Standardization of Verification & Validation for Computational

Weld Mechanics

Paper V&V2012-6116

Session: 11-1 Standards Development Activities for Verification and Validation: Part 1

ASME Verification and Validation Symposium (V&V2012)

Planet Hollywood Resort & Casino, Las Vegas May 3, 2012

Dave Dewees, P.E.

The Equity Engineering Group, Inc., On behalf of the AWS A9 Committee on Computational Weld Mechanics

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AWS A9 CWM Committee • The American Welding Society (AWS) A9 Committee on Computational Weld

Mechanics (CWM):

• Special thanks to the committee, Chair S.S. Babu and Vice-Chair G. Sonnenberg for the opportunity to present the proposed standard on their behalf

• The content of this presentation is largely taken directly from meeting minutes, committee publications and the draft standard itself; therefore the content is attributable to many people

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Introduction

• Distortion, residual stress and altered material properties are a fundamental outcome of the welding process

• The welding community is largely forced to apply a trial and error approach to obtaining a required end product, which is costly and time-consuming

• Computational welding mechanics (CWM) has emerged over the last decades to try and address these challenges; that is to reduce risk, cost and span, while improving quality and predictability

• The use of CWM has however lagged behind related technologies such as computational solid mechanics (CSM) and computational fluid dynamics (CFD)

• This is in large part due to a lack of a standard verification and validation framework, particularly since the typical CWM analysis is considerably more involved than the typical CSM analysis

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Introduction

• In 2007, the American Welding Society (AWS) established a technical committee (A9) with members representing the academic, research and industrial communities to develop a standard for CWM

• This (draft) standard has now been completed and is in the balloting stage, with publication expected in 2012

• The standard specifically addresses verification and validation of CWM

• Verification tests the chosen mathematics, while validation demonstrates that the reality being modeled (e.g. distortion, residual stress, microstructure) is predicted with sufficient accuracy, robustness and reliability

• The motivation and result from this multi-year process are presented here

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From Initial Meeting, 2007

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From Initial Meeting, 2007

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Organization

• Initial task group has become current AWS A9 Committee on Computational Weld Mechanics

• AWS is accredited by the American National Standards Institute (ANSI) to produce American National Standards (ANS)

– All AWS standards must follow a formal and rigorous consensus review and approval process prior to publication

– All AWS technical committee operate under the AWS Technical Activities Committee’s (TAC) Rules of Operation

• AWS is required to make attempts to establish a balance of interests on each technical committee; this is to help ensure that

– ANS are produced in a open forum

– and that the resulting standard is acceptable to a majority of those who may be affected

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Membership

• Roster has changed somewhat over the 4+ years of the committee, and many people have provided insight and guidance

• The current roster is as follows:

• Note that John Gayler of AWS served as the committee secretary for several years and guided the development of the standard so that it meets the stringent requirements of AWS and an ANS

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Outreach

• As mentioned, varied and robust participation is a continued goal

• Welding Journal has been a key vehicle for this

• Participation and contribution is always encouraged

January 2010 Welding Journal

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CWM Standard

• Standard is titled “AWS A9.5:2012, Guide for Verification and Validation in Computation Weld Mechanics”

• Abstract: “This standard provides guidelines for assessing the capability and accuracy of computational weld mechanics (CWM) models. This standard also provides general guidance for implementing verification and validation (V&V) of computational models for complex systems in weld mechanics.”

• 26 working drafts leading up to committee approval at the beginning of this year, and subsequent submission to the AWS Standards Committee for review and ballot

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High Level Goals

• The document should be kept relatively simple and not get into too many details

• It should provide a general approach to weld modeling

• The level of the content and language should be accessible to non-simulation specialists, i.e., stakeholders, engineers

• Document should not be so prescriptive that it limits innovation and creativity

• It should refer heavily to already published material

• ASME V&V, Guide for Verification and Validation in Computational Solid Mechanics, should be used as an ideal template

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Specific Goals

• Standard should establish just the bare minimum requirements which other proprietary models could be based upon

• Further publications should add (non-mandatory) detail:

