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Practical Fatigue Theory

Course Overview

Practical Fatigue Theory is a technical concept class designed to help you understand the role of fatigue in product life.

Important durability concepts are taught by explaining the necessary fatigue theory used in performing fatigue analysis. Emphasis is placed on the practical side of fatigue, with our expert trainers focusing on best practices for engineers.

In this course you will explore common fatigue analysis methods: stress-life (SN), strain-life (EN), and crack growth. For each of these methods, the course defines the basic procedure and assumptions, and provides an understanding of practical applicability. Software is not used during this course, instead focusing on practical concepts that provide an in-depth explanation of what’s going on behind the software. It is equally applicable to test and CAE-based fatigue calculations.

Class time is split between lectures and hands-on sessions where you will put the concepts into action by performing calculations. Case studies are shared to highlight practical applications of theory.

Who Should Attend?

The course is aimed at engineers involved in structural durability, including fatigue life estimation, improvement, or validation testing.

It is assumed that attendees are familiar with material behavior and general structural mechanics, typical of most practicing engineers.

Course Agenda

Duration: 1 or 2 days

  • Introduction to Fatigue
    • The definition of fatigue
    • Historical and modern practice
  • The Physics of Fatigue
    • Structural failure mechanisms
    • Basic physics and metallurgy
  • An Overview of Fatigue Analysis Methods
    • Crack initiation vs. crack growth
    • Common methods of assessing durability
  • Stress-Life Approach - SN
    • Concepts of high cycle fatigue and endurance limits
    • Definitions of loading and issues affecting accuracy
    • Stress concentrations
    • Rainflow cycle counting
    • Mean stress effects
    • Probability of failure: understanding scatter and its implications
    • Miner’s Rule for damage accumulation
  • Strain-Life Approach – EN
    • High and low cycle Fatigue
    • Materials properties and their measurement
    • The stress-strain curve and the cyclic stress-strain curve
    • Stress concentrations
    • Localized plasticity and Neuber notch corrections
  • Multiaxial Fatigue
    • Fatigue under complicated stress states
    • Common methods for understanding multiaxial stresses
  • Fracture Mechanics and Crack Growth
    • Why cracks are the ultimate stress concentration
    • Quantifying stress on a crack
    • Fast fracture and a crack’s strength
    • Crack growth and various growth rules
  • Applications and Summary
    • Fatigue with measured strain gauge data
    • Fatigue with FEA stresses
    • Method comparison – SN vs. EN vs. crack growth
    • Discussion of fatigue modelling and the 5-box trick

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