in the model as changes in the elastic modulus values and the critical resolved shear stress (CRSS). The results suggest that the number of dominant slip systems (slip systems with the highest resolved shear stress) and the size and the shape of the plastic zones around the notch are both functions of the orientation as well as the test temperature. A comparison between the absolute values of resolved shear stresses near the notch at 28°C and 927°C on the {111} slip planes revealed that the plastic zone size and the number of activated dominant slip systems are not significantly affected by the temperature dependency of the elastic properties of the SCNBS, but rather by the change in critical resolved shear stress of this material with temperature. The load required to initiate slip was found to be lower in specimen II than in specimen I at both temperatures. Furthermore, at 927°C the maximum resolved shear stress (RSS) on the notch surface was found to be greater on the {100} slip planes as compared with the {111} slip planes in both specimens. The results from this study will be helpful in understanding the slip evolution in SCNBS at high temperatures.

Characteristics of Ordinary ½⟨110] Slip in Single Crystals of γ-TiAl

1998 ◽  
Vol 552 ◽  
Author(s):  
S. Jiao ◽  
N. Bird ◽  
P. B. Hirsch ◽  
G. Taylor
Keyword(s):  
Shear Stress ◽  
Single Crystals ◽  
Yield Stress ◽  
Dislocation Slip ◽  
Slip Systems ◽  
Different Temperatures ◽  
Critical Resolved Shear Stress ◽  
Thermal Reversibility ◽  
Edge Dislocations

ABSTRACTA study of the occurrence of ordinary slip in single crystals of Ti 54.5 at% Al with various orientations at different temperatures shows that the critical resolved shear stress is approximately the same for ¼⟨110] slip on {111} and {110} planes near the peak of the yield stress anomaly. However the shapes of the glide loops are quite different, suggesting that the order of relative mobilities of screw and edge dislocations is reversed in the two cases. The reason for this and its possible effect on the mechanism responsible for the yield stress anomaly of ½⟨110] {111} slip are discussed. Experiments on the thermal reversibility of the yield stress when either ordinary- or super- dislocation slip systems are operating at both temperatures have shown that the yield stress is reversible for the latter but not reversible in the former case.

The slip modes of titanium and the effect of purity on their occurrence during tensile deformation of single crystals

1954 ◽  
Vol 226 (1165) ◽  
pp. 216-226 ◽  
Keyword(s):  
Shear Stress ◽  
Slip System ◽  
Single Crystals ◽  
Tensile Deformation ◽  
Interstitial Impurity ◽  
Slip Systems ◽  
Slip Planes ◽  
Critical Resolved Shear Stress ◽  
Interstitial Elements

Single-crystal test specimens of van Arkel titanium were obtained by a modification of the strain anneal technique.The modes of slip have been identified as (101̄0) [112̄0],(101̄1) [112̄0], and (0001) [112̄0]. It has been shown that not only does the interstitial impurity affect the magnitude of the critical resolved shear stress but also the relative values for the three slip systems. (101̄0) is the principal slip system and is favoured by increasing purity. A possible mechanism for the role of oxygen and nitrogen in this effect is put forward wherein it is shown that the interstitial sites occupied are such that interstitial elements render slip more difficult on two of the three slip planes in titanium.

CRSS of Mg-X(X=Zn, Y) Binary Solid Solution via First-Principles Study

2018 ◽  
Vol 913 ◽  
pp. 614-619 ◽  
Author(s):  
Su Qin Luo ◽  
Ai Tao Tang ◽  
Bin Jiang ◽  
Ren Ju Cheng ◽  
Fu Sheng Pan
Keyword(s):  
Solid Solution ◽  
Shear Stress ◽  
First Principles ◽  
Slip Systems ◽  
First Principles Calculations ◽  
Binary Solid Solution ◽  
Pyramidal Plane ◽  
Stress Curve ◽  
Strain Stress ◽  
Critical Resolved Shear Stress

To investigate the deformation behavior of Mg-X(X=Zn, Y) binary solid solution, the strain-stress curve of crystal cell along [0001] for Mg-1.85at.%X(X=Zn, Y) alloy were simulated using first-principles calculations in this study. The simulation presents directly the critical resolved shear stress for pyramidal plane slip systems for Mg-1.85at.%X(X=Zn, Y) alloy. The results show that the minimum critical resolved shear stress (CRSS) of Mg, Mg-1.85at. %Zn and Mg-1.85at. %Y for pyramidal plane slip systems is 2.24, 2.72, 2.96 GPa respectively.

