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Fatigue & Fracture Mechanics in FEA

What are the technologies used in fatigue analysis and fracture mechanics – how do the approaches differ?
What is the difference between high-cycle and low-cycle fatigue?
What approach should I use in assessing fatigue and damage tolerance?

Fatigue & Fracture Mechanics in FEA

The prediction of fatigue is a requirement for most products. However, the application of fatigue analysis is not easy and a good background is essential to be able to use the powerful FEA method as a basis for fatigue analysis. Much of the terminology used in setting up a fatigue problem through a modern GUI is confusing and the choice of options is not always clear.

The objective of this course is to break down the fatigue analysis process into clearly defined steps, give an overview of the physics involved and show how to successfully implement practical solutions using Finite Element Analysis.

Topics covered include; High Cycle Fatigue Methods, Notch Effects and Low Cycle Fatigue, Multi Axial Fatigue, Fracture Mechanics and more.

What will you learn?

  • The difference between various Fatigue Life techniques
  • The technologies behind Fracture Mechanics
  • How and when to use the different types of techniques
  • The difference between a Fatigue and a Fracture Mechanics approach, and when to use each of them.
  • The importance of accurate stresses for Fatigue Life prediction.

 

Who Should Attend?

  • Newcomers to fatigue and fracture mechanics
  • Engineers who want a foundation in fatigue and fracture
  • Experienced engineers wanting to recap or revise their knowledge
  • Engineers and designers looking to use fatigue in the most effective way
The course is completely code independent.

This is a 5-session online training course, with each session lasting for approximately 2.5/3 hours, depending on homework submissions, questions & discussions.

You can attend the sessions live, and/or stream on demand. When you register you will get access to a dedicated course forum where you can contact the tutor with questions, submit homework, download pdfs of course notes and access all session recordings. To get the most out of the course, participation in forum discussions is encouraged.

Questions? Contact us on e-learning@nafems.org


Free Fatigue Life Calculator

All attendees on the course will be able to download a fully functioning Fatigue Life Calculator. As well as forming a useful tool for many of the homework tasks set, attendees will be able to explore the implications of both High Cycle and Low Cycle Fatigue as discussed in the class.

A tutorial guide is also available for download. Basic Material Data and Strain Life Material data is input, or derived from fundamentals. Neuber notch and Plastic material intersection points are found allowing a hysteresis cycle to be plotted. The strain life curve is plotted and the number of cycles to failure is calculated.

The Calculator has been steadily developed over the last few years of delivering this course and attendees will be entitled to future upgrades.


    Course Programme

    Note: This is a five-session course. Each session represents one 2.5-hour* session. The length of each session can vary, depending on Q&A, homework responses, and other contributing factors.

    (click to expand)

     

    Session 1

     

    • Introduction to Fatigue
    • High Cycle Fatigue Methods
    • Mean Stress Effects
    • Fatigue Correction Factors
    • Loading Environment
    • Low Cycle Fatigue Overview
    • FEA Application of Fatigue
    • Homework Session 1
    • Q and A

     

    Session 2

     

    • Homework Review
    • Notch Effects in High Cycle Fatigue
    • Notch effects Low Cycle Fatigue
    • Low Cycle Fatigue - Overview
    • Low Cycle Fatigue - Mean Stress
    • Low Cycle Fatigue - Data
    • Cycle Counting Methods
    • Homework
    • Q and A

     

    Session 3

     

    • Homework Review
    • More FEA implications
    • Stress Concentrations
    • Multi Axial Fatigue
    • Q and A

     

    Session 4

     

    • Background to Random Analysis
    • The PSD specification
    • Vibration Fatigue Analysis
    • Examples
    • Q and A

     

    Session 5

     

    • Introduction to Fracture
    • FEA Implementations
    • Fatigue in Composites
    • Q and A


    PSE Competencies addressed by this training course (click to expand)

     

