thermal mechanical fatigue life prediction

[fedilux]

can i use Ansys to perform thermal mechanical fatigue life prediction for anisotropic material. is there some models for life prediction integrated to Ansys. I know that is possible in Abaqus.

Thanks

 

[jiahongbo]

I am facing similar problem.
It seems ansys can only predict fatigue life for a specific point, not the contours of the whole body.
To make things worse, I use ansys workbench.......

Can anyone help?

 

[TGS4]

Fatigue is a "failure-at-a-point" mechanism. High stress will initiate a fatigue crack, which will then propagate until either the function of the part is impaired (such as a leaking pipe) or the part will fail catastrophically due to a brittle fracture. Fatigue is NOT a "whole body" failure mechanism.

And as far as "can I use ANSYS..." the answer is "yes", but remember that the analysis is only as good as the analyst (and not the software that s/he is running).

 

[cbrn]

Hi,

1- Ansys can do fatigue analysis and also fracture analysis, though not, as far as I know, "high-speed" fracture, i.e. the one with extremely high propagation rate such that you have in machining for example (fracture is not always an unwanted phenomenon... ;-) )
2- In order to do that, a license with sufficient authorizations is needed (not "structural" for example)
3- If you don't have that, you can extract from the FE model the high-stress zones with stress concentrations (or even calculate a FE model without geometrical stress concentrations, and calculate them with Peterson, Roark-Young or others), and then conduct the fatigue prediction "by hand" since you know the Richter curve of the material. As regards variable-amplitude load histories, you can rely on Miner's rule and use rainflow or other methods in order to determine the equivalent stress amplitudes and average values (then remember to scale the Richter curve with Haigh or other methods...). It's very straightforward, and relatively fast also, the longest operation being to determine stress state in the component, but this step you do with FEM...
4- By extension, you can also perform fracture propagation prediction "by hand", there are several analytical methods for that.
5- as TGS4 says, YOU must know where it is important to perform the fatigue analysis / fracture analysis. Pay extreme attention also on ambient factors (wet environment, for example)

Regards