Fatigue

Ref : FATIG01

Residual Stress, Fitness for Service, Fatigue Design on welded structures

This course will provide a unique opportunity for attendees to learn the details of the mesh-insensitive structural stress method for fatigue evaluation of welded structures, from its mechanics basis, numerical implementation to S-N data correlations and life predictions. Through this training courses, participants will become familiar with some of the most important issues associated with fatigue of welded joints and existing design and analysis methods.

Présentation de la formation

Objectifs pédagogiques

Learning objectives

Participants, with hands-on experiences gained during the training course, should be able to:

  • Solve basic fatigue design problems
  • Effectively interpret fatigue test data
  • Perform computer-based fatigue life estimations for small-scale fatigue problems

The second day is dedicated to welding-induced residual stresses and distortions which can have significant impact on the manufacturability and structural integrity of welded components 

  • provide a critical assessment of the “state of art” residual stress modeling, analysis, and measurement techniques
  • demonstrate effective modeling and analysis procedures for various industrial applications
  • train participants to define and solve day to day residual stress and distortion problems, e.g., how to effectively:
    • mitigate residual stresses and distortions
    • incorporate residual stresses in fracture and fatigue assessment procedures

Méthodes pédagogiques

Training methods
Pedagogical method focuses on an amphitheater course alternating theory and practice through case studies or directed work

Moyens d'évaluation

Assessment method : Certificate of end of training

Profil du formateur

Trainer profile :
The course will be taught by Dr. Pingsha Dong of Battelle, who has published over 180 peer-reviewed papers in archive journals and major conference proceedings. He has lectured internationally as a keynote or invited speaker on fatigue/fracture of welded structures and advanced process computational modeling techniques for welding/joining processes.

Personnel concerné

Staff involved : Technician engineer, BE, design, R&D

Pré-requis

Prerequisites : Fatigue knowledge

Le programme de la formation

TRAINING SEQUENCES

Day 1  - Residual Stresses Distorsions et Fitness for Service Assessment

 8.30 – 10.15

  • Why should we be interested in residual stresses?
    • Weldability
    • Structural manufacturability
    • Structural integrity
  • Residual stress/distortion development mechanisms
    • 1-bar, 3-bar, and n-bar model based descriptions
    • Plastic zone versus shrinkage zone
    • Shrinkage mode versus distortion types
    • Basic principles for controlling residual stresses and distortions
    • Application examples

10.15 - 10.45 Coffee Break

10.45 - 12.30

  • Basic requirements for FE modeling procedures
    • Shrinkage force versus shrinkage strain method
    • Thermoplastic modeling procedures
    • Buckling distortion modeling method
  • Comments on residual stresses
    • Available techniques
    • Assumptions and limitations
    • Why measurements can be wrong!
    • How to interpret measurement results
    • How to devise an effective measurement plan
    • Some well-documented examples

12.30 - 13.30 LUNCH

13.30 - 14.30

  • Residual stresses in weld repairs
    • Key differences between repair and initial fabrication welds
    • Key controlling parameters
    • Mitigation techniques

14.30 - 15.30

  • Post-weld heat treatment (PWHT) and local PWHT
    • Residual stress relief mechanisms in PWHT
    • Limitations of local PWHT
    • Alternative stress relief procédures

15.30 - 15.45 Coffee Break

15.45 - 17.00

  • Residual stresses as secondary stresses for FFS or ECA
    • Modern interpretations of primary and secondary stresses
    • Fracture mechanics treatment of secondary stresses
    • A full-field residual stress profile generation method
    • Residual stress profile extraction
  • Closure and Q/A

19.30 Diner

 

 Day 2 - Advances in Fatigue Design and Life Evaluation Methods for Welded Structure 

  

8.30 - 10.00

  • Fundamental aspects of weld fatigue
    • Some relevant terminologies and definitions
    • Unique fatigue issues associated with welded joints
      • A brief overview of conventional fatigue evaluation procedures:
      • Stress definitions and calculation procedures
      • Code-recommended S-N curves and assumptions
      • Unresolved critical issues

10.00 - 10.15 Coffee Break

10.15 - 11.30

  • Mesh-insensitive traction stress method – I
    • Traction stress definition and mechanics basis
    • Numerical implementation
    • Simple calculation procedures
    • Measurement techniques and validations
    • Treatment of weld toe versus weld throat cracking

11.30 - 13.00

  • Mesh-insensitive traction stress method – II
    • Generalized calculation procedure
    • Mesh-insensitivity validations
    • Multi-axial stress state
    • Examples

13.00 - 14.00 LUNCH

14.00 - 15.00

  • The Master S-N Curve Approach
    • Fracture mechanics consideration
    • Master S-N curve formulation and validation
    • Treatment of load- versus displacement-controlled conditions

15.00 - 16.00

  • Fatigue evaluation procedures using traction stress based master S-N curve method
    • Structural stress calculations – do’s and don’ts
    • Other weld types, e.g., spot welds, laser welds, friction stir welds, etc.
    • Treatment of weld root/throat failure
    • Life prediction examples

16.00 - 16.30 Coffee Break

16.30 - 17.30

  • Special topics
    • Treatment of low cycle fatigue using structural strain method
    • Structural strain based master E-N curve
    • Treatment of multi-axial fatigue and non-proportional loading
    • A hybrid method for simplified treatment of spot welds

17.30 - 18.00

  • Closure and Q/A