– Recommended Practice for Describing Thermal Boundary Conditions

– Recommended Practice for Modeling Thermo-Mechanical Phenomena

– Recommended Practice for Describing Clamps and Fixtures

– Recommended Practice for Modeling Microstructure

– Recommended Practice for Integrated Models

– Recommended Practice for Verification, Uncertainty Estimation and Sensitivity

– Recommended Practice for Documentation

– Exceptions and Modifications with reference to Materials 1: Steels

– Exceptions and Modifications with reference to Materials 2: Aluminum

– Exceptions and Modifications with reference to Fusion Welding – Arc

– Exceptions and Modifications with reference to Fusion Welding – Laser

– Exceptions and Modifications with reference to Fusion Welding – Resistance

– Exceptions and Modifications with reference to Thin and Thick Plate Geometry

– Exceptions and Modifications with reference to Large Scale Geometries

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Specific Goals

• Initial issue of standard should be focused so that it can be detailed enough to be useful – arc welding established as sole focus of initial issue

• Thermo-mechanical effects, microstructural effects, residual stress, and distortion should be covered in standard

• Standard should not be biased towards any particular commercial software

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Initial Development

• In addition to the high level intent just discussed, initial detailed goals were established through brainstorming and then voting:

• An industry survey was then performed, based on the initial member survey, but with minimal feedback

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Implementation

• V&V as it relates to CWM, and as implemented by the A9 committee is as follows (Welding Journal, Jan. 2010)

– Verification tests that the computational model solves the mathematical equations that are the essence of the model with sufficient accuracy, robustness, and reliability

– Validation tests that the computational model predicts the reality relevant to the decision maker with sufficient accuracy, robustness, and reliability

• A computational model that has been verified and validated for a given end use can be used as a predictive tool for that end use before any experiments are performed.

O.D.

0.5 in

Cone 5 Side

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V&V vs. Calibration

• Computational models that must be fitted to experimental data before they can be used are called calibrated

• These calibrated models cannot predict the reality relevant to a decision maker before the required experimental data are provided

• This is the reason that computational models that are verified and validated are much more valuable and more useful than calibrated computational models

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Contents of the Standard

• 6 sections and 3 annexes, currently 45 pages total

• Bulk of technical material is in Sections 5 and 6

• Document is intended for a range of users, from engineers performing CWM to project managers responsible for the incorporation of the results into the larger project framework

• Written in a format of increasing technical information within each subclause

• As a convenience, essential high-level information is written at the beginning of each subclause rather than dispersed throughout them

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Section 5

• 5. Discussion of Computational Weld Modeling Methods and Influences on Analysis

– 5.1 Overview

– 5.2 Current State-of-the-Art in CWM

– 5.3 Key Analysis Inputs

– 5.4 Modeling of Heat Transfer During Welding

– 5.5 Microstructural Analysis

– 5.6 Modeling of Residual Stresses

– 5.7 Distortion Prediction

• Addresses the various components that make up a CWM, including common or key simplifications, and their qualitative impact on analysis accuracy

• Underlying discussion is the assumption that a CWM problem may be thought of as falling in a continuum between analysis complexity and required V & V

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Section 6

• 6. Validation of Residual Stress and Distortion Models

– Specific guidance and best practices on design and execution of experiments for V&V of CWM

– Ranges from temperature measurement to microstructure V&V

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Technical Cooperation

• “DIN SPEC 32534-1, Numerical Weld Simulation – Execution and Documentation: Part 1: Overview” published in 2011

• Is consistent with AWS A9 development through contributions and coordination by Dr. Christopher Schwenk (also an active AWS A9 committee member)

• Attempt at coordination with IIW working group on CWM was less successful, though work on an ISO standard is in the planning stages

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Final Thoughts

• As discussed in the 2010 WJ article, the fundamental question for CWM is can the effects of welding be currently predicted?

• The conclusion of the committee is that it can and has been – but V&V is the missing ingredient for consistent, successful application of this technology

• The draft V&V is relatively focused in scope, but a host of detailed recommended practices are planned, and with the current momentum, and increased participation, hopefully will continue to close the implementation gap