scholarly journals Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 905
Author(s):  
Chun-Yu Ou ◽  
Rohit Voothaluru ◽  
C. Richard Liu
Keyword(s):  
Shear Stress ◽  
Additive Manufacturing ◽  
Crack Initiation ◽  
Strain Hardening ◽  
Elastic Constants ◽  
Crystal Plasticity ◽  
Stress Strain ◽  
Hardening Modulus ◽  
Critical Resolved Shear Stress ◽  
Effect Of Microstructure

There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material from the bottom up. It has the distinct advantages of low preparation costs and a high geometric creation capability. However, the wide range of industrial processing conditions results in large variations in the fatigue lives of metal components fabricated using AM. One of the main reasons for this variation of fatigue lives is differences in microstructure. Our methodology incorporated a crystal plasticity finite element model (CPFEM) that was able to simulate a stress–strain response based on a set of randomly generated representative volume elements. The main advantage of this approach was that the model determined the elastic constants (C11, C12, and C44), the critical resolved shear stress (g0), and the strain hardening modulus (h0) as a function of microstructure. These coefficients were determined based on the stress–strain relationships derived from the tensile test results. By incorporating the effect of microstructure on the elastic constants (C), the shear stress amplitude (Δτ2) can be computed more accurately. In addition, by considering the effect of microstructure on the critical resolved shear stress (g0) and the strain hardening modulus (h0), the localized dislocation slip and plastic slip per cycle (Δγp2) can be precisely calculated by CPFEM. This study represents a major advance in fatigue research by modeling the crack initiation life of materials fabricated by AM with different microstructures. It is also a tool for designing laser AM processes that can fabricate components that meet the fatigue requirements of specific applications.

Slip systems and critical resolved shear stress in pyrite: an electron backscatter diffraction (EBSD) investigation

2008 ◽  
Vol 72 (6) ◽  
pp. 1181-1199 ◽  
Author(s):  
C. D. Barrie ◽  
A. P. Boyle ◽  
S. F. Cox ◽  
D. J. Prior
Keyword(s):  
Shear Stress ◽  
Slip System ◽  
Single Crystal ◽  
Electron Backscatter Diffraction ◽  
Lattice Rotation ◽  
Slip Systems ◽  
Boundary Trace ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
Critical Resolved Shear Stress

AbstractA suite of experimentally deformed single-crystal pyrite samples has been investigated using electron backscatter diffraction (EBSD). Single crystals were loaded parallel to <100> or <110> and deformed at a strain rate of 10-5s-1, confining pressure of 300 MPa and temperatures of 600°C and 700°C. Although geometrically (Schmid factor) the {001}<100> slip system should not be activated in <100> loaded samples, lattice rotation and boundary trace analyses of the distorted crystals indicate this slip system is easier to justify. Determination of 75 MPa as the critical resolved shear stress (CRSS) for {001}<100> activation, in the <110> loaded crystals, suggests a crystal misalignment of ~5—15° in the <100> loaded crystals would be sufficient to activate the {001}<100> slip system. Therefore, {001}<100> is considered the dominant slip system in all of the single-crystal pyrite samples studied. Slip-system analysis of the experimentally deformed polycrystalline pyrite aggregates is consistent with the single-crystal findings, with the exception that {001}<11̄> also appears to be important, although less common than the {001}<100> slip system. The lack of crystal preferred orientation (CPO) development in the polycrystalline pyrite aggregates can be accounted for by the presence of two independent symmetrically equivalent slip systems more than satisfying the von Mises criterion.

ORIENTATION DEPENDENCE OF YIELD IN BODY-CENTERED CUBIC METALS

1967 ◽  
Vol 45 (2) ◽  
pp. 1091-1099 ◽  
Author(s):  
D. Hull ◽  
J. F. Byron ◽  
F. W. Noble
Keyword(s):  
Shear Stress ◽  
Deformation Behavior ◽  
Orientation Dependence ◽  
Compressive Deformation ◽  
Slip Systems ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
The Asymmetry ◽  
Critical Resolved Shear Stress ◽  
And Tungsten

Recent observations relating to the critical resolved shear stress for slip in tantalum and tungsten are reported. The results of tensile and compressive deformation are discussed in terms of the operative slip systems and the possible asymmetry of {112} [Formula: see text] slip. It is concluded that the asymmetry hypothesis is unable to account satisfactorily for anomalies in the deformation behavior of these materials.

scholarly journals Ca-induced Plasticity in Magnesium Alloy: EBSD Measurements and VPSC Calculations

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 67 ◽  
Author(s):  
Umer Masood Chaudry ◽  
Kotiba Hamad ◽  
Jung-Gu Kim
Keyword(s):  
Shear Stress ◽  
Magnesium Alloy ◽  
Slip System ◽  
Basal Slip ◽  
Room Temperature ◽  
Prismatic Slip ◽  
Slip Systems ◽  
Electron Backscattered Diffraction ◽  
Self Consistent ◽  
Critical Resolved Shear Stress

In the present work, Ca-induced plasticity of AZ31 magnesium alloy was studied using electron backscattered diffraction (EBSD) measurements supported by viscoplastic self-consistent (VPSC) calculations. For this purpose, alloy samples were stretched to various strains (5%, 10%, and 15%) at room temperature and a strain rate of 10−3 s−1. The EBSD measurements showed a higher activity of non-basal slip system (prismatic slip) as compared to that of tension twins. The VPSC confirmed the EBSD results, where it was found that the critical resolved shear stress of the various slip systems and their corresponding activities changed during the stretching of the alloy samples.

