ML18270A092

Exploring Capabilities of Xfem for Use in Flaw Evaluations

ML18270A092
Person / Time
Issue date:	09/24/2018
From:	Giovanni Facco NRC/RES/DE/CIB
To:
Michael Benson
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ML18270A088	List: ML18270A089 ML18270A091 ML18270A092
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Download: ML18270A092 (13)

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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

=

• ASME Code analysis determines PWSCC crack growth behavior using a similar power law relationship

=

• 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