We show endurance when it comes to fatigue

Fatigue strength analysis

Assemblies, components and parts are often subject to repeated, recurring loading over their product life. Over time the component can fatigue and develop crack initiation.
In the worst case this leads to loss of function or to fracture, and thus to failure of the component.

Where loading is frequent, static sizing for one-off peak loads is no longer sufficient. Fatigue strength analysis is required here, assessing fatigue and service life.

Fatigue strength analysis takes the typical influencing factors into account, for example:

  • notch support effect through stress redistribution
  • surface roughness
  • mean stress effect
  • technological size effect
  • survival probability

The results are presented as safety factors or utilisation levels for the relevant load cases, either as colour plots or in tabular form. Where necessary, the number of load cycles that can be sustained is determined by comparison with (synthetic) S-N curves.

An important aspect of fatigue strength analysis is knowing the loading situation — what loads (forces, accelerations, temperature, ...) the components actually experience over time. Assumptions that are too conservative risk over-sizing the product.
Service life is estimated using S-N curves, which describe a logarithmic/exponential relationship between load and life. Typically, for notched, unwelded regions of a component, the service life is halved if the loads increase by just 10%.

Codes and standards

Fatigue strength analysis is implemented in a wide range of codes and guidelines. We work in compliance with the following standards and guidelines:

  • FKM guideline
  • VDI 2230
  • AD 2000
  • ASME
  • EN 13445
  • EN 13001
  • EN 1993
  • IIW
  • and others

Tools

Compared with static analysis, fatigue strength analysis is demanding. Working with specialised software tools that meet the various requirements for efficiency, reproducibility and reliability is essential.
We use the following tools for this:

  • Femfat
  • Rifest
  • WCD
  • our own validated Excel-based or web-based tools, such as MagicBOLT

This enables us to carry out fatigue strength verifications in compliance with the applicable codes and to document them accordingly.

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