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FEM post-processor for fatigue analysis

P-FAT is a software that post-processes results from FEM analyses in order to compute fatigue damage in structures. The software is designed to support engineering workflows, and provides easy access to some advanced fatigue models.

Contact person

  • Paul Qvale

    Paul Qvale

    Research Scientist Materials and Nanotechnology

P-FAT, SN analysis and Crack growth analysis


P-FAT
imports the stress field from a linear, static FE analysis of a structural component. The analysis is done assuming an undamaged component (fatigue cracks need not be modelled). The stress field has been computed by applying a "unit load" to the component. In P-FAT, unit loads are multiplied by load histories, typically obtained in a dynamic analysis of the structure as a whole. This results in a complete description of how the stresses evolve over time at each point within the component, and provides the base for the fatigue analysis.

SN analysis
P-FAT can compute the fatigue life using the widely accepted engineering procedure of using a Wöhler (SN) curve, typically a conservative "design curve" from engineering standards, combined with rainflow counting and Palmgren-Miner summation.
The traditional engineering criteria provide binary answers (acceptable/unacceptable). P-FAT allows to go beyond that and evaluate the probability of failure of a given component based on weakest-link theory, provided that a) the uncertainty on the load side is negligible and b) the scatter of SN data is available. The probability of failure computed by P-FAT takes into account the "volume effect": for a given stress amplitude, if a larger volume of material is loaded, the probability of failure increases.

Crack growth analysis
If a fatigue crack pre-exists in the component, crack growth is traditionally computed using Paris law (or refinements of it). If the un-cracked component has strong stress gradients, then computing crack growth using the highest stress (computed using a stress concentration factor) can be very conservative. Design codes permit a more precise analysis which accounts for the stress, but this is seldom used in practice because the computations are more complex. P-FAT makes this option easily available.