Midas NFX Fatigue Analysis

Definition

NFX fatigue analysis estimates fatigue damage and life from finite element stress or strain histories. The manual covers stress-life, strain-life, and random vibration fatigue approaches.

Stress-Life Method

The stress-life method uses S-N curves and is positioned for relatively low stress levels where elastic behavior dominates. The manual describes stress amplitude, mean stress, rainflow counting for variable-amplitude histories, S-N curve correction factors, Miner cumulative damage, and life as inverse damage.

Mean-Stress Corrections

The source includes Goodman, Gerber, Soderberg, Morrow, and Smith-Watson-Topper style mean-stress correction ideas. This matters for solver verification because identical FE stress histories can produce different fatigue lives depending on correction method.

Strain-Life Method

The strain-life method is positioned for higher stress/strain concentration regions where plastic strain can control life. The manual includes elastic/plastic strain decomposition, cyclic strength/hardening parameters, and Neuber-rule based recovery from linear elastic results.

Random Vibration Fatigue

For complex load histories, the manual also treats frequency-domain random vibration fatigue. That workflow connects modal/frequency response outputs to fatigue damage rather than relying on explicit time histories.

Solver Development Use

For a custom solver, fatigue is primarily a postprocessing harness problem. The FE solver must first produce trusted stress/strain histories at documented locations; only then should rainflow counting, S-N/E-N interpolation, mean-stress correction, Miner damage, and random-response fatigue be tested.

Connections

Finite Element Modeling and Convergence Checks connects fatigue accuracy to stress recovery and mesh quality.
Abaqus Progressive Damage and Failure provides a broader damage/failure comparison.
Midas FEA Fatigue Analysis is the sibling MIDAS fatigue reference.

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