    IDCompetence Statement
    FATkn1List the conditions necessary for fatigue failure.
    FATkn2List the possible sources of cyclic loading in your company products.
    FATkn3List potential sites for fatigue in your company products.
    FATkn4Sketch a sinusoidal stress variation and show the maximum stress, minimum stress, mean stress, alternating stress (or stress amplitude), stress range and stress ratio.
    FATkn5List a common source of harmful tensile residual stress in your company products.
    FATkn6List ways of inducing beneficial compressive stresses in your company products.
    FATkn7Sketch a fatigue diagram, showing the Modified Goodman, Gerber, Soderberg and Langer/Yield lines.
    FATkn8Sketch typical welds, highlighting features detrimental to fatigue performance.
    FATkn11Define the terms Nominal stress, Notch stress, Equivalent stress and Weld-Throat stress.
    FATco1Discuss the initiation, propagation and fast fracture stages of Fatigue in metallic materials.
    FATco2Describe how the data used to construct an S-N curve are obtained.
    FATco3Discuss the term high cycle fatigue, highlighting a common source in your company products.
    FATco4Discuss the statistical nature of fatigue and explain how this is handled in relevant design standards and codes of practice.
    FATco5Discuss the salient features of an S-N diagram for steels and explain the terms endurance limit, infinite life and low cycle fatigue.
    FATco6Discuss the typical appearance of a fatigue failure surface in a metallic component and explain how the source of the fatigue failure is commonly identified.
    FATco7Discuss the observed relationship between endurance limit and static tensile strength for steels and explain why this relationship does not hold for welded steels.
    FATco8Discuss the philosophy of Safe Life Design.
    FATco9Explain the term Damage Tolerant Design.
    FATco10Contrast the Stress-Life and Strain Life / Manson-Coffin approaches to fatigue assessment.
    FATco11Explain the use of Endurance Limit Modifying Factors in Stress-Life based fatigue assessment.
    FATco13Discuss the effects of corrosion on fatigue life and highlight how this is typically handled in relevant standards and codes of practice.
    FATco14Discuss the term Fatigue Strength Reduction Factor in relation to stress concentrations and explain how this has traditionally been handled in relevant design standards and codes of practice.
    FATco15Discuss the concept of cumulative damage and explain how this is commonly handled.
    FATco16Explain why a multiaxial stress field can complicate an analysis and discuss approaches to handling this.
    FATco17Discuss the significance of the choice of equivalent stress used in the fatigue assessment of welded joints
    FATco18Outline a conservative approach to situations where the directions of principal stresses vary during a stress cycle.
    FATco21Discuss why weld toe grinding can be beneficial and explain how a design standards and codes of practice will typically allow for this improvement.
    FATco25Reflect on why fatigue is such a long-standing and persistent cause of failure.
    FATco26Discuss the nature of and typical locations for, stress singularities in a finite element model and explain how they would typically be handled in a fatigue analysis.
    FATco27Describe the approximations inherent in a plate/ shell idealisation of welded joints and how these could influence fatigue assessment.
    FATco28Discuss the term Effective Notch Stress and Nominal Stress.
    FATco29Explain how a Cyclic Stress-Strain Curve is constructed and used.
    FATco30Explain Neuber's Rule and its limitations and why corrections to the elastic strain range from an elastic analysis may be necessary.
    FATco31Discuss the term Local Plastic Strain Amplification Coefficient and Elastic Follow-Up.
    FATco33Explain why corrections for mean strain are often unnecessary for low cycle fatigue.
    FATco35Discuss the term endurance limit for many non-ferrous metals, steels in a corrosive environment and the possible effects of load sequencing.
    FATco37Reflect on how variable amplitude load sequencing can affect the prediction of damage accumulation and fatigue life.
    FATap1Employ a fatigue diagram, consisting of Modified Goodman and Langer lines, to assess fatigue performance of components.
    FATap2Carry out elastic fatigue assessment using design standards and code guidelines for components and structures including any special procedures for ancillary components such as bolts,
    FATap5Use Reservoir Counting / Rainflow Method or similar to specify the necessary stress ranges, number of cycles and loading history for any component to be analysed.
    FATap6Employ a finite element analysis system for the fatigue analysis of a component or structure.
    FATap7Use hot spot stress techniques (extrapolation and/ or linearization) to determine structural stresses for fatigue assessment.