Elastic and plastic anisotropy during growth from the melt of single semiconductor crystals

1988 ◽  
Vol 3 (3) ◽  
pp. 531-537 ◽  
Author(s):  
John C. Lambropoulos
Keyword(s):  
Shear Stress ◽  
Dislocation Density ◽  
Thermal Stresses ◽  
Numerical Solutions ◽  
Elastic Anisotropy ◽  
Plastic Anisotropy ◽  
Three Dimensional ◽  
Growth Direction ◽  
Slip Systems ◽  
Crystallographic Slip

The effect on dislocation density of elastic anisotropy (relation of growth direction to elastic stiffness tensor of cubic symmetry) and of plastic anisotropy (relation of growth direction to crystallographic slip systems of {111} ≪110≫ type) is investigated for the growth from the melt of shaped, single-crystal semiconductors of III–V compounds (typically GaAs, InP) by the Czochralski method. The thermal stresses are determined numerically by using three-dimensional finite element techniques for growth along the ≪100≫, ≪111≫ or ≪110≫ directions. The equivalent shear stress is calculated and it is assumed that the dislocation density is proportional to the sum over all slip systems of the excess of the resolved thermal shear stress over the crystal's yield stress in shear. It is shown that proper account of both elastic and plastic anisotropy is necessary in order to correlate numerical estimates of dislocation density to experimentally determined patterns. In particular, it is shown that the effect of elastic anisotropy is to produce significantly higher dislocation densities, especially for the case of ≪111≫ and ≪110≫ growth. For moderate levels of elastic anisotropy, the dislocation density levels during ≪111≫ and ≪110≫ growth become significantly larger than density, during ≪100≫ growth, at specific locations within the crystal. The correlation between dislocation density and equivalent shear stress is presented, and the effect of plastic anisotropy is thus discussed. It is shown that the assumption of elastic isotropy leads to dislocation density levels that considerably underestimate the levels but, for a given growth direction, are qualitatively similar to the dislocation density patterns corresponding to the three-dimensional numerical solutions in which elastic anisotropy is accounted in full.

Delamination in the scoring and folding of paperboard

TAPPI Journal ◽  
2012 ◽  
Vol 11 (1) ◽  
pp. 61-66 ◽  
Author(s):  
DOEUNG D. CHOI ◽  
SERGIY A. LAVRYKOV ◽  
BANDARU V. RAMARAO
Keyword(s):  
Finite Element ◽  
Plane Deformation ◽  
Strain Analysis ◽  
Local Strain ◽  
Uniaxial Stress ◽  
Material Model ◽  
Element Model ◽  
Plastic Behavior ◽  
Stress Strain ◽  
Strain Fields

Delamination between layers occurs during the creasing and subsequent folding of paperboard. Delamination is necessary to provide some stiffness properties, but excessive or uncontrolled delamination can weaken the fold, and therefore needs to be controlled. An understanding of the mechanics of delamination is predicated upon the availability of reliable and properly calibrated simulation tools to predict experimental observations. This paper describes a finite element simulation of paper mechanics applied to the scoring and folding of multi-ply carton board. Our goal was to provide an understanding of the mechanics of these operations and the proper models of elastic and plastic behavior of the material that enable us to simulate the deformation and delamination behavior. Our material model accounted for plasticity and sheet anisotropy in the in-plane and z-direction (ZD) dimensions. We used different ZD stress-strain curves during loading and unloading. Material parameters for in-plane deformation were obtained by fitting uniaxial stress-strain data to Ramberg-Osgood plasticity models and the ZD deformation was modeled using a modified power law. Two-dimensional strain fields resulting from loading board typical of a scoring operation were calculated. The strain field was symmetric in the initial stages, but increasing deformation led to asymmetry and heterogeneity. These regions were precursors to delamination and failure. Delamination of the layers occurred in regions of significant shear strain and resulted primarily from the development of large plastic strains. The model predictions were confirmed by experimental observation of the local strain fields using visual microscopy and linear image strain analysis. The finite element model predicted sheet delamination matching the patterns and effects that were observed in experiments.

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