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.
Last Software updates:
Lifing Release 4.0.00 issued.
- With the new features introduced in Release 3.4.00, now LIFING can introduce and propagate a crack in a 3D FEM, built with a QUICK2DFEM script.
Lifing Release 3.4.00 issued.
- Module QUICK2DFEM extended to generate and solve a 3D FEM by linear or circumferential extrusion.
- M-Integral calculation implemented.
Lifing Release 3.3.00 issued.
- Module Growth enhanced with the capability to run crack growth analyses based on da/dN curved provided in tabular format.
Two interpolation methods are available: simple logarithmic interpolation and Walker point-by-point interpolation.
- Several bug fix on the GUI.
Lifing Release 3.2.00 issued.
- Performances improvement: multi-threading is implemented, improving significantly the computational speed (batches of elements are solved in parallel).
- Several interface minor bug fixes
- QUICK 2D FEM capability extended with the possibility to model a 'misdrilled' hole
- Fatigue at critical distance (or gradient correction) implemented
- CG analysis based on 2D user defined SIFs
- Documentation update
LIFING has been developed by engineers, with solid background on fatigue, fracture mechanics, stress and FEM.
As a result of such a technical background, LIFING has the following characteristics:
It is based on a simple and intuitive workflow process. Both the user interface and the post-processor are designed with the target to define in few steps all the parameters to run the fatigue analysis quickly and easily.
It provides to the fatigue engineer the vast majority of capabilities which are required for a fatigue or damage tolerance assessment.
It provides all analysis details, such to allow the analyst to trace the calculation, step-by-step.
It is modular: ad-hoc methods and be easily coded and integrated.
LIFING Includes three modules:
LIFE is the module for the Fatigue Analysis of structural components.
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 methods
PSD fatigue with Dirlik and Narrow Band method
Virtual strain gauging
GROWTH is the module for Crack Growth analysis in 2D (or quasi-2D) structures.
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 material da/dN curves provided as NASGRO Equation or tabular format
NASGRO database available
Generalized Willemborg Crack Retardation model integrated
QUICK2DFEM is a module, not optional, integrated by default in LIFING, solving 2D plane stress or plane strain models created by defining edge geometries and conditions with a simple format.
Created models can be used for both Fatigue and Crack Growth assessments, where Stress Intensity Factors are calculated with J-Integral.
From Release 4.0, this module has been enhanced to create 3D meshes (by extrusion from the planar mesh) and solve the FEM with a 3D solver.
Crack fronts can be integrated and Stress Intensity Factors calculated with M-integral.