    FATsy1Prepare a fatigue analysis specification, highlighting any assumptions relating to geometry, loads, boundary conditions and material properties.
    FATsy2Plan a fatigue analysis, specifying necessary resources and timescale.
    FATsy3Prepare quality assurance procedures for fatigue analysis activities within an organisation.
    FATsy4Specify whether a Fracture Mechanics approach is more appropriate.
    FATev1Assess the significance of neglecting any feature or detail in any idealisation being used for fatigue assessment.
    FATev2Assess the fatigue significance of simplifying geometry, material models, loads or boundary conditions.
    FAFMkn1Give an overview of the historical development of fracture mechanics
    FAFMkn2Summarise the scope of fracture mechanics for the different types of cracks and material situations
    FAFMkn3Define stress intensity factor and state the relationships between G and KI, KII and KIII for plane stress and plane strain crack tip conditions
    FAFMco1Explain the Griffith criterion and the significance of the toughness parameter Gc
    FAFMco3Identify the key field variables (displacement, strain, stress and principal stress) relevant to a general 3D crack profile and sketch their components.
    FAFMco6Describe the significance of the strain energy release rate G
    FAFMco8Describe a range of solutions to the more common geometrical configurations in both 2D and 3D, the latter having both straight, elliptical and circular crack profiles
    FAFMco9Explain how a pre-existing crack propagates in a new loading field that exhibits both mode I and II behaviour at the crack tip, and discuss FE techniques useful for predicting the new crack propagation direction
    FAFMco10Discuss the main components required of a FE model to represent the main features of a cracked structure, to include the discrete crack geometry, material properties and mechanical/thermal loads
    FAFMco11Describe, from the results of a FE analysis, how it is possible to calculate K and/or G at any position along a crack profile; explain the difference between substitution and energy methods
    FAFMco12Describe how the following energy methods work, their applicability, and limitations: the potential energy difference technique, the virtual crack extension method, J-integral (both as line and domain integrals), and crack closure work
    FAFMco13Describe how special finite elements are use to represent the crack tip singularity and the availability in user's FE software
    FAFMco15Describe the mechanism of plasticity in the context of its existence around a crack tip
    FAFMco21Describe how cracks grow under fatigue conditions and the factors that affect this growth
    FAFMco22Explain why there is a tendency for fatigue crack growth to be under LEFM conditions, the relevance of stress intensity factor; and the Paris law to describe growth rates
    FAFMco23Describe how FE analysis can be used to calculate both the growing crack length and direction change from an initially cracked geometry under mixed mode conditions
    FAFMap1Determine the meshing requirements for any FM approach being employed.
    FAFMap2Employ an analysis system effectively for LEFM and use the Westergaard Equations (displacement or stress) to determine Stress Intensity Factors in components.
    FAFMap6Use documented solutions for standard stress intensity factors to check FEA results or to benchmark FEA procedures.
    BMPSap2Employ appropriate techniques to retrieve hot-spot and other stress quantities for the assessment of welds.
    MASco8Explain, in metallurgical terms, how fatigue cracks form and grow in metallic materials.
    MASco11Discuss the terms elastic-perfectly plastic, kinematic hardening, isotropic hardening, Bauschinger effect, hysteresis loop.
    MASco19Discuss common material characteristics and typical manufacturing related flaws in welding.
    MASco20Discuss common material characteristics and typical manufacturing related flaws in hot and cold rolled plate and tubes.
    MASco21Discuss common material characteristics and typical manufacturing related flaws in forgings.
    MASco22Discuss common material characteristics and typical manufacturing related flaws in castings.
    MASap2Determine whether any allowance needs to be made to the material data for the effects of environment and variability.
    PLASco33Explain Neuber's Rule.

    Details

    Event Type eLearning
    Member Price £357.19 | $395.00 | €404.97
    Non-member Price £547.08 | $605.00 | €620.26
    Tutor: Tony Abbey

    Dates

    Start Date End Date Location


    Session Times







    Online

     

    Fatigue & Fracture Mechanics in FEA

     

    Five-Session Online Training Course

    2.5/3 hours per session
    PDH Credits - 12.5

    Attend the live sessions, or view the recordings at your convenience.

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