Practical Fatigue Theory

Duration:

1 or 2 day offered. Please contact your local support office to discuss course length.

Course Outline

“Practical Fatigue Theory” is a technical background course designed for those who want to understand fatigue calculations and tests. It is ideally suited to software users, such as nCode GlyphWorks Fatigue & Crack Growth or DesignLife, or even those who want to perform them by hand. The course does not use any software and is not software specific; it is equally applicable to test and CAE based fatigue calculations.

It focuses on preparing engineers to understand calculations and tests (and the results created by software users) by giving them the necessary fatigue theory that they need to complete the required inputs, understand the terminology and understand how software, if they use it, performs an analysis. The course is very specific in terms of how to apply and use fatigue theory – during the course you will perform calculations by hand. For instance, the course not only defines the parameters required for material characterization, but shows how to determine these parameters from test data or estimate them if they are not available.

The course is divided into the following sections: Introduction, Stress-Life, Strain-Life, LEFM, (being the main body of the course) and also some advanced topics of a practical nature. For each of the 3 analysis methods, the course first defines the basic procedure, which give the student the basic concepts for that method. More details associated with each part of the process are then provided, which build upon the basic concept. The course contains hands-on calculations within each section to reinforce the concepts and methods that are described.

Audience

Anyone involved in fatigue assessments and testing. It assumes a prior knowledge of material behaviour and general structural mechanics, typical of most practicing engineers.

Course Schedule

• Introduction to Fatigue
  • History and modern practice
  • Basic fatigue mechanisms – the basic physics
  • This helps put attendees knowledge into perspective
• Stress-Life Approach -SN
  • Concepts of high cycle fatigue and endurance limits
  • Definitions of loading and issues affecting accuracy
  • Rainflow cycle counting
  • Mean stress and surface finish effects (Goodman etc)
  • Estimating fatigue properties
• Several simple hand calculations
• Understanding scatter and its implications

• Paper clips – a real fatigue test

• Component SN vs material SN and welds

• Strain-Life Approach – EN
• High and Low Cycle Fatigue
• Materials properties and their measurement
• The stress-strain curve, and the cyclic stress-strain curve
• Localised plasticity and Neuber notch corrections
• More advanced hand calculations – bring a calculator.

• Multiaxial Assessment
  • A discussion of the topics & how to identify different multi-axial conditions

• Fracture Mechanics and Crack Propagation - LEFM
• Stress fields and cracks
• K-solutions (compliance functions)
• Static fracture
• Crack growth and the Paris Law
• Corrosion and notch effects.
• Hand calculation of critical crack sizes
• NDT criteria and damage tolerance
• Hand calculation of a crack growth problem

• Summary
• Method Comparison – when to use each one
• Discussion of fatigue modelling and the 5-box trick

Course Timing

Course timing is flexible and will vary to suit the attendees and the questions asked. There will be time to ask questions and attendees are encouraged to bring examples with them for discussion; broken parts are particularly welcome.