Reply To: Material modelling of ABS for fatigue analysis

[John Doyle]

A good place to start would be to determine if your application is small strain-high cycle fatigue or high strain-low cycle fatigue.  It would also be helpful (necessary), to study up on the ABS material and how it fails in fatigue.

If it is small strain, high cycle fatigue at room temperature, you might be able to perform a classical stress based fatigue analysis.  

If it is high strain-low cycle fatigue, it will be more complicated.  ABS is a thermoplastic material.  The plastic strain development under cyclic loading is highly dependent on rate of loading and unloading as well as temperature. 

Most polymers also become more brittle with age, so it might depend on how well the material is cured and how long it was on the shelf before it was put into service.

While Ansys has a Three Network Model (TNM) designed to represent thermoplastics, its accuracy will depend largely on how well the material model inputs have been calibrated and validated for the specific application.  Please refer to MAPDL Material Reference Guide (Release R2024-R2) Section 4.6.13.1, for background on TNM and Section 7.8.1, for a curve fitting example.

Whatever you do, your approach needs to be carefully calibrated and validated.