Multiscale crystal defect dynamics: a dual-lattice process zone model

2014 ◽  
Vol 94 (13) ◽  
pp. 1414-1450 ◽  
Author(s):  
Shaofan Li ◽  
Bo Ren ◽  
Hiroyuki Minaki
Keyword(s):  
Process Zone ◽  
Crystal Defect ◽  
Zone Model ◽  
Dual Lattice

Multi-length scale micromorphic process zone model

2009 ◽  
Vol 44 (3) ◽  
pp. 433-445 ◽  
Author(s):  
Franck Vernerey ◽  
Wing Kam Liu ◽  
Brian Moran ◽  
Gregory Olson
Keyword(s):  
Process Zone ◽  
Zone Model ◽  
Length Scale

On a ferroelastic mechanism governing the toughness of metastable tetragonal-prime ( t ′) yttria-stabilized zirconia

2007 ◽  
Vol 463 (2081) ◽  
pp. 1393-1408 ◽  
Author(s):  
C Mercer ◽  
J.R Williams ◽  
D.R Clarke ◽  
A.G Evans
Keyword(s):  
Gas Turbines ◽  
Process Zone ◽  
Yttria Stabilized Zirconia ◽  
Cubic Phase ◽  
Zone Model ◽  
Toughening Mechanism ◽  
Stabilized Zirconia ◽  
Prior Literature ◽  
Reasonable Choice ◽  
Individual Grains

This article investigates the toughness of yttria-stabilized zirconia (YSZ) with the tetragonal-prime ( t ′) structure. Such materials are used as durable thermal barriers in gas turbines. Their durability has been attributed to high toughness, relative to materials in the cubic phase field. Based on prior literature, a ferroelastic toughening mechanism is hypothesized and this assertion is examined by characterizing the material in the wake of an indentation-induced crack. Assessment by transmission electron microscopy, Raman spectroscopy and optical interferometry has affirmed the existence of a process zone, approximately 3 μm in width, containing a high density of nano-scale domains, with equal proportions of all three crystallographic variants. Outside the zone, individual grains contain a single variant (no domains) implying that the toughening mechanism is controlled by domain nucleation (rather than the motion of pre-existing twin boundaries). The viability of the ferroelastic toughening mechanism is assessed using a process zone model that relates the observed toughening to the stress/strain hysteresis accompanying domain formation. Based on the measured process zone size, the known tetragonality of t ′-7 wt% YSZ and the enhancement in toughness relative to cubic YSZ, consistency between the model and the observed toughening is demonstrated for a reasonable choice of the coercive stress.

scholarly journals FINITE ELEMENT MODELING OF THE CRACK PROPAGATION IN RC BEAMS BY USING ENERGY APPROACH

2015 ◽  
pp. 211-217
Author(s):  
Shahriar Shahbazpanahi ◽  
Chia Paknahad
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Cohesive Zone Model ◽  
Process Zone ◽  
Mesh Size ◽  
Energy Dissipation Rate ◽  
Energy Approach ◽  
Interface Element ◽  
Zone Model ◽  
Steel Bars

In present study, an interface element with nonlinear spring is used to simulate cohesive zone model (CZM) in reinforced concrete (RC) beam for Mode I fracture. The virtual crack closure technique (VCCT) is implemented to model the propagation of the fracture process zone (FPZ). This model can be calculated the energy release rate by using new method from energy approach. Energy dissipation rate by steel bars is obtained to affect on the crack propagation criterion to implement in finite element method. The numerical results are compared with references result available in the literature. It is observed that the FPZ is increased linearly and then stay constant. It may be due to effect of steel bars or inherent behavior of FPZ. The results show that the proposed model does not depend on mesh size.

Cycle-Wise Process-Zone Model for Prediction of Delayed Hydride Cracking Initiation Under Flaw-Tip Hydride Ratcheting Conditions

2018 ◽  
Author(s):  
Steven X. Xu ◽  
Jun Cui ◽  
Douglas A. Scarth ◽  
David Cho
Keyword(s):  
Structural Integrity ◽  
Process Zone ◽  
Operating Conditions ◽  
Zone Model ◽  
Evaluation Procedures ◽  
Fuel Bundle ◽  
Pressure Tubes ◽  
Delayed Hydride Cracking ◽  
Technical Basis ◽  
Hydride Cracking

Flaws found during in-service inspection of Zr-2.5Nb pressure tubes in CANDU(1) reactors include fuel bundle scratches, debris fretting flaws, fuel bundle bearing pad fretting flaws and crevice corrosion flaws. These flaws are volumetric and blunt in nature. A key structural integrity concern with in-service blunt flaws is their susceptibility to delayed hydride cracking (DHC) initiation, particularly for debris fretting flaws under flaw-tip hydride ratcheting conditions. Hydride ratcheting conditions refer to situations when flaw-tip hydrides do not completely dissolve at normal operating temperature, and accumulation of flaw-tip hydrides occurs with each reactor heat-up/cool-down cycle. A significant number of in-service flaws are expected to be under hydride ratcheting conditions at late life of pressure tubes. DHC initiation evaluation procedures based on process-zone methodology for flaws under hydride ratcheting conditions are provided in CSA (Canadian Standards Association) N285.8-15. The process-zone model in CSA N285.8-15 predicts whether DHC initiation occurs or not for given flaw geometry and operating conditions, regardless of the number of reactor heat-up and cool-down cycles. There has been recent new development. Specifically, a cycle-wise process-zone model has been developed as an extension to the process-zone model in CSA N285.8-15. The cycle-wise process-zone model is able to predict whether DHC initiation occurs or not during a specific reactor heat-up and cool-down cycle under applied load. The development of the cycle-wise process-zone model was driven by the need to include flaw-tip stress relaxation due to creep in evaluation of DHC initiation. The technical basis for the development of the cycle-wise process-zone model for prediction of DHC initiation under flaw-tip hydride ratcheting conditions is described in this paper.

Modeling of In-Situ Hydride Growth in Zr-2.5%Nb

2011 ◽  
Author(s):  
Feng Xu ◽  
Don Metzger
Keyword(s):  
Process Zone ◽  
Hydrostatic Stress ◽  
High Energy ◽  
Diffusion Models ◽  
Zone Model ◽  
Structural Level ◽  
Finite Element Program ◽  
And Diffusion ◽  
Elastic Strains

The presence of Zr hydrides can greatly reduce the ductility and fracture toughness in a pressure vessel made of Zr alloy. Understanding how the hydrides form and grow is critical to flaw assessment for the pressure tubes. The process of hydride growth in Zr-2.5%Nb has been monitored in-situ in high-energy synchrotron X-ray radiation. The C-shaped specimen with a V-notch was held under constant load at a temperature where hydride formation was ensured. The development of hydride size and elastic strains in both the hydrides and the Zr matrix was recorded. Afterwards, the hydride morphology was characterized by Scanning Electronic Microscopy. A finite element program in combination with a process zone model and a diffusion model has been used to interpret the experimental data for better understanding the hydride growth process. The hydride length and morphology are well predicted, given that the information of hydride size and hydrostatic stress is properly updated and exchanged between the process zone and diffusion models. The effect of creep has been included in the modeling but found relatively small compared to that of hydride volumetric expansion. The elastic strains in Zr are well reproduced except that disagreement with the experiment is found in the hydrided region. This analysis provides further evidence that the process zone and diffusion models can be used to predict the hydride size and morphology development. Further modeling at a micro-structural level is needed for improving predictions of the stress/strain state in the hydrides, which is essential to the development of a sound hydride crack initiation model.

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