Impact fatigue

Ovunc

Hello, 

I am examining the fatigue that occurs when a thin metal plate hits another metal. I modeled the thin metal plate with shell elements (The shell element properties I use are attached.) and I used M1_Elast metarial card.  

For simulate this impact motion, I'm making a time-dependent solutions with radioss solver. I transfer it (.h3d ) to hyperlife with an upload type "transient response" and I study high cycle fatigue (SN approach) . The life output I get is a very low value like e-2.

For the scenario I mentioned;

• What should be the shell element properties ? What do you recommend?
• Why is the life value so low? (I thought it might be because I use the M1_Elast material.)
• How should we determine "stress combination" in Hyperlife? 

Thank you. 

Best Regards, 

Ovunc

 

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Polyvios Romanidis

Hello,

The recommended values for shell element properties are the ones that you have inserted already.

As for the material, it is suggested to use /MAT/LAW2 instead of /MAT/LAW1, because it can produce more accurate stress distribution through the thickness.  To use this law for elastic only material you have to set the Yield Stress equal to a high value that is not reached (1e+30 is proposed).   /MAT/LAW1 uses global integration only, one integration point, which is less accurate.

Finally, you can use thick shell elements, which are preferred for higher accuracy in stress distribution through thickness.  When you use Thick Solid elements it is recommended to insert the /H3D/NODA/GPS and /H3D/NODA/GPSTRAIN engine file outputs that will let you see the results for stress and strain in the outer nodes (that might be higher).

Additionally, you must be careful with the results you display.  For example, different Averaging Methods in Contours can include or not the precise values on nodes and may give only an average value.  In the following images you can see the same element contour without and with an Averaging Method.  This can lead to a change in the displayed maximum value (see images).