Learning Forum

[mehmetyaylaciinfo]

Hi,

I want to analyze the fatigue life of a component. When I looked at the options in the nCode DesignLife, I saw the Certainty of Survival which is 50%. I use Al7075-T6 materials which is in the nCode Design Life datas. How can I determine the Certainty of Survival options? Should I choose 50% or 99%?

[Avnish Pandey]

Hi,

 

You can check these links to get more information on how to determine it.

/knowledge/forums/topic/what-is-certainty-of-survival-in-fatigue/

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v232/en/mech_addon/ds_fatigue_designlife_settings.html

 

https://innovationspace.ansys.com/forum-rules-guidelines/

All the best !!!

 

[mehmetyaylaciinfo]

Firstly, thank you so much the answer, however there is a different situation. I have read the some articles, and have learned the Certanity of survival. I find the life of component which is 150000 cycle, but the certanity of survival is 50%. When I change it from 50% to 99%, the life decreases. How Can I decide it? Is this related to its material? or is it up to me to choose the certanity of survival

[Avnish Pandey]

Hi,

There is no direct relation betwen the certainty of survival and life expectancy.

You compute one of them by defining the other as per your design requirements. The two will vary with the material you chose for your simulation. 

Normal distribution is associated with certainty of survival. There are few parameters you take into account to decide for it.

Generally, in most designs a certainty of survival of 97.7% is used.

Check this useful link.

While modeling, mesh quality can also affect the fatigue life as discussed here.

 

Regards,

 

 

[mehmetyaylaciinfo]

Hi, 

You said, there is no direct relation betweent the certainty of survival and life expectancy. However, when I change the %50 to %97, the life of component decreases. I'm sorry, but I don't understand. Although I have searched for 2 days, I don't know should I change the certanity of survival parameter or not. I can't still decide it.

 

These are properties of Al7075-T6. Should I choose certanity of survival using these properties?