ML18270A092
| ML18270A092 | |
| Person / Time | |
|---|---|
| Issue date: | 09/24/2018 |
| From: | Giovanni Facco NRC/RES/DE/CIB |
| To: | |
| Michael Benson | |
| Shared Package | |
| ML18270A088 | List: |
| References | |
| Download: ML18270A092 (13) | |
Text
EXPLORING CAPABILITIES OF XFEM FOR USE IN FLAW EVALUATIONS Public Meeting 9/24/2018 Giovanni Facco RES/DE/CIB 1
Objectives Introduce Plan to Investigate Use of xFEM Methods to Investigate PWSCC Growth
- Motivation, Plan, Preliminary Results
- Feedback Discuss International Efforts/Collaboration 2
Motivation
- RES has identified that future PWSCC flaw evaluations may involve 3D Finite Element Models of crack growth with complex stresses in asymmetrical components.
- In order to be able to properly evaluate this kind of model RES plans to continue building upon its computational expertise in this potentially regulatory significant area.
- Developing these capabilities and sharing what we learn we hope to improve and modernize how these issues are evaluated in the future 3
Current FEA Application
- Model WRS in complex geometries by simulating weld parameters
- 1. Perform thermal analysis
- 2. Impose thermal history in mechanical analysis to generate WRS profile
- Multiple weld histories can be explored without the need for new model or re-meshing
- These Results can then be used to calculate crack growth rates No Repair OD Repair No Repair OD Repair Root Repair Large ID Repair Root Repair Large ID Repair 4 Thermal Model Mechanical Model
Traditional FEA vs xFEM Traditional FEA xFEM
- Results in very accurate SIF and
- Mesh-independent analysis of stress states discontinuities and singularities
- Requires re-meshing for any
- Can quickly calculate SIF of multiple change crack size or geometry cracks and crack lengths without major
- Analysis usually limited to modifications to model idealized crack shapes and planar
- Can model realistic 3D crack growth crack growth due to complexity of without re-meshing models Traditional FEA Crack Growth 5
Current Crack Growth Rate Methods
- Crack growth calculations based on ASME Methodology
- 2D approximations
- Uses idealized crack shape and growth model (semi-elliptical)
- Assumes planar crack growth, perpendicular to pipe wall
- WRS profile for crack growth is path dependent and user defined 6
Research Project Plan PWSCC Crack Growth Development
- Reproduce PWSCC Growth Behaviors
- Investigate Cracking Property Response
- Investigate Simulation Parameter Response Model Material Behavior
- Develop material property relationships using experimental component geometry (e.g. C(T)
Specimen) to benchmark model response.
Industry Relevant Models
- Compared xFEM results to similar industry relevant models evaluated using traditional methods.
7
Methodology
- ABAQUS can simulate fatigue crack growth using a Paris Law type relationship
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=
- G and K are interrelated by a linear relationship in LEFM 2
=
where E'=E for plane stress and = for plane strain (12 )
8
Initial Results Stress Intensity Factor Calculations Fatigue Crack Growth 2D Single Edge Notch (Video)
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Comparison of Nondimensional Stress Intensity Factors Contour ABAQUS RES % % Error (Handbook Benchmark Model Difference Value of 2.826) 2 2.8537 2.8712 0.61098 1.599 3 2.9643 2.9815 0.57967 5.504 4 3.0027 2.9956 0.23679 6.001 5 2.9696 2.9726 0.10218 5.189 9
Status
- Successfully used ABAQUS simplified fatigue crack growth method, to grow a crack in a static stress field (externally applied or internal) in a 2D model
- Developed preliminary parameter relationships between ABAQUS fatigue model and PWSCC model
- Cracking parameter response (G & K) for 2D models shows good agreement with handbook values 10
International Benchmarking Efforts
- In cooperation with Committee on the Safety of Nuclear Installations (CSNI) the NRC is taking part in a technical round robin project exploring X-FEM Capabilities.
- Multinational group (Public and Private, 12 Countries)
- Focus is on an preliminary comparison of the X-FEM capabilities of the different codes used in the nuclear industry
- Goal is to share Methodology and Results in order to evaluate capabilities and develop best practices.
11
International Benchmarking Efforts
- Three benchmark problems
- Surface Crack in Plate
- Embedded Crack in Plate Subjected to Shear Load
- Underclad Crack in Core Shell of an RPV
- Evaluate stationary cracks
- Thermal and mechanical loading
- Static and transient conditions 12
Summary
- Developing xFEM Techniques
- Investigate Use of xFEM for PWSCC Growth
- International Collaboration Efforts
- Feedback 13