Structural components and assemblies are designed against specific requirements of strength and stiffness. Over the years many tools have been developed to facilitate the job of designing a structure. The Finite Element Method (FEM) is nowadays the principal one.

However, the increasing demand of optimized structures, mainly for economic reasons, tends to reduce the design margins of safety, or reserve factors. In such conditions, the durability requirement gets as important as the previous mentioned two.

 

Lightweight structures, such as an airframe, have to be designed such to fulfil strength/stiffness requirements, but also such to survive a defined number of loading cycles. Generally the tighter the safety margins are, the more prone the structure is to fatigue failure.

For this reason, Fatigue and Damage Tolerance (i.e. understanding how an intact structure gets cracked during its life due to loads which are well below the static allowables, and understanding how the cracks develop over the life once nucleated) are more and more topics that must be considered by the structural engineers with special care.

 

The physical mechanisms that are involved in crack nucleation are at a length scale for which the structure is not a continuum. This puts the problem complexity to a higher level with respect to the stress analysis. As a consequence, while the stress analysis of a structure involves consolidated tools and methodologies (because based on classical continuum mechanics theory), fatigue analysis is rather an open field, for which many methods and approaches have been developed over the years (stress based or strain based approaches, multiaxial solvers based on equivalent stresses or critical plane approaches, …).

For the same reason not many fatigue analysis tools are available in the market. Moreover, those which are available (at least the best ones) do not provide unique or absolute solution to the problems, but multiple options. It is the analyst, not the software, that must decide which method is more suitable to the problem being solved.

LIFING is a fatigue solver, with its own post-processor. Based on FEM, it copes with all aspects which can be involved in a fatigue assessment: crack nucleation (handled by the module Life), crack growth (handled by the module Growth).

What differentiate LIFING from other similar commercially available software are the following characteristics:

- Intuitive and fast analysis workflow.

- It dumps in a ASCII file all analysis details which allow the user to follow step-by-step the entire analysis process.

- It is customizable: being coded in a modular manner, user specific analysis methods an be implemented.

- It includes the GROWTH (optional) module which performs FEM based crack propagation analyses (see the dedicated page for details).

September 2019

   Lifing Release 2.5 issued.

   News:
   - Nodal stresses can be handled (this function is preliminary to next implementations:

        - Calculate Fatigue Life at critical distance

        - Calculate Crack Growth in a solid section using Weight Functions capabilities

   - Several minor bug fixes

August 2018

   Lifing Release 2.4 issued.

   News:
   - QUICK 2D FEM implemented, for fast fatigue (both crack initiation and crack growth) assessments

   - Several minor bug fixes

December 2017

   Lifing Release 2.3 issued.

   News:
   - Improved calculation performance (about x10 times faster with huge models and long time histories)

   - Analysis of readings from commercial strain gauges (uniaxial or rosettes 0-45-90, 0-60-90, 0-120-240)

August 2017

   Lifing Release 2.2 issued.

   News:
   - Improved Ansys interface

   - Implementation of the Köttgen-Barkey-Socie Pseudo-Material method with Mroz-Garud Cyclic Plasticity model

LIFE

LIFE is the module for the Fatigue Analysis of structural components.

Topic addressed:

  • Uniaxial and Multiaxial Fatigue

  • Strain based Fatigue Analysis

    • Neuber and ESED Glinka methods for elastic-plastic stresses calculation

    • Morrow's, Smith-Watson-Topper, Brown-Miller, Fatemi-Socie, ... Fatigue parameters

    • Multiaxial Proportional and Non-Proportional loadings addressed

  • Stress based Fatigue Analysis

    • MMPDS S-N database

    • Standard S-N curves

    • Mean stress corrections with Goodman, Gerber, Soderberg, Haigh, ...

    • Dang-Van, McDiarmid, Carpinteri-Spagnoli methods

    • PSD fatigue with Dirlik method

  • Weldings analysis (seam welds and spot welds)

  • Virtual strain gauging

  • Multiaxial Assessments

GROWTH

GROWTH is the module for Crack Growth analysis in 2D (or quasi-2D) structures.

Topics addressed:

  • FEM remeshing for propagation of multiple cracks

  • Crack stop drill holes

  • Stress Intensity Factors calculated with J-integral, Displacement correlation

  • Crack kinking captured

  • Crack Growth calculated with NASGRO Equation

  • NASGRO database provided

  • Generalized Willemborg Crack Retardation model integrated